Calculating actual solar panel output?

[Number21]

I'm considering investing a large amount of money into solar panels for my home and take advantage of Oregon's solar energy tax credit. My question is, how do I know what the average output of my panels is going to be, for calculation purposes?

For example, I live in NW Oregon, we don't get much sun. If I put 1000 watts of solar panels on my roof, how many total watts could I expect daily or monthly? On a sunny day, will they actually produce 1kw? How many hours a day do they usually output? Is there some kind of pre-determined average for solar output in different regions?

[Basil]

I can tell you this mush. Tracking will let you get all you can out of your panels. ( Fast pay back )The best I have seen it 50 to 80 percent of the rating of a panel. I have a small system and I plan to keep adding. ( Just to have lights, a fan and so on when power goes out, ) I rate ever thing at half rating and that's with tracking. I'm sure you could search the board or net and find solar calculators.

[GaryGary]

Hi,

It seems like PVWatts would tell you?

http://rredc.nrel.gov/solar/calculators/PVWATTS/

I find Version 1 easier to use than Version 2.

Gary

[imsmooth]

I have 12.25kw mounted on my roof facing slightly south of east.  Conditions such as temperature and weather affect your output.  I can say that in NJ at a lattitude of 41 degrees averaged over the year each one KW of panels produced 1400-1480 KW-hours/year.  The longest days have 16 hours and the shortest have 6 hours.  My bill has been zero for the year.  I hope this helps.

[Clifford]

The problem with Oregon...  and the northwest is not that there isn't any sun...

but that it is all concentrated in the summer...  say June, July, August, September...

See the stats on the pages:

http://www.city-data.com/city/Portland-Oregon.html

http://www.city-data.com/

When I was testing my system earlier, I estimated that I got about 1/10 the power generation on a cloudy day as I would get on a sunny day.  And, I am far below the rated power generation which I attribute to having purchased well used panels.

The other thing you will have to determine is which resources you wish to convert to solar, and how to deal with it.  On grid?  Off grid?

Many homes in Oregon only have electric systems...  heat, water, stove, etc.  

Water is best to heat directly...  rather than generating electricity then using an electric hot water heater.  And, if you are in Oregon, you'll want a backup system.

Same for home heating (except for the problem with cloudy days).

If you are going off grid, then you will need other heating, wood, gas, propane, etc.

As far as hours per day at peak output...  that depends a lot on your system.

If you mount your panels flat on your roof...  then only twice a year the sun will be at the optimal angle at noon, and realistically speaking, you'll have near peak power production for 4-6 hrs / day.

The problem is that while you can calculate the area exposed to the sun at various angles with geometry, however you will actually experience greater power loss due to reflection, and loss of efficiency with less sun exposure.  This is why, if you are making a large system & have a place to put it, consider a tracking system.

Now...  I guess this gets us back to the cloudy day issue...  There are a couple of companies that are making bifacial solar panels...  Sanyo is one that distributes them in the USA.

http://us.sanyo.com/solar/index.cfm?productID=1555

While I am not convinced of the utility of a bifacial panel on sunny days, I would think that on cloudy days one might get a higher percentage of the light on the back as reflected light (assuming they are mounted in a place that would allow reflected light to the back.  So...  I guess the question would be whether a 186 watt bifacial panel would be worth the same as a 200 watt standard panel.

Anyway, hopefully I will be able to do more testing this winter.

[shay]

tracking plus reflection could get you more power. On a conventional setup I was used to 175 amps at 12v but without tracking, a cold day, cold wires, and snow, after a cloud it was well above 200 amps. Add reflection, tracking, and bifacial panels at higher voltages and the output could be worth the extra bucks & effort. Might even be worth distilled water cooling of the panels. I've heard in northern areas over snow and on yachts with reflected sunlight the panels can be permanently mounted vertically at right angles to the sun and still be worthwhile in practice.  

[shay]

In our climate (desert Callifornia) just space the average panels off the ground for cooling and buy an extra panel to make up for the power lost from not tracking :-)