We currently live in a rural area and use solar power for all our electricity needs, this is fine in summer and the living is easy, but in winter the daylight hours are significantly shorter and we have to sit in the dark to watch tv. During winter however we always have a fire going, what i propose is a method of extracting electricity from the heat wasted at the top(the outside bit) of the chimney.

The device is cylindrical and fits around a standard chimney, it has 3 layers... the inner layer is a water jacket and is used to heat the household water. The middle layer is peltier chips (if you don't know about these see link) to produce electricity. The outer layer is heatsinks.

The peltiers produce electricity using the heat differential between the hot water and the heatsinks which are exposed to the chilly air outside.

The water jacket regulates the temperature of the peltier chips, making sure they don't become too hot and crack, water flows through this jacket and into a hot water cylinder for household use, excess hot water can later be recycled through the system long after the fire has gone out to keep the peltiers producing power.

any suggestions? does it need a diagram?
-- greyfiend, Jul 16 2006

peltier chips http://www.peltier-info.com/
info on peltiers [greyfiend, Jul 16 2006]

Stoves make electricity http://www.tegmart....electric-generator/
It has been done before. I read various thing where stoves were used to generate electricity. [travbm, Nov 01 2015]

lessee... it is going to take heat out of the exhaust air, which makes it cooler and therefore more dense. It will then rise out of the chimney more slowly, so your heat extractor will have exactly the same effect as a damper. You will need to be able to control the rate of heat extraction so that you don't put in too much damper effect and end up in a smoky room.

Conversely, when using the hot water to heat the chips in non-fire time, you will also heat air, which will then rise up out of the house. If used in winter, the air being sucked out is likely heated air in your living space, and you might end up drawing out more energy than you gained at the peltiers.

Just caveats, not show-killers.
-- lurch, Jul 16 2006


They're both very interesting points... Plenty of houses use water jackets on their chimneys to heat the household water, I wonder if this creates a noticeable difference in the way the fire draws? Conversely, this means that an insulated chimney would draw more efficiently than a thin steel one, perhaps an insulated section above/below the device would netralise this problem?

Also, we already close the fire down when we go to bed to stop the warm air in the house escaping up the chimney.

I don't know if these effects would be noticable but it's definatley worth thinking about.
-- greyfiend, Jul 16 2006


I saw on a cooking show yesterday (Good Eats) that leonardo davinci designed a rotiseree spit that was powered by chimney exhaust. Why not add a small turbine at the very top, just as an added bonus. also, the surplus hot water might work better as a radiant heat (in the floors).
-- bleh, Jul 17 2006


I have been thinking about this. [Greyfiend], I am surprised that a household which is 100% solar still has a fireplace where the combustion chamber draws air from inside the house. Here are my thoughts on halfbaking up an efficient firepowered house.

1: Modern fireplace. These come in 2 forms: radiant and convection. For this setup, I think convection is the way to go, because you can turn off the blower and stop heating the house. Also, the hot air could be routed through existing ductwork - not possible with a radiant fireplace.

A little background: both of these types have air intakes from the outside. The convection type pulls room air into a circuit of pipes within or above the fire, and blows the heated air back into the house. They are more furnace like.

2: Hot water. Now that you have a more furnacelike fireplace, why not put the hot water heater right above it? This way instead of heat transfer from hot air somewhere in the chimney, you directly heat the tank with the fire.

3: Now you have a watertank sitting above a heat source. Make it into a boiler for a steam generator! The technology to do this has been around for a hundred years. There is your electricity.

Of course, each of these uses will take away from the others - for example, if you have a lot of hot water needs you will deplete your ability to generate steam. Likewise if you crank up your convection house heat, you will have less steam and hot water.
-- bungston, Jul 17 2006


Thanks for the response [bungston] there are a number of reasons why I believe the peltier design may have advantages over ripping out the existing fireplace and replacing it with a steamtrain:

1. The device is retro-fittable to any old fireplace meaning there's no need to buy a new expensive fireplace or furnace.

2. Putting the hot water above the fireplace will suck heat out of the room. Putting it around the chimney outside utilises heat that's being wasted anyway and the peltiers take advatage of the temperature differential which is at it's maximum around the chimney. The primary function of the water jacket is to regulate the temperature the peltier chips are exposed to, (they'll crack if they get too hot or are exposed to rapid temp change), free hot water is just a bonus.

3. My initial idea for this device was exactly as you suggest, a steam or stirling engine attached to an alternator, however it was the potential noise factor that turned me off and got me researching peltier chips, I'm not sure I want an engine in the lounge chugging all through the night. Also I think this device has the potential to be manufactured very cheaply. Far cheaper than a steam or stirling engine.
-- greyfiend, Jul 18 2006


With a modern wood stove there isn't much available energy at the top of the chimney. The stove gives off 70-80% as heat to the room it's in and the rest is needed to keep the chimney drafting and carry out the evaporated water. So, we can't say that the heat at the chimney top is wasted. If you cool the smoke so much that it starts condensing, then you get real problems, creosote, acids, etc. So, you can't cool the smoke to less than about 300 F without getting into difficulties. For electricity and heat, go for a wood fired sterling engine generator.
-- m homola, Oct 23 2007


I've rarely used a wood/coal stove but found them quite annoying in that they necessarily take in a lot of air, heat it up and get rid of it to the outside. This is then replaced by cold air from outside. Can some form of counter current heat exchanger not be retrofitted to a stove, so it extracts heat from it's own exhaust to warm incoming air. Much more efficient.
-- bs0u0155, Jul 27 2010


I too heat my home with wood-fired stoves and have often wondered why we couldn't fit a turbine to the chimbley. A turbine wouldn't cool the rising air at all but could generate a little extra 'leccy. Couldn't it?
-- squeak, Jul 29 2010


Now I had thought about a chimney MHD power plant. But using a 17 Tesla magnet may be prohibitive.
-- travbm, Nov 01 2015



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