One of the most difficult things about purchasing a solar system is comparing one system to another. Some suggestions: Compare annual kilowatt-hours (kWh) output instead of DC watts. This is what you’re truly buying — electricity. Systems designed by different companies with different components will deliver different amounts of energy. A microinverter system will yield 5% to 25% more energy than a traditional string inverter system.

Ultimately, you want the most energy for your dollar, so ask for an estimate of annual electrical production. It doesn’t matter if one system is larger or smaller than another if they give the same output. And ask for their methodology. Make sure it is backed up by a sun-shade analysis and location-specific sun data.