I think you are also forgot the price of a Building permit - in this county 1-2K
Doc
----- Original Message ----- From: "Robert Bruninga" bruninga@usna.edu To: "'Greg D.'" ko6th_greg@hotmail.com; ptrowe@yahoo.com; amsat-bb@amsat.org; wb3jfs@cox.net Sent: Friday, October 02, 2009 11:27 AM Subject: [amsat-bb] Re: Solar Power (I was wrong)
... I have... a roof angle exposure that is not solar-friendly...
That was another error I had made in my situation.
Again, there is a BIG difference between solar design for stand-alone battery systems (must point south, optimum angle, etc) and grid-tie systems that can be anything from SE to SW and even FLAT and still be only a few percent off peak!.
The economics are entirely different.
The remote/battery system, MUST provide a minimum power on the worst winter days and weather of the year. It MUST be optimized for winter.
On the other hand, the grid tie system only has to have a good AVERAGE power averaged over a year. And you can make more money in a month of summer sun making money at HIGH payback rates than you can get all winter (3 months).
Even a FLAT array makes more power in the 3 summer months than the optimum tilt angle array does.
And lastly, anything pointed SE to S to SW is about the same for a grid-tie system. You lose at most about 5% SE or SW compared to South. Again, the reason is not obvious. But any tilted array is only going to see the sun for 180 degrees of path across the sky. Even the ideal South facing tilted array does not see the morning sun nor the evening sun in the summer when you are getting your most payback.. It only sees the midle 6 hours. Since the sun is up much longer than that most seasons, then getting those 6 hours averaged before noon (SE) or getting them in the afternoonn (SW) makes little difference for a grid-tie array, though, I'd favor SW, since peak electric rates apply longer in the afternoon than in the morning. So you want to maximize your power when electricity rates are highest.
Again, I am sharing this off topic with everyone, because I too learned that my thinking was all wrong based on my previous experiences with stand-alone power systems and that a grid-tie-system has completely diffeerent economics to my normal thinking...
You can play with all the angles and directions for grid-tie systems on-line with the solar energy calculator here:
Yes, SOUTH with a latitude tilt is best... But based on annual AVERAGEs: Southeast only lost 5% Southwest only lost 5% Droping the tilt to the angle of my roof 25 deg only lost 1%! Droping the tilt to FLAT on the ground only lost 14% (but if I tilt them up to 45deg Sept to April) I GAIN 20%! And that is a +5% over optimum south.
http://www.nrel.gov/rredc/pvwatts/version1.html
On the other hand, ANY shade will significantlly cut into your power budget.
Bob, Wb4APR
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