This is a very general question asking for some specific answers. Essentially, I would like to take a vehicle and strip it down, and to turn it into a generator. I’d like to take advantage of the transmission to increase efficiency of the generator(go to appropriate gears depending on strain), as well as to use multiple alternators on a belt to provide adequate power for different areas of the home all from one motor. What all do I need to know to better ask this question or answer this question?

  • Welcome to Motor Vehicle Maintenance & Repair! Mar 25, 2018 at 18:54
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    Consider also that a generator expects to operate at a steady rpm under load and no-load conditions. You may be able to use a gearbox to locate the correct rpm, but you would not be changing gears to establish a balance depending on load.
    – fred_dot_u
    Mar 25, 2018 at 20:34
  • @fred_dot_u well what can I do to maximize efficiency depending on load automatically. Mar 25, 2018 at 20:36
  • a conventional generator has reasonably tight rpm control. It would be necessary to have some form of feedback loop on the engine. When the rpm drops due to increased load, the feedback would increase throttle and vice versa. That's out of my league, however. A grass-roots approach might be to create this loop using cruise control, as they can be fairly responsive.
    – fred_dot_u
    Mar 25, 2018 at 20:39
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    I'm voting to close this question as off-topic because it is not motor vehicle maintenance it is really about Renewable energy and living space design.
    – Solar Mike
    Mar 25, 2018 at 20:49

3 Answers 3


The one point you should consider that you have not is to use the waste heat produced by the engine to provide hot water for the house.

The cooling radiator can be directed into the hot water tank easily, but to really improve the conversion efficiency you should arrange a heat exchanger to get the heat out of the exhaust gases as well.

For the generator, then you should match the design speed of the generator to the best power point of the engine ie when considering the best fuel consumption (known as BSFC brake specific fuel consumption) - this is not the same as max power...

If you size the generator appropriately then you can either do away with the alternator and charge the battery from the main generator or keep it, but you should not need to use multiple alternators as the losses reduce the total efficiency.

For more information look at CHP (Combined Heat and Power) and Micro CHP Some links are : http://www.greenspec.co.uk/building-design/micro-chp/ http://www.cogeneurope.eu/medialibrary/2015/05/19/d6648069/miro-CHP%20study_merged.pdf https://www.rural-energy.eu/solutions/8/366/Micro-combined-heat-and-power-micro-CHP#.Wrf3I2aQ0UE

further interesting links: http://www.icrepq.com/icrepq%2712/839-kadar.pdf https://www.theguardian.com/environment/2014/jun/13/golf-vw-car-power-plant-germany https://www.bnl.gov/isd/documents/74453.pdf

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    Love this, but is it possible to go over some more specifics. For example, I’d also like to use the air conditioner from the car to provide air conditioning throughout the house, and I’d like to essentially be able to run the entire house off of one or multiple daisy chained deep cycle batteries. I am a big fan of the idea to use the radiator to heat water, and I’d probably use the already implemented heating system to heat the house. I also would be putting this all inside of a room with the exhaust piped out and the air intake also piped out, another point however would be... Mar 25, 2018 at 20:21
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    ... to also use the heat from the exhaust to help provide air heating. How possible is all of this and am I trying to go too far with the idea? Mar 25, 2018 at 20:22
  • A\C from car to cool house : really - have you considered the car system is designed to cool a volume of the car about 4 metres cubed and you think that will suffice for a house which can be 40 or more times larger... You should read all of the links I provided and do some thorough research as extracting the heat from the exhaust gas is possible... And it is not going too far - it helps maximise the overall efficiency of the system.
    – Solar Mike
    Mar 25, 2018 at 20:41
  • alright, and the A/C idea is simply me trying to prevent having to compensate in electrical power to run my central ac system, as that increases the draw greatly. I will read them as soon as I get the chance since my internet is somewhat slow where I am currently but when I get home I will be able to. Also, are there any alternatives to electric a/c that could be implemented into this system? Mar 25, 2018 at 20:45
  • Why not think about the design of the house : in Australia one person used a suspended roof over the living space to allow free air circulation over and around the living space : it turned out that they did not need A\C at all...
    – Solar Mike
    Mar 25, 2018 at 20:48

Years ago I considered something similar. The devil is in the details. I wanted to use an automotive diesel engine, and utilize the waste heat to heat the house.

Fortunately, I did some prototyping. The first thing I found was that unless I was making lots of power, there was not enough fuel being burned, in a fairly efficient engine, to have enough waste heat to heat the house.

Similarly, the air conditioning unit put out about 5000 BTU equivalent cooling, which was too little to chill my modest house. I would do a room, just not a house. (Of course, if the air conditioning compressor was running there was a little more heat, go figure.)

Generating the 240/120V power was not a problem, as the 48 hp diesel could potentially power a rather large alternator. Also frequency regulation was possible within reasonably good bounds, by adapting the cruise control to be a frequency control.

But without using inverters, or perhaps some kind of a CVT or similar transmission, the engine would run at pretty much the same RPM all the time, and that was noisy.

Modern day automobile engines, are rather efficient systems. And the 48hp diesel engine that got 52 mpg simply didn't waste much heat at about 1200 RPM, which is what would have been a good point on the power curve to generate power for the house.

Today, I might consider using a hybrid car, with an inverter off the drive battery, if I were interested. Then the car could manage the engine start/stop and charge cycles automatically.

  • Interesting. How long did your engine last? Did you run it enough to get a useful figure for its lifetime? How often did you do oil changes?
    – juhist
    Dec 10, 2018 at 16:18
  • I did not, in the end, decide to use the car engine for power and heat. So I never ran it much more than to do some testing and get a few data points. For the IDI engine I was playing with there were lots of torque/RPM/HP plots available, so fitting the engine parameters was easy. I do know at least one business in Alaska which did use a similar setup. The diesel engine I was intending to use has instances of non-rebuilt engines getting 400 to 800k miles on them. Longevity did not appear to be an issue. A hybrid with inverter looks much easier today.
    – mongo
    Dec 10, 2018 at 16:26

One rule would be: don't (unless you only need intermittent on-demand backup power)

Car engine costs perhaps 8000 EUR if purchased separately. It provides about 100 kW or so. It's 80 EUR / kW. (When purchased along with a car, the cost of the engine itself is probably much lower, perhaps even as low as 40 EUR / kW).

Heavy-duty combustion engines such as those made by Wärtsilä (disclaimer: I own some Wärtsilä stock) cost far more: 400 EUR / kW or so, despite the fact that they are much bigger and thus benefit more from economies of scale. Usually, you'd expect economy of scale results in lower prices, but this time the prices are higher. The units by Wärtsilä and similar are also heavier per watt, being stationary or attached to huge ships.

Why this nearly one order of magnitude price difference? The reason is capacity factor and lifetime.

Car engines are designed for intermittent use. 95% of the time, a car is parked. So you get only 5% capacity factor. However, 95% of the time (or I would actually say 100% of the time), you need electricity and heat.

A car can be driven 20 years only because it is parked 95% of the time. Some people claim this is inefficient because the capacity factor is too low. They envision a shared car that is used >50% of the time and parked only <50% of the time. The truth is, the shared car wouldn't last 20 years like it would in ordinary use.

If you keep a car engine continuously running, you can't expect more than a year of lifetime. Perhaps two. With oil changes twice per month! To get the desired 20 year lifetime, you need a far more expensive and a far heavier power plant by Wärtsilä or a similar company.

Your tiny little powerplant made from a car engine wouldn't last very long. I would be looking at solar power and batteries instead. In distributed generation, in many sunny regions, they are actually the cheapest power option. If you really want to burn fossil fuels, go look at some generators that have been built for the required capacity factor.

If you need intermittent backup power, an option worth looking are the small inverter generators by Honda et al. You can get a small unit for less than 1000 EUR / USD / ${CURRENCY_SIMILAR_TO_EUR_AND_USD}. However, be warned that these are only for intermittent use. Perfect for complementing a solar system as backup power for extended non-sunny periods, though.

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