Free Liberal

Coordinating towards higher values

Power (Plants) to The People!

By Carl S. Milsted, Jr.

In my previous column I half-jokingly suggested that it might make more sense to plug your house into your hybrid car than to plug your hybrid car into your house. This was assuming a plug-in hybrid with an engine that is quieter, cleaner and more efficient than a gasoline engine – a Stirling engine, perhaps.

The idea is rather silly, but is worth contemplating nonetheless. Consider a suburban homeowner with a solar powered home. Solar may work fine when the sun is out, but fails when it is dark outside. Then, the homeowner either needs expensive batteries or a connection to the grid.

Solar homes selling energy to the grid during the day and buying from the grid at night does make some sense since overall electrical demand is higher during the daytime. However, there are significant inverter losses when you mix solar power with alternating current. And then there is the possibly more important emotional issue: where is the fun in going solar if you still have to be hooked up to the grid?

Enter the automobile as generator. A quick check of my homes breaker box indicates a theoretical 30 kilowatts of peak use before all the breakers go off. Average power consumption is considerably lower, of course. The Chevrolet Volt has a 53 kilowatt generator. If our imaginary quiet-engined hybrid can run its engine efficiently at a significantly lower than peak level, then it could be used to power a typical home with peak load headroom to spare. Then, battery power would only be needed for those times when the sun is out and the owner is not at home.

OK, so it would be rather inconvenient, plugging your car into your house every time you get home, and what if you want to run your dishwasher while you are out on the town at night? But this thought experiment does reveal something very important: should GM develop an ultra clean/quiet/efficient engine to run its hybrid cars, it could also use the same technology to sell engines for home power generation.

But does home power generation make sense? Due to the high duty cycle and large scale of operation, it can pay to build a centralized power plant that maximizes efficiency at the cost of huge capital outlay. It is unrealistic to expect mass produced home generators to achieve the 60% efficiency achieved at the better generating stations. This holds even when you take into account transmission losses (roughly 7% on average).

The answer is: home power generation does indeed make sense, even if the efficiency is only 40% (in the diesel range). That’s because the other 60% can be used as heat. For those who have electric hot water heaters, or electric heat (in the winter), a significant fraction of electricity usage is for heat. Suppose we could recover 70% of the waste heat from our generator. We would then have an overall efficiency of .4 + .6 * .7 = 40% + 42% = 82% efficiency! No more grid! No more ugly power lines!

Right?

Maybe not. Consider all those homes in the north that use fuel oil or natural gas for heat. Place a heat engine between their fires and heat exchangers and these homes may well generate a surplus of electricity to sell through the grid. We might well turn off some natural gas fired generating stations in the winter.

So message to GM: develop that quiet/clean engine for your hybrid cars and you can sell more than cars.

P.S. WhisperGen Limited of New Zealand is already building such home generators using a Stirling engine.

Carl Milsted is a senior editor for The Free Liberal.