If you decide to get more than one bid for the installation of your photovoltaic system (always a good idea), make sure that all bids are made on the same basis. For example, a bid for a system mounted on the ground is usually very different from another bid for a rooftop system.
Similarly, some photovoltaic modules generate more electricity per square foot than others. Bids should clearly state the maximum generating capacity of the system (measured in watts or kilowatts). If possible, have the bids specify the system capacity in “AC watts” under a standard set of test conditions, or specify the output of the system at the inverter.
Also request an estimate of the amount of energy that the system will produce on an annual basis (measured in kilowatt-hours). Because the amount of energy depends on the amount of sunlight—which varies by location, season, and year to year—it’s unlikely the contractor will quote a specific figure, but a range of ±20% is realistic. Bids also should include the total cost of getting the photovoltaic system up and running, including hardware, installation, connection to the grid, permitting, sales tax, and warranty.
Your warranty is a very important factor for evaluating bids. A solar rebate program may require that systems be covered by a two-year parts-and-labor written installation warranty, for example, in addition to any manufacturers’ warranties on specific components. The installer may offer longer warranties. Also, ask yourself, “Will this company stand behind the full-system warranty for the next two years?”
It might not be. You generally get what you pay for, and it’s possible that a low price could be a sign of inexperience. Companies that plan to stay in business must charge enough for their products and services to cover their costs, plus a fair profit margin. Therefore, price should not be the only consideration, and quality should probably rank high on the list.