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Heating water


Col_T

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We have a narrow-boat with hot water supplied by either engine or Mikuni diesel fired boiler, which is fine for our present 'holiday boating' pattern of use. However, we will soon be setting off on a series of 'mini-cruises', each of 4 to 6 weeks in length, and will be fitting about 500W of solar panels so that we don't need to run the engine every day to keep the batteries topped up. We are not power-hungry boaters - no TV, electric kettles, coffee-makers or hair-driers(!), and I estimate that we'll be using about 60Ah over-night (mainly the fridge) out of a 450Ah battery bank. The solar array should get the batteries recharged by mid-morning most days, and I'm thinking  of installing an immersion heater into the calorifier as an additional source of hot water, the idea being that the excess capacity of the solar panels can be busy warming / heating water whilst we are away from the boat, exploring the local area.

The options seem to be either a 240v immersion, which will require the Sterling 1500W modified sine wave inverter to be on, or a 12v immersion.

All / any advice and / or experience would be much appreciated.

 

Colin T.

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What Solar Controller you using?   Some have a PWM output that can be matched to a suitable Solid State Relay for driving a immersion for a varied output.   Using 12v immersion is prob best in this case as I've read reports PWM on a Inverter for this usage isn't good.

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54 minutes ago, Col_T said:

We have a narrow-boat with hot water supplied by either engine or Mikuni diesel fired boiler, which is fine for our present 'holiday boating' pattern of use. However, we will soon be setting off on a series of 'mini-cruises', each of 4 to 6 weeks in length, and will be fitting about 500W of solar panels so that we don't need to run the engine every day to keep the batteries topped up. We are not power-hungry boaters - no TV, electric kettles, coffee-makers or hair-driers(!), and I estimate that we'll be using about 60Ah over-night (mainly the fridge) out of a 450Ah battery bank. The solar array should get the batteries recharged by mid-morning most days, and I'm thinking  of installing an immersion heater into the calorifier as an additional source of hot water, the idea being that the excess capacity of the solar panels can be busy warming / heating water whilst we are away from the boat, exploring the local area.

The options seem to be either a 240v immersion, which will require the Sterling 1500W modified sine wave inverter to be on, or a 12v immersion.

All / any advice and / or experience would be much appreciated.

 

Colin T.

Immersion heaters even small 1kw ones use lots of power and to heat a decent sized cauliflower takes a long time. Doing it from solar wouldnt be my choice. Our engine run for only one hour whacks plenty of charge into the batteries and gives copious amounts of hot water and then the solar can fully charge and maintain the  batteries thereafter. Its very rare we stay in one place more than just overnight so today we moved a couple of miles and two locks and now have tank of hot water and nearly charged batteries. I suppose it depends on how efficient your systems are and how noisey.

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2 hours ago, Robbo said:

What Solar Controller you using?   Some have a PWM output that can be matched to a suitable Solid State Relay for driving a immersion for a varied output.   Using 12v immersion is prob best in this case as I've read reports PWM on a Inverter for this usage isn't good.

Thanks for this, @Robbo. The solar setup has yet to be specified, but will definitely include an MPPT charge controller, probably one of the Tracer family.

@mrsmelly, our travelling pattern, to date, has been very much like yours is now - motoring every day. However, we've been down to Bristol a couple of times and were lucky enough to find electricity bollards at the mooring site opposite the Great Britain that even had credit left on them! It seemed a shame to have to run the engine just to get hot water, and my guess is that electric bollards on the majority of the canal network are few and far between - as someone before me once said "you can't plug into to a hedge", hence the investigation into alternative ways of generating hot water.

I dare say someone will suggest a Whispergen, that can generate electricity and hot water at one and the same time, but I suspect those are even more rare than a hedge one can plug into!

Thanks for the opinions, chaps.

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I once made the mistake of leaving the immersion heater switched on after disconnecting the land line.

Drawing 100amps it didn't take long to seriously deplete the batteries.

I didn't make the same mistake again.

 

If you get 50amps 'spare' from the solar, the immersion is still going to draw 50amps from the batteries.

It will probably be using that for 2 hours + (depending on the size of the cauliflower)

I would seriously suggest not doing it - unless you know you have a large / huge amount of 'spare' Solar generation - and then I would make sure the immersion heater was on a timer socket for just a couple of hours - relying on memory to switch it off just doesn't work.

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1 hour ago, Col_T said:

Thanks for this, @Robbo. The solar setup has yet to be specified, but will definitely include an MPPT charge controller, probably one of the Tracer family.

It’s the output load relay control I meant by PWM not the controller type.  Controllers like the OutBack have a configurable load output and one option is PWM.  Which means it can lower the load output to what solar is available.

46 minutes ago, Alan de Enfield said:

I once made the mistake of leaving the immersion heater switched on after disconnecting the land line.

Drawing 100amps it didn't take long to seriously deplete the batteries.

I didn't make the same mistake again.

 

If you get 50amps 'spare' from the solar, the immersion is still going to draw 50amps from the batteries.

It will probably be using that for 2 hours + (depending on the size of the cauliflower)

I would seriously suggest not doing it - unless you know you have a large / huge amount of 'spare' Solar generation - and then I would make sure the immersion heater was on a timer socket for just a couple of hours - relying on memory to switch it off just doesn't work.

A basic solar controller can turn on the load when in float.  If there is not enough solar for the load it will not be in float mode so will turn off the immersion.

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Turning sunlight in to electricity with photovoltaic cells is not terribly efficient. Only 12% or so if I remember. Depends on the cells and is slowly improving. Directly heating the water with a solar collector is much more efficient. I have it on my boat. Trouble is every example I have seen, including mine, is a home made set up. No one makes a boat specific kit as far as I am aware. My solar collector gives me a calorifier full of hot water most days between May and September and on sunny days the months each side, including today. They are not common on boats though.

If you do run an immersion heater on solar generated electricity I would want it arranged so it only used excess power once the batteries were fully charged and not be allowed to draw on the batteries at all as per what Robbo describes.

Jen

Edited by Jen-in-Wellies
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1 minute ago, Boater Sam said:

Immersion heaters are landline devices, your alternators and solar really are not up to supplying enough power.

But you have a diesel fired heater, why not turn off the radiators and fire that up?

You can get 250watt 12v/240v immersion’s that are for this type of thing.

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4 hours ago, Col_T said:

.. the idea being that the excess capacity of the solar panels can be busy warming / heating water whilst we are away from the boat, exploring the local area.

MY REPLY (Sorry can't seem to insert text outside of quote on tablet) 

For this to work I would think you would need to have a decent size battery bank, fully charged and in a good state if health

. Scenario: Nice day, wander of to explore, 15 minutes later cloud comes our, sun drops, insufficient output from solar panel. Immersion heater sucks the life out of batteries at an alarming rate. Happens a couple of times and decent batteries recede beyond recovery. 

Personally I think this is a very bad idea, but please don't feel bad about my comments as I also had the same idea once and discovered it was a very bad idea

Even with the engine running the inverter soon, within a couple of minutes,  started to flash red low voltage warning light. 

Just to add I tried it with a 1kw heater, maybe you might have a bit more success with a 250w.

Simple test before you commit. 

Plug in a 250w electric  heater and run it on full power for a couple of hours using just using solar power, this should give you some idea of what to expect. Repeat this test a number of times and then decide yourself whether you want to commit long term.

Would be interested to know the outcome of this test. 

Edited by reg
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44 minutes ago, Robbo said:

You can get 250watt 12v/240v immersion’s that are for this type of thing.

Just wondering how long that would take to heat a full tank of water, my 1kw took well over an hour when connected to mains power. So the 250w would take upwards of 4 hours on mains power and I would think a lot longer, if it even achieved it, on solar power. 

Looks like the sort of nice gritty  calculation MTB might like to get his teeth into. I look forward with interest. 

 

Edited by reg
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39 minutes ago, Robbo said:

You can get 250watt 12v/240v immersion’s that are for this type of thing.

How long will a 250 watt immersion take to heat a decent sized cauliflower? and how much sun without shade do we REALY get in the UK. In reality immersions are for landlines/gennies etc. Running the boat engine for even only one and a half hours per day will give copious amounts of hot water and do the main bulk of battery charging for about £2 in diesel ish and its not much wear on the engine/s.

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1 minute ago, reg said:

Just wondering how long that would take to heat a full tank of water, my 1kw took well over an hour when connected to mains power. So the 250w would take upwards of 4 hours on mains power and I would think a lot longer, if it even achieved it, on solar power. 

 

If the batteries are charged by mid morning as the OP said, then they should be no issues taking 4hours to heat the water up?   It's only extra power that will go no where if not setup, so why not heat up the water, even if it's only a little it will just mean less diesel used if you need to heat up via another method.

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29 minutes ago, mrsmelly said:

heat a decent sized cauliflower

See I had to force myself not to say that. 

28 minutes ago, Robbo said:

It's only extra power that will go no where if not setup, so why not heat up the water, even if it's only a little

I believe I have read somewhere of the use of a water heating shunt that could be used to warm water using excess solar power, can't find details at moment and may be completely wrong. 

Eta

Discussion on this very topic at ybw helpfully reminded me that I read about it in Nigel Calder bible. 

http://www.ybw.com/forums/archive/index.php/t-169688.html

Edited by reg
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You may be better looking into a online gas water heater, most continuous cruisers swear by them.

I have 600W solar and on a nice day the batteries are indeed fairly full by midday. Once your batteries are over 85% getting charge in is slow, on a good day I get 25+ amps at first but by 11:00 the current is down to  10 amps and at 13:00 down to 5, only then can you say the batteries are full.  One day a week if lucky, building shadow, tree shadow, nice white clouds and big black ones seem to rule the other six days.

Edited by Detling
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3 hours ago, Detling said:

You may be better looking into a online gas water heater, most continuous cruisers swear by them.

I have 600W solar and on a nice day the batteries are indeed fairly full by midday. Once your batteries are over 85% getting charge in is slow, on a good day I get 25+ amps at first but by 11:00 the current is down to  10 amps and at 13:00 down to 5, only then can you say the batteries are full.  One day a week if lucky, building shadow, tree shadow, nice white clouds and big black ones seem to rule the other six days.

Yep instant gas heaters are the biz.

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Regardless of what voltage or what power your immersion heater is it is still going to require the same amount of energy Kwh to heat your water. a 1 Kw one will take 3 times as long as a standard 3Kw one and a 250 Watt one 12 times as long. You can Google how much energy is needed.

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As has been pointed out, if you want to use the sun to heat up hot water, it's far more effective (several times more efficient) to do this with a solar water heater (like you see on every roof in Greece) than using solar panels to produce electricity and then use this to heat the water. There must be plenty of suppliers for systems like this, but maybe not so many in the UK and there aren't many narrowboats in Greece...

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22 hours ago, Col_T said:

... and I'm thinking  of installing an immersion heater into the calorifier as an additional source of hot water, the idea being that the excess capacity of the solar panels can be busy warming / heating water whilst we are away from the boat, exploring the local area.

Whilst I may of said I don't think this is a good idea mainly due to the relatively small size of a boats solar array it doesn't mean that it isn't achievable. Came across this on the Bimble site

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

It looks like you could try out your idea relatively cheaply. 

300w water heater circa £26

http://www.bimblesolar.com/extras/dumpload/12v-300w-screw-in-water-heater

12v Split charge relay circa £16

http://www.bimblesolar.com/extras/dumpload/12v-200a-relay

So cost wise it might be worth playing with, although I won't be trying it. 

Only real downside I can think of is that in practical terms you would need to swap the heating element back to a mains powered element at the end if your touring season. 

Edited by reg
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It was the Bimble site that gave me the idea to be honest, @Reg. As for swapping between solar-powered and mains-powered immersion heaters, I wouldn't bother, to be honest. We don't have an immersion heater at all at the moment, and swapping between two would be just inviting leaks I reckon, particularly with my plumbing skills!

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1 hour ago, Col_T said:

It was the Bimble site that gave me the idea to be honest, @Reg. As for swapping between solar-powered and mains-powered immersion heaters, I wouldn't bother, to be honest. We don't have an immersion heater at all at the moment, and swapping between two would be just inviting leaks I reckon, particularly with my plumbing skills!

I could certainly see this working for a large solar array on a house but as I said gave my doubts with use on a narrowboat however I've started a separate thread on the use of the controllers  load terminals as I can see a use for the dump relay mentioned on Bimble site, so not a waste of time. 

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11 minutes ago, reg said:

I could certainly see this working for a large solar array on a house but as I said gave my doubts with use on a narrowboat however I've started a separate thread on the use of the controllers  load terminals as I can see a use for the dump relay mentioned on Bimble site, so not a waste of time. 

The system would work better on a vertical cauliflower the hot water is taken from the top.    On "Economy 7" type water tanks they have a additional low wattage immersion at the top for keeping the water hot during the day after been heated up overnight.

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2 minutes ago, Robbo said:

The system would work better on a vertical cauliflower the hot water is taken from the top.    On "Economy 7" type water tanks they have a additional low wattage immersion at the top for keeping the water hot during the day after been heated up overnight.

Good point for the modest outlay of £42 might be worth a try, possibly could be useful in slowing down the cooling process inherent in all cauliflowers. 

Unfortunately mine is horizontal so probably not worth the effort

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