Electric galley kwh sizing based on propane usage

[rslifkin]

Originally Posted by BillKny

If you are running a generator, there is NO WAY your cooking will be cheaper than propane--if you are honest with the costs. Fuel, maintenance, and depreciation for generator and batteries will be significantly more expensive than propane.

This depends on your other needs. Running a generator just for cooking is expensive. But the small increase in fuel burn by cooking while you're already running it for something else is minimal. So needing a generator to run the stove isn't a big deal if you already need the generator once or twice a day for other purposes. But I wouldn't put in a generator that only gets used for a stove.

[Jammer]

Originally Posted by BillKny

Everybody talks about "efficiency", but most of the time they are avoiding the REAL question (at least to me) what is the cheapest? I have no real interest in the amount of energy input or how much power is lost, all I care about is the dollars expended.

The equation is really simple for most boats. Most boats will not be able to cook using just solar power, they need to run a generator. If you are running a generator, there is NO WAY your cooking will be cheaper than propane--if you are honest with the costs. Fuel, maintenance, and depreciation for generator and batteries will be significantly more expensive than propane.

Most modern boats have some solar and also have a generator, or a high-output alternator on the propulsion engine. With a well designed system, most of the power can come from solar.

My analysis gives me $0.80 to $1.00 per kwh from a generator. Most of this is fuel and scheduled maintenance with capital costs and repairs being about a quarter of it. The cost per kwh works out about the same for (boat-sized) diesel generators as it does for suitcase gasoline generators, which use more fuel.

In reality on a boat solar power that goes through a LiFePO4 bank and an inverter is going to cost about the same given the high capital costs and the fact that even serious cruisers aren't on the boat every day of the 10 year life of the system.

Propane systems cost money to install and maintain too, and as Adelie points out the logistics of purchasing propane are difficult, sometimes particularly so depending on your situation, and the worldwide trend towards bottle exchange is making this worse.


If the dollars matter most then the break-even point is around $11 a gallon or around $24 for a 10# cylinder, assuming you start with a boat with a complete, working propane system. In most cases the fill itself is less than that, but not always, especially if you're stuck dealing with a bottle exchange vendor.

[noelex 77]

Refilling propane/butane tanks can be a pain, especially when regularly traveling between different countries, but propane/butane cooking also has advantages. The system is reliable, makes no noise/vibration and takes very little maintenance.

Swapping a propane/butane system for electric cooking powered by solar has many advantages, but swapping it for a system dependent on a generator is often a backwards step in my view.

If you do this, at least make sure you have a backup cooking option that is reasonably effective. A (reasonable sized) portable bottle with a single burner or a high power alternator that is capable of delivering a couple of kilowatts are some possible options.

It is always a shame to see a boat stuck in marina missing out on the sailing season while they are waiting for spare parts or specialist knowledge to repair their generator. This is not uncommon on boats that are highly dependent on their generator for mission critical systems such a cooking.

[Lodesman]

Originally Posted by Jammer

The 90% figure Lodesman quotes upthread has not been reproduced in other studies.

The 90% figure is often quoted by the vendors, so can be somewhat suspect, but truthfully the testing methods are also somewhat suspect. From experience, induction gets you to "hot" way faster than either propane or standard electric, maintains the temperature better and gets the job done sooner - factors that don't always get measured in a lab test. This study shows near-90% efficiency: https://cao-94612.s3.amazonaws.com/d...-July-2019.pdf

[Adelie]

Originally Posted by Lodesman

The 90% figure is often quoted by the vendors, so can be somewhat suspect, but truthfully the testing methods are also somewhat suspect. From experience, induction gets you to "hot" way faster than either propane or standard electric, maintains the temperature better and gets the job done sooner - factors that don't always get measured in a lab test. This study shows near-90% efficiency: https://cao-94612.s3.amazonaws.com/d...-July-2019.pdf

I read the report. Poor methodology, though results are similar to mine, except for the gas burner where their efficiency is 30%ish instead of 50%.

Their methodology is poor because they didn’t actually measure the electricity or gas as far as I could tell. They just said the burner is rated for this output at full and we timed how long it was on so we can do the math for how much energy was used.

[Lodesman]

Originally Posted by Adelie

Their methodology is poor because they didn’t actually measure the electricity or gas as far as I could tell. They just said the burner is rated for this output at full and we timed how long it was on so we can do the math for how much energy was used.

You're probably right, that their methodology could be improved, but the tests seemed to be designed to compare performance in "real world setting" more than pure efficiency. They did indicate they confirmed actual was within 5% of spec:

6. Verify the test voltage at full burner input is within 5% of specification
7. Verify the tested input rate is within 5% of specification during water heat-up test

[Adelie]

If they wanted to compare real world performance they should still be measuring the quantities used, just over the long term. Hook up people’s stoves to meters and let them go for a month.

[Adelie]

Checking the voltage doesn’t tell you how much current is being used, it tells you how good the house wiring and the service from the street is.

They got into the ballpark so to speak but I’m going to say they are within 10% at best.