Mystery 5% power loss

[TET1968]

My recently activated CEC-AC 4.854kW solar system is consistently topping out at 4.6kW rather than 4.854kW...about a 5% deficit. My Enphase app shows me production in 15 minute increments. Enphase tech support analyzed my array's performance and told me my system is working correctly and that I am correct to expect it to reach 4.854kW. Can anyone here give me an idea that might explain this apparent 5% production loss? Enphase tech support could not explain it.

[oregon_phil]

14 REC400 panels with Enphase IQ8(M) microinverters.

per datasheet IQ8M peak output power= 330 watts

14 x 330 watts = 4620 watts

You have a brand new system with practically zero cell degradation, zero soiling, zero everything. Your system is producing IQ8M peak power. It's not going to get any better than this.

IQ8M max continuous output power = 325 watts or 4550 watts total. There's probably some temperature/time threshold where peak power is throttled back to max continuous output power. I'm just guessing since the specs aren't available.

[TET1968]

Thanks, I figured a system rated CEC-AC 4.854kW would give me at least 4.8kW peak power. Bad assumption on my part.

[SolTex]

I see from your other post that your system consists of 14 REC400 panels with Enphase IQ8(M) micro inverters. Since you live in St. Louis, MO I'm not sure why you are looking at the CEC-AC (Calif Energy Commission) rating for your panels, but in this case I think this rating is misleading. I have a Enphase system, so I'm familiar with the way it works. The maximum AC output of your system is limited by the maximum AC output of your inverters. The IQ8M inverter has a Peak Output Power of 330W and a Maximum Continuous Output Power of 325W. Since you have 14 inverters, the Peak output of your system cannot exceed 14 times 330W = 4620W. The Max Continuous power would be 14 times 325 = 4550W.

The Enphase app rounds off the power numbers so it shows your system topping out at 4.6kW which is right at the Peak output of your inverters (4620W = 4.6kW). In other words, your system is performing optimally and exactly as designed.

A common system sizing tool in the solar industry is called the Inverter Loading Ratio (ILR). This ratio is also called the DC/AC ratio, and will ideally be around 1.25 for the maximum system performance per dollar spent. In your system, you would calculate the ratio by dividing the nominal (STC) DC rating of your panel by the Max Continuous AC output rating of your inverter. 400 divided by 325 = 1.23 which is a excellent ILR number. Another sign of a properly designed system!

[TET1968]

Thanks, SolTex. The proposal Astrawatt Solar sent to me said it was for a 5.6kWDC 4.854kW CEC-AC system. Not being knowledgeable about the matter, I assumed the CEC-AC figure would apply to the system they were proposing to me.