Propane Generator Efficiency: Am I Calculating It Correctly?

I'm looking at the specs for the Kohler 14 kW RESA Generator, and it consumes 81 CFH of propane per hour to generate its full output of 14,000 Watts/Hr.

1 CFH = 2,500 BTU of LP/Propane (one source said 2,516)

81 CFH x 2,500 BTU's/CFH= 202,500 BTU's per hour of propane consumed by the generator at full output load of 14,000 Watts per hour

Propane has 96,500 BTU's per gallon (so it burns 2.1 gallons of propane per hour to deliver 14,000 watts/hr. of electricity)

14,000 Watts x 3.412 BTU's/Watt = 47,768 BTU's per hour equivalent delivered by the generator at full output

47,768 (BTU's equivalent out) / 202,500 (BTU's in) = 0.236

0.236 x 100 = 23.6% efficiency in converting propane into electricity for this generator

Overall that seems to be quite good. But am I calculating the correctly?

i think you calc'ed it out correctly, although I only have had one cup of coffee and I only did a rough estimate comparison to my 10k gas generator which burns about 1 gal / hour.

Given the BTU difference between propane and gas and the kw difference between your gen & mine, the gal / hour you calc'ed seems within reason. I believe the efficiency calc is also correct.

titleist1 wrote:Given the BTU difference between propane and gas and the kw difference between your gen & mine, the gal / hour you calc'ed seems within reason. I believe the efficiency calc is also correct.

I don't own it. Just looking at it.

I have looked into buying a generator like that one and have rejected the idea. A friend of mine has one and had no power for 6 days during one of those horrible storms. He had to refill his 100 gall tank every two days which the propane company agreed to do as he is a cardiac risk. This is not a back up strategy in my book. Then there is the weekly exercising for 30 minutes that sucks up more propane so that when you need it the tank is not even full and no the propanet company will not come every week or two to put a few galls in the tank. My backup plan is that I opened up two chimneys in the house and put in hand fired that require no electricity. I only really care about long term backup in the winter. I have a couple of small generators for emergency use (e.g. fridges/lights etc.) and that is all she wrote. I do have two lister CS6s (coupled to two 5KW alternators) that run on just about anything, so farm kerosene tanks will be brought into play if needed.

During the months when we use no air conditioning we consume (on average) 16,738 Watts of electricity per day. But much of that consumption likely comes over only an hour or two per day (when we are cooking and doing laundry). A generator capable of delivering only 14,000 watts per hour might be marginal for our house. (???) It would perhaps take a 20,000 Watt generator to assure that we can cover all of our peak hourly demand needs.

16,738 Watts per day = 510 KWH per month. The electric company (where I live at least) bills you based upon KWH's consumed per month.

16,738 Watts per day should theoretically require about 2.5 gallons of propane per day (on average) at 23.6% efficiency.

Ive always thought that money is better spent by making yourself less dependent on electricity, most importantly a large water supply or buying a non-electric backup pump on a well. A non-electric heat source. Gravity water filters, etc. A propane refrigerator would be nice too. Most other things are for convenience. But if a person has health needs it may not be enough. I'm not blaming anyone for having or wanting a generator as it would be nice, but thats my 2 cents.

I'm paying about $67 per month (on average) now for our utility company supplied electricity, If I could make my own electricity using only 2.5 gallons of propane per day (on average), then for about an extra $100 per month I could take my house off grid. This is precisely what some of the Mennonites and less strict Amish in my general area are doing. I shop at a Mennonite/Amish bulk foods store that generates all of its electricity with generators (having both a propane primary, and an oil back-up generator).

$167/month ~= $5.50/day

$5.50/day / 2.5 gal propane per day = $2.20 per gallon for propane (which sounds about right)

This of course assumes that the generator will last forever and not cost one dime in maintenance and upkeep, and that the price of propane will never increase.

lsayre wrote:I'm paying about $67 per month (on average) now for our utility company supplied electricity.

You live alone in a 400 sq. foot house?

cArNaGe wrote:

lsayre wrote:I'm paying about $67 per month (on average) now for our utility company supplied electricity.

You live alone in a 400 sq. foot house?

The wife and I have 1,680 sq-ft of upstairs along with an 840 sq-ft finished walk-out basement (our family room). $67 for us averages out to 13.1 cents per KWH. Our last bill came out to closer to 13.3 cents per KWH. The rate per KWH fluctuates month to month. Highest I ever saw was 14 cents.

What is your electricity rate? How many KWH's do you use per month on average (for the non air conditioning months)? We do pay more in the summer when the AC is running.

We use about the same ... but my bill is $90+ all the time! Surprise. surprise - welcome to MASS ...

SMITTY wrote:We use about the same ... but my bill is $90+ all the time! Surprise. surprise - welcome to MASS ...

I'm going to guess that your typical cost is about 18 cents per KWH.

$92/510 KWH = $0.18/KWH

No - it's .06 cents per. It's all the transmission fees and taxes that get ya.

MA taxes the crap out of utilities for their infrastructure - poles mostly. They (idiot leftists on Beacon Hill) think they're doing us a big favor taxing "big electric" instead of us poor guys. They have zero understanding of economics ... yet, they're supposedly superior in intelligence to all of us, due to their academic credentials ...

For example - my last bill was extremely cheap, due to our 2 weeks spent out west last month. 390 kWh @ .07 cents per = $28.28 .... then, $30.61 for delivery services ...

SMITTY wrote:No - it's .06 cents per. It's all the transmission fees and taxes that get ya.

MA taxes the crap out of utilities for their infrastructure - poles mostly. They (idiot leftists on Beacon Hill) think they're doing us a big favor taxing "big electric" instead of us poor guys. They have zero understanding of economics ... yet, they're supposedly superior in intelligence to all of us, due to their academic credentials ...

Same here, only about 6 cents per KWH, but that is only part of the story for an electric bill. I'm paying a tad more than 13 cents overall. I bet that if I had solar panels I would only get 6 cents to sell excess back to them, even though they charge me over 13 cents. They call this 1:1 net metering. Hum???

Looks like it's gone up to .07 here - Actually 7-1/4. Just looked at my bill. I edited the post above to show how much they screw us on delivery charges here.

Two of the three electric feeds to the farm are switched off for 7 months so of the year and it all gets fed underground from the house. Orange and Rockland have "visited" me 7 times in this last quarter, replaced meters etc. They can't work out how I do it and want to charge me $1000 a month to switch on a few lights on in the barn. I use their power for A/C briefly in the summer and then off it goes.....phkm. The last guy asked me how I do it and I mutter darkly, solar...... Solar what a joke, around here that would run a cell phone at best.