Solar design software is software in which solar installers design a rooftop system, size it and quote it to the home owner. An installer is the company that fits the panels on the roof. Before it can quote a price, it must decide how many panels fit on the roof, how much power they will make and which inverter to use.
The software does this in four steps. First, it shows the roof from above, using maps and satellite photos, from a geographic information system (GIS). Second, the installer marks the roof outline and places solar panels on it. The software shows which parts of the roof are in shade at different hours, because a shadow on one panel can cut the output of every panel wired in series with it. Third, it calculates how many units of electricity the panels make in a year and picks the solar inverter. A unit here is one kilowatt-hour, the unit on the electricity bill. Fourth, it adds up the costs and produces a quote with the expected saving on the electricity bill, which the home owner can read and sign. In India, the quote also shows the central government subsidy that the home can claim.
Take, for example, an installer in Jaipur who must quote for a flat, shadow-free roof. The roof is 60 square metres, but after leaving room for a water tank and a walkway, about 25 square metres can hold panels. The installer draws this area in the software. About 8 panels of 550 watts each fit, for a total of 4.4 kilowatts. The software estimates that the system will make about 6,500 units a year. It then compares this with the home's electricity use, which the home owner reads from past bills, and prints the quote. (These numbers are only illustrative.)
Some solar design software is free for installers. Its maker earns from partners, such as panel makers, lenders and suppliers, who pay to offer their products inside the software. Other solar design software charges installers a fee. The aim is to make the installer's work quick, since every extra visit to a roof costs money. The finished design is the first step in rooftop solar. The home owner can later add a smart electrical panel to control the system.