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4 Factors to Help Determine Your Solar System Size and Output

Kyle Ritland

July 2022

lockerby_gilbertOne of the most frequently asked questions we receive goes something like this: ”I have a 2,300 square foot home and like to keep my thermostat around 75 degrees in the summer. How much will a solar energy system cost me?” The fact of the matter is we need a little more information than that to produce an estimate. 

Don't get us wrongthis is a perfectly legitimate question. The only issue with it is it's not a question we can answer in this relatively short blog because there are a number of variables beyond the size of your home and what you keep your thermostat at to reach a final number.

In order to calculate how many panels you will need to purchase, you first need to know the following information: how much energy your family uses monthly and annually, available roof area and orientation, the wattage and efficiency of the panels you are considering, solar rate plans offered by your local power utility, and whether energy buyback programs are available through your utility provider.

While this probably sounds like a lot to the casual reader. The easiest way to answer the “how many solar panels will I need?” question is to consult with a solar integrator, who will give you a free evaluation and quote. But to get your wheels turning, let’s take a closer look at each of these four factors.

 

1. Your Personal Energy Use

Your utility bills are a gold mine of information. Each bill shows your total energy used on a month-by-month basis, with a comparison to the same month from the previous year. You can even see day-to-day and hour-to-hour consumption. With this data, a qualified solar installation company can easily calculate how many solar panels you will need by multiplying your hourly energy consumption by the sunlight hours that strike your available roof area, and then dividing that number by a panel’s wattage.

A house with more kilowatts used on average will generally need a larger solar energy system than a similar house with lower usage. But this can also depend on your goals; if you're looking for bill elimination rather than simply reducing your monthly utility bill, you will also need a larger system to achieve that. Talk with your solar installation company about your usage and goals to arrive at an appropriately sized system for you and your home.

 

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2. Roof Area and Shading

The amount of roof space available to solar panels and the amount of sunlight that strikes that area are key to determining solar energy production. Fortunately, here in the Valley of the Sun, we enjoy more than 300 sunny days every year. So for us, the most important thing is to avoid shading. Trees, adjacent buildings, chimneys, and other structures can all reduce panel output. 

The orientation of your roof also influences how much solar energy you'll produce. The ideal direction for your roof to be facing is south. This orientation will give your solar panels the most direct sunlight exposure, and will allow your panels to create energy into the late afternoon when you might be getting home from work and drawing larger amounts of energy. But don't fearif your roof isn't south-facing, you can still install solar and reap the many benefits it has to offer.

3. Panel efficiency

Not all solar panels are created equal. The most commonly used residential solar panels offer wattages ranging from 360 to 420 watts per panel, depending on size. Higher-grade panels create more electricity from less surface area than lower-grade panels. So, if your roof space is limited or shading structures cannot be removed, a higher-efficiency panel may cost a bit more, but will produce more electricity from less space.

 

4. Buyback programs through your utility provider

In the vast majority of cases, solar works in partnership with the grid, which is essential to ensuring that your home has electricity even at night. Both electricity purchased from the utility, and electricity generated by your solar panels is measured by the same meter. The meter runs forward when being supplied by the grid, and backward when your solar PV system is generating excess electricity.

Some utilities will give you a credit for any excess solar energy sent back to the grid. You can draw from these credits when you’re buying conventional power, such as at night. With that said, determining how your local power utility provider calculates these credits is a critical factor in determining how many panels you buy and how much money you can ultimately save. The more credits you want, the more panels you will need. 

As you can tell from the four main points discussed in this blog, there are a number of factors to analyze when considering solar for your home. A qualified solar installation company will be able to help walk you through these details to ensure installing solar is a smart fit for you and your home.

 

If you'd like to schedule an educational and low-pressure consultation with one of our experienced solar integrators, request a free, customized solar quote today. You can also learn more by downloading our complimentary solar whitepaper, "Is Solar Right For You?" that dives into other considerations to take into account when researching solar.

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