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Old 12-21-2012, 04:56 PM   #1
Jps101
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Default Cost of Energy Experiment

Cost of Energy to Produce 5 gallon batch:

Let me set the stage for you. I love the idea of converting my system over to electricity. As I read the posts on this site I am amazed at some of the backgrounds on here, Mechanical Engineers, Electrical Engineers, Chemists and the list goes on. My background is finance…in other words part of the fun in this hobby for me is the cost of things and how can I produce something as cost efficiently as possible. I think we would all agree once we start adding our respective incomes on an hourly basis – the cost of goods sold line in the income statement would change dramatically. Nonetheless, this thought process led me down the rabbit hole to see if I could try and figure out the economic viability of changing my system over to electric to bring my cost per beer down. Might also serve as an argument to the wife why I should spend 2k upgrading service, equipment, etc. Enough of the background, let me get on with the experiment.
Some of the base information: I live in Southern California, which means my electric service comes from Southern California Edison, my Natural Gas service comes from So Cal Gas and my propane is provided by Camping World just down the street.

Current Cost of Energy:
1 kWh from SCE = $0.21 (average cost over the tiers that we use)
1 Therm of Natural Gas = $0.72/.85 (NG is 15% less efficient than propane) = $0.85 (rounded up)
1 Therm of Propane = $3.34 (1 gallon of Propane = 91k BTU’s @ $3.67 gallon / 100k)

A few quick conversions of kWh to therms:
1 kWh = 3,414 BTU’s: 100k BTU’s = 1 therm: 100k/3,413 = 29.3 kWh: 29.3 kWh = 1 therm

Step One: Conversion to standard measure of energy cost
Natural Gas: $0.72/therm
Propane: $3.34/therm
Electricy: 29.3 kWh * $0.21 = $6.15/therm

Step 2: Convert 8 gallons of water from 60* to 160* (strike temp)
Need 1 BTU to raise 1# of water 1*F; Water weighs 8.34#/gallon
8 gallons * 8.34# = 66.72# of water
66.72 * (165*- 60*) = 7,005.6 BTU’s needed to raise 8 gallons of water from 60 degrees to 160 degrees
7005.6/100,000 = .0701 therms

Cost to raise water to strike temp (highest to lowest)
kWh: 0.43; LP: 0.23; NG: 0.06

Step 3: Bring Wort to a Boil (I am at elevation water boils at 210)
(210 – 152 mash temp) = 58* x 66.72 weight of water = 3,869.76 BTU’s needed to boil
Cost = kWh: 0.24; LP: 0.13; NG: 0.03

Step 4: Maintain boil for 60 min
Admittedly, this is where I ran into a bit of an issue, and perhaps where the math may fall apart a bit. I had a difficult time coming up with a formula to calculate heat loss and reduced energy needed to maintain a boil once reached. Therefore, I went with 60%. Why 60%. I have seen numerous times on this forum, where brewers will set there PID’s to a 60% cycle setting. That is what I went with.

Using a 5500w element, running for 60 min to calculate energy used.
5500 * .6 = 3300w / 1000 = 3.3 kWh * 3,413 (conversion factor of kWh to BTU) = 11,263 BTU’s
11,263 BTU’s / 100k = .1126 Therms * $6.15 = $0.70 to maintain a boil for 60 min.

Natural Gas:
.1126 therms (from above calc) * $0.85 (cost of a therm) = $0.10 (rounded up)

Propane:
.1126 therms * $3.34 = $0.38

TOTAL COST OF ENERGY TO BREW A 5 GALLON BIAB BATCH:
kWh = $1.37
LP = $0.74
NG = $0.19

Conclusion:
I need to come up with another angle to sell the conversion to all electric to the wife, the math isn’t gonna do it!

On a somewhat more serious note, I would like to think I thought through this pretty well. I had to make a few assumptions here and there. Nonetheless, it was a fun exercise doing the conversions and just seeing how expensive electricity has become in So Cal. Not to mention seeing how much energy is required to complete certain tasks. By the same token, how inexpensive Natural Gas has become. If I were to purely make decisions only on the math, there is no discussion, I could easily argue I should run a natural gas line to where I brew and doing everything on Nat gas. Further, I should look to convert over to Nat Gas fired electricity. I did not take into consideration heat loss to pots, ambient temp, and yes I know those will play a role. However, when you look at the disparity in cost, there is no way whatever inefficiencies there might be with NG it is highly unlikely in my opinion they will overcome the expense of electric. That said, time to convert to all-electric, why? Just too cool not to!

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Old 12-21-2012, 05:06 PM   #2
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Sooo, how much propane (pounds) did you use to make that batch?

I think you got the right number for the electric. (though my electric cost is much less than yours)

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Old 12-21-2012, 05:08 PM   #3
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I don't see any adjustments for efficiency. An outdoor burner on a pot is 50-60% efficient on a good day. Add some wind and you're lucky to get 25%. An immersed element will give you almost 100%

I doubt you'll be able to beat the cost of NG, but propane should be an easy foe. I decided on electric because of the ease of automation. An SSR relay is cheap vs an automatic gas valve.

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Old 12-21-2012, 05:08 PM   #4
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I like the level of thinking that went into this.

My math is a bit simpler but here is my cost for brewing All Grain using propane:

Cost for 15 lb propane fill: $14.50
# of gallons brewed on one fill: 46.2 (11 gal batches x 4.2 batches/cylinder observed average)
Cost per gallon: $0.31.
Cost per 12 oz bottle: $0.03
Ingredient cost per 12oz bottle: $0.23
Total cost / bottle $0.26
% cost (energy) 11.5%

Conclusion: Energy is just over 10% of total cost to brew. To reduce costs looking to cut ingredient cost is a more effective way of cutting total costs.

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Old 12-21-2012, 05:16 PM   #5
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Quote:
Originally Posted by brewfreeordie View Post
I don't see any adjustments for efficiency. An outdoor burner on a pot is 50-60% efficient on a good day. Add some wind and you're lucky to get 25%. An immersed element will give you almost 100%

I doubt you'll be able to beat the cost of NG, but propane should be an easy foe. I decided on electric because of the ease of automation. An SSR relay is cheap vs an automatic gas valve.
It's really easy to weigh the tank before and after brewing to know the amount of propane used. No reason to guess. Then you can back-calculate the number of BTUs that were used and you'll know your effeciency.

I see 0.1 therm above, which looks like 0.1 gallon, which I think is less than half a pound of propane. That can't be right, so maybe I'm missing something (I admit to skimming the math above).
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Old 12-21-2012, 05:18 PM   #6
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Quote:
Originally Posted by brewfreeordie View Post
I don't see any adjustments for efficiency. An outdoor burner on a pot is 50-60% efficient on a good day. Add some wind and you're lucky to get 25%. An immersed element will give you almost 100%

I doubt you'll be able to beat the cost of NG, but propane should be an easy foe. I decided on electric because of the ease of automation. An SSR relay is cheap vs an automatic gas valve.
Agreed. I plan to brew on Christmas day or day after and figured I would take some copius notes on weight of tank before/after as well as time measurements. Like i stated in the OP, I was looking to have a little fun with this and I know I am missing a few pieces. Efficiency of energy source being one of them.
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Old 12-21-2012, 05:40 PM   #7
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I'm about 2 weeks ahead of you on this (just picked up an enclosure so I can start assembling) and I've run the numbers a few times myself. Propane is about $4/gallon for me and I'm guessing I use about a gallon give or take per 5 gallon session.

5500w @ $.20/kwH cycled @ 50% is about $.50/hr. About 1/4 the cost of propane for me. I figure if I drink 9383 more beers I'll starting getting a return on my investment.

And then it's like printing my own money!!!

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Old 12-21-2012, 05:57 PM   #8
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I did this math as well, and I would have to get new service put in from SCE, including a new main breaker panel as the one on the side of the building is already full, in addition to running new lines out to wherever to carry 240V, and assembling/retrofitting my rig to use electric instead of propane. And, then I have to disconnect or otherwise disable that 240V line when I move, since it will be in a rental unit and I don't want to pay to run someone else's welder. The cost is in the multiple thousands. It is actually cheaper for me to wait until we buy another house where we are likely to have 240V already installed, or at least where I have enough extra capacity in the service that I can add a 240V outlet without much trouble.


Also in your calculations, you really do need to account for efficiency. I am pretty sure I've never gotten 10+ batches of beer on a single propane tank. 4-5, maybe. I'd say most often it's in the 3-4 range.

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Old 12-21-2012, 06:08 PM   #9
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As one of those engineers, I love the math. It was brought up, but the efficiency is important here. Near 100% of the energy from the electric element goes straight to the water. A burner pumps a lot of heat into the atmosphere before even heating the water.

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Old 12-21-2012, 06:21 PM   #10
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Agree with most of what you all are saying. My first, very basic calculation went something like this. I have filled up the propane tank 2x. Average cost per gallon of fill is 3.67 tax included. If I back into some numbers. Ie take a full propane tank, use it, go get it filled, added 3.34 gallons of propane. Thus I used 3.34 gallons to produce 37.5 gallons of finished beer, strange but true. Another way of thinking about it 11.2 gallons / gallon of propane. At $3.67 average cost per gallon propane = 32.7 cents per gallon X 5 gallon batch = $1.64 per five gallon batch of beer. Or another post stated in my case about 3 cents a glass. I am on my way to refill propane and will adjust some of the math upon my return.

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