What is the difference between system power output and system energy production?

The AC energy production of a solar array is measured in kilowatt hours (kWh). This is measured over periods of months and years to compare with sizing and long-term performance expectations of your solar panels. Solar kWh energy production is also typically given on inverter output displays or remote monitoring sites and applications. This can be compared with a household’s total kWh electricity consumption, as seen on a utility bill. This is best used to get an overall sense of your power production by lessening the impact of days of intense or low sunlight.

The AC power output of your solar array, measured in watts (W) or kilowatts (kW), is typically found on inverter output displays or remote monitoring sites. This is an instantaneous measurement, which is determined by the rated DC power output of the solar array, inverter efficiency and system losses, and is proportional to solar irradiance on the array. This is best described as a snapshot of your energy output in that instant.

Is it true that solar panels rarely produce their rated power output? Is there a problem with my PV system?

Solar panels will typically operate at around 80% of nameplate DC power rating. This will occur even in weather conditions that might be considered “ideal”. The nameplate rating of a solar panel is a DC rating measured under factory conditions. This means that their rating is determined at a cell temperature of 77°F and perfect sun conditions of 1000 W/m2. The power output reading seen on an inverter is an AC rating. Many factors such as DC to AC conversion losses, wiring losses, temperature losses, losses due to shading and dust, and losses due to non-optimal tilt and orientation of the array will affect the instantaneous power output and cumulative energy production of your solar array.

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