Solar Module overproduction

tom08588

Member
My company instructed me to design solar arrays in our simulation software (Aurora solar) to 80% of the customer's consumption. The reasoning is that someone heard solar panels will actually overproduce their nominal rating, so we can build smaller arrays and they will still cover all the usage. I asked where they got this information and I feel like it is merely wishful thinking. I don't doubt that a solar array might overperform, but not consistently 20% more.

Has anyone encountered any studies that might back this claim up? I've been trying to convince them it is not reliable information and we are undersizing our systems, but they are convinced it is true and is helping them close deals by selling smaller arrays.
 

electrofelon

Senior Member
I think someone is confused. Perhaps they are mixing up things like the the Xtra 1.25 required for ampacity for potentially higher irradiance than STC and/or the higher voltage/wattage than STC in cold conditions. That or it is just plain old dishonesty that is common with many solar proposals. As far as I know, energy estimates from say PV watts or other software is pretty close. I am three weeks away from my anniversary and I won't make estimated production.
 

tom08588

Member
Thanks, I've run our actual production numbers on 5 of our systems for the past 6 months and all of them are within about a +/- 5% of the simulations. I can't find any academic resources that support this "extra 20%" claim. I feel it was an exaggeration someone "in the business" offhand mentioned that sounded good to our salesteam, so it's imprinted on them.
 

electrofelon

Senior Member
or it is just plain old dishonesty that is common with many solar proposals.

I just want to clarify that I dont think solar people are any less honest than anyone else in an unrelated industry who is trying to sell an item, particularly one sold based on an efficiency improvement or payback term. Probably the majority of such things, solar or not, will be sugar coated...
 

jaggedben

Senior Member
The 80% thing sounds like either a misunderstanding, or perhaps a misapplication of something than might have been more true in different circumstances. (See below.) I agree with electrodfelon.

With that said, a key point is that it depends a lot on the estimating software you use and the assumptions you input into it. At one company I worked at it was felt that the estimating calculators we used were conservative. This was less based on any thorough study than on a few spot checks and the fact that 'none of our customers have ever complained about underproduction' (when their systems were fully functioning, that is). We had a guideline that if the actual shade readings on site survey were less than 85% of what a salesperson had estimated pre-site survey, that was okay. i.e. we didn't go back to the customer with a new estimate. I think part of what was going on in our case was also that we were always using micro-inverters or optimizers so large shade factors applied to the whole sytem were too conservative.

In any case, my point is is that "someone heard solar panels will actually overproduce their nominal rating" might have some basis in something that was going on with some other estimating situation that 'someone' was a part of. But if your study shows that's not happening with your current software and hardware, then you're correct to discount it. You might want to find a way to adjust Aurora down 5% or so, just so you don't have complaints later on. It's a sales strategy choice to consider. (Do you overpromise to capture market share and then apologize or discount later? or underpromise and get more good customer reviews for the marketing dept?)
 
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