How to Size your Solar Panel Array

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  • June 16, 2015
dreamstime_l_24406315 Saving money, going green, or having emergency power are all good reasons to go solar. But no matter what your motivation for investigating in solar, an important part of your decision will be determining how many panels and what your total energy production should be. This week we are discussing the factors to consider when sizing your solar panel array. 25486728

Electric Consumption

Knowing how much electricity you use, when you use it, and how your utility’s net metering program works are all factors that are important. Putting solar panels on every square inch of viable roof space is great for the environment, but it might not be the most financially optimal. Let’s look into how the solar credits work under the Rocky Mountain Power net metering program:
  • Power is generated from your panels and gets used by your house’s consumption first.
  • Excess generation flows back into the grid and generates a credit. To put this in terms everyone understands, these are your “rollover minutes”.
  • Your rollover minutes are used when your production doesn’t meet your usage, and you need to pull from the grid.
That is simple enough. But what many people don’t know is that Rocky Mountain Power clears out your “rollover minutes” each year on March 31. So producing 100% of your monthly bill is nice, but it likely means that you will be leaving some “rollover minutes” on the table come April. Kelly Curtis, Director of Operations at Solaroo Energy explains, “We usually advise clients to produce around 70%-80% of their annual electric consumption so they don’t risk losing their credits. You just want to make sure that you get the financial benefit of those last few panels you install.”

Graduating Tiered Rates

Understanding how you are being charged by Rocky Mountain Power, or other utilities, is also a factor that can help you know how many panels you should put on the roof. Rocky Mountain Power charges residences in blocks, or tiers. As of September 1, 2014, the summer rates go as follows: First 400 kwh – 8.8498 cents/kwh Next 600 kwh – 11.5429 cents/kwh All additional kwh – 14.4508 cents/kwh Basically, the more you use, the higher the price goes. With regards to solar, it means that the first panels you install take away the most expensive energy first, and the last panels you install take away the least expensive energy. So even though you might save money getting down to zero usage and no utility bill, you can see that your ROI goes down as you take away the 14 cent tier, then the 11 cent tier, and finally the 8 cent tier. Curtis remarks, “If breakeven and ROI analysis are important factors for you with solar, then tier shaving will be as well. Solaroo can work the numbers to determine exactly what number of panels will give you the best bang for your buck.”

Production vs. Consumption

“A kilowatt-hour saved is a kilowatt-hour earned.” Ben Franklin didn’t say it like that exactly, but he might as well have. Improvements such as LED lights, Solar Attic Fans, Radiant Barrier, and having energy efficient appliances all have a cost associated with them and a corresponding savings they will produce. Any amount by which you can reduce your consumption means that you will need that much less production. Curtis explains, “A solar attic fan, or radiant barrier might save you what 2 or 3 solar panels would produce for you, but at a lower cost. Any effective and thorough solar plan should incorporate improvements that will reduce consumption as well.” Knowing all of this, it might be most important to have a good solar energy consultant who can provide you with the analysis to clearly see what size of a solar array makes the most sense for your house. Contact us for more details: 801-826-4888.