Fuel Use vs Load for Gasoline Powered Generators

[Cujet]

I had briefly considered getting a diesel genset with liquid cooling. The house is heated by an oil fired water heater, so plumbing the genset into the heating system would allow me to recover most of the heat lost through the cooling system, and reduce the oil usage for heating. Winter is when the genset would be most likely required.

Combined heat and power (cogeneration) is indeed a viable way to use fuel efficiently. Although, at 92%, not significantly more efficiently than the better modern oil burning furnaces, which supposedly can peak at 98%. But are generally just over 85% to 90%.

Check this out, kinda cool.

Honda Technology｜Honda

Honda Technology｜Honda

global.honda

 

[Jetronic]

Combined heat and power (cogeneration) is indeed a viable way to use fuel efficiently. Although, at 92%, not significantly more efficiently than the better modern oil burning furnaces, which supposedly can peak at 98%. But are generally just over 85% to 90%.

Check this out, kinda cool.

Honda Technology｜Honda

Honda Technology｜Honda

global.honda

the furnace is from 1973.... and I'm not changing it.

 

[Astro_Guy]

I had briefly considered gettin a diesel genset with liquid cooling. The house is heated by an oil fired water heater, so plumbing the genset into the heating system would allow me to recover most of the heat lost through the cooling system, and reduce the oil useage for heating. Winter is when the genset would be most likely required.

That's actually a really good idea considering that fuel oil and off road diesel are more or less the same thing. I'd do this in a heartbeat if I had an off grid cabin somewhere up north. Back in the day my in-laws had a wood burning stove with a water loop to the oil burner. They also had a loop from the wood burner to the high bay two car garage. When it was really cold they would heat the garage, which was below the living space. The cars started easily even if it was below zero outside, and any excess heat rose to the living space.

 

[Cujet]

the furnace is from 1973.... and I'm not changing it.

Many older units are very well made, and relatively easy to keep working properly. The idea that they are inefficient is largely in error. It is mostly a sales tactic to sell new units.

My grandfather helped engineer the steam catapult for aircraft carriers during the war. After the war he was involved in NYC heating programs to move businesses away from coal. The natural gas efficicicies he talked about were as high as 90%, even in the 1950's.

 

[thastinger]

The generator in question here is a Westinghouse iGen 4500DF inverter. They are getting 9.5 hours on 3.4 gallons of gas and run the generator 3 hours per day. Using the 4.5KWH/gal figure above, that suggests 4.8 KWH per day of consumption. Theoretically their generator would be a little more efficient. Best case daily solar production is 6X the panel nameplate, worst case is 3X. This implies that they need 800 to 1600 watts of panel array to meet their daily needs. Designing for five days of autonomy would require 24 KWH of storeage - ouch!

Would need a 50KW battery bank if they wanted them to last, no battery will take a 100% depth of discharge very many times, and their inverter would shut down, due to low voltage, before they got there anyway.

 

[Astro_Guy]

Would need a 50KW battery bank if they wanted them to last, no battery will take a 100% depth of discharge very many times, and their inverter would shut down, due to low voltage, before they got there anyway.

LiFePO4 batteries can take a 100% discharge if needed and still be good for 2-3000 cycles. I've discharged several sealed lead acid batteries 20-30 times, and they were toast.

 

[thastinger]

LiFePO4 batteries can take a 100% discharge if needed and still be good for 2-3000 cycles. I've discharged several sealed lead acid batteries 20-30 times, and they were toast.

The cutoff voltage is built into the LiFePo4 battery/BMS or appliance using it. Try taking a 26650 cell down to 1V and see if you get it back, they won't survive total DoD same as any other battery, they are just more careful in the management so that they don't get there.
Few could afford a 50Kwh LiFePo4 battery bank, that is 5 Tesla walls in series, likely worth more than their house if they are living on 12Kwh a day.

 

[Jetronic]

Many older units are very well made, and relatively easy to keep working properly. The idea that they are inefficient is largely in error. It is mostly a sales tactic to sell new units.

My grandfather helped engineer the steam catapult for aircraft carriers during the war. After the war he was involved in NYC heating programs to move businesses away from coal. The natural gas efficicicies he talked about were as high as 90%, even in the 1950's.

Even if I changed a 50% efficient furnace with a 98% efficient furnace, the numbers wouldn't add up, I simply don't use enough fuel. I'd break even after 20 years if nothing went wrong with the new unit. I'm not liking those odds

 

[Astro_Guy]

Even if I changed a 50% efficient furnace with a 98% efficient furnace, the numbers wouldn't add up, I simply don't use enough fuel. I'd break even after 20 years if nothing went wrong with the new unit. I'm not liking those odds

Are you assuming constant fuel prices over those twenty years? It seems likely that fuel prices will double long before that. At the present rate of inflation they will double in 8 years.

 

[Jetronic]

I went with higher than ever average fuel prices. I can save about 100 gallons of fuel per year right now. The money is better spent elsewhere.

 

[slammds15]

If money isn't a factor and 240V is not required Onan QD series is great, they are also available in an inverter/diesel.
350hr service interval is a bonus as well. They always start, I've ran them after 3 years of sitting with no maintenance.

 

[eljefino]

Acknowledging this is an older thread...

I myself have an off grid cabin with solar. The inverter doubles as a generator-powered battery charger and charges my lead acid battery bank rapidly, like in 3 hours. I would prefer 10 to be easier on the batteries. Anyway. I'm in the early stages of planning a 3hp diesel to 12 V, 100 amp alternator, to 12-60 VDC step-up power supply, to solar charge controller setup. Hoping the power supply can be adjustable to a sweet spot on the diesel's powerband as well as being softer on the batteries. Also hoping that by not going to AC and back to DC to save on conversion losses. Just spitting ideas out here.

As for generator fuel consumption, get a kill-a-watt meter and video camera. Warm the generator up for a normal load, and run it out of gas. Put in a specific weight of gas (I find weight easy to measure precisely) and run the generator at a test load, with a camera on the kill-a-watt meter showing elapsed kwh. Eventually the generator will run out of gas, with you not watching, so review the tape and see what your reading was when it cut out. Repeat for whatever other load levels you want to try.