ECN Forum Forums General Topics of the Trade General Discussion Area Hydrogen by electrolysis

I think the problem with the bike generator is about the same as the gas turbine on your natural gas line. Too much machinery for miniscule amounts of power. It might make some sense simply as a symbolic punishment for Enron executives but I think you would save more energy letting inmates cut grass with push mowers.
In the case of the gas turbine you are only moving the pumping energy from the gas plant to the customer's turbine. "There ain't no free lunch".

I understand your point gfretwell. I'm only suggesting getting 60-70% efficiency in energy conversion by making the burning process "work" before we take the heat from it verses the (20%? + or -) from the straight burn. It cracks me up to see a high efficiency furnace claiming 92%. I also understand no free lunch. I'm only suggesting brown-bagging some left-overs.

And I should restate the begining of my previous post from "the answer" to "one possible contribution".

[This message has been edited by Jps1006 (edited 08-14-2006).]

JPS, I think you're out of luck on your cogeneration plan. Those "92% efficient" furnaces and boilers really are in that range. They actually condense the water vapor out of the combustion gases, and the final result is exhaust that's cool enough to be vented out in PVC piping. There is pretty much no energy left to extract at that point.

We had a thread recently about a NZ-built ac generator which used the waste heat from the engine for space heating. It had a natural or propane gas fuelled Stirling hot-air engine, I think, and fed excess power to the Grid. I believe it fitted into the airing cupboard.

Now, provided the engine has a nice 'clean' burn, so as not to waste gas, and the exhaust gasses heat can be captured efficiently and not lost up the flue, the actual thermodynamics of the engine are irrelevant [within limits]. The overall efficiency has to be better than most power-stations since there, the waste heat is mostly lost to the atmosphere in the cooling towers. It all depends though on the price the poco pay you for your excess juice.


So, there may just be free lunch after all!

Alan

Now this coming from high school and some college education:

I don't doubt 92% efficiency at extracting heat, (and yes I know that's what they are talking about) but how about extracting energy. It's the expansion of the heated gas (that could be driving a motor) - I believe it is referred to as kinetic energy as opposed to thermal (convection or conduction). There's more than just heat in that there fuel.

I don't have the education or the background to really throw out stats & specs, but my gut tells me there could be something to it.

jps, your gut feeling is absolutely right. 92% efficiency is true too, no BS, [for 'condensing' boilers].
What the ads don't tell you is that the guts rot out of them in 3 or 4 years because what 'condenses' is.....acid.

For the Munchkin boilers perhaps. The Vitodens boilers, which use a stainless steel heat exchanger, are generally considered to be a 50-year boiler.

Jps, by the time they've extracted that much heat from the combustion gases, there is very little expansion left. The energy just ain't there--it's been used to heat the water.

[This message has been edited by SolarPowered (edited 08-14-2006).]