While all predictions are tough, especially about the future, solar users have the means available to help them estimate their system’s production. This is important because knowing your system’s production tells you how quickly your solar system’s payback period.
Every solar panel has its own wattage rating. This is the amount of direct current (DC) power that it is capable of producing in testing conditions at any given instant. For example, A 260-watt-rated panel is capable of producing a maximum of 260 watts under test conditions at any given moment. But, unless you live in a solar testing laboratory, the output for your home’s panels will be different.
Your system is measured by the total combined wattage of all the panels of the in the system. This is usually measured in kilowatts. One kilowatt equals 1,000 watts. For example, a solar array consisting of twelve 250-watt panels would be a 3-kilowatt system. But, this figure doesn’t tell you how much electricity your system is producing.
The electricity output of solar PV Systems is measured in kilowatt-hours (kWh). The kilowatt-hour production of a solar system is a function of how much sunlight and for what amount of time that sunlight hits the panels. This depends on local solar resource, weather conditions, panel orientation, amount of shading, system design and type of mounting (ground or roof mount).
The National Renewable Energy Laboratory has put together a useful website, PV Watts, that can estimate your system’s performance. It takes into account the factors above and calculates the expected output your system should produce, as well as the financial value of the electricity generated.
You can then use this figure to estimate how long it will take your system to pay for itself.