sunmetrix solar panel plugFinally the big day has arrived: after waiting months, your 10 kW solar PV system is installed and you are eagerly monitoring the initial production of your investment. Lucky for you, it's a picture perfect day for solar energy with hardly any clouds in the sky. After tallying up the production for the whole day, you realize that you are nowhere close to what a 10 kW constant output should have produced. The good news: there's probably nothing wrong with your system. The bad news: you are mixing up energy and power.

The "10 kW" in your system specifications is the nameplate capacity, or rated power, of your system. In ideal laboratory conditions, your panels would actually produce 10 kW of electricity each hour (hence an output of 10 kWh in electrical energy). However, real life is far from these ideal conditions. Most of the time, your system will produce less than 10 kWh. This is perfectly normal. The average level of production can be expressed (in percentage terms) as the "capacity factor". If your system has a capacity factor of say, 15%, then your average production will be 10 kW x 15% = 0.15 kWh. The capacity factor itself is largely determined by your location (e.g., orientation and shading of your roof)  and your local climatic conditions.

Another way to look at this is to think of your installed capacity as the maximum speed of your car. Even though your speedometer may max out at 150 mph, you would seldom find yourself driving at that speed. Most of the time, your actual speed would be well below the maximum level. Likewise, you won't be seeing your solar energy system produce at its rated power very frequently.

In order to determine your system's capacity factor, you can consult Sunmetrix Discover. Using Discover, you can play around with different system specifications and location variables to give you a very good idea about your average expected energy production rates.