5.8 kWh per Gallon Honda Generator to DC @ 93% efficiency

[C&K]

"after an 18 hour run" sounds much slower than a furnace. How long does furnace take under similar conditions? (different outdoor and indoor starting temperature will confound calculation somewhat, but maybe we can get BTU within 20 ~ 30%.)

"12.4kWh per gallon of diesel fuel." - how many kW is the electric load you feed? (or gallons used per day?)

I actually think they are about the same. I never let it get below freezing in the shop, the oil furnace is set for 35 deg. If I intend to work in the shop it takes a full day for the oil furnace running constant to get it up to 60-65 when the outside temp is below zero.

The electrical load on the generator is 25kW, which is its prime rating, 30kW standby. It burns just about dead on 2 gal/hr @ 25KW load and when battery charging with it we have electric baseboard heaters in the house that sequence on with CT switches to keep the load on the generator at minimum 92A. If the load on the generator goes above 105A the CT switches cycle the baseboard heaters out, so the load varies from 92 to 105A. I didn't design the system, it was here when we bought the place.

 

[Hedges]

92 to 105A, 13A cycle, For a moment I was going to say you should consider heat pump to get far more heating out of your 25kW, but this resistance heater is just 13% of total electric load.

Your batteries accept ~ 20kW charge rate? I'll assume FLA, maybe 150 kWh? But "all day" charging batteries suggests 2x that capacity, 4x if 50% DoD.
If FLA, how do they do regarding temperature, and is heat generation wasted or put to use?
I've read lead-acid is 70 ~ 90% efficiency round trip, so could be considerable energy available there.
Lithium, I think the batteries themselves are high 90's efficiency. Most inverters have lower efficiency that that.

So you think you're getting 125,000 BTU from coolant and exhaust while producing 25kW of electricity.

BTU to kWh conversion calculator

BTU to kilowatt-hour (kWh), energy conversion: calculator and how to convert.

www.rapidtables.com

1 BTU = 0.00029307107017 kWh, 125,000 BTU = 36.63 kWh

25 kWh / (25 + 36.63 kWh) = 40.6% of usable energy is electric, 59.4% is thermal
There would be additional energy loss, whether thermal to generator's environment, exhaust above ambient temperature, and unburned fuel.
However, I find mention of diesel generators converting 40% of input energy to electricity, so maybe you're getting near 100%?

Diesel Generator vs. Gas Generator: Which is More Efficient?

If you're considering a commercial backup generator for your business, you'll have a lot of decisions to make. One of the first things to consider is the fuel source. One common question is, are diesel generators better than gas? The answer is, it depends on the needs of your business. To...

www.genpowerusa.com

Seems like you're doing great (at least for energy capture, if not retention of heat). What are the loads you power?

 

[C&K]

Seems like you're doing great (at least for energy capture, if not retention of heat). What are the loads you power?

I don't think it's 100% because #2 diesel is 137,500 BTU/gallon, so input to the engine in fuel is about 285,000 BTU. So the electric output would amount to about 85,000 BTU, according to your conversion. The captured heat output would amount to about 125,000 BTU. That's a total of 210,000 BTU, which is only about 73-74% efficient with still losses of ~75,000 BTU. Those losses would probably amount to mechanical, exhaust heat that can't be recovered, and radiated heat from the engine block, oil pan and exhaust manifold/turbocharger turbine. The exhaust manifold and turbocharger turbine is wrapped with that silver high-temp insulation, but that still gets hot enough that you don't want to touch it. On the compressor side of the turbocharger, the charge air cooler lines are also wrapped with that silver insulation because the charge air cooler is air-to-water type, so the heat from the charge air is absorbed into the cooling system that goes to the Modine heat exchanger. Some turbocharged diesels use air-to-air charge coolers.

But I would say 73% efficiency is about right. A poorly designed CHP will do 50%. Some gas turbines can approach 85% with a combined-cycle turbine. Most diesels are in that 70-75% range with well-designed heat recovery.

The generator powers twin Schneider/Xantrex XW6048's charging a 1700ah (at 20hr rate) forklift battery at 180 amps, plus powering house loads, shop loads and the baseboard heaters in the house that help reduce our wood consumption (when the generator is running) in the fireplace and wood-fired forced-air furnace that we normally use to heat the house. And it works fairly well. In the winter when we don't get much solar the generator runs average 12-14 hours every three days.

The battery draws constant 180 amps until bulk charge stage is done, then the battery amps start to drop during absorb stage, but the CT switches switch in more of the baseboard heaters to keep the load on the generator at least 92A. We actually enjoy it when the generator starts in the winter at 20 below. Both the house and shop are nice and warm, and we got virtually unlimited power because the generator and inverters together (in gen support mode) can put out 37kW, which is more than our entire place can draw if we turn everything on. If it's 35 below like it was here in January, then it's not quite enough heat and we have to run the forced-air wood furnace in the house when the generator is running because the baseboard heaters run a little short on keeping the house at 68 deg (2,700 sq ft split-level). But we're happy with it and we burn about 800-1,000 gallons of #2 diesel in a year in the generators (we also have a smaller 6.5 kVA Perkins peaking generator) and the shop oil furnace.

 

[C&K]

The largest CHP installation on earth is at Amundsen-Scott South Pole Station in Antarctica. They power and heat the whole outfit down there with four Cat 3512's in what is probably the most severe totally off-grid conditions on earth. In the dead of winter there is no way in or out of that place and they trust their lives and survival to those Caterpillar gensets.

 

[C&K]

Another consideration that we have to keep in mind is that we have a 1,000 gallon fuel tank that we get filled in the fall and that will last us (with hopefully some left over) until the next fall. Because in winter there is no way to get fuel to our place with a delivery truck. If we would run out for some odd reason before spring, the only way to get fuel here is with snowmobiles pulling sleds. For any off-grid situation using CHP, and being inaccessible in winter and depending on it, this is an issue.

At Amundsen-Scott South Pole Station, obviously those big Cat generators burn a lot of fuel. Way more than what can be hauled to the south pole by aircraft. In the dead of winter the sun sets in the first part of May and does not rise again until first part of August. It is totally dark and average -70F for three months, so obviously solar isn't going to work. Wind turbines have been tried and they fail in the extreme cold. Nuclear reactors have been experimented with and they fail. The only thing that works and can be relied on is good old diesel power.

How do they get fuel down there to sustain life in the most inhospitable place on earth? With overland traverse convoys in the summer when it's average -20F on a nice day, pulling huge fuel bladders with Cat Challenger tracked agricultural tractors.

 

[faccnator]

C&K are you ChrisOlson from another board?

 

[saen]

The largest CHP installation on earth is at Amundsen-Scott South Pole Station in Antarctica. They power and heat the whole outfit down there with four Cat 3512's in what is probably the most severe totally off-grid conditions on earth. In the dead of winter there is no way in or out of that place and they trust their lives and survival to those Caterpillar gensets.

p.s.
Volvo Penta with Perkins engine have same in container box.
Drink 16 liters of diesel per minute