There are many factors to determine what makes a roof ideal for solar, but here are the top three:
(1) Solar Access
(2) Tilt and Orientation Factor (TOF)
(3) Total Solar Resource Factor (TSRF)
Solar Access is the ratio between the amount of energy a house receives at peak sun hours and the amount of energy a house receives in full darkness. Any shading that might be present on a roof is also used when calculating this ratio. This ratio is important because for a solar system to work efficiently, it needs to be supplied with enough sunlight to produce enough electricity for a home.
Tilt and Orientation Factor (TOF)
TOF is the ratio between the actual tilt and orientation of the roof and the ideal tilt and orientation of the roof. When figuring out if your house is ideal for solar, it is important to know where the sun rises and sets with respect to your house. This is because you want the sun to be as perpendicular with your solar panels as possible. The longer the sun is shining on a solar panel, the more electricity the panel produces.
Total Solar Resource Factor (TSRF)
TSRF is the multiplication of the Solar Access and the TOF. This is the total percentage of available solar energy of a home.
Irradiance is the amount of energy produced on a surface throughout a day. The total irradiance of a building is calculated using the Solar Access, TOF and TSRF. When figuring out if a house is ideal for solar, typically an irradiance map of the roof is generated. An irradiance map shows where on a roof the sun shines most and where the most shade occurs. This map is helpful when designing a solar system because it allows the designer to see the ideal location for the panels. Below is a sample of what an irradiance map looks like. Ideal panel locations are places with the brightest yellow.
Author: Taylor Frothingham, Solar Analyst