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Old 17-03-2014, 11:23   #1
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Solar panel efficiency

Hey,

I'm looking into getting some solar panels, but I'm left with some questions regarding their efficiency. Mostly the info you get are the wattage and the type (mono/poly), but it's a lot less clear what their efficiency is. An older 100w panel won't put as many amps into the batteries as a newer one, but how do you spot the difference? At what point is the difference not worth the financial gain anymore?
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Old 17-03-2014, 11:40   #2
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Re: Solar panel efficiency

Easy,

STD reference insolation is 1000 W/m2.

Calculate panel surface area from dimensions given and refer panel wattage to its area and then to std insolation. There you have it.
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Old 17-03-2014, 11:44   #3
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Re: Solar panel efficiency

As far as brands, Sunpower is the most efficient (if you can actually buy one), followed by Sanyo.
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Old 17-03-2014, 11:47   #4
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Re: Solar panel efficiency

The higher the STD the better? 1000w/m being what?

I read about, say 20% efficiency in panels sometimes, how does that relate to STD?
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Old 17-03-2014, 11:54   #5
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Re: Solar panel efficiency

Standard insolation is the amount of available solar power per square meter used by manufacturers and test labs. It is set at 1000 W/m2 - just a constant, a reference point.

Example calculations:

panel data:
  • power: 250W
  • dimensions (LxHxW) (mm): 1650x990x40

checking:

1.65m * 0.99m = 1.6335 m2


250 W / 1.6335 m2 = 153.05 W/m2


153.05 W/m2 / 1000 w/m2 = 0.153 = 15.3% panel efficiency.
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Old 17-03-2014, 12:04   #6
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Re: Solar panel efficiency

kewl, thx!

However, that would mean that any 250W panel with those dimensions will be equally efficient. Is that the case? Are the "better/more efficient" panels just the same wattage with smaller dimensions?
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Old 17-03-2014, 12:51   #7
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Re: Solar panel efficiency

Quote:
Originally Posted by Orchidius View Post
kewl, thx!

However, that would mean that any 250W panel with those dimensions will be equally efficient. Is that the case?
In standard conditions - yes.

Quote:
Are the "better/more efficient" panels just the same wattage with smaller dimensions?
More often it is same panel dimensions with less (or more) efficient cells, but both are a possibility.
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Old 17-03-2014, 17:17   #8
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Re: Solar panel efficiency

A 10 y.o knackered Siemens (Neste) puts out 4 Amps, a brand new Chinese equivalent puts out 4.5 and a brand new back linked gizmo about 5.

b.
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Old 17-03-2014, 17:40   #9
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Re: Solar panel efficiency

Quote:
Originally Posted by mrm View Post
Standard insolation is the amount of available solar power per square meter used by manufacturers and test labs. It is set at 1000 W/m2 - just a constant, a reference point.

Example calculations:

panel data:
  • power: 250W
  • dimensions (LxHxW) (mm): 1650x990x40

checking:

1.65m * 0.99m = 1.6335 m2


250 W / 1.6335 m2 = 153.05 W/m2


153.05 W/m2 / 1000 w/m2 = 0.153 = 15.3% panel efficiency.
+1 - Efficiency is just a measure of size vs. output, so you can calculate it just from panel power rating and dimensions.

Quote:
Originally Posted by Orchidius View Post
...An older 100w panel won't put as many amps into the batteries as a newer one, but how do you spot the difference?...
This is a little harder, panels do degrade with age and will produce less power over time. You can't buy the same panels you could by 10 years ago (or even two years ago), so you can't go with real-world experience on specific panels. Which leaves you stuck with overall company performance and reputation. You can ask in places like this, and you can check warranties. Some panels offer 80% at 20 years, some 80% at 25 years, etc. The longer the warranty and the higher the guaranteed output the more confidence the producer has. Of course, you even have to be careful with that, if the warranty isn't backed by third-party insurance then it's only as good as the company that's offering it.

[Edit] - Don't count on the warranty to protect you, the marine user - it probably won't. It may be an indication of quality, but other than that is pretty useless once you put a panel on a boat. [/Edit]
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Old 17-03-2014, 19:01   #10
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Quote:
Originally Posted by Orchidius View Post
Hey, I'm looking into getting some solar panels, but I'm left with some questions regarding their efficiency. Mostly the info you get are the wattage and the type (mono/poly), but it's a lot less clear what their efficiency is. An older 100w panel won't put as many amps into the batteries as a newer one, but how do you spot the difference? At what point is the difference not worth the financial gain anymore?
A 100W panel is a 100W panel. They produce the same. One may be smaller than the other, wich would make that the mor efficient one.
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Old 17-03-2014, 19:07   #11
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There is not much difference in efficiency in panels today. For the little there is you pack a huge premium.

You usually can buy the same panel size from the same manufacturer in several power ratings. For example you may find panels 280W 300W and 320W. Basically, the tested all the cells and graded them by efficient. Than put the top 1/3 in the 320W panel and so on. The 280W panel may cost $0.80 per W, while the 320W panel cost $1.10 per W.
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Old 17-03-2014, 19:31   #12
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Re: Solar panel efficiency

Solbian panels advertise 22.5% efficiency...
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Old 17-03-2014, 19:42   #13
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Re: Solar panel efficiency

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Originally Posted by Brian T View Post
Solbian panels advertise 22.5% efficiency...
At what premium though. Certainly not anywhere near $1.00 W.
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Old 17-03-2014, 20:10   #14
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Re: Solar panel efficiency

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Originally Posted by downunder View Post
At what premium though. Certainly not anywhere near $1.00 W.
Price is not a factor for efficiency ratings. For almost every piece of gear, more efficient translates to more expensive. If you want to spend less money up front, you can't get high efficiency.

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Old 17-03-2014, 22:02   #15
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Re: Solar panel efficiency

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Originally Posted by roetter View Post
A 100W panel is a 100W panel. They produce the same. One may be smaller than the other, wich would make that the mor efficient one.
A 100W panel is a 100W panel at STC (1000 W/m2, 25C). Check two panels at 45C (typical NOCT) and you may find that one loses .45%/C and the other loses .35%/C. On a 100W panel that means a difference of 2W at normal operating temperatures. That means that at normal operating conditions one of those panels is a 91W panel and the other is a 93W panel. Nitpicking? Yes, but a better panel, with smaller losses, will produce more power overall, even if both are rated 100W at STC.
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