I have my doubts about your diesel generator idea once you scaled it up to the point of wholesale fuel and heat costs along with full bore EPA environmental reporting, infrastructure, water permits, etc, etc.
The critical point here is that I
wasn't talking about scaling it up. Wholesale fuel I can 'sort of' get since I have a 1k gallon fuel tank already. And I can only justify it if I'm utilizing the vast majority of the waste heat.
I'd love to see those calcs, Firethorn.
Out of country right now, so don't have the original calculations. Don't even have an electricity bill handy. It 'helps' that I'm in Alaska and therefore electricity is expensive. $.20 per kwh.
#2 Fuel Oil@$4/gallon, 138k BTU. 1 kwh = 3.4k BTU. 40kwh per gallon.
Now, a high quality generator will burn approximately ALL of the fuel, but will hit about 30% for transforming it into electricity. So, in a pure generation mode, you'll only get 12 kwh per gallon, or 33 cents per kwh. Ouch. You can survive paying it, but way too expensive.
But remember, Alaska, much more need for heat than cooling. So we hook the cooling system for the generator up to the hot water pipes for the boiler system as well as putting a heat exchanger on the exhaust. The important concept to remember here is that every BTU we scavenge here is a BTU we don't have to generate by burning even more oil; IE cogeneration. How much heat can we pull? I used 80% - the efficiency of my boiler, rounded down.
This means I'm utilizing 32 of the 40 potential kwh in a gallon of diesel, or 12.5 cents per kwh marginal cost. Keep in mind that capital costs aren't included in this figure. That 8 cents saved per kwh means that it'll take 125k kwh to pay off for a system that I'm ballparking in the range of $10k. Given that I use about 700 kwh/month and figuring I can only use the waste heat for 6 months of the year, you're looking at a straight payoff of 30 years for the capital costs, and the engine won't last that long. Heck, I haven't even put maintenance into there yet - things like replacing the oil in the generator every so often. On the other hand, I haven't figured avoided costs like boiler maintenance either.
Where I work there 8 engine test cells where the run tests on 13L diesel engines. 5 of those cells use A/C dynos, and when it's absprbing engine power they do use the electricity to partially power the facility. But the cost of running the engines make it stupidly expensive to run them solely for the power produced.
Like I was just saying - it doesn't make sense if you only use them to provide electricity. It makes much more sense if you need the heat energy as well.
The byproducts from an engine are pretty darn corrosive. What would you use to capture the heat?
Part of the heat would be scavenged from the engine's cooling circuit. More would be pulled from the exhaust using an extremely heavy duty heat exchanger made from acid resistant material. Ideally the unit would indeed be condensing, but I recognize that the unit to do so would be expensive, and cooling the exhaust that much can lead to interesting airflow concerns. Ideally the last step before venting outside would be to have a last heat exchange between incoming(normally below freezing) air destined for the engine and the outgoing exhaust.
Otherwise I love the idea of being self contained or more self sufficient.
Since the capital costs are such that it'd never make financial sense from that perspective alone, you have to justify it along the lines of 'I'm getting a backup generator anyways...'.
So if it's $10k for the whole system, I consider the costs for a simple gasoline generator - ~$4k as 'I want backup power'. After that I look at the increase of going to a diesel generator and hooking it into my fuel oil tank as a 'it's only $x more expensive to be able to utilize my existing fuel tank and cheaper bulk fuel, and not have to worry about running out all month'. Once I have the diesel generator, going from standby to prime rated generator and adding the heat exchange parts isn't that bad either.
I'm still having to find a 'cheap' prime diesel generator for the core of the system though.