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 Home Brew Forums > Check my calcs! How quick will electricity pay for itself?
05-06-2010, 07:33 PM   #1
DKershner
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 Check my calcs! How quick will electricity pay for itself?

OK, this is going to get a little complicated, but I just need to know if everything I am writing makes sense. I am considering a switch to electric and am just trying to see how long it would take to pay for itself in # of batches. Bear with me here.

OK, so I currently use high pressure propane in 20lb tanks. I buy the propane at a gas station which charges \$2.19/gal. 20lb propane tanks would hold a 4.71gal of propane. This means the propane tank costs about \$10.31 to fill. How much propane I use depends on season, weather, etc, but on average I use about 1/3 of the tank for a 10gal brew session, or about \$3.43. I also use my hot water heater to heat the water if this number seems low, but that would be the case for either system.

Since the tank has about 400,000 BTUs in it, that means I use about 133,333 BTU/session. At 25% efficiency, which I think is common for burners, that means I get 33333.25 BTUs to the wort. To achieve that many BTU's with electric, I would need 9.7kW (3412BTU/kW). I pay about \$.13/kW around here, or \$1.26/session.

\$3.43 (propane) - 1.26 (electric) = \$2.17 savings/session.

I figure to wire a 240V outlet and get a system from brewmation to handle the HLT and BK would be around \$1000, with some misc costs that we will call \$100.

\$1100 / \$2.17 = 506 brew sessions.

Does anyone see an error here? Do my calculations seem biased somewhere? I realize the benefits of automation are not accounted for, but anything else?

DK

05-06-2010, 07:49 PM   #2
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What it looks like is you are trying to calculate the ROI on purchasing equipment. You found your savings number with \$1.40 per session. That is your compared savings in relation to your process.

785 brews would be your ROI for the equipment if you are calculating this only with your process savings. You have to also consider other Variables. Life cycle of old system and it's replacement cost. Maybe too the time savings with electric. You might save even more money if you can build the system yourself and do the wiring yourself.

785 brews is not a realistic number for ROI. If you are strictly sticking to that number. Then it would not make sense to upgrade. You will never see a savings.

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05-06-2010, 07:59 PM   #3
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Right, apologies on this, I should've been a little more clear. This is just a comparison for ME. There are much more cost effective ways to go electric and knowledge can save you quite a bit. I do not have this knowledge and would kill myself making an electric system.

I also do realize that 785 brews is a number that is basically the same thing as saying 'not worth it'.

Your life cycle point in an interesting one, however the replacement cost on turkey burners is pretty low, and would last fairly long. Anything else in my system would be reused on the electric system.

Time savings is an interesting point. It would probably heat a little faster and would require much less attention. I may assign a value to that.

05-06-2010, 08:00 PM   #4
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I think this would be similar but looking at it from a different perspective:

To heat 10 gallons from 60 to boiling:

[212-60]x10gal(8.35lb/gal)=12692 BTU / 3412 BTU/kWH = 3.7kWH @ .13 = \$0.481

propane has 21584 BTU/lb: 12692BTU/lb / 21,548 = .59lbs @ \$0.90/lb = \$0.531 (insert your propane cost)

if propane is 25% efficient propane heating cost would be x4 = \$2.124

So, 2.124-0.481= \$1.64 savings to boil 10 gallons.

Propane theoretically looks to be about 4.5 times more costly assuming 25% for propane.

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05-06-2010, 08:06 PM   #5
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\$.9/lb for propane seems costly. Is this the price to exchange Blue Rhino tanks? According to my calcs, I am paying about half of that. If I pay \$2.10/gal of propane, and 4gal is about 18lbs, that means about \$8.4/tank, or \$.46/lb.

Are any of those assumptions wrong?

I agree that your model looks to be doing the same thing as mine, but mine is about showing about a 2.25x cost for propane, not 4.5x.

05-06-2010, 08:24 PM   #6
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Quote:
 Originally Posted by dkershner \$.9/lb for propane seems costly. Is this the price to exchange Blue Rhino tanks? According to my calcs, I am paying about half of that. If I pay \$2.10/gal of propane, and 4gal is about 18lbs, that means about \$8.4/tank, or \$.46/lb. Are any of those assumptions wrong? I agree that your model looks to be doing the same thing as mine, but mine is about showing about a 2.25x cost for propane, not 4.5x.
I am sure you know what your cost is. Are you talking a 20-lb tank. In my experience only bulk fills are calculated by the gallon. I am not sure of the exchange costs. I have an electric HLT and I boil with propane and use a 100lb tank. Last fill It cost \$76. That is .76/lb. I assumed smaller quantities may be more expensive. Just plug in your cost per pound and see where that puts you.

I have never calculated how much propane I use per brew. I am not sure how accurate 25% efficency for propane is either. I am sure it would vary with conditions. The caculations I showed assume 100% efficiency which will be close with electric. Just apply what you feel as a reasonable efficency for propane.
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05-06-2010, 08:30 PM   #7
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Quote:
 Originally Posted by lschiavo I am sure you know what your cost is. Are you talking a 20-lb tank. In my experience only bulk fills are calculated by the gallon. I am not sure of the exchange costs. I have an electric HLT and I boil with propane and use a 100lb tank. Last fill It cost \$76. That is .76/lb. I assumed smaller quantities may be more expensive. Just plug in your cost per pound and see where that puts you.
If your 100lb tank costs .76/lb, I must be off on my calculation. I am using 20lb tanks and fill them at a gas station. It isn't a swap, it's a fill, just like you would a car. The current cost is around \$2.10/gal at the ones near my house.

OR

For your 100lb tank to cost \$76, I calculate that as 23.5gal, or \$3.23/gal. Is it possible you are paying a delivery charge? Or maybe its just a regional cost difference?

Thanks for all your help on my sanity check btw.
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05-06-2010, 08:43 PM   #8
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Quote:
 Originally Posted by dkershner If your 100lb tank costs .76/lb, I must be off on my calculation. I am using 20lb tanks and fill them at a gas station. It isn't a swap, it's a fill, just like you would a car. The current cost is around \$2.10/gal at the ones near my house. I pulled the figure of 4gals per tank from here: http://answers.yahoo.com/question/in...6040854AAdKgt4 ORhttp://wiki.answers.com/Q/How_many_g...pane_tank_hold For your 100lb tank to cost \$76, I calculate that as 23.5gal, or \$3.23/gal. Is it possible you are paying a delivery charge? Or maybe its just a regional cost difference? Thanks for all your help on my sanity check btw.
Well, like CO2 the gas volume is dependant on the pressure. That is why it is generally sold by the pound. For bulk propane to be sold by the gallon it must have a standard pressure at which it is dispensed. I dont know for sure.

It has been a while but the last time I filled a #20 tank I believe it cost me \$18.00. That is where I got the .90 figure from. I live in a small town so cost may well be more here.

One way to know for sure how many pounds your tank holds is to weigh it empty (tare weight...may even be stamped on the tank and is usually about 18lbs for a 20lb tank) then weigh it after filling.

I like electric for my brewing. I plan to convert my kettle some day also. It is not easy to compare costs as there are so many variables but I do like not worrying about running out of propane. The upfront costs of electric are definately more and It may not be reasonable to try to recover the costs.
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05-06-2010, 09:12 PM   #9
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Quote:
 Originally Posted by lschiavo One way to know for sure how many pounds your tank holds is to weigh it empty (tare weight...may even be stamped on the tank and is usually about 18lbs for a 20lb tank) then weigh it after filling. I like electric for my brewing. I plan to convert my kettle some day also. It is not easy to compare costs as there are so many variables but I do like not worrying about running out of propane. The upfront costs of electric are definately more and It may not be reasonable to try to recover the costs.
I need a refill right now, I will weigh it before and after.

Thanks for all the input lschiavo, there are definite other benefits to electric to think about, but I guess it matters how much convenience matters to the individual.
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05-06-2010, 09:29 PM   #10
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Quote:
 Originally Posted by dkershner I need a refill right now, I will weigh it before and after. Thanks for all the input lschiavo, there are definite other benefits to electric to think about, but I guess it matters how much convenience matters to the individual.
No problem at all. If you haven't already, check out the electric build threads here. With all the details others have provided, I am sure you could build something yourself and you can go just as simple or complicated as you like.

Let me know what you find for your cost out of curiosity.
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