Friday, July 14, 2006

Solar Thermal update

Our solar thermal system is installed and operating. Woot Woot! Now we will start examining our utility bills to see if we notice the savings. We should.

At our latitude we can expect our solar collectors to collect ~1300 BTUs/sqft a day on average according to Revelle. (I've just had time to skim Revelle's website but it looks info packed!) I'm told our panels are mounted at 52 degrees (not 45 as assumed by Revelle) although to be honest they looked closer to 60 degrees to me. This orientation means the panels will collect more energy in winter and less in summer, but will the average be higher, lower or unchanged?? (I plan to take my camera and get some shots next time I'm there.)

The installer suggested the collectors would collect 1000 BTU/sqft a day, so I'll use that for now. With three panels, we have ~70 sqft of collector area. Finally 1 kWh = 3,412 BTU (since I have no intuition as to what a BTU looks like.)

1000 BTU/sqft * 70 sqft * 1kWh/3412BTU = 20.5 kWh/day

20.5 kWh/day * 30 day/month * $0.065 kWh = $40/month

I think we will notice $40/month savings :)

Although if our electric rate remains at $0.065 kWh (unlikely but...) it will take 175 months (14.5 years) of $40/mth for a simple payback on our system (~$7,000). ~10 years if we could take advantage of $2k fed tax credit (which doesn't help AMT tax payers).

Sigh! this seems to be a long payback for a solar thermal would drop to ~11 yrs if Revelle is right about 1300 BTU/sqft. And who on this globe (except us) only pays $0.065 kWh electric rates?


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