Using excess solar PV to heat water

[Adelka]

We have installed 500W of solar (with another 250W panel to be fitted). We have an MPPT charge controller (MorningStar TS-60) and these sunny days, it takes no time to fill our batteries, especially as our fridge is out of action. I'm wondering if there's a straightforward (inexpensive) way to divert the excess power to our immersion heater to heat the water tank? I think it's a 1kw immersion heater. We have a 1kw inverter also. I guess a more low powered immersion heater would be needed?

 

 

[Ex- Member]

There's just been a thread about this here.

 

http://www.canalworld.net/forums/index.php?showtopic=66982&hl=

 

240v element is possible, but apparently there have been some issues. I much prefer the 12v element approach which I'm currently trying to source.

Edited July 28, 2014 by Julynian

[Adelka]

I missed this. Brilliant, thanks.

[peterboat]

I missed this. Brilliant, thanks.

I used the 12v version and it burnt out it was 300w and I had 300w of solar on it worked for a while then gave up the ghost! Now have a timer on my 1kw 240 immersion which comes on for a couple of hours 11 till 1 and its working fine I have 900w of solar and a 3000 watt inverter. As their is a temp unit on the immersion it turns itself off long before the couple of hours are up

 

Peter

[Adelka]

Thanks Peter, that does look like the simplest solution. Assuming we have 330Ah of battery storage full at 11am (about 4kWH), putting the immersion on for two hours (2kWH) shouldn't do much damage, assuming that there's strong sun. Now the questions is whether we can run the immersion from our inverter...

[Ex- Member]

Thanks Peter, that does look like the simplest solution. Assuming we have 330Ah of battery storage full at 11am (about 4kWH), putting the immersion on for two hours (2kWH) shouldn't do much damage, assuming that there's strong sun. Now the questions is whether we can run the immersion from our inverter...

 

The idea of dump load is to use the excess energy your batteries can't absorb and diverting it to the water tank element. Heating water up daily for 2 hours would put a massive strain on batteries let along the amount of time it would take to replenish the batteries. Also if you're using 240v then inverter losses also need to be taken into account as well. A 330 amp bank won't be up to the job IMO even if just heating water and running nothing else on the boat.

[peterboat]

 

The idea of dump load is to use the excess energy your batteries can't absorb and diverting it to the water tank element. Heating water up daily for 2 hours would put a massive strain on batteries let along the amount of time it would take to replenish the batteries. Also if you're using 240v then inverter losses also need to be taken into account as well. A 330 amp bank won't be up to the job IMO even if just heating water and running nothing else on the boat.

It works on mine although I do have 1500 ah of full traction batteries. I popped back at lunch today an hour after the immersion had been on my meter was still showing 13.2 volts so the sun was doing its stuff tonight I had a hot shower boiled the kettle watched tv played on the puter etc etc its about size of solar array and battery bank plus how well the sun is shining

 

Peter

[Staarek]

It works on mine although I do have 1500 ah of full traction batteries. I popped back at lunch today an hour after the immersion had been on my meter was still showing 13.2 volts so the sun was doing its stuff tonight I had a hot shower boiled the kettle watched tv played on the puter etc etc its about size of solar array and battery bank plus how well the sun is shining

 

Peter

 

Same here. I've had it for 6 weeks now and it works a treat. It's 500w 240V element with dedicated inverter triggered by a timer. I have it on for 3-4 hrs a day between 10-14 (depends on the forecast) My panels are capable of producing up to 80amps, the element uses around 40amps so it covers the demand easily.

[Ex- Member]

 

Same here. I've had it for 6 weeks now and it works a treat. It's 500w 240V element with dedicated inverter triggered by a timer. I have it on for 3-4 hrs a day between 10-14 (depends on the forecast) My panels are capable of producing up to 80amps, the element uses around 40amps so it covers the demand easily.

 

Hi Staarak

 

Where did you obtain a 500w 240v unit btw?

 

I do have an older 1500w inverter I could use if I were to consider a 240v element option, I do have a 1kw element already fitted though anyway. I'm unsure if I can set the temp on it, I do recall a small White dial in the unit tough.

 

I don't quite understand the use of a timer, if it's not sunny, surely it's going to use a lot of battery energy, or is this way set up to harness excess energy only. I'm assuming this still requires use of a relay too?

 

Our 740w of panels could produce up to 60a, very rare we see over 45a with the panels set flat. We do plan to add 200w though.

[Ex- Member]

I used the 12v version and it burnt out it was 300w and I had 300w of solar on it worked for a while then gave up the ghost! Now have a timer on my 1kw 240 immersion which comes on for a couple of hours 11 till 1 and its working fine I have 900w of solar and a 3000 watt inverter. As their is a temp unit on the immersion it turns itself off long before the couple of hours are up

 

Peter

 

Hi Pete

 

What temperature have you set your water. We were thinking about 40c

Edited July 29, 2014 by Julynian

[Staarek]

 

Hi Staarak

 

Where did you obtain a 500w 240v unit btw?

 

I do have an older 1500w inverter I could use if I were to consider a 240v element option, I do have a 1kw element already fitted though anyway. I'm unsure if I can set the temp on it, I do recall a small White dial in the unit tough.

 

I don't quite understand the use of a timer, if it's not sunny, surely it's going to use a lot of battery energy, or is this way set up to harness excess energy only. I'm assuming this still requires use of a relay too?

 

Our 740w of panels could produce up to 60a, very rare we see over 45a with the panels set flat. We do plan to add 200w though.

 

Hi Julynian,

 

I bought the element from surecal.co.uk.

There is also 12V option which i found after placing the order with surecal, so I didn't bother:

 

http://www.ebay.co.uk/itm/Water-Heater-Immersion-Element-Solar-Wind-12V-24V-600-watts-1-inch-NPT-/291157301496?pt=UK_Gadgets&var=&hash=item89711364cd

 

The timer acts as a on/off switch for the inverter & it's being set up daily accordingly to the weather forecast (it's bit of a pain but it seem to work well so far). At the beginning I was keeping an eye on it during the weekend to see the voltage drop during cloudy periods of the day but it was never really going bellow 12.9V.

 

I tried to use Outback dump load option but it didn't really work as I expected. I set it up the way that it would trigger the inverter when reaching floating stage, but it wasn't producing enough amps to cover current demand, even though it should.

[peterboat]

 

Hi Pete

 

What temperature have you set your water. We were thinking about 40c

Hi Julynian,

I have set mine at 60c its all the warnings about legionaires that stopped me using my 3 spare panels on it and only producing warm water, so I use this timer method now

 

Peter