Electric cooking in the wilderness – a rough analysis
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I know what you are thinking – Are you crazy? Who would cook with electricity in the wilderness? Why?
I'll run the numbers, so we'll see how crazy that might be.
But first:
– Most backpackers use a battery-powered flashlight or headlamp, instead of a candle or no light. Are they crazy?
– Some backpackers use a battery-powered GPS instead of a compass, paper maps, and navigation skills. Are they crazy?
– Some backpackers use a battery-powered cell phone, satellite phone, or satellite messenger, instead of developing more self-reliance, and more tolerant families. Are they crazy?
Why would someone want to cook with electricity in the wilderness?
– Fire bans, which are becoming more common because of the left-wing global warming conspiracy.
– Some people are afraid of cooking over a flame. Don't laugh, I have friends who grew up with electric stoves and are afraid of cooking with flames.
Important concepts
Energy is potential work. The energy in a battery is like the gasoline in a car's tank. Electric energy can be measured in Watt-hours.
Power is how fast you spend energy. Some batteries can push out energy faster than others. The power of a battery is like the engine in a car. Electric power can be measured in Watts.
Some cars have large tanks (high energy) and small engines (low power); some have small tanks and large engines; most are in between. Batteries are similar.
So how could we cook with electricity in the wilderness?
Caveat: I am not an engineer. If you are, please be kind in your comments!
Goal: Bring 2 cups of 1° C (34° F) water to a boil in about 10 minutes.
That's a a little slow, but tolerable.
To raise 2 cups of water by 99° C takes about 55 watt-hours of energy.
Delivering 55 watt-hours in 10 minutes takes 330 watts of power.
… assuming we have 100% conversion of electricity to heat (good assumption), and 0% heat loss from the stove and pot (bad assumption).
Assuming our stove and pot are 67% efficient, we need about:
83 watt-hours of energy
500 watts of powerHow do we deliver 500 watts to a pot holding 2 cups of water?
Four 120-watt immersion heaters would be close enough:
Crammed into a pot with a cozy:
Someone could make a better setup, these are off-the-shelf.
Where do we get 83 watt-hours and 480 watts of electricity?
Option 1: Lithium AA batteries
One Energizer Ultimate Lithium AA battery can supply 4.5 watt-hours at 4.5 watts (being generous).
We need to supply 12 volts to the immersion heaters. We could use an 8-battery pack like this:
We need 4 battery packs running in parallel, for each heater, to get enough watts.
128 batteries total cooks almost 7 meals, weigh about 1856 grams (4 pounds), about 265 grams (9.3 ounces) of "fuel" weight per meal. At $2 per battery, that's about $37 per meal.
Total weight about 2600 grams (5.7 pounds) for batteries, cases, wiring, and immersion heaters.
This particular setup might have other problems. A custom design could be a little lighter and more efficient.
But almost any backpacking stove on the market will be much lighter and much cheaper, even this one:
Option 2: Alkaline D batteries
Consumers cannot easily buy Lithium D batteries, so we'll try Alkaline D batteries.
Alkaline D batteries have more energy than Lithium AA batteries, but D's are much less powerful (bigger gas tank, smaller engine).
We need about 640 Alkaline D-cells weighing over 200 pounds to deliver 480 watts. I won't do the rest of the math.
Rechargeable batteries
We can choose from many different rechargeable battery chemistries – Lead Acid, AGM, NiCad, NiMH, several varieties of Lithium, and more. Lithium batteries are clear leaders in power and energy per gram, though rechargeable Lithium batteries store much less power per gram than single-use Lithium batteries. For more than you really wanted to know about batteries, try Battery University at http://batteryuniversity.com/learn/.
We want rechargeable Lithium batteries that yield 480 watts and 83 watt-hours for the lowest weight – assuming we can recharge completely every day.
There are hundreds, if not thousands of different rechargeable lithium batteries available. After about one hour of searching, I settled on this lightweight motorcycle battery:
Each battery yields 240 watts and 252 watt hours, and weighs 1,370 grams (about 3 pounds). We need two of these batteries to supply enough power, but we can cook about six meals before requiring a recharge.
That's 6 pounds of batteries, and we don't have a way to charge them yet.
With more research, we might find batteries that yield 480 watts and 83 watt-hours.
But the total battery weight is likely to be at least 2 pounds, and we still need a charging system.
I'll stop here.
Super Capacitors
Super capacitors sound sexy, but their energy density is 20x-40x lower than lithium batteries, their voltage drops linearly with discharge, and they have other engineering challenges. Not analyzed.
Conclusion
Surprise! Electric cooking in the wilderness is not very practical. But if you really need to, you can.
I'll stick to Esbit tablets in a Trail Designs stove.
— Rex
The lightest portable generator I could find with a few minutes of searching generates 450 watts continuous (about right), but weighs about 11 kilograms (24 pounds) with fuel and oil (not good):
On the other hand, you could cook 20 meals with a full tank, using only 51 grams (1.8 ounces) of fuel per meal!
— Rex
>How about using the new hydrogen battery technology seen at outdoor retailer?
Most portable fuel cells are designed to recharge small electronic devices over USB, supplying 5 to 10 watts.
You need 48 of those fuel cells to boil 2 cups of water in 10 minutes.
You can buy larger portable fuel cells, like this one:
but you need 10 of them, and they weigh 3 kilograms (6.6 pounds) each with fuel cartridge.
— Rex
A small Freeplay hand-cranked generator weighs 310 grams and generates about 8.5 watts if the FreeCharge is cranked energetically enough.
If you had 59 of these generators (and 59 people to crank them) you could bring 2 cups of water to boil in about 10 minutes.
If you had a 100% efficient battery (exercise left to reader), one person could generate enough energy to boil two cups of water with about 1.4 hours of cranking.
I suggest switching hands from time to time.
— Rex
More entertainment – Electronics on the floor: generators from wind-up torches.
and a microwave.
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