Using solar PV to heat water in an immersion heater.

Slammeddeluxe

Hi - we have a house in France and the only source of hot water is an immersion heater. If we put some solar panels on the back of the house and 'trickle' charged the immersion heater would this be enough to supply us hot water ? I have heard you can buy a 220V / 12V immersion heater element. So my question is - if I can supply 12V to the immersion heater for say 12 hours a day would this heat enough hot water to have a couple of showers ? House is SW France so pretty sunny in the summer ? Thanks - Paul

NigeWick

We're in Lincolnshire and we got hot water from the solar for washing hands & dishes yesterday. We have an electric diverter to the immersion. Northern France you'll be a little better than here. Southern France, you may even have enough on sunny winter days.
If your shower and/or bath come from the immersion, you'd need to ask a professional.

Pile_o_stone

If you're only going to use the solar PV panels to heat water than you'd be better off fitting solar thermal. My advice would be to fit PV but with an inverter so you can use the generated electricity for everything in the house. You can fit an iboost device to divert unused PV to your tank. We have this setup and on sunny summer days we spend much of our days off grid and get a full tank of hot water. 

Reed_Richards

I cannot believe that there can be such a thing as a 220 / 12 V immersion element.  Ohms Law V = I*R so power = V*I =V*V/R.  The resistance R must be a fixed property of the immersion heater so if it dissipates W watts at 220 V it will dissipate W*144/48400 at 12 V which means it is going to take 336 times longer to heat the same amount of water.  Are you sure 12V is the correct figure anyway?  It might be better to consider the power output capability of you panels.  

silverwhistle

I'd go with pile-o-Stone's route if you can. Today in Hampshire I put 3.51 kWh into my immersion tank, but that's from the main 240v system, and March to October I hardly use the gas boiler.

Having said that I'm pretty certain I've seen 12v immersion elements, (yep - search   "12v immersion elements"),  though I think most will be more for camping and boating purposes. Presumably you have come up with this idea to avoid the cost of an inverter etc?

Solarchaser

Reed_Richards said:

I cannot believe that there can be such a thing as a 220 / 12 V immersion element.  Ohms Law V = I*R so power = V*I =V*V/R.  The resistance R must be a fixed property of the immersion heater so if it dissipates W watts at 220 V it will dissipate W*144/48400 at 12 V which means it is going to take 336 times longer to heat the same amount of water.  Are you sure 12V is the correct figure anyway?  It might be better to consider the power output capability of you panels.  

Its a very good point, id imagine its a dual element, single bulb design, but yeah, you still wouldn't want to be trying to heat water with 12V

Screwdriva

Does using your tank's immersion heater via iBoost cause premature failure? I can't see it as something designed for daily use.

silverwhistle

Premature failure of what? There's no complicated mechanicals or electronics to go wrong. Mine's been in use for 6years with no issues.

Hexane

silverwhistle said:

Premature failure of what? There's no complicated mechanicals or electronics to go wrong. Mine's been in use for 6years with no issues.

Indeed, the technology is the same as in an electric kettle or anything else. Huge numbers of flats have a hot water cylinder that's heated by an immersion heater (usually on Economy 7 or similar), those will run intensively on a nightly basis for decades. I've lived in three such flats without experiencing or hearing about any kind of problems. And such arrangements will run the immersion heater at maximum power (3000W?) for as long as it takes the thermostat to cut out (hours if need be). By contrast my solar diverter ramps up very very slowly starting from 100W, and on many days of the year won't divert power to the immersion heater at more than 500W all day. So that's probably less stress on the immersion heater too.

Ectophile

Screwdriva said:

Does using your tank's immersion heater via iBoost cause premature failure? I can't see it as something designed for daily use.

What do you think people with no gas supply use to heat their hot water?

Pile_o_stone

This site has information about linking a 200w 12v immersion heater that;s connected to a wind turbine. I think you have to have a load on a wind turbine or they spin to bits in stormy weather, so they often attach a heating element for backup. I assume the basic information can be applied to solar rather than just a turbine.

http://www.reuk.co.uk/wordpress/heating/200w-12v-immersion-heater/

Here's a 300w element on amazon:
https://www.amazon.co.uk/Aiicioo-Heating-Element-Immersion-Submersible/dp/B01D4U23O8