Help Understanding Production Ratios (??)

[entgegnen]

Hi everyone - Great Forum!

1. I am confused about "production ratios." I am currently trying to educate myself about solar - I am considering the purchase of a home system.
2. When I look at my annual kWh usage, I am at around 11,000.
3. Most quotes I have received suggest a 7-7.5kWh system (e.g. 24 panels @ 320w/panel)
4. Most quotes give a "production ratio" (anywhere between 1.4 to 1.7)

So here is my confusion - wouldn't a 7-7.5kWh system simply create 7-7.5kWh of electricity?
If the panel ultimately creates more than 320w... then why does the manufacturer say it is just a 320w panel?

I am trying to understand whether production ratios are:

(a) wishful thinking based upon the hope of lots of sun?
(b) or does it represent the use of additional hardware (e.g. extra optimizers or extra inverters) that are able to capture "overage" from the panel? (which returns me to wondering why the panel isn't rated at something higher than the stated 320w... or whether installing extra optimizers of inverters may deviate from a panel manufacturers recommendations?)

I have read an artlce about "power limiting" and "oversizing (the array)" as it relates to inverters.... am I on the right track?

Thanks in advance for any guidance on this.

[bcroe]

Annual production can be rated in KW HOURS, that is ENERGY comparable to gallons of gasoline. Your system is rated in
KWs (no hours), thats POWER comparable to miles per gallon. Multiply power by time to get energy. Bruce Roe

[J.P.M.]

If you are serious about adding solar PV to your home:

Start by understanding how you are charged for electricity and how that may be changing for you.

Download and read "Solar Power Your Home for Dummies", free download on the net. Pay special attention to the conservation portions. Those measures are far more cost effective than any solar improvements. Any solar additions after conservation efforts will be smaller and less expensive. The smart choice is usually about getting a lower electric bill, not about throwing expensive solar at a self inflicted high electric bill.

After that, run PVWatts from NREL after reading the help/info screens. Make a few runs using what you learned from the help/info screens and the book.

Learn/brush up on time value of money analysis to aid in the financial tradeoffs as best fits your needs/choices/wants.

Get your roof inspected/serviced as needed. solar PV will last a long time on a roof. Repairs under an array are expensive/disruptive.

Ask questions here to fill in knowledge gaps.

Knowledge is power. Get some of both before getting quotes. For a few hours of time and a bit of homework, you'll get better quality equipment and installation for a better price, and get screwed less.

Welcome to the neighborhood and the forum of few(er) illusions.

[entgegnen]

Annual production can be rated in KW HOURS, that is ENERGY comparable to gallons of gasoline. Your system is rated in
KWs (no hours), thats POWER comparable to miles per gallon. Multiply power by time to get energy. Bruce Roe

Bruce -

Thanks for this very simple analogy. It makes much more sense now. When a quote gives me a 1.4 ratio, it is merely being conservative about the miles per gallon I should expect... whereas the 1.8 is just a less conservative estimate about my system's mpg.

JPM -

Thanks for the recommendation about "Solar Power Your Home for Dummies." Just located it on the net. Will start reading today... and will finish it before I make any purchase. (all 370 pages...)

[J.P.M.]

JPM -Thanks for the recommendation about "Solar Power Your Home for Dummies." Just located it on the net. Will start reading today... and will finish it before I make any purchase. (all 370 pages...)

For my part, you're welcome. Get your own answers. Question everything everyone says. Caveat Emptor.

[bcroe]

Bruce - Thanks for this very simple analogy. It makes much more sense now. When a quote gives me a 1.4 ratio, it is merely being conservative

A 7.5KW system running for (the equivalent of) 1400 Hours will give you 10,500 KWH. So the ratio is 1400 Hours, or 1400 if you chose
to drop units. Bruce Roe

[sensij]

A ratio of 1.4 is very conservative in southern ca unless you have a very suboptimal system or lots of shade. If you haven't tried it yet, run the pvwatts model for your system and see what it says. A loss factor of 10% or less is appropriate for many installations, and most panels going up today fit the model's definition of "premium".