Inverter Clipping
“Inverter clipping” refers to your solar inverter limiting the potential of your solar system's total power output. It seems counterintuitive to realize that inverter clipping can save you money by reducing power output.
How this works:
When designing a solar system, we select a solar panel and an inverter. The inverter inverts (shocking) the DC solar power to AC power for use in the home. We analyze the chosen solar panel's Nameplate Rating and make sure that the inverter is capable of handling the inversion efficiently, with as little loss as possible, or so you would think!
By slightly undersizing the inverter's capacity compared to the solar panel's peak output we can save more money in inverter costs than we lose from the loss of production from the solar panel. Below is a table that demonstrates a real life example:
Solar System : Silfab 370 Elite
Nameplate Rating of Module: 370 Watts (W) at Standard Test Conditions (STC)
Inverter Comparison
Enphase IQ7+ (295W peak output power)
Enphase IQ7A (366W peak output power)
The 366W inverter seems to be the correct choice and in some scenarios it is. However, a 370W rated solar module will practically never produce 370 watts (learn more about this topic by understanding Total Solar Resource Fraction (TSRF) vs STC).
Assumptions:
Annual Rate increase of 4% (historical reality).
0% degradation of solar module (not reality)
This table demonstrates that the cost difference of the inverters ($927.20) is greater than the total potential of lost power ($832.92). We accurately assumed that the 200kWh of lost production would be worth increasingly more as rates rise. We did not however assume any loss to solar production. Solar panels degrade linearly over time, this Silfab 370 Elite will produce 82.6% of its nameplate rating after 30 years. In this example, we lose 1.44% of total production due to inverter clipping. Once the solar panel degrades by 1.44% of its nameplate rating, inverter clipping will actually not be an issue. The Silfab 370 Elite degrades at .58% per year so in just about 3 years there will be no loss due to Inverter clipping.
This is how we design inverter clipping into our designs to better serve our customers.
