Honda has announced a cooperative venture with Climate Energy LLC of Massachusettsto produce a "micro-cogenerator" (photo link) based on a Honda engine (hat tips: Green Car Congress via Peak Oil Optimist). The specifics are:
Poster Gene DeJoannis at the GCC discussion notes that 3 kW of heat is only about 10 kBTU/hr, which is not enough to supply the peak winter heating requirements of a small row house, let alone a single-family home. It follows from this that the cogenerator is not capable of functioning as a stand-alone heating system; it would require extra heat. The concept is that the engine runs continuously, and heat requirements beyond the CHP system are provided by a conventional combustion boiler. This is included in the auxiliary furnace. (These graphics answer some questions regarding the odd-looking cogenerator efficiency numbers; it appears that the cogen exhaust does not allow recovery of the latent heat of the water vapor and is also a separate unit from the air handler; as a consequence, heat losses are higher from the cogenerator side than the backup furnace.) It also appears that the full heat demand of a house can be met by the pair, and that the $8000 cost of the two units covers the entire heating plant. Earlier, I had objected that a $8000 capital expense is very hard to pay off with a $600/year revenue stream; it appears that the incremental cost of the cogenerator over a conventional furnace is considerably smaller, and the payoff quicker.
The stated purpose of this cogen is to meet the average electrical demand of the typical house, without generating surplus power to feed the grid. I believe that this is a mistake:
But this isn't going to happen, because it's just too small. The designers thought too small.
This one looks like it's under the limit. It needs to grow some; throw it back.
 The low efficiency is a disappointment too. Cummins claims BSFC as low as 0.32 lbm/hp-hr for some of their diesels; assuming #2 diesel at 19,110 BTU/lbm this works out to over 41% thermal efficiency (and that's the higher heating value to boot). It ought to be possible to achieve much better than 21% efficiency from a gas-fired reciprocating engine; perhaps this requires the freedom to begin with a clean sheet of paper.
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