Hi AC
I did as you said and found some great information. It got me thinking about a co generator, so I did some number crunching. I am kind of confused about the pro’s and con’s to a co generator.
I have a portable generator with an air cooled 11hp Honda engine. It is rated at 8250W surge and 5500W continuous. The manual that came with it says at full load it uses 1 gallon of gasoline per hour. Gasoline would be a hassle for a co generator, so I would want to convert it to propane. We use propane to heat our house anyway.
If I could find an equivalent 11hp liquid cooled motor, it would require 1.26gl of propane per hour. Propane at our local gas station costs $2.65/ gallon. So it would cost $2.65/hr. to run it. Our highest electric bill is ~550kWh/ month. The generator would have to run 100hrs. / month to provide 100% of our electricity. 100hrs./month would be 3.33hrs./day and use 4.2gl of propane/day and cost $11.13/day or $333/month.
For heat I would use a liquid to liquid heat exchanger to keep the motor cool, instead of a radiator. So, ~5hp produces 12,000btu, an 11hp engine would produce (rounding off) about 24,000btu/hr. If my math is correct our house uses an average of 3,455,900btu/month. The co generator would have to run for 144hrs. to produce that much heat. It would require 181gl of propane/ month. It would cost about $480/month for propane to supply 100% of our heating.
Without a co generator we use 450gl of propane/yr. for heat and 4,225kWh of electricity per year. To me it looks like the co generator is an expensive way to produce heat and electricity. The initial cost is bad enough, but the operating cost isn’t any better.
I am no math wizard, and I may have made a mistake in there somewhere, so please correct me if you see any mistakes. I know some things I rounded off and I probably should have used cost/ year in my examples, but the cost/hour would still be the same, and it looks expensive to me. The cost/btu or cost/Watt seems high compared to using the grid and a standard boiler.
I know that every time energy is converted a large portion of energy is lost. Maybe a more efficient engine would change things. Maybe a turbocharged 8hp motor that puts out 12hp? If I remember right, forced induction motors are more than 100% efficient. To be fair I also don’t think the generator would always be at full load, so fuel usage would be proportionately lower.
What am I missing? Thanks for the feedback.
Jeff