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Production expectations unrealistic?

Eury

New Member
Jun 30, 2016
2
0
NH USA
Hello, I had my PV system with 2 Powerwalls installed in early February. Not a lot of sunny days in NH between then and now, but I've had some that have been clear. My question is, are my expectations unrealistic as far as how many KW I should be producing?

According to the plans and our purchase paperwork, we purchased a 7.2KW system, that has a "System Production" of 8924 kWh. I have 24 Hanwha Q Cells: QPeak G4.1/SC300 and a Delta Solivia 6.6 TL RGM Inverter.

So, reading through all that. I don't see how I could ever produce anything near what they say I will with a 6.6kW inverter, just quick off the top of my head math would get me the 6.1-6.2kW that I am currently seeing from my PV system with the expected losses.

Hopefully someone can help clear this up for me.
 

liuping

Active Member
Jul 23, 2013
2,242
897
San Diego
To calculate you expected daily production, you need to find the "Peak Sun Hours" for you location. That times your panel rating - losses should be roughly your average production.

Annual System production of 8824kWh for 7.2kW of panels (assuming 10% losses) is using a peek sun hour rating of around 3.77 average over the year. That sounds about right for New Hampshire.
 

miimura

Well-Known Member
Aug 21, 2013
6,483
6,234
Los Altos, CA
About the same for me at its worst. Typically more like 1/3rd, though. I'm also down in a canyon.
Mine is really 5:1 every year. Typical Winter low is 5kWh/day and typical Summer peak is 25kWh/day. The gray line is a simple forecast model which does not account for the shading.

Solar production Multi-Annual Chart.jpg


My brother-in-law has the same type 18 micro-inverters mounted on his house without the shading and split directions and his really is 3:1.
 

arnolddeleon

Supporting Member
Supporting Member
Jul 21, 2012
892
948
SF Bay Area
Hello, I had my PV system with 2 Powerwalls installed in early February. Not a lot of sunny days in NH between then and now, but I've had some that have been clear. My question is, are my expectations unrealistic as far as how many KW I should be producing?

According to the plans and our purchase paperwork, we purchased a 7.2KW system, that has a "System Production" of 8924 kWh. I have 24 Hanwha Q Cells: QPeak G4.1/SC300 and a Delta Solivia 6.6 TL RGM Inverter.

So, reading through all that. I don't see how I could ever produce anything near what they say I will with a 6.6kW inverter, just quick off the top of my head math would get me the 6.1-6.2kW that I am currently seeing from my PV system with the expected losses.

Hopefully someone can help clear this up for me.

Doesn't seem that crazy, that's about 23 kWh/day. As a *very very* rough rule of thumb I've used is 4 to 5 "full hours" equivalent as an approximation for the bay area in CA including some losses. Your system is expecting about 3.7 "full hours" per day over the year (using 6.6 kW as the limit). (Forgot to hit post after I wrote this, I see @liuping makes a similar point)

arnold
 

wwhitney

Member
Nov 2, 2017
967
1,317
Berkeley, CA
FWIW, it is normal to design solar installations in which the sum of the ratings of the panels exceeds the inverter rating. I think ratios of up to 120% or so are common. When the solar panels are able to produce more power than the inverter is rated for, the inverter will "clip" production to its maximum rating.

But this clipping typically only happens for a short period of time around solar noon each day, and only in the summer. That means the economic value of the lost production is fairly small. Because string inverters only come in fixed sizes and are a fairly significant part of the equipment costs, using extra panels in this way can be economically optimal.

Cheers, Wayne
 
Jun 22, 2017
527
337
Bay Area, California
My breakdown between summer and winter months (with band splits at May 1st & June 1st). I get 62% of my solar production in the summer band and 38% in the winter band. I have zero shading, located inland near the Factory, and away from coastal clouds and fog. For the OP, the best summer band is yet to come.

I get clipping in the early spring, where the winter rains have cleaned the panels, and low temperatures enhance PV performance. I was taken back by clipping in May-June for 1-2 hours a day. I voiced out to my contractor why a 4000VA wasn't spec'd out instead of my 3840VA inverter. I did the calculation and the money lost was only $50 over 25 years, so they send me a gift card for that amount. 3840VA is a perfect match for a 20A breaker. All-in-all, nothing wrong with clipping.
 
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