How much solar energy potential does your location offer? Here are the ways to discover if a solar PV system can benefit you.
Look at the maps
Insolation (not to be mixed up with insulation) is short for “incident solar radiation” and is measured at ground level with instruments known as pyranometers. A large network of pyranometers has been used to collect data from all over the world for decades. An advantage of these tools is that they factor in latitude, sun angle and climate. Check out the solar map.
The numbers on the maps are “equivalent full-sun-hours” or “peak sun-hours”, identical to kilowatt-hours per square meter per day. On the first map, the month of January in the Northern Hemisphere is shown. It’s not surprising that January is the worst insolation month of the year. The second map showcases insolation in June, which for most northern locations is the best month of the year.
The worst month includes essential information for off-grid PV systems, but doesn’t tell the whole story. Every kilowatt-hour matters when selling electricity to the utility company. The solar map depicts the average yearly insolation in the United States and these numbers are what you should focus your attention on. If you install a 1-kilowatt PV array on your roof and multiply the average full-sun-hours, you’ll learn how many kilowatt-hours of electricity you’ll generate per day.
You should also take the system derating factor into account, usually about 0.8. This compensates for dust and bird poop on the PV modules, and electrical losses in the system as it changes direct current (DC) electricity to alternating current (AC). To correct this, multiply your predicted kwh by 0.8. Next, multiply your corrected daily kwh output by 365. Then, compare this to your utility bill.
Online Solar Calculators
If the math seems perplexing, there are easier ways. There are a wide range of solar energy calculators online. An easy calculator to use is the National Renewable Energy Laboratory’s PV Watts Version One. This gives projected production figures for a variety of locations. PV Watts Version two has an interactive map. NREL also offers a tool called In My Backyard. This tool includes satellite mapping complete with cost and payback estimates. You can find a simple and quick solar calculator.
Remember, cost estimates can vary and are calculated using different criteria. Prices and incentives are known to change quickly. No two solar installations are alike, and every vender may offer a different price. For current pricing, it’s best to contact a PV installer that serves your area. It helps to contact two or three companies to gain understanding of what your investment may need to be. Most PV installers will offer a site evaluation, sometimes for free or they may refund the evaluation if you purchase a PV system.
Obtaining a professional site evaluation is a wise idea, even if it shows solar energy isn’t right for your location. Even the tiniest shadow falling across part of a PV array can significantly reduce total output, so it’s essential to install everything in the best location on your property. Shadow problems can change with the seasons as well. Site evaluations can identify any obstructions that could cause potential problems. They will let you know precisely which months of the year and times of day any shadows would occur, and how much energy would be lost. It’s possible to obtain a site evaluation online using satellite and other aerial imagery.
Say you’ve met with numerous local PV installers and most likely received quotes varying from $5 per watt to about $10 per watt depending on your location. The initial cost might still seem very high even though the system is designed to meet your annual electricity needs and reduce your utility bill to zero. That’s why there are plenty of incentives at the federal, state and local levels to help make solar PV a reality.