I don't get my rated KWh, do I just have to live with it?

System · July 2008

I had a 3.3 KWh system installed about 4 years. They are 165 watt mitsubishi panels. The best I've ever seen on my inverter is 2.4 KWh. The installer stated that the optimal south facing roof was still not optimal. Still, this is a 30% discrepancy from the rated amount. My HOA won't allows solar panel, but they can't be propped up. Do I just live with it? It still provides 90% of all the electricity that I need.

newenergy · July 2008

Re: I don't get my rated KWh, do I just have to live with it?

165W is their STC rating. That's 25 degrees C. The cell temperature is generally going to be considerably higher and thus the power output will generally be lower. Mitsu 165s have about 147W CEC rating (California Energy Commission), which is closer to what they should actually get under real conditions. That gives you 2940 Watts.

Your inverter is probably about 95% efficient. That brings you down to 2793. There are small losses in the wires and the modules will have some dust/dirt on them.

Then there's shading and orientation losses.

BB. · July 2008

Re: I don't get my rated KWh, do I just have to live with it?

My Grid Tied system with 3.5 kW (not kWhr) of solar panels has, just a few times, peaked to 2,998 Watts maximum... Mostly, it runs around 2,300 to 2,500 Watts.

Of more interest is how much power has your system generated in one year... It should be pretty close to what is predicted by this link:

http://rredc.nrel.gov/solar/codes_algs/PVWATTS/version1/

If I plug Los Angeles CA into the calculator, and use 3.3 kW worth of panels (default everything else), I get 4,850 kWhrs per typical year...

Summer should be around 450-480 kWhrs per month, and winter in the low to mid 300's kWhrs per month.

Year over year, you may see a +/- 5% or so variation (see here, choose California and look for Los Angeles).

Unless you are logging--it may be difficult for you to see peak power output (mine typically happens and hour or so before noon--when it is still cool in the morning.

-Bill

Telco · July 2008

Re: I don't get my rated KWh, do I just have to live with it?

Where are you located, and have you checked the actual LAWS yet? Your HOA may not have a say in whether you have solar power or not depending on local laws, regardless of what the HOA rules say. Check into it.

BB. · July 2008

Re: I don't get my rated KWh, do I just have to live with it?

Assuming you are in Southern California, from this website:

Los Angeles - Zoning Code
Solar Easement and the Solar Shade Control Act
Solar Rights Act

The amount of power you will receive with your panels laid flat (I missed that part):

Flat array:
Month Solar Radiation
(kWh/m2/day) AC Energy (kWh)
1 2.84 202
2 3.66 241
3 4.64 342
4 5.95 420
5 6.50 472
6 6.73 473
7 7.17 512
8 6.71 475
9 5.44 375
10 4.17 299
11 3.19 219
12 2.64 183
============================
Year 4.98 4213 kWhrs per year

Vs angle set you your latitude of ~34 degrees:

Month Solar Radiation
(kWh/m2/day) AC Energy (kWh)
1 4.43 326 kWh per month
2 5.00 335
3 5.52 405
4 6.20 435
5 6.12 440
6 6.09 422
7 6.63 466
8 6.79 474
9 6.18 424
10 5.46 394
11 4.81 341
12 4.34 318
======================================
Year 5.63 4781 kWhrs per year

On average, year over year, you will get about 16% more power with tilted panels (all else being equal)... Or about $70 per year worth of electricity...

Only you can decide where to proceed from here.

-Bill

I don't get my rated KWh, do I just have to live with it?

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