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Off-grid ways to quickly boil water and heat up food? Will an induction hotplate work?

 
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For most of the time, we cook on a wood stove, but I really like a hot cup of tea early in the morning (and we use less wood by not lighting the fire until 11am), and there are days when we are out all day and don't light the fire at all, so I need to boil water and sometimes heat food up on those days as well.

We have a fairly small off-grid solar system - 1200w inverter, around 7kwh of lead acid battery storage, 1300w of panels.

The portable induction hotplates I am looking at say they use 2000w, but they also have 300w or 400w settings on them. Does this mean that there might be a 2000w surge, or a 2000w default startup setting, which would mean it wouldn't work with my inverter? Or if I use it at 300w, will it just draw 300w?

Is 300w enough to boil water? Would it take a long time to get it to boil at that wattage?
 
pollinator
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an induction hotplate is probably overkill for a cup of tea. A smaller electric kettle usually would pull between 700 and 1100 watts and would be a better bet for tea. Heating up food a lower setting on the induction would work fine just take longer. Unless designed for 20 amp plugs an induction hotplate could not draw 2000 watts. A 15 amp standard plug can only put out 1800 watts without blowing the breaker. A conventional hotplate usually ranges from 700-1200 watts maybe a better place to start. As long as your inverter can take it and the batteries are fairly charged short duration electric heating tasks are no problem.
Cheers,  David
 
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What about a small camp stove , propane maybe?
OR... a mini rocket stove ? ha ha rocket stoves of all kinds are my thing.

Myself I wouldn't tax my solar system to heat water, but a small tea kettle wouldn't take long.
 
Kate Downham
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Thank you both for your responses.

I'm currently using a gas canister camping stove for this, but I'd prefer not to use gas.

I have wondered about twig and rocket stoves, I looked one up and it said not to use indoors, and also I imagine that it might get  a bit tricky to know whether it's going to keep burning once I've made my tea and am out of the kitchen. I can't rely on telling people to not touch it, so I don't like the idea of smouldering twigs being there when I'm not in the room.

I had a look at the gosun fusion, but it is a a bit out of my price range, and I'm also not sure if the 150w element would boil water in a reasonable time. This would have the benefit of being a solar cooker as well though. Has anyone here used it for boiling water?
 
thomas rubino
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Hi Kate;
No twigs will be left burning in a rocket stove.   Fast , Furious and then completely out .  
If you have the time / means, then experiment.  Small rockets can be built many ways.
Even the stove itself will cool quickly.  Or build one outside in the ground.
Have fun with it!
 
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Are you talking tea for an army or 8 - 16 floz of  water for some nice Twinings?


1 pound of water (~16 floz or two cups) will raise 1 degree f , for every BTU of energy put into it.   To get 1 lb from 40 to 212 degrees would ideally take 172 BTU.  1 BTU is about 0.3 Watt hours.   The cup of tea should take about 50 watt hours of power... with losses it'll take a bunch more, maybe twice as much beacuse you'd be heating the cup and the heater, etc.

Induction may be more efficient if your vessel is metal, it's also a lot more complicated.  A $30 '1000 watt electric burner' should be simple, last forever and do good enough.  In that ideal case it would boil your water in ~3 minutes.   In reality it'll take longer to heat the tea pot, etc. etc.    It's about the same sort of math people use for microwaves.  1000 watts for a few minutes, doesn't use up that much overall.

While you are at it, grab a kill-o-watt and it'll tell you how much AC power you are using each time you use it.  

As a backup there these kelly kettles https://www.amazon.com/Kelly-Kettle-Anodized-Emergencies-Hurricanes/dp/B004GLGXF0 , or there  are some tea warmers that take alcohol or little candles to run.    Or Erika's tea stump : https://permies.com/t/25974/tea-stump-stove-plans


I can't wait to hear which way to go and how it worked out for you and why.    I'm eventually hoping to have a nice off grid permiculture tea house somewhere in my life and would enjoy the different perspectives and results.  
 
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so i feel i have some experience to add

We have a Salton induction cooker.

Here are the settings it has 300w 500w 700w 1000w 1200w and more.

The 300 watt setting comes on and off as apposed to only using 300 watts(continuously) like it says. Ours will come on for a few seconds and than turn off for a few more seconds. so it is using the full power for 2-3 seconds and than turns off. its really terrible for simmering

the 500w setting does the same function as the 300w coming off and on . also not great for simmering.

the 700w setting is continually on same with every other setting. When i use it is either on 700w or 1000w. It is ultra fast at bringing a 1 liter pot of water as well as it heats a cast iron up very quickly.

The Salton is seasonal really, where i am at least. We use it mostly in the summer and can only really use it from 9am to about 5pm during the summer(so late breakfast and early dinner, which doesnt always work). It really sucks power. We have a 2000w system running at 24Vdc
 
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Biolite might suit your purpose well. Or perhaps a small electric immersion heater.

 
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Mike Barkley wrote:Or perhaps a small electric immersion heater.



The immersion heater would be my bet. I've used them successfully in the past for a single cup. Worked well. As mentioned, the induction cooktops are either on or off -- full power or no power. They just cycle on/off yielding an average wattage setting of whatever you select. The 300 watt setting will consume 300 watts per hour, but when it is "on" it draws the maximum rated wattage.
 
pollinator
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I think some of the posters have missed that the OP is in Australia so a "mains" induction plate would be rated to work on 230v not 120v which would mean it can easily draw 2000W.
I would suggest a small electric kettle, you might have to look at a travel kettle, because I see checking our kettle it is rated at 2200W.
 
Kate Downham
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I looked into kettles, and the only ones I saw on an online kitchen shop were all 1800w or more : (

I'll do a search for travel kettle and see what turns up
 
David Baillie
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Skandi Rogers wrote:I think some of the posters have missed that the OP is in Australia so a "mains" induction plate would be rated to work on 230v not 120v which would mean it can easily draw 2000W.
I would suggest a small electric kettle, you might have to look at a travel kettle, because I see checking our kettle it is rated at 2200W.

totally missed that...
 
David Baillie
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So I did a little playing tonight with my Kill a Watt
500 ml of water on my hotplate took 6 minutes to come to a boil Peak watts 1000 total power consumed: 100 WHr or 0.1 kW Hr
500 ml of water in my kettle took 3 minutes to come to a boil Peak watts 1400, total power consumed 50 or 0.05kW Hr
 
pollinator
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Funny I just posted a new thread about my Kelly Kettle.

I am able to do 6 cups of water to boil in 8 min.


My instant pot takes 15 min to boil the same amount of water.



IMG_20201218_094738.jpg
Kelly Kettle
Kelly Kettle
 
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I have nearly identical electrical specs as the OP.  All appliances feed w/1200W SW inverter via 48Vdc FLA bank.

Consumption measured via Kill-a-Watt - 16.9 fl/oz (500ml) water temp from 68*F to 212*F (elevation 3740ft.)

Single cup Coffee maker                    520W    @3min 31sec.  (max 175*F) (without strainer or coffee)
Microwave                                           1107W   @ 2min 33sec
Induction cooktop (small coil only)   760W   @ 1min 50sec  (cooktop has 2 coils - a small center coil & larger outer)
 
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For one quick cup of tea, I would go with the immersion heater as mentioned by Mike. All of the electricity goes to heating the water, and the appliance is tiny and simple, easy to clean and store.
 
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Why don't you like gas?  If it's the expense of 1lb bottles, there's a solution for that which I did myself.  For years my cabin's kitchen stove was a little propane camping stove.  I replaced the 1lb bottle connection with a 5gal connector like this.  So, you can run a gas stove off a 5 gallon bareque tank which is far cheaper to refill.
https://www.walmart.com/ip/Gas-One-Propane-Hose-Adapter-1lb-to-20-lb-converter-4ft/346322711
It would last months for me.
 
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If you're looking for a non-electric option to use indoors that's a touch more environmentally friendly than gas, alcohol stoves (that run off of ethanol, methanol or isopropanol) can be made easily and VERY cheaply. Burn clean enough to use indoors and don't use much fuel to boil a cup or two of water. I've used them backpacking quite a few times...

https://en.wikipedia.org/wiki/Beverage-can_stove
 
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Eugene Kenny wrote:[Single cup Coffee maker                    520W    @3min 31sec.  (max 175*F) (without strainer or coffee)


Thanks for running the experiment! (No need for bold, message received.)

I should caution that 175F is not hot enough for proper tea. Or so I am told by DW, whose grandmother was a Brit war bride and was very particular about tea. So that wattage value may be problematic.
 
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