KW Energy from LPG Gas

Brianellul · May 2012

Hi

I would like to know/calculate how much energy is in a local 12Kg LPG gas bottle. Basically I would like to compare the KW of energy obtained from Gas to our local electric company

Regards
Brian

Cariboocoot · May 2012

Re: KW Energy from LPG Gas

I think you'd need to look at a specific generator, as some may be more efficient than others.
It's a matter of how many Watt does it produce using how much fuel per hour.

I've looked at propane gens and discounted them as being incredibly fuel-hungry. Okay if the propane is significantly cheaper than gasoline, but a pain if you have to swap out tanks often.

One example: 3500 Watt generator runs 8 hours @ 50% load on 20 lbs. That's 1750 Watt hours on roughly 2.5 lbs. Around here that would be a fuel cost of $3.75, or $2.14 per kW hour which doesn't compare at all to the $0.10 per kW hour BC Hydro charges. Nor does that include maintenance and depreciation of the generator.

It might be a bargain somewhere, but not here. How are the prices in your area?

Brianellul · May 2012

Re: KW Energy from LPG Gas

Thanks for your answer,my fault I didn't specify that the I'm comparing gas vs electric for an oven, since i'll be needing to replace soon. A 12KG bottle cost 18 Euros here.

Regards

Cariboocoot · May 2012

Re: KW Energy from LPG Gas

In that respect I can only tell you that I wouldn't use an electric stove/range/oven if there were any other choice.
At the moment I have an electric stove at one house, a natural gas at another, and propane at the cabin. The NG one replaced an electric with a resulting significant drop in over-all utility bills. The propane one at the cabin keeps the off-grid system manageable. The all-electric household is miserably expensive (but don't tell anyone as we're trying to sell it) and that's on the $0.10 kW hour hydro.

It is my experience that gas is much better cost-wise than electric when it comes to direct heating applications; stove, furnace, hot water. It also "cooks" better because you have better control over temperature in both oven and burners.

Right now a Euro is about $1.29 CDN.

Some data you can work with: a gallon of propane is 91,333 btu's. 1 kW hour of electric is 3.414 btu's. So a gallon of propane is about 26.7 kW hours of electric. Take your LPG price per gallon and divide by 26.7 and see what you get. If your pricing is in pounds it's about 4.2 pounds per gallon, so a 20 gallon tank is roughly 4.75 gallons. 18 euros / 4.75 = $3.79 per gallon. $3.79 / 26.7 = $0.14 per kW hour electric equivalent. So how expensive is your electric?

Anyone who wants to double-check my data and calculations please do so.

GreenerPower · May 2012

Re: KW Energy from LPG Gas

Use this spread-sheet - http://extension.missouri.edu/webster/webster/agric/FuelCostComparison.xls

GP

vtmaps · May 2012

Re: KW Energy from LPG Gas

Cariboocoot wrote: »

Some data you can work with: a gallon of propane is 91,333 btu's.
<snip>
Anyone who wants to double-check my data and calculations please do so.

Since you asked to be double checked....
According to the US DOE propane is 91,330 btu per gallon
According to Am Gas Assoc propane is 91,600 btu per gallon

I found this over at heatinghelp.com forum:

the generally accepted value for propane is around 91,502 per gallon according to the national propane gas assn. based upon a Specific Gravity of 0.504 or a vapor density of 1.50 . That's pure propane. However, LP gas is a blend, often a witches brew of heavier hydrocarbons with vapor densities up to 1.58. With the heavier hydrocarbon content, the BTU content goes up. The better the grade, the lower the BTU content.....Your gallon of LPG may run as much as 96,000 BTU/ gal. I have an LPG pipeline near me that delivers HD-5 grade good stuff that analyzes out at about 91,600 BTU/ gal.

--vtMaps

Cariboocoot · May 2012

Re: KW Energy from LPG Gas

That's exactly what I mean: you can find different references that will give you different data on the conversion. So the best you can do is say "it's about ..."

westbranch · May 2012

Re: KW Energy from LPG Gas

91,000 works for me as one can never be sure about the 'exact' amount of LPG that is in the tank, based on the way they determine just how much to put in to the tank... that is, they do not weigh the empty tank before filling, so they use an average weight and add the approx weight of the propane they will put in... ambient temp has an effect too. Too cold and you do not get full delivery.

RCinFLA · May 2012

Re: KW Energy from LPG Gas

A propane gas stove is about 87% efficient in converting BTU of fuel to delivered heat.

Electric is variable depending on how long the heating process is. It can take some percentage of efficiency just getting the element up to temp and there is generally a poorer heat conduction transfer from an electric element. A good overall average for cooking is probably about 90 % for electric.

1 gallon of propane (about 4.24 lbs.) = 91,547 BTU's x 87% for cooking = 79,646 BTU's of yielded heat.
1 kWH of electric = 3413 BTU's x 90% efficiency for cooking = 3072 BTU's of yielded heating.

With efficiencies, 1 gallon of cooking propane = 25.9 KWH's of cooking electric.

Now install your cost per gallon of propane and cost per KWH of electric to compare.

At $3.25 per gallon for propane and $0.20 per KWH of grid electric the advantage goes to propane, delivering 24,506 BTU's per buck compared to electric delivering 15,360 BTU's per buck . A 60% improvement over electric in delivered heat per buck.

Natural gas is variable BTU's depending on what the dinosaurs had for lunch. Ranges from about 800 BTU's per cu-ft to 1200 BTU's per cu-ft. 1050 BTU's per cu-ft on average. At $12 per 1000 cu-ft, that would be 69,125 BTU's of yielded heat per buck, blowing away the competition.

Brianellul · May 2012

Re: KW Energy from LPG Gas

Cariboocoot wrote: »

So how expensive is your electric?

Where I live, a KWH cost 0.16 Euros....

peakbagger · May 2012

Re: KW Energy from LPG Gas

To further confuse the issue BTU ratings have two bases, Higher Heating Value and Lower Heating Value. Europeans tend to use HHV, US uses LHV. THe difference is the energy in the exhaust stream, HHV assume all the vapor condenses to liquid which gives off heat while LHV assumes the vapor goes up the stack. LHV is usually the one to use unless you have use for low temperature heat and a piece of equipment designed to extract that heat. I expect on a standard gas stove the vapor goes into the air in the house and acts as a humidifier.

mike95490 · May 2012

Re: KW Energy from LPG Gas

Electric INDUCTION cooktops/hotplates/hob, deliver 90+ % of the power to the pan. Gas and electric have much lower (50% ?) transfer rates.

Cariboocoot · May 2012

Re: KW Energy from LPG Gas

mike90045 wrote: »

Electric INDUCTION cooktops/hotplates/hob, deliver 90+ % of the power to the pan. Gas and electric have much lower (50% ?) transfer rates.

But they are not a substitute as they can not be used in all instances. For instance, they're not an oven.

RCinFLA · May 2012

Re: KW Energy from LPG Gas

You will likely use less electric for inductive heating and that is cost saving.

Efficiency numbers can be deceiving depending on what is or is not included, the conditions of use, and who prepares the numbers. The government rating calculates efficiency going back to raw source and the amount of energy used to process and transport the fuel to final consumer. When you calculate this way then electric is about 50% efficient. Natural gas is again the winner as it requires the least processing energy expenditure prior to end consumer.

There is efficiency loss in the high frequency switcher (25-30 kHz) converter used in inductive heating. The AC in to high freq inductive drive is in the order of 89-95% depending on power level.

The biggest saving, depending on your cooking cycle, is the 'jack rabbit startup' often used in a conventional electric element. Convention elements are higher raw wattage then inductive drive. Just about everyone that put a pot of water on the stove to boil will put the temp setting to maximum. There is a lot of heat loss during period before point of boiling water. Inductive heating has less raw high end power then conventional electric elements. The direct pot inductive heating helps offset some of the lack of raw startup power.

You also gain some with inductive heating by less sideways radiant heat loss during high power heating.

If you are a real chef, cooking dishes requiring long simmer cook times then inductive heating won't yield much over conventional elements. Heat loss from the pot becomes the dominate factor.

LucMan · May 2012

Re: KW Energy from LPG Gas

Brianellul wrote: »

Hi

I would like to know/calculate how much energy is in a local 12Kg LPG gas bottle. Basically I would like to compare the KW of energy obtained from Gas to our local electric company

Regards
Brian

Here you go www.eia.gov/neic/experts/heatcalc.xls

techntrek · May 2012

Re: KW Energy from LPG Gas

RCinFLA wrote: »

If you are a real chef, cooking dishes requiring long simmer cook times then inductive heating won't yield much over conventional elements. Heat loss from the pot becomes the dominate factor.

The answer for that problem is working with a radiant barrier to trap the heat instead of constantly replacing lost heat. Long-range backpackers will build radiant barrier pouches to cover their pot or heat-proof bags. Bring the food to a boil, cover, and turn off the heat. Energy conservation for a backpacker is even more important than for a homesteading off-gridder - the only energy they have is what they carry with them. No 500 gallon propane tanks available.

BB. · May 2012

Re: KW Energy from LPG Gas

I have suggested Thermal Cookers before... Not cheap for a good quality unit (basically a large thermos with a separate pot to pre-heat the food prior to placing in a thermos).

We use it all the time for things that take awhile to cook (stew meat, beans, etc.). Heat to a boil, place in the thermos for several hours (re-heat once if needed). And your food is done with running a stove or oven the entire time.

If you have an Asian/Chinese market nearby--they may have in stock.

-Bill

techntrek · May 2012

Re: KW Energy from LPG Gas

Something to add to my "want" list.

KW Energy from LPG Gas

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