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

[Interview] Learnings from Ball State and the Largest Geothermal Project and What It means for Selling District Heating Geothermal

A few months ago, I heard about the largest geothermal heat pump installation was breaking ground at Ball State University. Clearly, this is amazing project that could change the whole industry. Also, I always noticed PR for huge solar PV projects and knew that we needed to get out the world about ground source. So, I wrote an article in Climate Progress about the project.

Jo Ann Gora, the president of Ball State University, reached out to Joe Romm, the editor of Climate Progress to thank him for the piece and he forward it to me.

I reached out Ms. Gora wanting to understand more intimately how the decisions was made within Ball State to under take such a large project that a huge accomplishment on so many levels. I wanted to learn a few things

 I wanted to understand their buying process and internal decision making. As an industry, if we can start to understand how large institutions, like Ball State, invest ~60 million dollars into geothermal, we’ll be able to sell more projects.
I wanted to understand if there were any issues that almost killed the project within Ball State.
Lastly, I wanted to learn what they learned about the technology and if there were any technical bottlenecks that almost killed the project.

I spoke with Ms. Gora for about 20 minutes, I also spoke with Jim Lowe who is the Director of Enginneering, Construction and Operations at Ball State.

Here’s my conversation with Ms. Gora

Q: What was the inspiration behind the project? Was someone pushing it within the university or was it advised to your by an outside engineering firm?

A: It’s a really great story. In December of 2005, our board approved the purchased of boiler equipment and to sell bonds to finance the project. So, we were going with a traditional system and we had received authority to release bonds to replace our existing equipment.

We were going down this route and what we discovered, when we completed the sale of the bond, 2 years later, is that prices for the original equipment had gone through the roof. We no longer had enough money. Also, due to the size of the project, we were going to have to buy the parts from outside the US. We were getting a hard time getting bids and we didn’t think we could get a competitive price. So, it forced us to ask ourselves if there was alternative and better way.

We’re a university and we figured we’re going to be around for another 100 years, so we started talking to a lot of people about alternatives, something that would be really sustainable.

Being aware that fuel prices are volatile, that the push for energy efficiency was really, and not liking the idea of spending the money outside of the US, we started asking ourselves internally if there is a better way.

We turned to our Senator, and he arranged a call with NREL and Oakridge Laboratory and they put us in touch with top geothermal experts. They told us that only recently had the technology matured to a point where you could heat and cooling many buildings, and not just one.

[…]

August 3rd, 2012|Categories: Drilling, Geothermal and Solar Design and Installation Tips, Geothermal Heat Pumps, Solar Sales & Marketing|Tags: , , , |
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Part 3: How to Design Grid-Connected Solar PV Inverters, Strings, and Conductors

This is a the third installment in a three-part series on residential solar PV design. The goal is to provide a solid foundation for new system designers and installers.  This section is dedicated to the basics of inverter sizing, string sizing and conductor sizing.
Download the full PDF “Solar PV Design and Installation Guide”

Part 1: How to Design a Solar PV System: The Basic Terms
Part 2: How to Design Solar PV – A Walk-Through of Array Sizing and Estimating Power Production
If you’re looking to start a solar business, check out our free solar startup guide.

This post is specifically focused on basic technical understanding of solar PV projects. However, more and more we’re getting questions from contractors who need to understand how to finance commercial solar projects.

Register for our Solar Executive MBA Training and learn how to finance, structure, and model commercial solar projects.
Join the LinkedIn group “Best Practices for Financing Commercial PPAs Between 200kW and 5MW” and continue the conversation about best practices.
Listen to this 60-minute interview: Advice from a $20MM Solar Tax Equity Investor to Commercial Solar Installers
Check out How to Finance Non-Profit Solar Projects, a 50-minute session answering 5 key questions.
Learn best practices for setting up commercial solar power purchase agreements (PPAs).

We also get a lot of questions about NABCEP certification from people looking to design solar projects.

Click here to learn what is NABCEP and whether 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.

The goal of the article is to convey the basic process for sizing an inverter, strings, and the conductors. You may not be an expert at the end of the post, but you’ll have a better understanding of how to do these things.

As always, having specific numbers is the most useful for examples, so we’ll continue with the example from part 2 on sizing an array and estimate power production. The house was located in Houston, TX and the roof, given local shading conditions, has enough room on the roof for 20, 205 watt modules. (Read Part 2 to see how we arrived at this number.)

Here is the specification sheet on the Sanyo HIT 205 module we’ll use for the example.

So, the largest possible size of the array we can fit on the roof at STC is 4,100 watts. We can go lower then this but not higher.
1. Inverter Sizing and Selection
Given that we know how many modules can fit on the roof, how do we use this data to size the inverter? The size of the inverter is driven by answering two questions:

1 – What is the capacity of the existing electrical service?

Per NEC 690.64B2 (2008) 705.12 D2 (2011), an existing electrical service is only allowed to backfed up to 120% of the rated capacity.
What does this mean with a typical home?

100 amp service X 20% = 20 amp backfed breaker allowed

20 amp X 80% (for continuous load, we’ll talk about this below) = 16 amp continuous inverter output current

16 amps X 240 volts (or 208 volts, depending on the homes location) = 3840 watts. This is the maximum allowed AC power output of the inverter.
There are a few ways of getting around this, by upgrading the service, performing a line-side tap, and it can sometimes be accomplished with subpanels. However, for this example, let’s keep it simple.

If the existing service only  had room for a 20amp breaker, we would not be able to have an inverter that has a rated AC continuous output that would exceed the 16 amp (see example above) or 3840 watts AC.

Per NEC 690.8 A3 the maximum AC output current from an inverter is defined as the manufacturer’s continued rated output current.
Max Current (inverter AC circuits) = continuous current output.
For our example, we’ll assume that the existing electrical service can supply an additional 25 amp back-fed breaker, 20 amps continuous allowed. This limits our choice of inverter to either a PVI 3000 or PVI 4000 inverter based on the electrical service capacity, as the PVI 5000 has a continue output current at 208 VAC of 20.7 amps.

Figure 1 – A Sampling of Solectria Residential Inverter Specs
2 – How many modules can we fit on the roof?
It’s very critical that you perform proper site visits before design the system, so you know the roof that you’re dealing with.

Performing high quality and efficient site visits is absolutely critical to the success of profitable and well designed 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.

Back to our example. From our example, we know that we can fit 20, 205 watt Sanyo modules on the roof.

Here is the specification sheet for the module:

Figure 2 – Spec sheet for Sanyo 205 Module

First, we need to guess the size of the inverter. It’s a good rule of thumb to size the inverter, based on the rated AC continuous output, to be 80% smaller then the rated STC output of the array. The reason for this is that there is a lot of inefficiency from the array to the inverter, so if we undersize the inverter, the array is more likely to hitting the upper limit of the input ranges of the inverter and will more likely be operating within the MPPT operating range of the inverter.

For example, for our array size at 4,100 watts DC STC, we’ve guessed that the inverter would have a AC continuous output range of 80% of 4.1kW, or 3,280 watts AC.

You’ll notice that the naming of Solectria inverters (PVI 3000, 4000, 5000) also seem to match this relationship between the DC rated power of an array (the name of the inverter) and the AC continuous output of the inverter (2700W, 3400W, 4300W, respectively)

We will choose the Solectria PVI 4000 for our example from our choices between the PVI 3000 and 4000

3. How do we size the strings?

Right now, we have concluded two things. First, the inverter we’d like to use the PVI 4000 based on the number of modules that can fit on the roof and how their capacity relates to the inverter. Second, we know the number of max modules we can fit on the roof. Now, we must begin string sizing.

String sizing is the number of modules that we will connect in series and parallel before connecting them to the inverter. The size of our strings will determine the voltage and amperage that is inputted into the inverter.

When string sizing, our goals are:

Make sure we NEVER supply the inverter with too much voltage, which will kill it –> Maximum string length
Make sure that we can ALWAYS supply the inverter with enough voltage to turn on, given the array is receiving full sun –> Minimum string length

What is the maximum voltage allowed for the system? How many modules we can connect in series?

NEC 690.7 specifies that our worst-case voltage, the highest voltages that the DC array can create, must fall within the limits of the inverter.

The exact definition states that: The Voc of each module times the number of modules in a string, correct for lowest expected ambient temperature in the array’s location.

For the PVI 4000, maximum acceptable voltage is 600 VDC.

To calculate the maximum number of modules allowed, we need a few pieces of data

Voc at STC for the module at 77F/25C = 50.3 volts
The temperature coefficient for the module. Typically given in volts per degree C or % voltage per degree C. You will find all this data on any module spec sheet = -.14V/C
The lowest and highest temperatures seen in the specific jurisdiction. Below is the data for Houston from weather.com = 9F or -13C

Here are the calculations for the max system string size. The goal in determining the maximum system voltage is to make sure that power production from the array will never kill the inverter.

Temperature coefficient. -13C lowest temperature – 25C STC = -38C change from STC
-38C  X -.14V/C = 5.32 voltage increase. (negative times a negative is a positive)
50.3 volts + 5.32 = 55.62 is the highest voltage we will ever expect to see from each module, and this is the voltage we will use to determine the maximum number of modules in a string.
600VDC (highest acceptable inverter voltage) / 55.62 = 10.78 modules.
We round down to 10 modules, because we cannot go over 600 volts.
Maximum system voltage (MSV) = 10 modules X 55.62 = 556 volts

[…]

July 24th, 2012|Categories: Geothermal and Solar Design and Installation Tips, Solar, Solar Design & Installation|Tags: , , , , , , , , , , , , , , , , , , , |
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“What’s the Most Efficient?” Geo VS Solar Thermal VS Solar PV

 I’m doing some sales consulting work in NYC, and there’s one question I’m getting a lot from property owners: “What is the most efficient renewable energy technology?”

In the city, they are mainly speaking of solar PV vs solar thermal, because generally there’s not enough room for geothermal in the city. However, for fun, I’ll expand it and include geothermal.

The answer is, of course, it depends on how you’re defining efficient.

 Which technology produces the most energy in the least amount of area
Which technology produces the most valuable energy
Which technology has the best financial return. Again, however you’re defining return.

There are two ways that I’m going to frame the discussion to search for an answer, or a methodology for finding an answer: 

 Efficiency of the technology (is this a good design for this specific application)
Efficiency of cash, which takes into consideration the site characteristics and policy (is this a good investment?)

As always, it’s easiest to see this when we look at a few examples, being clear to highlight when and where the examples might be different in the real world and how said sensitivity might impact our results.

1. Technology Efficiency. Right now, let’s just look at GROSS INSTALLED Costs and raw energy production. 

Here’s what I’m going to calculate: Gross Installed cost / Net energy produced in year 1 (energy produced / energy used)

Again, I’ll keep it in residential for simplicity. And I’ll focus on Boston because I’m most familiar with the solar resource available and the average heating degree days needed when understanding geothermal production.

Our example home will be:

1500 square feet
Average home shell construction.
South Facing roof, no shading, 10 pitch, that is 60 feet by 12 feet.

Solar PV: $25,000 /  6,843 kWH produced per year = 3.65, which means that you must invest 3.65 dollars in year 1 to get 1 kWh of production

5kw DC Installed @ $5.00/watt  = $25,000
Avg Insolution = 5 hours of full sunlight per day.
We’ll derate from DC to AC is .75, which is extremely conservative.
AC Production = 3.75 AC output
3.75 X 5 hours per day = 18.75 kWh production per day on average.
18.75 X 365 = 6,843 kWH produced per year

$25,000 /  6,843 kWH produced per year = 3.65, which means that you must invest 3.65 dollars in year 1 to get 1 kWh of production

Solar Thermal: $8,000 / 4,982kWh = 1.6. For every $1.6 dollars invested you get 1kWh of production.

3 to 4 family home
Gross Installed Costs for a simple drawback system by a well trained crew is ~$8k
Each Module will likely produce around 85 therms per year, totally 170 therms per year
170 therms is 17,000,000 BTUs / 3,412 = 4,982 kWH equivalent.
$8,000 / 4,982kWh = 1.6
For every $1.6 dollars invested you get 1kWh of production.

Note: For solar thermal, unlike solar PV, production of solar energy and usage of that energy doesn’t necessarily match. For this example, I’ll assume it does.

Geothermal: $27,000 / 13,478 kWh equivalent = 2. You must invest $2 in year 1 to get 1kWh of energy production.

We’ll assume the heat pump is only heating, to make the calculation more simple and keeping in mind that our ratio of dollars invested to energy produced will be a little larger, if we considered cooling.
63 MBTU average heating load
Avg COP of 3.75 (this is important, because lower efficiency will increase the tonnage needed for the same btu’s delivered, all else equal)
3 Ton system
9k ton X 3 tons = 27k
Energy Produced = 63 M BTU –> Let’s convert BTU to kWh equivalant
63 M BTU = 18,463 kWH (Remember that 1kWh = 3,412 BTUs. Thus long calc is 63MBTU = 630 Therms (10 therms = 1MMBTU) 630 therms = 63,000,000 BTUS divide by 3,412 = 18,464)
Many will point out that geothermal uses energy (in pumps and fans) to produce more energy, which is true. However, we want to find out what EXTRA energy that was created by the system, this is the renewable part. With an average COP of 3.75 it means that 3.75 units of energy was created for every equivalivent energy put into the system.
3.75 means we need to reduce the energy produced by 26.66% (1 / 3.75) to find the amount that was produced by the system.
18,464 X 73% = 13,478 kWh equivalent produced
27k installed costs gross / 13,478 kWh = 2 in equivalent energy produced. Which means, that for you must invest $2 in year 1 to get 1kWh of energy

Here is our conclusion about gross installed costs and energy produced: 

Solar PV: $25,000 /  6,843 kWH
Solar Thermal: 8,000k / 4,982 kWh
Geothermal: 27k installed costs gross / 13,478 kWh

A few things to note about the sample examples

PV: $5 a watt is average and there are much higher installed costs.
Thermal – Production of modules and usage don’t necessarily match. Also, assumptions around water usage are not accurate. ~8k is also for a great site and a well trained crew. It’s common to see $10k+ projects.
Geothermal – Only assumed it was heating. Assuming 72 set point and 62MMBTU needed to heat the home. 3.75 COP also impact the energy produced from that invested cash. Higher COP = greater output, all else equal, per dollar invested.
As we’ll discuss in section 3, site characteristics can change the analysis of any one of these by making some technologies, cheaper or non-available in certain areas.

[…]

July 9th, 2012|Categories: Geothermal and Solar Design and Installation Tips, Geothermal Heat Pumps, Solar, Solar Design & Installation, Solar Thermal|Tags: , , , |
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Geothermal Performance Case Study: Closed Loop vs. DX vs. Kelix Thermocouple

(This post has received a lot of feedback as expected, I’ve posted some update information at the bottom of the post from Sam Johnson’s team and from Kelix themselves)

Last month, I published an interview about the Kelix ground coupling system and there was interesting response. Here’s why I did it: I always want to speak with anyone who is actively working on making geothermal more kick ass. By kick ass, I mean profitable and increasing adoption of the technology.

The main item that struck me after I published the post is the few nasty emails I received. Instead of fellow geothermal pros supporting one another and figuring out the best places for new technologies, I noticed it seemed the industry was trying to show where a new technology WOULD NOT work, instead of where it would work. This is childish and we shouldn’t tolerate it.

After the piece, Sam Johnston approached me and offered to share some AMAZING DATA on a comparison study they did between a closed loop geothermal system, a DX system and the Kelix technology.

A few more notes before Sam begins. 

First, The main issue I’ve noticed, and the Kelix article highlighted, is that the geothermal industry seems (someone correct me if I’m wrong) to not have a standardized testing process and way of communicating different products to the market. What this causes is a “she said/he said, manufacture vs manufacturer debate”. This tends to increase the risk associated with using the technology both for property owners and EPC contractors who want to get into the business. Anything we can do to create a more standardized way of communicating and testing new products will DRASTICALLY improve the industry.

Second, please don’t email me any comments about the article. Put all of your comments and recommendations publicly in the comment sections. The reason I’m stating this is simple, I’m assuming I’m going to get some angry emails from EPC contractors, engineers, architects, and manufactures about something that isn’t exactly correct in this analysis and that it’s not 100% perfect. What we need to take away from this case study is the intent behind the individuals who performed it. What are they trying to accomplish and WHY?  If we believe that they were trying to make the industry better then we should figure out what makes sense and is useful about their analysis and where it could be improved.

The reason I asked Ryan Carda to provide his feedback is that I know his goal is never to bad mouth other people but to move the industry forward. His comments about the data are amazing and will be useful to anyone who is going to do further testing and analysis on ground source technologies.

If you have any questions, comments, etc about these case studies please don’t hide, leave them publicity in the comments and they will be addressed. If you have any serious problems with the information, give me a call 617 702 2676, but if you’re goal is simple to cut people down, I’m likely not going to listen to you.

Enter Sam Johnston from JTI Energy

During my experience with Environmental Compliance Services, Inc. (ECS) I had the privilege to be part of a team that was to demonstrate geothermal alternative energy in a very special way.   This effort was to become central to a branded division named Terraclime.  What follows is my article distilled from many individuals who participated in this comparative systems effort. The main purpose of this article is to promote alternative energy, especially geothermal by telling this story and revealing lessons learned.

As a member in a partnership, ECS acquired the Mill, some 150,000 square feet in 2007.  The Mill was seriously contaminated and considered a “brown-field” property.    ECS’ core business is remediation; remediating equals changing  “dirty-dirt and dirty-water”.  The Mill became a great “brown-field to green-field” story.

The Mill had its beginning in the early 1830’s when modern industrialists of that time were attracted to the nearly 30’ water fall drop of the adjacent Mill River.  This hydro power would help develop their silk plantation and needed silk processing.

[…]

June 3rd, 2012|Categories: Drilling, Geothermal and Solar Design and Installation Tips, Geothermal Heat Pumps|Tags: , , , , , |
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Part 2: How to Design PV – A Walkthrough of How to Size a Solar Array and Estimate Power Production

This is the 2nd article in a series about how to design solar PV projects. We started with solar 101, the basics. If you’re brand new or need to brush up on the basics, please read it first. It discusses electrical theory, key solar terms needed to design any system and the relationship between irradiance, temperature, amperage and voltage among other things. If you’re looking to start a solar business but are brushing up on the technical side, read our solar startup guide article to get more free guidance on solar sales and finance.
Download the free full PDF “Solar PV Design and Installation 101” guide here
Also, this post is specifically focused on basic technical understanding of solar PV projects. However, more and more we’re getting questions from contractors that need to understand how to finance commercial solar projects.

Click here to sign up for our Solar MBA and Learn how to Finance Commercial Solar PPAs from A to Z. Click here to test drive the Solar MBA for free. 
Click here to join our Linkedin group “Best Practices for Financing Commercial PPAs Between 200kW and 5MW” and continue the conversation about best practices.
Listen to 60 Minute Interview: Advice from a $20MM Solar Tax Equity Investor to Commercial Solar Installers – Focus on a Niche, Be Fast, and Standardize your Operations
How to Finance Non-Profit Solar Projects – 50 Minute Session Answering 5  Key Questions
60 Minutes of Video Answer 7 Questions on Best Practices for Setting up Commercial Solar Power Purchase Agreements.

If you’re brand new to solar, I also get a lot questions about the NABCEP Certification.  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.

This section is dedicated to sizing an array based on customer needs and site characteristics – it also discusses estimating power production. The main focus is residential applications, but I’ll also highlight slight differences in commercial projects.

The goal of the article is to provide a basic process for you to understand how to size an array and provide you with further resources you’ll need to continue your learning. There will be some overlap in this discussion with more advanced topics, like string and conductor sizing that will be covered in future articles, and how the design will impact the financial returns of a system, which will be discussed in a future article on Solar PV financing. If you need to read on up renewable energy finance, you can start with Finance 101 for Renewable Energy Professionals.

First, let me outline what we’ll talk about, then I will go into each part with more detail and depth.

Below is the process for designing a solar PV array.

In the field, most of the power production estimating is done with software. However, I’d argue that it’s still important to understand the theory behind power production estimates and the variables that impact power production so you can make sure to gather the correct information when performing a site visit.

1. Customer Constraints. What about a specific customer will impact the size of an array? The most common restraints are:

Energy Usage
Client Budget

2. Site Constraints.  What about the client site will limit array size? These are the most common details about a site you need to gather and we’ll discuss how these variables impact the size of an array:

Local Shading
Horizontal Shading
Available Roof Space and Roof Characteristics (dimensions, tilt, azimuth)
Module Size and Racking Considerations

3. Determining Irradiation. In order to compute power production, you need to understand how much energy is hitting your specific area.

Measured in kWh/M2/day or Sun hours per day

4. Estimating power production based on irradiation, customer constraints, and site characteristics.

Sun hours per day adjust for site characteristics
Power production estimates based on solar resource and the amount of modules you can fit on the roof.

You Need to have standard process to collect all of this information. 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.

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.

Sunify will eliminate paper notes so you no longer have to copy and paste notes into emails and waste time.
Sunify will ensure that you, or the sales people that you manage, capture the information that they need to on the first visit.
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.
It’s all the tools you need in one place, so you’ll never loose your notes again.

Click here to check out Sunify. 

1. Customer Contraints. 

A. Energy Usage

A possible constraint on the size of a solar project is the client’s energy usage. Because of how net-metering programs are set up, typically it does not make sense to produce more then 100% of a client’s annual energy usage. However, because most property owners use so much power, and the power density of solar PV is so low, it’s rare to have an array that can produce 100% of the power with solar power. It’s typical that the solar fraction of a project (total power used / power supplied by solar) is less then 30%.

Commercial Considerations

For a commercial client you will need to understand their demand charges and usage charges. In order to understand if the solar array will reduce their demand charges you need to understand the load profile of the building and when exactly their demand is the highest to see if solar will shave that demand. For example, do they have the highest amount of demand in the summer or winter? What time of day, early morning, afternoon, evening?

We will not go into depth on demand charges for this post. However, WE WILL discuss the impact of different electric rates, demand and usage charges in the solar PV financing article because it’s critical to understand the value of the power that a solar project produces. Right now, we’re just concerned with pure design.

If you need to learn more about what demand charges are, I’ve found these are good resources:

Understanding demand charges
Demand Charges Explained

What you need to collect about energy usage:

Yearly average kWh used by the client
Cost of power
The value of a kWh of solar is directly related to the cost of the power it offsets. On a site visit make sure to get a few months of electric bills.

Example

Let’s assume a customer uses lives in Houston, TX and uses 550 kWh of AC power on average per month and wants a solar system that will produce 100% of the power they use in a year. How large would you need to design the system? You need to reverse engineer the problem, here’s how:

550 kWh/month / 30 days per month = 18.33 kWh per day
Calculate and Adjust Irradiation based on site characteristics. According to PV Watts, Houston gets an average of 4.79 sun hours per day. For now, let’s assume the roof is directly south and at 30 degrees (the latitude of Houston) so it can harvest 100% of the 4.79 sun hours per day. See section 4 for how we adjust irradiation based on a roofs characteristics
18.33 kWh per day / 4.79 adjusted sun hours per day in Houston = 3.83 kW AC needed in production. Now we need to convert to DC
3.83 kW AC / 80% (to make up for the inefficiency of converting to DC to AC. 80% is a rule of thumb. You will read more about this in the next part of this series when we talk about string and conductor selection, inverter selection and derating) =  4.78kW DC

If the customer wanted to produce 100% of their power from solar energy in Houston and they had a perfect roof, they would need a 4.78kW DC system.

We’ll discuss what happens if there roof is not perfect below.

B. Customer Budget

One of the most common client constraints is budget for the system, if they are purchasing with cash. If they are leasing the system, this will not be so much of an issue. Learn more about solar leases, prepaid leases and how to sell a solar lease here.

If your installed cost is $5.00/watt, a 4.78 kW system will cost you $23,900. If the customers budgets is only $15,000, you could only install a 3 kW DC system.

Things to remember:

Know if it’s a cash or lease sale. Learn more about lease sales in our free course about solar lease.
If it’s a cash customer, make sure you understand what their budget is. Make sure you understand if they are purchasing cash, or with a home equity line of credit or wrapped into a mortgage for new construction.

[…]

April 26th, 2012|Categories: Geothermal and Solar Design and Installation Tips, Solar, Solar Design & Installation|Tags: , , , , , , , , , , , , , , , , , , , , |
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