formula to calculate solar energy production per year

[solar2b]

Hello!
I'm trying to calculate the total energy production (in kWh) different PV systems are able to generate per year. I want to get the figures in different countries. Of cause it

[Mike90250]

Roughly, it's
PV STC value *.8 (80% of STC)
times hours of usable light (5 is a normal number) The sun may be up 12 hours a day in the summer, but the 3 morning and 3 evening hours, carry little power, so you can't count them.
Figure in a number for clouds.

2KW array =
(1600 *5) = 8000w day x 365 = 2,920,000 watts year, of sunny days, no clouds, no rain, perfect sun angle. You will NEVER exceed this #, and almost always fall short of it because of bad weather.

The PV WATTS website can give you better guesses with some local weather and sun angles figured in.

http://www.nrel.gov/rredc/pvwatts/

[danzaslap]

I believe your units should be Wh. As in 1600W x 5h = 8000Wh * 365 = 2.92MWh, which is ALOt.

[russ]

watts per m2

Hi Mike, STC calls for 1000 watts/m2 but according to my weather station we never see that. Back in May I had an hourly average of 1001 watts/m2 - that one time only.

Averages for this year since I got my station up W/m2 global solar radiation:

Oct Sept Aug July June May hour
299 354 466 434 409 518 - 1000
450 516 629 693 727 734 - 1100
530 640 768 825 854 874 - 1200
558 725 846 902 914 944 - 1300
569 736 867 922 890 932 - 1400
459 699 829 887 830 851 - 1500
359 606 742 801 758 705 - 1600
227 441 602 672 659 547 - 1700
sum for best 8 hours in kW/m2
3.45 4.72 5.75 6.14 6.04 6.11

I would have to further derate the panel from the 1000 watts/m2?

[Mike90250]

The PVwatts site takes into account 10 -20 years of recorded irradiance values, so it shold be a pretty good guide. I think pvwatts2 has a map you chose from, so you can be sure go click on your side of the local microclimate cells.

[P.S.]

Europe and pert of Africa

For region fro Subj: you can use http://re.jrc.ec.europa.eu/pvgis/imaps/index.htm , it is quite sceptical, but good for calculation.

[solar2b]

Thank's P.S. I have used this source. By the way what do you think do the figures of solar irradiation in this site already include cloudy and rainy days?

[P.S.]

Thank's P.S. I have used this source. By the way what do you think do the figures of solar irradiation in this site already include cloudy and rainy days?

Yes, but they are using history of 10 years of meteo data, and climate is changing.

[Elena]

Back to the initial question

Hello,

I am trying to figure out how to estimate the solar productions if I know that for a place A the annual solar radiation (flat) is 1500 kWh/m2 and for B is 1250. As there are differences in the cost of connection to the grid I would like to make the analysis and decide. Does someone know the formula for solar production?
The estimation Mike offered ( 80% * STC * 5 * 365) is site independent and does not help me in this specific case.

Thank you so much

[Mike90250]

Not much that I know of besides PV watts. The PVWATTS 2 site may be more flexable for your needs

[solardood]

Calculating in Payback

Well to simplify things the Ontario government released whats called retscreen. Well that was the goal anyway, once you figure out how to fill in all the blanks to get the answer you want!

You can find the download here: http://www.retscreen.net/ang/home.php
it's free!