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Connecting excess solar to water heater.


Neil T

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In brief - I have 750w of solar panels and want to add another 500w for which I have the roof space.

A Morning Star MPPT controller controls the charge into 500AH  of 2V AGM cells providing 12V to the boat.

 

Most of the time in summer my batteries are full and the controller is stopping further charge, even with the fridge and small freezer (Vitrifugo) on, loo fan going, lights, laptop etc.

I wish to pour all of the excess into my hot water tank which the controller is capable of doing.

 

At present the hot water comes from the heat exchanger of the BETA 43, or a 240V element.

If I switch on the inverter (Mastervolt) and simply flick the 240V heater element switch I draw 267A from the batteries..........  theoretically I could do that for 20 minutes and then turn off and let the solar recharge the considerable deficit in the batteries but I'm worried that eventually I'll damage them - especially if my mind wanders in that 20 minutes and I forget to turn off the heater........

 

Does anybody know of a good (great even) boat electrician who could help me or install the relevant equipment , including replacing the element in the tank with a 12V one? London area most convenient for me although I would travel for the right electrician.

Or should I get more batteries and just invert into the 240V element?

Help.

 

Thanks - all advice respectfully listened to.

 

BTW just in case I get 'why on earth do you want all that power' questions I am progressing in small steps towards 1.5 KW of solar and as electric a boat as I can have.

 

 

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Might not be much use, but I have what you are talking about on my house solar. The little gizzmo is called a 'solar iBoost'

https://www.cclcomponents.com/marlec-solar-iboost-solar-immersion-heater-control?gclid=EAIaIQobChMI9Jn38aeF3AIVwrTtCh1rQwiMEAQYASABEgKXvPD_BwE

any time I'm generating, but not using, the solar is diverted to the immersion heater, so I nearly always have hot water.

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33 minutes ago, Kev's Halcyon said:

Might not be much use, but I have what you are talking about on my house solar. The little gizzmo is called a 'solar iBoost'

https://www.cclcomponents.com/marlec-solar-iboost-solar-immersion-heater-control?gclid=EAIaIQobChMI9Jn38aeF3AIVwrTtCh1rQwiMEAQYASABEgKXvPD_BwE

any time I'm generating, but not using, the solar is diverted to the immersion heater, so I nearly always have hot water.

Looking at the description I don’t believe that can work on a 12V system.  

 

This question has been asked before and to the best of my knowledge there’s no simple automated way of achieving it. 

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You could try this 

https://www.bimblesolar.com/extras/dumpload

But you would need to establish if your controller can be setup to work with them. 

 

In a recent thread it was established that tracer bn controllers could not be used. However it might be possible that your morningstar controller could be used I would check with bimble first that this is the case 

 

I think, from memory, that one of the major downsides to doing this on a boat is the amount of cycling and switching that would take place between battery charging and water heating. It's possible with your 1500w this might be at an acceptable level. 

Edited by reg
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Well your first problem is that you are looking to power a 3Kw heater from 1.25Kw (Max) of solar. And that doesn't include the losses in your inverter and solar controller.

A 12v heater will not in itself reduce the current drawn. (Apart from removing the loss in the inverter.)

As a minimum you should consider a smaller immersion heater.

An alternative might be to use a phase angle controller to reduce the effective power of the heater, but I suspect you would be heading into uncharted territory regarding what the inverter would tolerate.

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After a bit of research I found this that looks like what you are aiming for.

He has a very simple way of running the 3Kw heater at a lower power, that the solar can drive.

I should have thought of this but have been retired too long! Brain is now in rest mode.

 

Should add that I dont think this is a job for your average electrician.

Also at the risk of telling you what you know the 12V heaters will require some heavy cabling.

A 12V 600W heater (As from Bimble) takes 50 Amps!

Whatever route you go care needs to be taken that the switching of power is done safely, or you could get a pretty big BANG!

 

Perhaps you should not be discouraged and if you sort it post back here and we can all copy! ?

 

Hope this helps

John

 

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Ah, Morningstar MPPT charge controller.  It doesn't get much better than those! 

Getting a lower powered 230v immersion heater shouldn't be too hard - Vetus do a nice low power one (link). 

 

Steve Timebeck (I think) at Denham Yacht Station might be worth chatting to if you're looking for an electrician near London. 

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Just a quick thanks to all you guys - I'm following up everything, and will for sure let you know what I come up with, although with the kids' summer holidays approaching it'll be the worst time of year for solar before I get there I suspect..  thanks again.  Neil

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