[aprssig] Shack backup power

Bob Bruninga bruninga at usna.edu
Mon Jun 6 08:42:05 EDT 2011

> I also have the disadvantage of a roof that basically 
> has East and West exposures...

Actually that is the BEST roof!  The southern facing roof produces the most
power in the winter, but misses out on several hours of morning and evening
sun in the summer when the sun rises in the NE and sets in the NW.  SO, it
turns out, that for a nominal 20 degree pitched roof, the EAST or WEST roof
can produce 85% the energy as the ideal south roof.  But!!!  If both east
AND west can see the sky, then that owner has the advnateage of putting up a
solar array that is TWICE as big.  The net result is that he can produce
170% of the power of the south facing roof.

All of this assumes grid-tie where the only thing that matters is the annual
total of energy produced, without any worry about producing minimum power
say in the winter.

Anyone can see the proof.  Google PVWATTS and run any simulation you want.

> , with East blocked by a hill

Yep, that will reduce eastern production somewhat.  And unfortunately,
PVWATTS does not have an entry for shade problems.  But it can be calculated
manually I guess....

Bob, Wb4APR

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