So how much power do solar panels in the Seattle, WA area generate?

Since people sometimes ask me (or question me) about just how much solar power can be made in a "rainy" place like Seattle, I have decided to post a year's worth of data regarding the output of my panels. But first, notice the images above - they are average "normal" solar radiation levels from a variety of months for the Pacific Northwest (you can see that we get a lot of solar radiation in the warmer months, not so much in the colder months; in fact Seattle gets roughly the same amount of solar radiation as Houston, TX because we have two more hours of sunshine during the warmest time of the year, and only an hour or so less during the colder months).

The output I am sharing is from a 2.7 kilowatt array - my current array is now approximately 4.0 kilowatts after I expanded earlier this month (the additional panels came online on 8/5/10), and figures below represent the readings generated by my inverter and reported to Solar Oregon (the cooperative I sell my renewable energy production to - at 1 cent per kilowatt hour - for resale to power companies and individual customers that wish to subsidize the deployment of additional renewable energy installations). Also note the difference in my estimated output for August 2010 compared to August 2009:

August 2010 (2.7 kw system upgraded to 4.0 on 8/5) - 455 kwh
July 2010 - 335 kwh
June 2010 - 277 kwh
May 2010 - 290 kwh
April 2010 - 219 kwh
March 2010 - 199 kwh
February 2010 - 101 kwh
January 2010 - 45 kwh
December 2009 - 58 kwh
November 2009 - 54 kwh
October 2009 - 122 kwh
September 2009 - 242 kwh
August 2009 - 290 kwh

This period was a little bit unusual, I think, in that we had much sunnier weather in the colder parts of the year (when there are fewer hours of sunlight) and less sunny weather during the warmer parts of the year (when there is more), at least compared to average. In any case, you can see that my 12 month production of electricity adds up to 2,687 kwh of electricity. I will re-post next year's data with a full year of 4.0 kilowatt output.

How much is that worth, carbon offset wise? There are free online carbon calculators you can use to figure out how much carbon the output displaces, but this varies entirely on region (Seattle area gets the vast majority most of its power from renewable sources like hydro, wind, biomass, solar, and such). Using the average figures for the USA though (which is MUCH more coal dependent than anywhere in the state of Washington), my 2,687 kwh for one year of solar energy production results in 1,452 kilograms (3,194.4 pounds) of carbon staying out of the air. Given that my solar panels should be generating electricity for at least 30 years, that adds up to around 45,000 kilograms (about 99,000 pounds) for 30 years worth of production (add 30 - 50% or so to this since the estimated lifespan of the panels is 40 - 50 years). And note, this is comparing electricity used to power a home; if this electricity is used to power a vehicle that would otherwise be burning gas or diesel, the actual carbon reductions should be much higher (I don't have any estimates, sorry).

how much is all that power worth, cash wise? Given that my power company pays me for every kilowatt hour I push back to the grid, and I don't have to pay the power company for all the power I make and use myself, I am looking at well over $10,000 worth of electricity generated by the panels assuming power costs and average of 12 cents per kilowatt hour over the next 3o years (which is a very conservative figure - I would estimate it would cost more like 15 - 20 cents, on average, over that time frame... also note I am using the last 12 months as my figure for calculating, now that I upgraded my system, my actual output should be about 50% higher... so I could say $15,000+).

Anyway, I also receive subsidies from the state of Washington for producing solar power (equal to about $350 - $550 a year) and a small amount ($65 - $75 a year) from selling production credit to Solar Oregon. So there you go... a break down of just how much money my solar panels generate (in case you wanted to know, I estimate a 10 - 12 year ROI, given current incentives in Washington state). What else would you like to know?