However, providing such information to homeowners via a website is complicated. This is due to a number of factors which are particular to the nature of rooftop solar:
- At the early stages of their solar research, homeowners often don’t know how much power they use each month or how this may vary over the seasons of the year;
- Solar energy production is different for different locations;
- Electric rates change from one utility company to another;
- Solar energy production (measured in kWh) will vary based on roof pitch and roof direction;
- Shade can affect power production from a specific roof;
- Possible system size can be limited by the available square feet of roof space; and
- Solar pricing changes by brand of solar panels and can also vary by location.
Achieving a high level of accuracy requires a tool with a significant amount of intelligence to tailor the results to the user’s home. An online consumer solar energy calculator is not going to be as accurate as a professional design tool. This is because consumers on the internet do not have the information at hand to complete the input fields required to use a professional design tool.
That being said, accuracy cannot be compromised to such a point that results become useless, or worse, misleading. So what is needed for consumers is a solar power calculator that find the right balance between accuracy and ease of use.
After an extensive review of calculators available, SolarReviews has chosen the Solar-Estimate.org solar calculation engine because:
- It tailors solar production for roof pitch and direction;
- It has a database of all utility rates charged by every American electric utility;
- It uses data published by the Energy Information Administration about electric use patterns to make an educated guess as to the homeowner’s energy use pattern over the course of a day and over the course of a month. This improves accuracy; and
- It is — by far — the easiest-to-use solar panel calculator.
Solar-Estimate.org partners with Genability for their calculations. Genability are the leaders in the calculation of avoided utility cost, so this partnership improves the accuracy of their savings forecasts. Many professional design tools also use Genability for their solar savings calculations and the accuracy of this tool has been audited by the National Renewable Energy Laboratories.
Because Solar-Estimate.org is also a price comparison marketplace for residential solar, the pricing data they use is both current and localized, making it far more accurate than other options.
What other web-based solar panel calculators were available?
There are many solar panel calculators online, but most are of low quality. It’s easy to tell the difference between higher-quality and lesser-quality offerings. Simply enter the details of two different homes in the same state and with the same monthly power spend, but with two different roof orientations and utility providers.
Low-quality solar calculators will usually show the same result for system size needed, production and potential savings. This shows that at the back-end their calculations aren’t taking these things into account.
The most accurate calculator in terms of solar energy production (in kWh) from a specific array of solar panels on a specific roof is the PVWatts calculator from NREL. However, this is harder to use than the Solar-Estimate.org solar calcuator and does not have a database of current solar prices through which to estimate savings accurately.