Geothermal and Solar Design and Installation Tips

The first challenge when entering the renewable energy industry is understanding how to design and install projects. These articles are dedicated to teaching you the basics of how to design and install solar PV, solar thermal, and geothermal projects.

If you’re brand new

Click here to learn what is NABCEP and wether or not you should need to get the certification. If you’re serious about the solar industry and you want to get the NABCEP Certification, but you need to understand how exactly to apply, you can read more about getting the NABCEP Certification here.

Articles That Will Help You
A Review of Solar and Geothermal Certifications, Licenses and Permitting
Solar Thermal Design and Installation Guide

Solar PV Design and Installation Guide
How to Design a Solar PV Array and Estimate Power Production
Geothermal Design and Installation Bundle

Understand the Key Grounding and Bonding Standards for Commercial Solar PV Projects in Less Than 30 Minutes

What are the differences between grounding and bonding in solar design? What are the most recent codes? Where are the codes headed? What are some of the changes that have happened? What does it mean for you and your installations?

In this free 20-minute video lesson, Ryan Mayfield identifies the key 2014 NEC code sections for PV system grounding and bonding and outlines general requirements of Article 250 – beginning part of code for Grounding and Bonding (and what he considers one of the most difficult and fun discussions). He also begins outlining Article 690 Part V: Grounding and Bonding Requirements.

Watch the full video below to learn more. If you have any questions about the content, please leave it in the comment section. If you’d like to connect with other professionals focused on designing, commissioning, managing, and installing large commercial solar projects, join our Megawatt Design Linkedin group.

The video covers the following:

  1. Key NEC standards for grounding and bonding
  2. Overview of Article 250 as it relates to solar PV
  3. Article 690 – Part V on grounding and bonding requirements
  4. How grounding and bonding changes will impact system design and installation

Watch the Lesson Here

Spend ten weeks learning from Ryan Mayfield, the Solar PV Technical Editor at SolarPro Magazine. Ryan, along with help from other industry leaders, has developed Megawatt Design, an online course to help experienced solar professionals get their projects permitted and installed faster and cheaper. This course goes beyond traditional solar training: it is technical, rigorous, and for experienced professionals only. We cover all types of large solar PV systems, with a heavy emphasis on commercial rooftop systems. Test-Drive Megawatt Design to access more free videos. The course is capped at 50 students with 30 discounted seats.


Ryan Mayfield has been working in the renewable energy field since 1999 and is the President of Renewable Energy Associates, a consulting firm providing design, support and educational services for electrical contractors, architectural and engineering firms, manufacturers and government agencies. Ryan serves as Photovoltaic Systems Technical Editor for SolarPro Magazine, regularly writing feature articles in SolarPro and Home Power magazines, and wrote PV Design and Installation for Dummies. Ryan was also a contributor and video team member for Mike Holt’s Understanding the NEC Requirements for Solar Photovoltaic Systems. Ryan teaches various PV courses across the nation for electricians, existing solar professionals, code officials, inspectors and individuals looking to join the solar industry. Class topics include National Electrical Code and PV systems, residential and commercial PV systems.

Posted in Geothermal and Solar Design and Installation Tips | Leave a comment

AC Coupling – How to Cost Effectively Add Battery Back-up to Existing Grid-Tied Solar PV systems

This is a guest article by Chris LaForge.

Chris is teaching an in-depth 6-week technical training on designing battery based solar PV systems that starts in September. You can read the full description and get a limited-time discount here. If you need to learn how to design, quote, and commission a battery based solar PV array, this is the best course for you.

In the past three years, three trends have converged to create higher demand for battery-based solar arrays: battery prices are declining, the penetration of grid-tied systems is exploding, and homeowners are becoming more interested in backup power.

Retrofitting existing solar PV arrays to include batteries is becoming an opportunity for added revenue for contractors.

Enter Chris LaForge –

AC Coupling

Since the advent of high-voltage battery free (HVBF or grid-direct) solar electric systems, some clients have been frustrated by not being able to use their systems during power outages. The re-work necessary to move to a grid-intertied system with battery back up is costly (GTBB or DC coupled system), inefficient, and, in some cases, unworkable.

Ac coupling can be used in both utility-intertied systems and in off-grid applications. This article will discuss the utility-intertied aspects of AC coupling.

With the advent of AC coupling as a means to introduce battery back-up to an existing HVBF system, an efficient and more workable solution has come to the fore.

AC-coupled systems use the HVBF system while adding a battery-based inverter that works in tandem with the HVBF inverter. It maintains the efficient operation of the PV system while the utility is available and then allows for its operation during power outages by having the GTBB inverter disconnect from the grid, power the back-up load panel and use the power from the HVBF system to power the critical loads in the back-up load panel. It also provides power to the GTBB inverter to charge its battery bank.  If this sounds a bit complicated, well, it is.


Courtesy of Schneider Electric

AC coupling provides the following advantages over traditional DC-coupled GTBB system designs:

  • Retrofit-able with existing HVBF systems (within manufacturer requirements and limitations)
  • Allows for employing the efficiencies of HVBF equipment while achieving back-up power for utility outages
  • Can reduce the number of components used in DC coupling
  • Can reduce losses do to low-voltage aspects of DC-coupled systems
  • Can provide for more flexible and efficient wiring configurations
  • For designs requiring long distances between the renewable energy resources and the balance of system components

As with any innovation, AC coupling has some notable challenges, especially when the design utilizes multiple manufacturers.

For several years, system integrators have completed AC-coupled designs using one manufacturer’s equipment or by using multiple brands of inverters.

SMA pioneered the AC coupled concept with its “Sunny Island” Inverter. Initially built to provide for the creation of microgrids on islands and other non-utility environments. The design lends itself to grid-intertied AC-coupled systems as well.

As shown in the diagram below, SMA’s design allows for multiple HVBF inverter outputs to be combined with the Sunny Island inverter to connect to the utility and have battery back-up.


Courtesy of SMA America

SMA’s design provides for an elegant method of regulating the battery state of charge as long as all the inverters can be networked with cat-5 cable. In this design the HVBF inverters can have their outputs incrementally reduced as the battery reaches a full state of charge. If the distance between the HVBF components and the Sunny Island is too great to network with cat-5 cable, the Sunny Island controls the output by knocking out the output of the HVBF inverters with a shift in the frequency of the inverter’s AC waveform.  The HVBF inverter senses an out-of-spec frequency and disconnects until the frequency is back in spec for five minutes.

This frequency shift method of regulating battery state of charge is often used when different manufacturers’ inverters are used to create the AC-coupled design. This has several drawbacks that we will discuss.

Several other battery-based inverter manufacturers have developed designs for using their inverters with other HVBF inverters to create AC-coupled designs. These include OutBack Power, Magnum Energy, and Schneider Electric. Both SMA and Schneider provide for single manufacturer AC-coupled systems because they manufacture both HVBF inverters and GTBB inverters. This presents the basic advantage of having one manufacturer provide and support the entire AC-coupled design.

OutBack Power and Magnum Energy manufacture only battery-based inverters and therefore require the mixing of manufacturers in AC coupling in order to bring in HVBF inverters.

Both companies provide design information and support for AC-coupled designs.

Schneider’s regulation

With Schneider Electric’s AC coupling, the battery is regulated by the frequency shift method. Schneider itself recognizes the drawback of this method in its AC-Coupling Application Note (see appendix): “Unlike its normal three-stage behavior when charging from utility grid, the Context XW does not tightly regulate charging in a three-stage process when power is back fed through AC inverter output connection to the battery. In this mode charging is a single-stage process, and the absorption charge and float stage are not supported. Charging is terminated when the battery voltage reaches the bulk voltage settings, which prevents overcharging of the batteries. Repeated charging of lead acid batteries in this way is not ideal and could shorten their useful lifetime.”

This can be improved by employing a diversion load controller added to the design.  The diversion load controller will limit the battery voltage by “dumping” excess power into a DC load during times of excess generation for the PV system. While this re-introduces the 3-stage charge regulation into the design it negates some of the benefit of AC coupling because it re-introduces the cost of a charge controller and adds the cost of the DC diversion load(s).

Magnum’s regulation

Magnum Energy also provides for frequency shift method battery regulation but in their White Paper titled “Using Magnum Energy’s Inverters In AC Coupling Applications” (see appendix) they indicate that frequency shift regulation should only be used as a back up to the employment of a diversion load controller. They are developing an innovative addition to their product line the ACLD-40, which will provide for diversion control using AC loads. One aspect of using diversion load controllers is that DC loads are often difficult to find and expensive. Magnum intends the ACLD-40 to be a solution to this issue by allowing the use of more common AC loads for diversion controlling such as AC water heaters or air heaters. This product is under beta testing at this time and is due for release in late 2014.


OutBack’s regulation

OutBack Power’s design provides for frequency shift method battery regulation. The disadvantages to this method can again be overcome by the introduction of a diversion load controller and this comes with the same issues as with the other manufacturers.   OutBack Power’s AC coupling white paper discusses both on and off grid applications for AC coupling (see appendix).

Disadvantages to AC coupling:

  • Frequency shift methods of regulating the battery state of charge are coarse and may create significant power loss if there is a miss-match of equipment leading to nuisance tripping of the HVBF inverter
  • Battery optimization may not be possible without re-introducing a charge controller as a diversion load controller
  • Complexity in systems mixing manufacturers can create systems that are difficult to operate
  • Care must be take not to void warrantees by using equipment that is not designed for this application


In many ways, AC coupling is a good tool for working with both the difficulties of retrofitting battery storage in existing HVBF systems and systems with long distances between resources and loads. As with any innovation in this field, be sure to get the right design and make sure that the application does not void product warrantees.





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SolarPro, HeatSpring, Ryan Mayfield Launch Megawatt Solar Design Class

 The online technical training experts at HeatSpring have teamed up with photovoltaic design and instruction professional Ryan Mayfield and technical media specialists SolarPro to launch a 10-week online course in megawatt-scale solar PV system design. To learn more about the course, register for one of two premium webinars being offered:

The Megawatt Design class is a technically rigorous and challenging 10-week course. Click this link for a complete commercial solar design training description and to claim one of thirty $500 bird discounts that are available.

The course has been developed for professionals who are responsible for designing, specifying, permitting, and managing the construction of megawatt-scale large-commercial solar projects and who need to stay current on equipment selection, design, budgeting, and code compliance. It is tailored to professionals with previous experience in large-commercial PV system design as well as those seeking to expand into the commercial market from a base of experience in residential PV system design. Students will use computer aided drafting, industry specific design tools and spreadsheet tools to complete the course.

Graduates of the Megawatt Design class will:

  1. Submit a complete set of drawings, equipment, budget, code references, and calculations for an actual megawatt PV system design project.
  2. Understand how to design projects that are cost effective, structurally sound, high performance and code compliant.
  3. Understand the current best practices for line side connections, grounding, rapid shutdown, fire regulations, and other complex and common design challenges for large projects.
  4. Be confident that their permitting package will be Code compliant the first time.

Course Outline

  • Project Qualification: In this opening week, we will review best practices for technical sales on large-scale commercial projects. Topics include: Establish major project goals, array location possibilities, rooftop/carport/ground mount, roof loading considerations, electrical infrastructure.
  • Equipment Selection: In this module we dive deeply into equipment selection. Pricing and equipment change rapidly in our industry. We’ll make sure you’re up to speed on the latest thinking. Topics include: Product selection thresholds, first cost, warranty, manufacturer service, module considerations including warranties and PID, inverter considerations, dc-to-ac ratio, micro/string/central inverter options, tracked and fixed racking, and system BOS.
  • Site Selection: This week we’ll cover requirements and best practices for siting your projects, covering both ground mount and rooftop systems. Topics include: Permissible shading allowances and  grading requirements for ground mounted arrays.
  • Software Tools: What software should you use to design large commercial solar projects? We’ll review the available options and help you to get the most out of your current or future program of choice, enabling fast, efficient design.
  • Designing Systems for Different Criteria: Every system design requires trade-offs. This week will cover how to optimize your designs for different criteria and how to minimize the downside of the trade-offs you make. Topics include: Lowest first cost, maximized energy production and targeted energy production.
  • NEC Considerations: Code, Code, Code. We could spend the entire course covering code, but we’re going to assume everyone in this course has a firm grasp of the NEC. This week we’ll discuss some of the 2014 updates and nuanced details to help you make fewer mistakes and get your jobs permitted faster.
  • Fire Code Considerations: Large-commercial rooftop systems require an in-depth understanding of fire codes and techniques for coordinating with fire departments, inspectors and owners.2012  International Fire Code (IFC) requirements will be covered.
  • Operations & Maintenance: Develop a detailed O&M plan that can be refined and re-used on your next large-commercial PV project.
  • Permitting: How do you get your permitting done faster and cheaper? That’s the multi-million dollar question. In this module we’ll provide tips and tools for getting your projects permitted more easily than your competitors.
  • Capstone Project: Students will receive all the inputs for a large-commercial rooftop installation, and develop and submit drawings, equipment and budgets to get the project installed as quickly and inexpensively as possible without compromising performance. Data for the capstone project comes from a real job. We’ve masked the identity of the project, but you’ll get to see all of the choices that were made and discuss the pros and cons of each as you do the work of designing your own system.

Continue reading

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5 Perspectives for Using Solar Subcontractors for Residential PV Installation

This is a guest post by Fred Paris. Fred teaches our 6 week Solar Startup Accelerator where students get the tools (budgeting, planning, pricing, project management) and business plan they need to start new solar business or solar division within an existing company, in 6 weeks. You can read more about the Solar startup class here. You can enter your email to get 1 of the 30 discounts available here. Fred is also hosting an awesome webinar on “How to Profitably Price Residential Solar” on Tuesday April 1st at 1pm EST. 

Enter Fred -

1. Define the Skills Needed of a Solar Subcontractor. 

To sell, design, and install PV without employees, you will need to work with subcontractors (subs) that have skills, tools, and construction savvy to implement PV projects to your specifications. Sounds a lot simpler than it is.

We sell, design. and install residential systems between 2 and 15kW. We need to hire three professional trades: electrician, roofer, and a general construction contractor. The electrician and roofer are required for most rooftop projects, while the construction contractor will work with the electrician for ground and pole mounts. We also use the construction contractor to reinforce trusses or roof rafters – as may be defined by a structural engineer.

Define the skills you need and specialize. Be careful of the subcontractor that says they can do it all. Perhaps they can, but as the PV project owner, you need to understand the detailed costs of the individual tasks. Only by understanding, the granularity of cost can you negotiate with contractors with clearly defined ‘scope of work’ statements.

2. Apply People Management skills

As the PV systems integrator, you may not have direct employees, but you will have vested interests in how the subs get along with each other. Having a clear scope of work is a good start, but you also need to see a working relationship develop between the subs. Subs need to work with each other ‘practically’ to determine that they will not be in each others way, and ‘financially’ to capitalize on such common needs as renting a lift. Both the electrician and the roofer might rent a single lift for roof top equipment and modules.

There is a need to recognize that installing rooftop solar energy requires ‘working on the roof’. There are good electricians that do not like high steep rooftops. In these instances, the roofer is ‘supervised’ by the electrician from a safe position or from the lift, bringing the electrician into visual and audible range of the roofer.

It is important the subs know how to work with each other and the management skills of the PV integrator is critical.  Help the contractors work with each other. Make sure they understand the scope of their individual tasks and how they integrate with the other trades. If your trades cannot work together, or are having inter-trade conflicts, find a new mix of subs.

Beyond the roofer and electrician, you will need access to general construction.  A general construction crew will build all the reinforcement for ground systems, ballast, or foundation, and will install pole-mounted systems. This contractor installs any rafters and truss reinforcement that may be required on a project.

The electrician is always positioned as the primary trade. The licensed electrician will often be the point of contact for rebate communication and relations with the state.

3. Define the Scope of Work

You will get to a point where you can call your electrician and say something as simple as: “Hi Joe, I have a new 7500 watt rooftop system going in downtown. They have 200 Amp service and I am planning on two inverters. When can you look at the project for me?”  You then make the same call to the roofer.

After a few projects the electrician and roofer know where one trade stops and the other starts.  For rooftop projects, the roofer and the electrician work it out to see who will install the mounting system and modules. In some instances, the roofer will install the mounting system and the electrician the modules. Understanding the details of work for each of the trades can avoid misunderstanding or ‘change of scope charges’

It’s key that you provide a very specific and detailed scope of work for each party involved and a process to verify that the work was done, and done how it was specified.

4. Make Payment Arrangements and Cash-flow Management

You need to be right up front with your subs about when they can be expected to be paid and how much. As the PV System provider, you may likely arrange a three-payment schedule with your customer. Perhaps you get some money up front, a payment when construction begins, and a final check when the system is turned on and all documentation completed.

That incoming revenue is part of your project cash flow. The other part is what is being paid out for hardware and services. Tracking “Cash Flow” on a project basis and plotting the payments to subs when they expect to be paid is important. Your payment arrangements with the customer need to cover hardware, software, labor, and fees. Your cash flow objective is to stay on top and in the green.  This is cash-flow management.

5 Document all Insurance

As we hire subcontractors (subs) you need to be sure they have the proper insurance coverage.  You need to ask the contractor for proof of liability insurance and workmen’s compensation coverage.  In many jurisdictions, if the subcontractor does not have workmen’s compensation you may be required to pay a premium for the people on your project.

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Best in Class Solar Thermal Monitoring: 50% Cheaper, 1/3 the Install time, No Moving Parts = Super Reliable


The Ohm by Sunnovations is a category killing, best in class, real time monitoring solution for residential solar thermal systems. If you think you’ve already looked into solar thermal monitoring and it’s too expensive, too complex and expensive to install, and not reliable enough, think again.

I’m constantly looking for technologies that will reduce risk for property owners that want to invest in renewable thermal technologies and that contractors can simultaneously use to increase sales, verify performance and decrease service costs.

Here is why the Ohm is better than any other option on the market for residential solar thermal monitoring.

If you want to learn more about the Ohm, click here to sign up for a free product training.

If you want to learn more about the Ohm, click here to sign up for a free product training.

Ohm Solar Thermal Monitoring

In the below interview, I spent 20 minutes talking with Matt Carlson the CEO of Sunnovations, the company that makes the Ohm system.

Below are what we talked about with minute markets so you can forward to what’s most interesting to you.

(Please note, I didn’t get into a fight the night before the interview, it’s poison ivy!)

  • 1:00 – What is the history of Sunnovations and what was the reason that you invented the Ohm?
  • 2:30 – What is the issue with the existing solar thermal monitoring technologies? What problem does this solve and how does your technology work?  [The most critical thing to understand is how much energy is being DELIVERED to the property owner, and the current BTU meters are expensive, and not reliable, the Ohm solves this]
  • 4:40 – How does the Ohm work and how it can understand a) solar thermal module production b) back up heat used and c) heat that is delivered and used by the property owners? Can it be used for both single tank and double tank configurations? [Quick answer, a long wire is installed in the tank over the length of the tank and it measures changes in average tank temperature. With this information and their algorithm, it can tell if the energy is coming from solar, back up heat, and what the property owner is using]
  • 8:20 – What is it that makes this technology so much cheaper, more reliable, faster to install and gather more useful data than anything currently on the market?
  • 12:00 – What are the most common installation and reliability issues with traditional BTU based monitoring systems?
  • 14:30 – Switching gears to industry trends, with all renewable thermal technologies a key obstacle is that there is a huge perception of risk to property owners with cash that want to invest in these technologies. Within these technologies, there’s not enough verification of system data that can be used to convince skeptical property owners. Is this something that the BEST solar thermal contractors are trying to solve and using monitoring for?
  • 17:30 – How  monitoring and easy access to data can provide an emotional attachment for homeowners to their system.
  • 18:30 – Can you speak to the accuracy of the system for the amount of energy that has been created by the modules AND delivered to the property owner? [Answer: Sunnovations commissioned a 3rd party study and it found a 1% error rate]
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You Must Master These 40 Steps to Install Residential Solar PV Profitably

Solar Project Management

This is a guest post from our instructor Fred Paris.

Fred teaches our Solar PV Installer Boot Camp + NABCEP Entry Level course. A portion of this course is dedicated to efficient project management. Click here to sign up for the next NABCEP Solar PV Entry Level Course.

If you’d like to download the image of Fred’s Gantt chart to use in your business, you can see do so below and at the very end of the article.

Download the Residential Solar PV Project Management Gantt Chart to Improve Your Operations

  • This is the email address that the Gantt chart will be sent to


If you look at the above Gantt chart, there are 40 steps (and depending on your utility, more than 40 documents required) to install a residential solar PV project. In order to install residential solar profitably, and cash flow positive, you must must these steps. This is true if you’re installing a single solar job per month, or if you’re installing 10+ jobs per month.

Performing high quality and efficient site visits is absolutely critical to the success of profitable solar projects, especially residential projects! You need to be able to capture all of the information you need to 1) quote the system correctly 2) design the project and 3) inform the installation crew what to expect. An efficient site visit process will lead to smooth operations and profitable jobs while complex process can lead to unprofitable jobs and a lot of confusion.

Also, if you’re going to be start a solar business and need to write a business plan, click here to RSVP 1 of the 84 discounts for our Solar Startup Accelerator. In 6 weeks, you’ll write a complete 20 page page business plan (for under $1,000 dollars) for your new solar business with expert guidance.

Click here to check out Sunify. Sunify is a simple mobile tool that solar sales people use to make sure they collect all the information they need on a site visit with the least possible effort. It’s so cheap it will pay for itself in one site visit. Sunify does 4 things that will make your site visits better.

  1. It will eliminate paper notes so you no longer have to copy and paste notes into emails and waste time.
  2. It will ensure that you, or the sales people that you manage, capture the information that they need to on the first visit.
  3. You’ll collect better quality information because you can collect video and audio notes in addition to photos and text answers. This will give lead to more accurate quotes, design, and an easier time for the installation team.
  4. It’s all the tools you need in one place, so you’ll never loose your notes again.

Click here to check out Sunify. 


Section 1. Project Management Tasks and Steps

Early Flurry of Activity

Our Gantt chart begins at the point where the contract is signed. This is the “Turnkey Contract”[1] with specific terms and conditions, many which have been defined by the CEC[2]. For new installers the Turnkey Contract has to be submitted to the CEC for approval. Once an installer has reached “expedited status” with the Massachusetts CEC, they begin to use the CECs’ Power Clerk system. A Turnkey Contract is still required, but does not need to be submitted for review.

Contract signing is a major milestone.  As soon as the contract happens, and we collect some early money (we call it ‘skin in the game payment’) the project really gets started.

Early activities include arranging and kicking off the requirements of the project that cost nothing.  The required energy audit – set it up. Utility net-metering application – get the application in early. Details for the structural approval must be gathered and in the hands of your engineer very early in the project.

The idea is that when an approval or authorization comes through, the project manager is ready to execute the next tasks.

[1] Samples included in class documents

[2] Massachusetts Clean Energy Center

Early Milestones

After the contract, the next most significant milestone is approval of the rebate application. Upon approved we collect some big money from the customer and order the hardware.  Sam collects 70% of the hardware[1] cost as defined in the cash flow of the proposal. Technically, you cannot qualify for the rebate if you start the project before the rebate is approved.  Recently however, (2013), as rebates amounts have lessened, Sam has been taking a chance and not waiting for the rebate to be approved. The logic is that if the rebate is not approved Sam would still want to do the project. For example, Sam would not walk away from a 5kW project sold for $29,000 with an expected $2000 rebate. When we quantify the risk, and consider the long history of successful rebates, Sam will start the project before approval. The savvy project manager takes prudent risk.

[1] Algorithms for pricing are reviewed in course material

Mid-Point Milestones

While Sam is waiting for the rebate to be approved, we initiated some of the required no-costs to the contractor activities. We arrange for the energy audit, we arrange for net metering, created the Bill of Materials (BOM)[1] for each supplier.  Continuing to wait, Sam has had discussions with our suppliers, we have firm pricing and shipping information, and we stand ready to “pull the trigger on the order” as soon as the CEC approval is in hand.

So then, it happens. We get a letter[2] from the CEC saying we can commence construction but we must be completed within a certain timeframe. We go to the customer with the good news and pick up a big check allowing us to order the hardware.

Sam shows the customer the original proposal and shows that the plan is moving forward and how this is the time for the next payment.

[1] Sample BOM Included in class documents

[2] Letter samples included in class documents.

Construction Milestones

Early on, Sam reviewed the project with his electrician and roofer to get prices that were marked up and included in the customers’ proposal. Now, Sam contacts the trades and test for start dates. There is no need to review the project; Sam works with the contractors to scheduling work the day the hardware arrives.

Getting to the Close

As the project is installed, Sam is tracking the installation. The electrician and roofer work together and the mounting system is installed according to Sam’s design. The electrician is installing the hardware and wiring, and at some point, we are ready to test the array. We activate the system to be sure it is working and then shut it down as we apply and wait for inspections.

The Paper, The training, and SRECs

Earlier in the project, we arranged with the utility to install a net meter and we defined the allocation of solar energy to different accounts (Schedule Z). Now, the utility gets a copy of the completed electrical inspection along with a certificate of completion[1]

The utility reserves the right to inspect the project, but they rarely do. In a few days, the utility sends a letter (email) saying that it is OK to activate the system.

The project manager arranges to have a closing meeting with the customer.  This is not just a casual thank you meeting. There are several important project objectives:

• Training the customer

The customer is walked through the project, shown the various disconnects and             switches, and informed on how they can gracefully shut down the system and             the sequence of activities to turn it back up.

• Delivering the Owners Manual[2] (written by the project manager).

• Review of each manufacturer’s warrantee papers.

• Contact information for future questions and support.

• Review of the on-line monitoring system and how to read the various reports

• Establish and complete the SREC application

• Collect the final payment

[1] Forms and documents provided in training

[2] Sample Owners Manual provided in training


For this project, we started when the contract was signed. In smaller firms, we often consider the scope of the project starting earlier  – as soon as a potential customer is identified.

The project manager defines: scope, project priorities, payment schedule, and sub contractor involvement.

The project manager and creates a systematic, step-by-step plan to get the system installed. This written plan – supported with a Gantt or PERT charts is shared with everyone, including the customer. Sharing this plan and getting others to acknowledge their part serves several objectives:

• All of the players will know when they need to deliver their part of the job.

• Contractors can see how any failure to deliver their services can affect the entire             project.

• The customer knows when payments will be expected.

Section 2. Tools and Techniques

Graphic Management Tools

Project management tools include Task charts; Excel based spreadsheets, Gantt charts, PERT charts, and many good homegrown tools based on spreadsheets and free on-line templates.

Contemporary on-line project management tools allow the entire installation team to share the same Gantt or PERT chart. Simple and free project management tools are available for the small installer, while larger firms invest in custom software. Custom project software can track any level of minutia that might be helpful.  For the small firm – keep the tools simple. The objective with software is to use the tools you need to help you keep on time, and in budget!   Many a project manager has felt captive by the very tools that were suppose to speed things up.

The Gantt Chart Snapshot

Looking at the Gantt chart (figure 1), we can see the Name of the Task the duration (in days), as well as start and end dates.

The three most important elements of a project plan include: cash flow, tracking resources, and projecting time toward end of the project.

Assumptions for the attached Project Gantt Chart

To discuss our Gantt chart and the underlying project, we need to make some assumptions about the project. In order to get to the fine details of this lesson, we should assume this is a very-small PV contractor (Sam). Sam is a one-person independent NABCEP solar practitioner with Entry Level credentials.

Therefore, Sam does everything including project management.  Sam made the proposal and sold the system. This is a cash deal and the customer will pay four payments along the way, (three progress payments and an early $2000 “skin in the game payment”- refundable later).

The Gantt chart reflects Sam using electrical and roofing contractors and managing all aspects of the project including collecting payments and tracking hardware delivery. Sam has worked with both the electrician and the roofer on several projects and has helped the electrician has gain “expedited installer certification” and is thus on the Massachusetts’ Power Clerk system. The contractor has met the insurance criteria for such qualification, and the system proposed meets the technical requirements of the Commonwealth Solar Program.

Section 3. Scope of Project Management

Project Geography

Massachusetts offers one of the most complex business environments for the residential PV installer. The Wind Sun Institute, having experience in other Northeast states and exposure to practices in other regions of the country, recognizes Massachusetts as having one of the most complexity implementation processes in the country.  For this reason, we selected Massachusetts as the template model for the lessons of this program.

Those who work in other states may not require every step, but they will gain insight into techniques and procedures used by a successful firm in a complex regulatory environment.  We believe that if you can manage residential PV installations in Massachusetts – you really know how to get PV installed.

 Scope Defined by Organizational Size

At the residential level, Solar PV is one of the most complex projects a manager may be challenged with.  When we seek to define the scope of project management we discover it largely depends on an organizations’ size.

For a smaller PV company, one person may be the only person of the company. In that instance we know who the project manager will be. In larger solar operations, with many simultaneous projects, several people will be touching every project, but there should be a clear hierarchy to a single person with responsibility and – just as important – corresponding authority, to get things done – this is the Project Manager.

Project manager can mean different things in different firms, In larger construction firms; the project manager may be the field person running solar operations at the site.  This person may not even meet the customer until the first day of construction – if at all.  In larger organizations, each person involved may define his or her segment or contribution as a project. The buyer in a large firm for example, will have responsibility for each “project” they need to buy and manage procurement and delivery for.

What do we look for in good project management?

It is clear that project management skills include: clear logical thinking, the understanding of sequence and flow, contractor relationships, understanding cash flow and payments, the ability to keep and update detailed records, all while having political sensitivity and diplomacy to get things done with people.

Large and Small PV firms

In larger organizations project work and tasks may be segmented into:

  • Sales – closing the deals – customer interface to the firm.
  • Buying – working suppliers, pricing, deliveries
  • Administration – paper pushing, contracts, letters, applications, permits etc.
  • Operations – technical design, and fieldwork installing the solar project.

At the other end of the spectrum, we have the small PV company – sometimes just a one-man show hiring contractors. For this person, the project and the documentation start when the phone rings and a potential customer ask a question.

As a PV firm grows, it is almost universal that the first step logical steps toward task-segmentation is having a dedicated person (typically inside) to push the paper, the forms, and the applications, and maintain records.

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How to Design Homes to be Solar PV Ready

Screen shot 2013-06-24 at 2.48.45 PM

Many homeowners  might be building a new home or doing renovations and they want solar, but not right now. The following is a guest post from Jamie Leef, an expert builder and solar installer at S+H Construction that will be helpful to general contractors and architects that are advising their clients. Jamie is also teaching a course for architects and engineers on design considerations for integrating solar in urban areas.

By making a few changes to the building while construction is under way, you can make installing solar MUCH cheaper when they finally decide to invest in solar.

Solar PV Ready For General Contractors, Engineers, and Architects

Download the checklist for designing a home to be solar ready.
  • The document will be sent to this email address

Enter Jamie Leef

This is standard document we provide to firms we work with to advise their clients. In any place where I say “we” you can substitute with “solar contractor”

If you’d like me to BID on a solar project. Here is my contact information

Jamie Leef

Division Manager

Renewable Energy and Green Building

Office: 617-876-8286

Cell: 617-901-5522

Design Homes to be Solar PV Ready Summary.

PV systems have three key components:  Roof- or ground-mounted panels, DC-AC power conversion equipment mounted either at the panels or in a mechanical space, and balance-of-system gear that measures, controls, and connects the parts to each other and to the electrical grid.

Keep these things in mind when designing or analyzing a residence for a solar PV project:

  • The roof needs solar access!  This generally means an area of flat roof, or pitched south-facing roof, that is unshaded and large enough for the panels.  A typical 4 kW array is about 270 SF.  Modules are in units of approximately 40” x 66”, though other sizes can be found.
  • The roof structure needs to be able to handle an additional load of 3 to 4 pounds per square foot.
  • Your client should like the way the panels and proposed layout look.
  • The roof cladding should have a standard manufacture’s detail for attaching something to it.  All typical materials do – fiberglass/asphalt, EPDM, TPO, slate, etc.
  • The building should have an electric meter owned by a customer who uses a good amount of electricity.  Condos, for instance, can get complicated.
  • The building should have electric service from a utility that offers net metering and PV interconnection.  Some space should be set aside near the main electric panel for solar power equipment.  The amount of space varies by system type, but is usually about 4’ x 4’
  • A conduit will be run from the PV equipment location to the PV panel mounting install area.  This can be inside the building, on on the outside.

Other Kinds of Installs

Okay, so your project does not look like the other cookies that the cookie cutter created.  Here are some other scenarios to consider.

  • Consider a ground-mounted system if your roof can not take panels
  • Within some utilities and areas you can share net metering credits with other meters, which can allow for installs in condos, for instance, to pay back to several residents.
  • If you can not get an interconnection agreement, consider going off grid!  We have even done this in downtown Boston.  Ask us how.
  • Remember that solar hot water takes less space on the roof.  It also works very well in multifamily buildings where there is a shared water meter and hot water distribution system.

Solar Ready Details.

The following are things that should be done to design or prepare a residence for a solar PV project.

  • Ensure the roof has the structural capacity to accommodate the panels
  • Rough-in an unbroken metal conduit from the PV equipment location to the PV panel mounting install area.  There are to be no accessible pull-boxes or ways to access the DC conductors.  Please refer to section 690 of the NEC, and to the local AHJ for the conduit material options.  Large systems with a central inverter might have several DC conductors in this conduit.  Micro-inverters will have conductors designed for AC.  Size the conduit accordingly. If you have questions about sizing conduit call S+H Solar HERE
  • Label the conduit with “Solar PV Circuit” labels as per 690 NEC
  • Please discuss the specific site requirements for future access to cathedral ceilings, attic spaces, and the possible exterior conduit paths.
  • For exterior conduits we strongly recommend metal pipe or flex rather than plastic pipe for durability and temperature correction reasons, even if code does not require it.
  • Provide a 4’ wide ¾” plywood mounting panel adjacent to the main electric panel that is at least 4’tall and centered at 4’ AFF, but can be taller if possible.  Ensure there are similar electric code restrictions to this space, such as no water above, 3’ clearance in front, and free air above and below, etc.  Micro-inverter systems do not require this much space, but it will never go to waste.
  • Ensure that the proposed PV system back fed breaker rating is no more than 20% of the bus-bar rating of the main electric panel. For example, for a 200 AMP main breaker, the maximum overfeed is 40 AMP.  There are other optional interconnection points, depending on the utility and the service details.   If you there are multiple breakers, if this is multi-family home, or a small service and you have questions, please contact S+H Solar:
  • Leave a two-pole breaker blank space at the bottom of the bus-bar reserved and labeled for use as the PV back-feed breaker (or the section of bus that is opposite the service cable feed lugs or breaker).
  • Endure space for a small AC side-arm disconnect next to the exterior service entrance (assumed to be an electric meter cabinet).  Install a capped, waterproof conduit to that location for future AC wiring from the PV equipment panel if that location will be otherwise hard to wire to in the future (for instance, complicated foundation finishes insulation, or finished basement).
  • Provide a terminated CAT5-E or better, data cable to the main house router for monitoring at the PV equipment mounting location.

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Real Time Data on Actual Geothermal COPs – Part 2 of Lessons Learned from 100,000 Hours+ of Real Time Geothermal Monitoring Data

This is a very nervous time for the geothermal industry and I can feel it when I’m on the phone with installers. There’s a lot of geothermal companies that have been around for 20+ years and now there’s a lot of innovation happening around policy, real time monitoring, and playing around with different ground loop heat exchangers, that industry veterans haven’t had to deal with before and it’s uncomfortable for them.

Here’s my main message to the geothermal industry: if you’re asking everyone to look at new ways to heat and cool buildings, you also need to be looking at new technologies, policies, and ways of doing things yourselves. Some of you are, but on average I notice more hesitancy within the industry than excitement about embracing (inevitable) change. I could be wrong on this, just my perception.

Monitoring projects means that we’re going to find great, good, and bad systems. In fact that’s the goal. Matt is a little more soft spoken so he wouldn’t say this, but yes, we will find bad systems.

With that being said, I’m super excited to be working with Matt and publishing this data. There’s only a small group of things the geothermal industry can do to proactively (unlike waiting around for fuel prices to increase by 300%) increase the adoption of the technology; including working for better policy, better ground loop innovations, decreasing customer acquisition costs, and verification of system performance.

Geothermal technology has a low margin of error, if anything is messed up during the design, installation and (most overlooked) operation of the system, the efficiencies will be shot. Here’s some of the interesting bits of information that can easily be found monitoring more than just kWh of the system:

  1. How much does the COP drop due to pumping losses
  2. Equipment failures; low refrigerate, valves, and pumps.

If you want more on monitoring check out these previous resource:

  1. Performance Based Contracts Are the Future of Geothermal
  2. Lessons Learned about Ground Loop Sizing from 100,000+ Hours of Real Time Geothermal Monitoring 
  3. Free Course: How to Install, Commission and Use Real Time Geothermal Monitoring

Matt and Ground Energy Support’s data is a robust but small sample size, compared to the whole industry. But it shows the possibilities of what we can figure out with a larger sample size and more data. If you’re a manufacture, distributor, installer or driller, utility, or state energy official and would like to go a monitoring and verification study. Feel free to call me, Chris Williams at 800 393 2044 ex. 33, or Matt Davis at (603) 867-9762

Future posts will include

  • Geo Monitoring Quality over Quantity: Why All Data is Not the Same
  • Characteristics of the Best Monitoring and Verification Study
  • How Monitoring can Eliminate, or Prevent, Angry Customers Once and For All
  • Expected Versus Actual Performance: Comparing LoopLink Predictions to GES Data

DOWNLOAD Geothermal Operating COPs

Give us a few pieces of information and download the whitepaper that provides an in-depth review lessons learned from real time monitoring on the operating COPs
  • The guide will be sent to this email.

Enter Matt Davis from Ground Energy Support


This article is the second in a three-part series prepared by Ground Energy Support LLC (GES) that will highlight some of the lessons learned from over 100,000 hours of real-time ground source heat pump (GSHP) monitoring data. This is written for GSHP installers of residential and light commercial systems who want to learn how to leverage real-time Performance Monitoring to build better GSHP systems, reduce their risk and callbacks, and ensure customer satisfaction.

The previous article focused on showing how data from real-time monitoring can be used to assess how the ground loop is performing relative to both the installed capacity and the measured heating load. The daily load profiles presented in that article are now available to GxTracker™ users as part of their Performance screens (login required to view Load Profile graph).

This article focuses on the overall system performance, factors that affect performance, how real-time monitoring can be used to evaluate performance of installed equipment, and identify and address issues before they become problems.

The number of sites represents a relatively small sample size and the different measurement techniques used at the sites result in different levels of accuracy.  In spite of these limitations, we are able to identify and illustrate several factors that affect system performance.   As more sites are instrumented with web-based monitoring systems that have the capability of quantifying ground loop performance, geoexchange, and electrical consumption, there will be an unprecedented ability to assess a wide range of GSHP designs over a wide range of geologic and climatic conditions.

Measuring GSHP System Performance

GSHP systems have the potential to significantly reduce the energy needs for space heating and cooling (an estimated 4 Quadrillion BTUS in the US) and reduce greenhouse gas emissions. However, these benefits will only be realized if the systems operate efficiently. Efficient operation requires proper design, installation, and maintenance.

One common method for assessing system performance of residential systems is to review the customer’s electric bills on a regular basis. While lower electric bills are a clear indication that the systems are operating efficiently, it is often difficult to parse out other factors that contribute to the overall electrical consumption. Additional challenges to using a customer’s electric bill to assess system performance include: new construction has no baseline for comparison; retrofits will often combine the addition of a heat pump with other efficiency measures, making it difficult to attribute the savings to the GSHP; and finally, when an electric bill is higher than expected, the cause may be unrelated to the GSHP system. One of the biggest disadvantages of relying on electric bills as a measure of system performance is that the homeowner is left to identify and report GSHP performance problems. In short, the most effective way to demonstrate that a GSHP system is performing efficiently, and thus ensure customer satisfaction, is to monitor the system in real-time so as to assess key performance metrics.

Many factors contribute to the overall performance of a GSHP system. Through our monitoring activities to date, we have found the main factors to be:

  1. Heat pump performance and ground loop temperature
  2. Pumping energy necessary to circulate loop fluid
  3. Heat pump cycling patterns
  4. Auxiliary electric heat

One of the key metrics of assessing how a GSHP system is performing in heating mode is the Coefficient of Performance (COP). The COP is the ratio of useable thermal energy to the thermal equivalent of the electricity used to operate the system.

While measuring the COP is not always the primary objective, all of our real-time monitoring systems include, at a minimum, measurements of entering and leaving water temperature (EWT and LWT), heat pump status, and an estimate of fluid flow. When power measurements are not available, power consumption is modeled using the heat pump specifications, a pump penalty based on type of system and flowrate, and measured runtimes. These methods provide representative values of COP with an error of +/- 20% and are intended to show overall trends in system behavior.

In some installations, a higher level of accuracy is desired and additional measures of power consumption and, if necessary, flowrate can be included. When accurate measures of both flow and power consumption are available, the accuracy of the COP improves to approximately +/-5%.

Because the accuracy of the computed COP varies from site to site and quality assurance measures are necessary to insure the values are representative, COPs are not computed automatically as part of our performance metrics. Rather, the necessary components are available by downloading either the minute-resolution observations or integrated daily values.

Daily Average System COPs


Figure 1. Daily Average Measured COP at 5 installations ranging from US Climate Zones 4 to 1. See Table 1 for site designations and seasonal average COPs. Power measurements are included for Sites B, C, and E.

The Daily COP values presented in Figure 1 and summarized in Table 1 illustrate some of the main factors that affect performance. Overall, there is an upward trend in performance as heat pump technology has gone from single stage to multi-stage compressors.

The system with the lowest performance (Site A) has single stage heat pumps using a standing column well. The two-stage heat pump on a standing column well (Site B) has a higher COP, but is adversely affected by the power required for fluid pumping. The COP of the two-stage system on the closed vertical loop (Site C) varies more through the year due to both the change in EWT and the use of the auxiliary electrical heat in late February. The performance of the two-stage system using two well groundwater loop (Site D) is comparable to, and slightly higher than, the other two-stage heat pump systems. The system with a variable stage heat pump (Site E) has the highest average COP. This is likely due to a combination of the variable-stage technology and its geographic location which enabled it to maintain higher EWTs throughout the winter.

These COP values are consistent with those reported by Puttagunta and others in their 2010 study of residential GSHPs. We have also found that, while the in-field performance is typically less than the AHRI rating, the systems are seen to provide a reliable technology for heating and cooling at consistently lower cost than conventional systems.

Table 1: Seasonal Average System COPs, Winter 2012-2013
Site System Description Average COP
A Standing Column Well, 2 Heat Pumps, Single Stage 2.74
B Standing Column Well, 1 Heat Pump, Two Stage 3.15
C Closed Vertical Loop, 1 Heat Pump, Two Stage 3.27
D Open Two Well System, 1 Heat Pump, Two Stage 3.33
E Closed Horizontal Loop, 2 Heat Pumps, Variable Stage 4.18

Factors that affect System COP

There are several factors that affect the overall GSHP system performance. Because of the wide range in GSHP system designs and equipment available, there is not a single best approach to optimizing performance. Rather, we show how monitoring can help characterize the elements that affect specific installations. Again, the lessons learned and examples presented in this initial series of articles focuses on heating mode and uses examples from installations ranging from US Climate Zones 4 to 1.

Heat Pump Cycling

It has long been recognized that rapid cycling of heat pumps diminishes performance and increases mechanical wear on the equipment. In recent years, more efficient dual stage heat pumps have become common that enable heat pumps to operate for longer cycles, produce lower heat output, and use less electricity.


Figure 2. Three examples of heat pump cycling patterns. Each diagram represents the GeoExchange for a six hour period of heating (heat extraction). Top image is from a system with two single stage heat pumps (5-ton and 3-ton units). Middle image shows the GeoExchange for a two-stage (4-ton) heat pump. Bottom image is for a variable stage (3-ton) heat pump.

Figure 2 shows the heat pump cycle patterns for three different systems: one with two single-stage heat pumps, a two-stage heat pump, and one with a variable-stage heat pump. While the single-stage heat pumps reach their expected heat of extraction (~22MBtuH for the 3 ton and ~40MBtuH for the 5 ton), the average production of the heat pumps (while running) over this same period was 17 MBtuH and 32 MBtuH, about 20% below their steady state production. In contrast, the two-stage heat pump is able to maintain its steady state heat production in part load for cycles of approximately 30 minutes and then, when additional heat is necessary, switch into full load. With two-stage heat pumps there is much less efficiency lost from cycling on and off. The final example is a new variable stage heat pump that operates over extended periods of time, adjusting the heat output to meet demand. In general, the lower stages provide greater performance by varying heat output over multiple stages thereby increasing overall performance.

Loop Temperature

Entering water temperature is well-recognized as one of the leading factors affecting system performance and heat pump manufacturers provide performance specifications for temperature ranging from 25 to 100 ° F.


Figure 3. Measured COP for 15-minute intervals during which heat pump was running continuously. (A) Measured COP for different times of the day relative to manufacturer COP for different loop temperatures. COP values in (A) include power from both compressor and flow center. (B) Same measured COP values (green) compared to the COP in (A) with the pump power removed (yellow)

In the example shown below (Case A from last week’s article on Loop Performance), the power consumption of the heat pump circuit (which includes the flow center), and the Auxiliary electric heat are being monitored separately with a WattNode power meter. The COP is calculated for 15-minute intervals through the 2012-2013 winter. To remove the variability of performance associated with the heat pump cycling on and off, we only include 15-minute intervals for which the heat pump was running continuously. The EWT ranges from 33 to 51 °F. While there is an overall correlation between COP and EWT, there is also considerable variability at a given temperature.

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Lessons Learned from 100,000 Hours+ of Real Time Geothermal Monitoring Data – Part 1

This is a guest article by Matt Davis, co-founder of Ground Energy Support (GES). GES provides a top quality real time monitoring package for monitoring geothermal heat pumps. Matt is an expert in geothermal monitoring. Matt has over 25 years of experience in data collection, analysis, geology and modeling of groundwater systems. He is now bringing that expertise and passion to help address the number one research priority in DOE’s recently updated GSHP Roadmap, see below “Collect/Analyze Data from GHP Systems”

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Matt is an extremely active member of the ASTM committee that is working to develop heat metering standards in the United States. This committee is extremely important for implementing production based incentives for renewable thermal technologies and the lack of such a standard has been holding up the implementation of New Hampshire SB 218, the first production based renewable thermal incentive in US. This standard will also have implications for Massachusetts Bill SD 1593, which will create a production based incentive for renewable thermal technologies in Massachusetts, if it passes.

Matt is without question a top US expert on monitoring ground source heat pumps and he has the data to prove it ;)

A Few Odds and Ends Really Quick

  • If you’d like a larger copy of the data and graphs in this article, you can download it here. 

DOWNLOAD Lessons Learned Monitoring Geothermal Ground Loops

Give us a few pieces of information and download the whitepaper that provides an in-depth review of the current state of geothermal monitoring.
  • The guide will be sent to this email.

This Series of Articles on Geothermal Monitoring Lessons Learned is for 2 Audiences 

1. Geothermal professionals that want to remove risk and improve their designs.

Never have angry customers again, because you can set up alerts.  Remove your risk, especially drillers, by being able to objectively calculate how much energy was extracted from the ground.

In the geothermal industry, I see three main groups. We can call them, the bottom 50%, the middle 45%, and the top 5%. The bottom 50% of the industry are the notorious, yet elusive “hacks” that everyone in the geothermal industry complains about. This technology is not for them, because it would show them how bad their work is. The top 5% is what I’ll call the geothermal old guard. These are companies that have been doing geothermal for 30 years+ and have a set standard of their ways, and don’t feel that they need to verify anything. They “know” it works. The middle 45% is really the group of contractors that is new to the geothermal industry, are extremely business savy and very confident in the quality of their designs and installations. You want monitoring to verify your designs, removes risk from your businesses and sell more jobs.

2. Policy Makers in New England

The second major group is policy makers in New England (particularly Massachusetts, hey guys!) that are now looking more and more into renewable thermal technologies and want real data on how the systems are performing. On the policy front, I’ll be doing following up posts on solar thermal and hopefully advanced biomass as well.

3 Geothermal Trends We Can be Proactive About

There are only four that I’ve been watching (click here to read 4 Trends Driving the Geothermal Industry) and working on lately that are exciting me about the geothermal industry. There’s only three that was can actually do anything about. First, policy. Second, how can we shove plastic in the ground in different configurations to decrease ground loop costs. Third, real time monitoring. Fourth is rising fuel costs, which we don’t have control over.

The geothermal industry is filled with people that think everyone outside of the industry are trying to stop the adoption of ground source heat pump. So, instead of thinking about what we PROACTIVELY do to further our industry, too much time is spent talking about what other people need to do.

Monitoring is critical because it is something we can proactively do that we solve a lot of problems.

1. “Geothermal is too expensive” –> Wrong, it’s not expensive. We don’t have the right policy in policy to support adoption. We need verified data to implement policy. Mark Faulkenberry from Western Farmers Electric Co-ops data is a good start on the utility side, we need more.

2. “The public needs to be better educated” –> Wrong. We, as in industry, need to be better marketers, salespeople, and communicators and prove the value to them. This starts with verifying performance claims.

What all of this means is that adoption of real time monitoring of geothermal systems is one of the most important things we need to start doing as an industry

Enter Matt Davis from Ground Energy Support

This article is the first in a 3-part series that will highlight some of the lessons learned from over 100,000 hours of GSHP real-time monitoring data. This is written for GSHP installers of residential and light commercial systems who want to learn how to leverage real-time Performance Monitoring to build better GSHP systems, reduce their risk and callbacks, and ensure customer satisfaction.

The overall goal of this Performance Monitoring series is to engage the GSHP community in a discussion of both 1) what is possible and 2) what is useful. This first article focuses on how web-based performance monitoring data can be used to assess the performance of the ground loop relative to installed capacity. The second article will focus on using performance monitoring data to assess the overall performance (COP) of the system and how the ground loop, heat pump, and loop pump all contribute (or limit) system performance. The third and final article will discuss how performance monitoring can be used to develop and implement performance guarantee contracts. This initial series of artilcles will focus on heating applications in residential and light-commercial installations. Cooling applications that will be addressed in future articles this Fall.

Loop Temperature

There is a growing consensus (e.g. “Ground Loop Performance”) that monitoring Entering Water Temperature (EWT) is important, relatively easy, and helps to identify problems in system performance. There is less agreement as to what the minimum entering water temperature should be for a specific application or whether adhering to a uniform standard (e.g. ISO 13256) is best for all clients under all conditions. Regardless of your design preference and practice, EWT should be monitored to ensure that your systems are operating within the design limits.

As shown in Figure 1, there is a wide range of behavior in the EWT of GSHP systems in the Northeast. The variation is due primarily to differences in design and use. All loops shown in the graph below are vertical boreholes, but they range in design from open diffusion (one well for groundwater extraction and another for groundwater return), standing column wells with various levels of bleed, to closed loop systems. Geographically, they range from Connecticut to southern New Hampshire. The residential systems are dominantly used for heating and the commercial installation has a significant cooling load for most of the year.


Daily Minimum Entering Water Temperature for a range of GSHP sites in New England. Values represent 1-minute sampling interval and are filter for conditions when heat pump is running.

While the minimum EWT is a good indicator of ground loop conditions, the average of the entering and leaving water temperatures [½(EWT+LWT)] is a more meaningful metric for evaluating how the ground loop is performing relative to heating and cooling load.

Building Load

Real-time monitoring data can be used to track building load under a wide range of conditions and assess system performance. Building load provides a critically important context for interpreting loop temperature data, as it enables the installer to demonstrate that their system is operating as designed and isolate factors that are outside of their control. For example, construction practices (insulation of windows and door jams, proper ductwork installation) can have a significant impact on an GSHP system. The installer is often provided the building specifications and leaves it to the building contractors to meet those specification and can’t be on site to inspect all phase of construction or renovation. If the building envelope is not on spec, problems that arise in the heating/cooling system will like fall in the lap of the installer — why isn’t the system working? Also, installers can’t control homeowner’s thermostat settings, some of which may affect the efficiency of the system. However, by monitoring the system load, installers can identify discrepancies between operating and design conditions — discrepancies that may impact system performance and customer satisfaction.



The total building heat load is the sum of the GeoExchange and the heat produced by the compressor. In this discussion of Performance Monitoring, we focus on the GeoExchange portion of the building load as it is readily measured and is most closely tied to Ground Loop Performance. GeoExchange [MBtu/hr] is measured by multiplying the temperature difference (EWT – LWT) by the mass flow rate and the specific heat capacity of the circulating fluid.

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Off Grid Solar in Downtown Boston

(Download this schematic at the end of the article)

Designing and installing solar PV in dense urban area is much more difficult than installing 5kW on a 10 pitch shingle roof in the suburbs. The challenges are numerous and include junky roof framing, town homes and apartments with low roof area-to-electrical load ratios, historical committees, and, interconnection to antiquated electrical grids.  For this reason, most pure play solar installers and financiers tend to stay away from the hard stuff, they’re still focusing on getting the lowest hanging fruit. However, clients in urban areas are asking more and more solar solutions.

This is the story of how Jamie Leef at the solar division of S+H Construction installed an off grid solar PV system; off-grid in the sense that it did not interconnect with the area network grid in downtown Boston. If you think off-grid/solar power backed-up systems are a thing of the past, think again. They’re likely a thing of the future, as one of nations largest utility IPPs, NRG Energy, is pushing towards solar + battery backed up.

Jamie Leef and S+H Construction are expert builders (see all their awards–>), used to dealing with integrating solar in complex existing systems and structures and is an expert at installing solar in urban areas. If you’re an architect or engineer and need to get advice about integrating solar PV into a complex structure, give Jamie a call.

Continuing Education Free Course

Jamie has created an amazing continuing education course for architects, engineers, and generators. Click here to sign up for FREE COURSE (for a limited time) “Solar PV Design Considerations in Urban Areas for Architects, Engineers and General Contractors

I had a quick conversation with Jamie about the installation. If you’re a general contractor, roofer, architect or engineer and need help with a difficult project, contact Jamie at S+H Solar here. 

Q: Let’s start at the top, what is the reason for having an off-grid system in downtown Boston?

A: There are several sections of Boston, Cambridge in Springfield Massachusetts where the grid is much older.

Normal electrical grids are radial networks where transmission lines come from a substation to transformers and feeders going to several homes.  It looks like a hub and spoke.

An area network is an older style of distribution that involves multiple grid feeds, transformers and building service access points.  It looks more like an Ethernet network.

The switchgear is much older.

Some utilities have been experimenting in different parts of the country with DG and back-feeding area networks, but engineers are very afraid of this because it’s easy to blow up one of the transformers and the nature of the area network can to shut down if there is any backfeeding.

Q: So, I’m guessing you had a client who wanted solar in an area network?

Our client wanted solar but they were in an area network. They have a house that had a substantial electric use. We were able to design a solar PV system on their property that serves their loads, but doesn’t back-feed into the grid.

We did this by using an off-grid style design where there are batteries fed by solar, and a backup generator. In this case, the backup generator is the grid.

Q: What is the design theory for this application? What loads are you matching? Is the project off grid in the sense that the PV array only charges the batteries, the batteries go to the inverter to supply house loads, but the grid can also charge the batteries?

A: The batteries feed all loads. If they become low, the inverter will switch to the grid until the solar has enough power to supply the load, or until the solar has charged the batteries enough to supply the load.

We designed the system to charge the battery bank in a reasonable period of time so that batteries can meet the average daily loads that is supported by the sun.

In this particular application, there are two parts of the condo each with it’s own electrical service panel.  One part includes several rooms and some general, non-essential loads. The second part includes the kitchen, some general lighting, and other circuits that are more critical loads that would be nice to be backed up in an electrical outage.

The nice thing about an off-grid solar system is that you’re actually your own utility. As long as the solar is powering the batteries, you have power.

Q: What were the building and utility integration considerations for building in downtown Boston?

The project is on the top of a 20 story building, so construction is always a little complicated. It’s on the top of a high rise with a ballasted roof, so the wind loads are high which have to be dealt with, but it’s nothing that our roofers are not used to dealing with.

It required a significant amount of negotiation with the utilities for the client to be able to satisfy the Commonwealth Solar Grant program.

There was a design challenge in sizing the solar array and the battery bank for the load that you want, this case the client had to decide how much of their home they wanted to be off-grid.  The hourly, daily, and seasonal profile of these loads determined how many modules were needed, and the size and cost of the battery bank.

Another challenge was locating the batteries. Traditional solar batteries are not well suited to be put into living spaces due to hydrogen build, fire hazard, and other issues.  We chose batteries very carefully.

The final item is to figure out house wiring. In the case of a renovation, it’s a little easier because the project electrician can place circuits as needed. In the case of an existing home, it can be a little difficult to break out loads in the most optimal way.

Q: You mentioned the largest challenge was getting the utility to sign off on the project. Why was this a challenge?

It’s easy for a solar installer to say “my system is not going to back-feed”. It’s a different challenge for a solar installers to sit in a meeting with 6 utility engineers that and PROVE that the UL 1741 listing for inverters is a guarantee that they can live with and guarantee that there will be no backfeeding. These are engineers that are very familiar with the nature of the electrical grid. This required us to bring in PE and do some pretty intense negotiation.

The reason we need a letter from the utility is to prove to the Commonwealth Solar rebate program that you can get the “interconnection agreement” and access grant funding form the Renewable Energy Trust.  They need to be grid tied to use their grant money, which comes from the Renewable Energy Trust.

In this, it’s connected to the grid, but it’s not interacting with the grid. There was no regulatory structure for what we were doing, so we had to create a structure.

We invented a new category for a non-interconnected, utility oriented system. In order to get this, we had to convince the utility engineers.

Q: What were the lessons learned and what is your advice for architects, engineers and property owners that might live in a radial network and want solar. If someone called you and wanted advice, what would you tell them?

The cost of the system with batteries is higher than the cost of a normal grid tied system per kW because of the high cost of the batteries.

However, we have many clients that want some kind of back-up generation in their homes. In the suburbs, people will get a transfer switch and a generator. People like having backup power.

One of the advantages with a battery based solar project is that you already have a backup generator. That is actually worth the money because getting solar with batteries is CHEAPER than getting solar with a backup generator.

Also, in a densely populated area, it’s harder to get a generator because it makes a lot of noise.

Battery backed up solar PV is silent and economical when compared with a backup generation if you were to buy a generator. If you want backup generation and have room for solar, having a battery back up is a great alternative.

The property described here also has solar thermal integrated into it and that can be just as good an option.  This is especially true in a condo situation where several owners want to share solar the resource.  The physical installation can be easier because shared mechanical infrastructure is common for domestic hot water systems.  At S+H we have innovated a fractional ownership model that will allow individual condo owners to monetize incentives.  Keep that option on the table.

Q: How do you determine if a client is a right fit?

They have to be committed to solar and have the roof space.

Condominiums are another issues to consider. If you live in a condo, you’ll need to confirm that you have the roof access and roof rights.

Q: If they are want to get a battery based solar system, how do they make sure the process goes smoothly?

There are two huge roadblocks for an installer who has not done this before. First, no having proper documentation of past projects to show to the utility. Second, not having the relationships in place to meet a construction schedule.

I know the exact person to speak with and I have a special letter from the utilities in case we want to do another one of these projects. We have a letter from upper management at a utility that we can use over and over again. If you don’t have this, it will take you a long time to go through the process.

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