12v water heater

StupidLikeAFox

Howdy,

I have an idea and would like someone with some knowledge to tell me if it will work or not. I came across this 12v submersible heater https://www.amazon.co.uk/Aiiciiou-Heating-Element-Immersion-Submersible/dp/B01D4U27NA

As it is 12v my idea was to hook it up to my solar panel and have it constantly tipping away at heating the water. The idea is that I could have it on more or less constantly and it would keep the water at a decent temperature. I don't need the water to be roasting, lukewarm/room temperature would be fine for a quick wash.

This is 12v and my solar panel obviously provides 12v power. However, this is 200W and my little panel is only rated at 30W - what is likely to happen if I hook this up? Will it be sufficient to heat the water at all or will the panel barely heat the element at all?

crabbypaddy

4.186 kJoules of energy to heat 1 kg of water 1 degree

To heat 20l from 20 degrees to 60 degrees

20 x 4.18 x 40 = 3344kJ

30W = 0.03kJ per second

3344/0.03/3600 = 30.96 hours ignoring heat lost.

In reality you 30w panel will generate a fraction of 30w for a fraction of the day while you lose heat through conduction, convection and radiation. So you would likely never heat the water.

Also bear in mind that water heaters are set to 60-70 degrees to reduce the risk of bacteria like legionella, a tepid water tank is perfect for breeding legionella.

Keep it simple, this is not an electrical problem with associated conversion and wiring inefficiencies.

Connecting a resistor directly to a solar panel will not work (except at midday in perfect conditions with an overspec-ed PV panel), in general the element will pull down the panel voltage reducing the current to the element to a point where it's impedance makes it redundant. If you use a battery the voltage will stabilise but it will take the shortfall from the battery running it at discharge.

A pv panel is ~18% efficient at converting the sun's energy to electricity. A black sack can be 70% efficient at converting the sun's energy to heat.

If you had a large enough PV panel say >400Wp...the problem being with 30W you'll rarely if ever have an abundance of power...there is a way to use your excess power to heat the water tank. It's rather elaborate and involved though.

You can add a wind turbine PWM diversion load controller set to power the element at slightly under the solar charge controller's absorption set-point voltage on the battery and use an element with a thermostat.
Or forego the solar controller and use a SPST NC relay driving an air heater with the relay coil downstream in parallel with the element thermostat from the diversion controller.
...did somebody say keep it simple? :pac:

StupidLikeAFox

Thats what I was thinking alright, thanks for the replies!

Sir Liamalot wrote: »

I actually have two of these - I was hoping for a more complex but still simple option though, I may keep looking or just settle for the shower bag!

Fill it with hot water from the gas hobs?

You need to upscale a lot for an electric solution.


(use PV instead of the wind/hydro arrangement)

crabbypaddy

StupidLikeAFox wrote: »

Thats what I was thinking alright, thanks for the replies!


I actually have two of these - I was hoping for a more complex but still simple option though, I may keep looking or just settle for the shower bag!

You could look out for a used boat calorifier and plumb it into the engine coolant.

http://www.surejust.co.uk/calorifiers