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.

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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 […]

By |September 25th, 2014|Categories: Geothermal and Solar Design and Installation Tips, Megawatt Design, Solar||

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, […]

How to Normalize Energy Consumption For Weather Influences Using RETScreen ® Plus

This is a guest post by Michael Ross from RER Energy Inc. Michael is teaching a 6-week, 30 hour class on Mastering RETScreen for Clean Energy Project Analysis. The class is capped at 50 students, and there are only 30 discounted seats. Get your discount here.

Article Goal 

This article shows engineers and energy data analysts how to “normalize” energy consumption or production to account for the variation in weather over time. By the end of the article, you should understand why normalizing for weather is important, and how it can be done, either in a spreadsheet or using a free tool called RETScreen® Plus.

Why Normalize for Weather?

The need to “normalize” for weather arises very often. For example, you have a year or two of utility bills for a facility, you plan on improving the energy efficiency of the facility, and you need to estimate what the energy savings will be in the future. One challenge is that the past energy consumption is determined not just by the equipment at the facility, but by the variations in the weather experienced by the facility. What if the winter covered by the utility bills was especially cold, and as a consequence gas consumption was higher than typical? Basing your estimates of savings on a single year, without “normalizing” for weather, or explicitly adjusting the consumption to reflect typical weather conditions, will cause you to overestimate the typical savings in the future.

Normalizing for weather is a good idea whenever an accurate understanding of the current energy consumption of a facility (a “baseline”) is needed; otherwise, as suggested in the previous example, estimates of future savings arising from improvements to the existing facility may be too high or too low, and consequently inferences that a proposed improvement is cost-effective may not turn out to be correct (or, conversely, a truly cost-effective opportunity may be missed).

The need to normalize may also appear in energy production projects. For example, a photovoltaic system might produce more electricity in one year than in the previous year. Is this merely because there was more sunshine in the second year? If so, did this additional sunshine hide deterioration in the system operation?

Sometimes normalizing for weather is not merely a good idea, but rather a requirement of a client or a utility or government funding program. For example, I recently conducted a study for a client who was seeking funding from the Federation of Canadian Municipalities (FCM). The client needed to show how much connecting his building to a district heating system would reduce overall natural gas consumption (and thereby greenhouse gas emissions). The FCM program stipulated that any study had to first normalize past energy consumption for variation in the weather, and then project savings into the future based on typical weather.

Normalizing for Weather: the Theory

Normalizing for weather is, in principal, straight forward:  you “fit” a statistical model (i.e., an equation) that relates you consumption data (e.g., utility bill consumption) to one or more variables that you think exercise an influence on consumption (e.g., heating or cooling degree days).  When “fitting” the model to the data, you adjust the coefficients of the equation until sum of squared differences between the actual consumption data and the modeled consumption data is minimized. Often a linear equation is used for the statistical model, and the process is called “linear regression”.

So, for example, you might produce a scatterplot of daily average gas consumption for each billing period against the average number of heating degree days per day for the billing period, as shown in the figure below.

 

I’ve superimposed a straight line on the scatterplot to make it evident that there is a linear relationship between the fuel consumption and the heating degree days. That is, I should be able to estimate with some accuracy the fuel consumption using an equation of the form[1]:

This equation has the right form, but what should I use for the coefficients a and b? A common approach is to select a and b in such a way as to minimize the “sum of squared errors”, or SSE.  To do this manually, I start out with a guess for these coefficients, and then I use this equation to estimate the fuel consumption for each billing period. I then compare these estimates with the actual fuel consumption for each billing period. If I square the difference of the two and sum over all billing periods, I’ll have the SSE. This is a measure of how well my choice of coefficients fits this equation to the data; I adjust the coefficients until the SSE is as small as I can make it (unless the line passes through every data point exactly, the SSE will not go to zero).

 

Then I’ve got my equation. For the data from the example above, it would be:

I can then use this equation to estimate the gas consumption based on the heating degree days. So, for example, imagine that for the location of this building, a typical month of March will have 620 heating degree days (°C·day). That works out to 20 heating degree days per day. If I wanted to know what the facility’s gas consumption in a typical March would be, I’d plug this into the equation:

This would tell me that on an average March day, I’d require 6.6 GJ of gas, so over the whole month I’d consume around 206 GJ of gas. To determine the gas consumption in a typical year, I do this same exercise for each month’s typical number of heating degree days.

Normalizing for Weather Using RETScreen® Plus

While this normalization can be done using a spreadsheet, my tool of preference is RETScreen® Plus, a sister program to the better known but completely different RETScreen® 4. (Both tools are available for download, for free, from the Government of Canada: www.RETScreen.net).

RETScreen® Plus is designed precisely for this type of exercise (as well as much more in-depth analyses to be discussed in later articles), and consequently much quicker and (less error-prone) than doing the manual exercise outlined above. The main program features that make it quicker and easier than the manual exercise are:

1)     Rapid access to up-to-date daily weather data for locations across the globe

2)     Tools for combining and regrouping data sets on different time bases.

3)     Automatic fitting of equations

4)     Optimization of the heating degree day reference temperature

Let’s examine each of these advantages by going through the key steps for normalizing for weather data using RETScreen® Plus.

I’ll start by asking my client for utility bills. He sends me a spreadsheet for the period of 2012 through 2013, indicating for each bill the billing date and the billed gas consumption (in GJ) for the period:

Note that the “monthly” bills are not all dated on the same day of the month, and the number of days in the billing period changes from bill to bill. Also note that I’m missing the bill for May 23. Such are the complications of the real world.

Next, I open RETScreen® Plus. The first key step is to tell it where my building is located; it will be apparent why we need to do this when we need to get weather data. There are a variety of ways to specify the project location, but the fanciest is through a map interface that lets me indicate the project location with a thumbtack:

 

Then I import my Excel spreadsheet of utility data into RETScreen® Plus. I tell it that the data I want to investigate is for “Fuel Consumption”, specifically natural gas measured in GJ. It opens a blank table:

I fill this table by “Importing from file…” and selecting my Excel file. A dialog box pops up and I see that it has correctly interpreted the headers in the file, with the exception of the gas consumption, which I have to pick from a drop down list:

 

When I click on the green checkmark, I get another dialog box identifying the missing data for May and giving me some choices for dealing with this, such as using the average for the whole data set, interpolating between adjacent data points, deleting the whole row, or repeating the previous value. I chose to simply ignore the missing data for now. RETScreen inserts this data into my table, automatically calculating the number of days in each billing period:

With that half my data is in the tool. But now I need to tell RETScreen what the “factors of influence” in this data are: that is, what variables are likely to exert an influence on the gas consumption. When normalizing for weather, the answer is pretty clear (it’s the weather, obviously), but in different applications of the tool it might be factory production, hotel occupancy, or something else.

Thus, I need to get weather data for 2012 and 2013. Ideally, this weather would be on the same time basis as my utility bills. That is, I’d have the average weather conditions for my site for the first, second, etc. billing periods.

[…]

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:

Cost Effective Megawatt Design with Ryan Mayfield on Tuesday May 20th at 1pm EST.

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:

Submit a complete set of drawings, equipment, budget, code references, and calculations for an actual megawatt PV system design project.
Understand how to design projects that are cost effective, structurally sound, high performance and code compliant.
Understand the current best practices for line side connections, grounding, rapid shutdown, fire regulations, and other complex and common design challenges for large projects.
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.

[…]

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 […]