Allotments 4 All
Allotment Stuff => The Basics => Topic started by: philistine on February 01, 2023, 17:57:15
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how many solar panels and car batteries would I need to boil a kettle 6 times a day?
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Take a vacuum flask!!
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how many solar panels and car batteries would I need to boil a kettle 6 times a day?
Boiling a kettle once is a big ask of a solar installation.
Some VERY approx estimations because efficiency would depend on location, weather, and time of year. Did you want to be able to achieve this year round? In the middle of the UK?
To boil a full 3kW kettle once uses approx 0.225 kWhour
So boil it 6 times and use 1.35kWhour
That's the easy bit.
A single 100W panel, facing South in the UK in the middle of summer might generate 75W at noon through to 10W at 4pm and 10W at 8am
so let's say 20W at 9am and 3pm, 40W at 10am and 2pm, 50W at 11am and 1pm.
Roughly generating (10+20+40+50)*2+75=315Whr = 0.315kWhr So operating all through a sunny day, it might capture enough energy to boil a kettle once.
In the depths of winter, expect less than 1/4 of that. So you might manage to boil a kettle once per day with 4 x 100 Watt panels
So... 24 x 100Watt panels might be just about good enough to boil it 6 times a day.... most days.
(You might buy 200W panels, where you'd need half as many.
You will need batteries with the capacity to store your 1350WHour. If it's a 12V battery that's 113Ampere Hours. But it would be insane to try to run a battery full to empty over the 30 minutes or so of kettle boiling. So quadruple it. Say 500 Ampere Hours. That's roughly 6 LARGE leisure batteries (at £200+ each)
Or maybe 10 car batteries at maybe £80 each.
You'd need something like a 3kW inverter at about £200 and a heavy duty solar charge controller.
As I say..... VERY rough estimate. YMMV
In summer you'd have wasted capacity, so run the washing machine as well :)
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Small solar trickle charger, 1 battery and a 12v cup heater. 6 cups? you will not get any work done but a lot of pee for the composting :tongue3:
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A Kelly Kettle (or other make) would boil water with just a few twigs
https://en.wikipedia.org/wiki/Kelly_Kettle
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Small solar trickle charger, 1 battery and a 12v cup heater. 6 cups? you will not get any work done but a lot of pee for the composting :tongue3:
I agree. Those cup heaters are marvelous..... Slow but effective. A small 50W panel, wired direct to a car battery. You wouldn't need a charge controller or inverter. If the battery ran low, you'd soon know by the lack of hot water.
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I take it we're talking cuppas at the lottie with no power source.
In which case, could I run a heated mat off a small solar panel and a car battery? The light levels in the polytunnel are so much better than in th ehouse, even on a bright window sill.
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I take it we're talking cuppas at the lottie with no power source.
In which case, could I run a heated mat off a small solar panel and a car battery? The light levels in the polytunnel are so much better than in th ehouse, even on a bright window sill.
Though those elements are good, they can boil dry.
Consider a heated cup/kettle with auto cuttoff.
https://www.amazon.co.uk/Stainless-Electric-Anti-Rust-Convenient-Drinking/dp/B0B8XQVVQ6/ref=sr_1_1?crid=1SCKF0O4NWGA5&keywords=12v+kettle&qid=1675521600&sprefix=12v+kettle%2Caps%2C121&sr=8-1
Typically take 5 amps / 60W so you could boil it up several times a day depleting a big car battery. But the battery is just a reservoir and your panel replenishes it as best it can with whatever sun it can capture. A 100W panel would be a fair start or a pre-owned 200W one. You need an 18V nominal one if you are to avoid spending an arm and a leg on an MPPT controller. Probably spend a tenner on a PWM controller, but not essential at this small scale.
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I have an old "roarer" parading stove and a calor double burner so no idea about solar panels I'm afraid. A neighbour 2 plots down is having a go at solar panels to run a sprinkler/trickle watering system with solar panels and a timer. Hope he makes it. :wave:
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IMO Solar would not be the answer to your 6 brews a day, a little gas camp stove would be more economical , if not 'green' . I use solar to run a watering system in the poly , a 25 Watt panel, 8 quid controller. small 12v battery and a bilge pump. it just manages to keep up the power required in the summer , I'm thinking of making a sun follower device, when i have time.
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Solar panels that heat water directly are potentially 100% efficient whereas retail PV panels are around 15% and cost exponentially more for higher efficiencies.
Admittedly thermal methods (such as a blackened metal bottle) drop off rapidly as the water gets hotter - only about 50% efficiency as it approaches the temp of a hot beverage, but pretty quick for black instant coffee - and you could always have another black bottle for milk.
PV ones use more visible than IR (more energetic electrons).
So you might think that clear days are essential for thermal, but both IR & visible* get through an overcast, and dark clouds basically stump both systems.
I suppose the sensible way to get to 100C is a black bottle with a reflector behind it to about 50-65C and then use your PV-charged lithium battery & element - that's if you absolutely have to use dried leaves in boiling water (or you don't even like modern coffee essences).
Cheers.
PS. * I didn't have time to find a % comparison between thermal and PV in an overcast - the answer must be out there, but buried >100 dud answers deep by both industries - is it just (pathetically normal) sloppy thinking? why would both want it kept quiet?