Natural Gas in Home

Depending on where you are you might want to look into a Fuel Cell instead. Using a natural gas fuel cell with co gen for heat and hot water can be very clean, efficient and depending on size supply your needs and send the extra kw to the grid. The hot water can heat your house, supply your hot water and even heat up a swimming pool. Residential sized units are being supplied to Europe and Japan by various manufacturers,Blue Cell in Australia for one.

Honda makes such a unit.

Yes it does, and it produces 1 kW electrical and 2.5 kW thermal max from a 1 cylinder engine. I couldn't find the cost or fuel consumption figures but I would estimate that it consumes about 1/8-1/10 therm per hour of full-load operation. Somehow I don't think a kW is going to make much of dent in the typical US household, and with NG prices falling so rapidly (now below $0.40 per therm), it will take quite awhile to payback the initial cost plus the maintenance every 6,000 hours. For folks with a hunting cabin, sure, but then you have to get LPG or NG to it. I sense that combined solar thermal/PV panels would be the way to go.

Yes, definitely falls into the "cute" class.

Gagauz,

The generic term for your suggestion is "cogeneration". The idea has been around a long time and can be valid in application. Unfortunately, the "devil is in the details". In general, you are looking at the energy efficiency of the total system. For a central generating plant producing electricity, the typical energy efficiency is 25-33%, with the balance being fairly well split between the cooling tower and the exhaust stack. Recovering some of this waste heat for process heat can increase the efficiency to 60% and occasionally more, but typically such heat is "low-grade"--i.e. with a fairly low ΔT between the inlet and outlet temperatures. Good candidates for such waste heat include comfort heating, water heating, absorption chillers, food drying, industrial drying, and similar projects.

The higher-efficiency heating furnaces trap some of the waste heat by condensing the water vapor back to liquid, thus capturing the heat of condensation in addition to the additional thermal energy from a cooler exhaust gas stream. Of course, this then requires positive draft through the burners--thus an induced draft fan or similar. Such methods result in thermal efficiencies as high as 94% or sometimes a little more. With a prime mover (such as natural-gas fired engine), your beginning efficiency will be in the 40% range, in converting the thermal value of the gas to electricity produced. You can't heat the incoming air into the engine, because this reduces its density, unless you have some form of turbocharging. You can, however, pass the exhaust gas through a condenser/heat exchanger to warm water or air (beware of the possibility of gas leaks within an air/air heat exchanger because of CO poisoning issues. Thus an indirect transfer would be safer and probably required--exhaust/water and then water/air.

In terms of storing the heat for later use, there are any number of storage media available, such as glauber's salt (phase change), rocks, concrete mass walls, water tanks, etc. All of these can be researched in the literature of solar energy.

The whole concept of cogeneration is good. However, because it includes multiple fields or multiple systems, we are less than good at implementation. This is because nearly all contractors for one system are not experienced/ready/able/licensed (or whatever) when it comes to combining two or more fields of expertise, such as a separate gas-fired electrical plant with utility interconnection for selling excess production at the avoided cost PLUS construction of a mass storage area PLUS connections to a new or existing water or comfort heating system.

Back when solar energy was the "hot issue" (1970's), a general rule of thumb was recommended--for every dollar spent on solar, spend an equal amount on conservation steps. This is probably more important today. Money spent on conservation and wise building design is spent once, but money spent on operating or living in the structure is money spent every day.

--John M.