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Fuel Savings from Solar DHW

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Posted by Ron Rosenfeld on September 8, 2005, 5:51 pm
How does one go about calculating the potential fuel savings from
installation of a solar DHW system?

At present, we have a propane-fired furnace, hydronic heat, and a separate
storage tank for DHW heated off the same furnace.

Maine has recently implemented a credit for solar DHW, even when off grid,
but I don't have any idea how to figure my fuel savings.

-- ron  (off the grid in Downeast Maine)

Posted by Christian Kaiser on September 8, 2005, 6:05 pm

first of all, you should know how much propane you need during a summer
month. Multiply this times 12, and you know a good estimation what you need
to heat your water up in a year.

This estimation is a bit too high, as during the cold month, your furnace
will be hot from the house heating anyway, so you don't need any energy to
heat up the furnace itself - what you do during summer.

Then it depends on the solar system, you can get 60-80% savings by it,
depending on the size of the system, isolation, amount of warm water needed,

Is that good enough for a rough draft?


PS: If you have a modern furnace, you might be able to save a lot of energy
by reducing the times when you heat up the water - I saved about 60% just by
reducing the times when the water was heated up to once in the morning and
once in the evening (it stayed warm enough for about 4-6 hours, we rarely
need warm water in the afternoon). Thus if you give up the idea of 24 hours
of hot water, this will save you a large amount. But this depends on your
personal situation and possibilites (and the isolation of the storage tank).

Posted by Ron Rosenfeld on September 8, 2005, 7:52 pm

Unfortunately for your suggestion, we also use propane for cooking; clothes
dryer, and our backup generator.

Thanks for your suggestion, though.

-- ron  (off the grid in Downeast Maine)

Posted by Paul on September 8, 2005, 6:39 pm

A google of "solar thermal"+"cost savings"
yielded among other links:
They have a PDF at the bottom.

Posted by Paul on September 8, 2005, 6:52 pm
 A further search of  "solar water heating"+savings yeilded:
That is a commercial site, but they list Maine.

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