How many panels would I need?

[Muon1]

Hi all,

Could some please help me with a calculation. I'm trying to work out how many panels I would need. I'm coming up with millions of panels. I really think I'm going wrong somewhere.

Here's the info

Solar Isolation: 0.5kwh/m^2/day
Total energy required per hour: 136 Mega Watts
Panel Rating: 240W
Panel Efficiency: 15%
Area of Panel: 1650mm x 990mm = 1.633m^2
Assume system efficiency: 75%

Thanks.

 

[Muon1]

Forgot to add something:

4 Peak hours of sunshine per day.

 

[DRWeig]

136,000,000 watts / 240 watts per panel / 0.75 system efficiency = 755,556 panels.

Or am I missing something?



Best to you,

Goober Dave

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[Muon1]

Hi,

Thanks for replying quickly.

Does the solar isolation or the panel efficiency not effect the number of panels? (this is probably why I'm getting the wrong answer).

I've looked at so many different websites, and most give different ways if calculating this.

 

[racookpe1978]

Specifically, what is your latitude? What is your longitude?

Your statement of .5 Kwatt/m^2 is about right for a fairly far northern latitude (or southern) but NOT for a "day" Per second? But averaged over an entire 24 hour day?

 

[Muon1]

My Latitude is 51 Degrees, Longitude is 0 Degrees. I'm in England.

 

[DRWeig]

Are you perhaps looking for megawatt-hours?



Best to you,

Goober Dave

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[Muon1]

Hi Dave,

I working on a figure of 200,000MWh per year. It's going to be a very very large solar installation.

 

[IRstuff]

Your numbers don't seem to be set up for a solar calculation. The sun is only available for part of the day, while your power requirement appears to be for night as well. Since the solar panels do not supply power at night, unless through battery storage, the problem is ill-defined. Has the demand been 24-hr averaged, or is it the correct real-time demand? If the former, then the entire 24-hr demand has to be supplied by excess capacity from the daylight hours and stored somehow.

Additionally, there seems to be redundant mis-information. The 0.5 kWh/m^2/day appears to be a calculated/averaged output from a solar panel; I get about 1.048 kWh/m^2/day using MIL-HDBK-310's maximum solar day and your efficiency numbers, so for a place like England, 0.5 kWh/m^2/day might even be optimistic. The 240-W power rating is simply the best that the panel could every do, and should not be used for any normal calculations. 1120 W/m^2 * 15% * 75% = 201.6 W, which seems lower than the 240-W rating, but if you use the orbital solar constant of 1366W/m^2, you get 245.2 W, thus making the spec power value a bit meaningless and misleading.

So, the way I would approach it is to figure out the total W-hr demand required from the panels, and divide by the 0.5 Wh/m^2/day * 1.633m^2 to figure out how many panels you need. Note here, the problem gets progressively worse the more hours/day you need to supply the 136 MW. At 9 in the morning and 4 in the afternoon, the insolation is only about 65% that of solar maximum. That means that you are required to supply 136 MW at that time, you'll need 1.5x the number of panels you would have just calculated. Of course, the problem gets even worse than that, since the numbers I'm using apply to a summer solstice day, i.e., a winter solstice day would have dramatically lower insolation, even at noon

TTFN
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