# Sun Light during winter

1. Jun 6, 2007

### philipc

I'm building a solar powered project to light a room. From what I find on the internet, the average of sun light is given. It seems like to make my calculations I need to know what the minimum amount of sunlight could be. I haven't been able to find a web site that shows the min and max sun light for a region, just the yearly average. Anyone ever done such a project?
Thanks
Philip

2. Jun 6, 2007

### Staff: Mentor

I googled solar power insolation, and got lots of useful hits. Here's one with min/avge/max for US cities:

http://www.solar4power.com/solar-power-insolation-window.html

The key to any google search is knowing a helpful unique keyword. In this case, it was "insolation", which is the term for the inbound solar flux. Hope that helps.

3. Jun 6, 2007

### philipc

Thanks that is exactly what I was looking for. To bad they left off the 4th largest city, Houston? But now I can use your key words.
Thanks again
Philip

4. Jun 6, 2007

### philipc

I would like to add one more question, when a PV panel is rated for X watts, under what conditions can I assume it will achieve these numbers? Is there some standard whr/m2 that PV panels are rated?

5. Jun 6, 2007

### Staff: Mentor

Sorry, I don't know the answer to that. You could probably figure it out from the datasheets for the panels, if you can find those at the manufacturers' websites.

My guess would be the output would be stated for the max insolation that could be expected, whatever the max is in the tables that you've found. That's usually how marketing speak works. It's not like the solar panels are going to blow up or overheat if they exceed their "maximum" power output

6. Jun 7, 2007

### NoTime

I'd be careful of those numbers.

A 170w Solar Panel covers about 1 sq meter.
The doc lists solar insolation as being 800w sq meter for a cell efficiency of about 21%.

The worst case shown above is 1000w while the best case is around 8000w.
I suspect the difference is that solar cells only work with certain frequencies of light.
While I've been poking around at this stuff lately I haven't gotten around to figuring out how one set of numbers relates to the other.

Anybody know the conversion factor?
What part of say 4000w is in frequencies applicable to solar cells?

Edit: I suspect it is around 10%.

Last edited: Jun 7, 2007