Solar Panel Powered Hot Water Immersion Heater

[dave1986]

I'm looking to build a system that allows me to dump excess solar power to an immersion heater to heat a small 12 litre tank of water for hot showers.

I have a 230Ah Lithium battery. The battery is monitored via a Smart Shunt, so I know exactly it's percentage charge. I was wondering whether there exists a smart controller (Victron Cerbo GX??) which could be programmed to send excess solar power to a 12v immersion heater under the following conditions:

1: Battery is at 98% or more state of charge.
I.e. if the battery dropped below 98% charge then the immersion heater would switch off and the solar power would go back to charging the battery.

2: Water temperature is below 40°C. So as soon as the water reaches 40°C (nice hot shower temperature ) then the immersion heater switches off.

I think that a Victron Cerbo GX smart controller device might be clever enough and have enough inputs from temperature sensors etc to be able to do this... Does anyone on here have experience with a Victron Cerbo GX to know if this can be done?

Can anyone advise me of suitable Immersion heaters and temperature sensors to do this?

Dave

 

[RunDSG]

I'm looking to build a system that allows me to dump excess solar power to an immersion heater to heat a small 12 litre tank of water for hot showers.

I have a 230Ah Lithium battery. The battery is monitored via a Smart Shunt, so I know exactly it's percentage charge. I was wondering whether there exists a smart controller (Victron Cerbo GX??) which could be programmed to send excess solar power to a 12v immersion heater under the following conditions:

1: Battery is at 98% or more state of charge.
I.e. if the battery dropped below 98% charge then the immersion heater would switch off and the solar power would go back to charging the battery.

2: Water temperature is below 40°C. So as soon as the water reaches 40°C (nice hot shower temperature ) then the immersion heater switches off.

I think that a Victron Cerbo GX smart controller device might be clever enough and have enough inputs from temperature sensors etc to be able to do this... Does anyone on here have experience with a Victron Cerbo GX to know if this can be done?

Can anyone advise me of suitable Immersion heaters and temperature sensors to do this?

Dave

This sounds amazing.

I have nothing to offer you, however, except that I want exactly this for my own van!!

 

[Samro]

You will be able to use the a Cerbo GX to do more or less do what you want, but some thought is required to set up the triggering of the relay.

A problem you may have is a potential lack of cell balancing of the battery cells, as you will find that the battery will balance its cells near the top of the charging voltage. You can get over this by setting a delay in the triggering of the relay, but just bear this in mind to prevent a problem.

To achieve what you want, you will need to set up the relay as though it is triggering a generator start up and then set the relay state to be inverted so that the relay switches on and off as you require. This is all straight forward and can be setup in the Victron Remote Console.

A problem that you will find is that the water heater will need 300w of continuous power to heat a small 12v water heater until it's thermostat cuts in. (such as Surejust 6ltr)
In really good solar conditions you may find that you achieve what you want but I fear that in the uk, you won't be getting much heat outside the peak solar period of mid may to early July.

This is all worth a go and you will have some success, but I suggest that you don't go mad on spending too much on this unless you have at least 400w of solar in the form of roof/portable panels and also are prepared for this to be next to useless outside of the peak solar months.

 

[Howzat]

I'd run the heater straight from the battery, maybe on a timer with an on on/off override switch and maybe a safety cut off when the battery gets down to XX% if that's a concern then let the solar controller just do it's normal thing.

This guy has a setup with timings.

In his example he heats 20 litres with a 150w element to about 40C in 2 hours which would draw at least 25 amp from the battery. No reason a 300w couldn't be used to speed this up.

A 200w+ panel should adequately replenish this and then some during mid spring to late summer.

Aside from the practical I'd also be concerned about bacteria at that temperature so I'd heat and use rather than maintain at that temperature for any length of time.