# from heat to electricity

Discussion in 'Home Power and Microgeneration' started by random, Jul 14, 2003.

1. ### randomGuest

We almost always have a wood fire going, either for cooking or just
cleanup. Lots of heat going to waste. Is there a good, economical,
reliable method of turning some of that heat into kilowatts?

Also what's the consensus on the best type of battery bank, golf cart
motors? I'm finding battery banks to be of marginal value, good for
smoothing (reservoir) but not much else. Is that your experience too?

2. ### garytulieGuest

I believe there is a device available working on the reverse Peltier
principle and capable of generating around 100w from a wood burning stove.
Alternatively you could use a small steam engine to drive a shaft.

3. ### randomGuest

Are these devices available cheaply in quantity? Takes quite a few
100w's to get into the useful category methinks. I'll see what I can
learn about the Peltier principle, maybe therein lies the clue.
Thanks.

4. ### randomGuest

Thought about that one. Don't claim to be an expert on Stirling.
Seems it's the temperature difference that determines available
energy, and the whole general area is hotter'n heck. Got to think
about it some more. Stirling would be great for a fire next to a cold
stream, but I'm talking more about just plain heat... fire in a desert
as it were.
I'll take a look... the name sounds expensive. Thanks.

6. ### PhysicsGeniusGuest

[pedantry=on]

Temperature and heat are not the same thing. Heat is an amount of
energy. Temperature is an amount of energy *per atom*. The ocean is
only about body temperature, but it has an enormous of amount of heat.
A pot on the stove can be boiling hot (temperature), but has a lot less
heat.

7. ### daestromGuest

[double-pedantry=on]
Actually, temperature is not the amount of energy *per atom*. Witness your
pot of boiling water, the water and steam are at the same temperature, yet
the steam atoms have much more energy than the water atoms. But you're
right that heat is an amount of energy. Two similar terms of heat are often
confused, the total heat in a body of fluid and the specific heat of the
fluid. Specific heat is defined as simply the heat per unit of mass. The
ocean has a relatively low specific heat, but if you multiply that by the
total mass (measured in the same units as the denomonator of the specific
heat), you get the enormous number you spoke of.

But temperature *does* play a part in how much of the heat energy can be
converted to mechanical energy. With only mild temperature differences,
even the 'enormous' amount of heat in the ocean is not very useful.

daestrom

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