solar water heating

[bobbingabout]

Hello forgive me if this is mentioned elsewhere but I could not find it if it is.

 

Currently my hot water comes from the engine via a calorifier it's a twin coil so I plan to link up to the heating system when I fit a stove with a back boiler in the spring as all plumbing rads and expantion tank are already in place.

I was originally going to put a solar water heater in line as a friend made his own and found it very successfull but it would have ment disconnecting either the engine feed or the stove feed or having an elaborate system of valves and stopcocks so that I was not heating the world via the solar collector on the roof.

So plan b as I've recently upgraded my solar panels I have been left with three 190 watt 36 volt panels that are sitting redundent one that has broken glass due to a poor tree felling exorcise.

My plan is to put two of these panels in series 70 volt total and connect them to a suitable heating element for the calorifier so sunny days will result in water heating which is what needed for the summer as stove will not be running.

I could just link up the element to my current solar controllers load function so when the batteries are charged the eccess would go in to water heating but I wanted to keep the systems separate in case something went wrong and discharged my bank.

That why I've decided to use two of the currently redundant panels to keep the systems seperate.

 

Now my question is (sorry if this has been long winded) what's the best way to go about it do I use a second controller and it's load function or the more simpler way just connect panels direct to the heating element with a inline stat to cut power when water temp is achieved in my head the panels direct with a stat seems the cheapest and simplest way to go about it.

The thing I'm lacking is the know how so if anyone is currently using this system or can throw any ideas my way as how to wire this up it would be awsome.

 

Cheers gary

 

[SamKingfisher]

It's not complicated to stop the calorifier heating the outside world. Just need a solenoid valve which defaults to off wired on same circuit as pump.

 

Hot water panels are much more efficient than PV.

 

Not trying to put you off, just saying.

[bobbingabout]

Totally agree that hot water panels would be a way more efficient way to go but for my situation having the solar panels already sitting there makes it a cheap option plus with my limited diy skills it would be way more simple placing cables rather then the epic plumbing that would be involved.

[SamKingfisher]

Fair enough. It's pretty simple plumbing though, can use hosepipe for much of it if you wanted.

 

Say you get 300w from your pv on a sunny day. Certainly going to make a difference, but unlikely to give actually hot water. Pretty hopeless on cloudy days but then so is evac tube collection.

 

 

Ps with what is basically a trickle heat source, make sure calorifier is really well insulated.

[bobbingabout]

Although it would be nice to get piping hot water from this system I'm realistic in what I hope to gain if it can be warmed enough for a shower and washing up then that would be great and the tank is big enough to shower using just the hot water and not the cold so the water temps would not need to be as high as it would if I was using the cold tap as well

[BEngo]

The biggest problem is likely to be getting a suitable immersion heater. If you want to do without a controller then 36 or 72v is not exactly a common operating voltage for immersions.

 

There are 12v and 24V available, though some seem to be for fish tanks, which won't be designed to work in hot water. A quick google doesn't find a matching power rating either, though I'm not sure how much that matters- it might depend on the controller.

 

 

Even if you find one 190W (on a good day) won't heat a lot of water very quickly and unless the cylinder/calorifier is really well insulated you will lose heat as fast as you put it in, giving you lukewarm water at best.

N

[smileypete]

If you connect the 190W 36V panels in series directly to a 240V 3kW immersion, you should get about 350W in optimal full sun conditions, bit less otherwise eg if the panels are off-angle or hot from the sun.

 

By happy coincidence the resistance of the 240V 3kW immersion gets you close to the 'max power point' of the panels.

 

ETA if it's a BIG upright cylinder, a shorter element MAY work better days with limited sun.

 

cheers, Pete.

~smpt~

Edited December 6, 2013 by smileypete

[ditchcrawler]

If you connect the 190W 36V panels in series directly to a 240V 3kW immersion, you should get about 350W in optimal full sun conditions, bit less otherwise eg if the panels are off-angle or hot from the sun.

 

By happy coincidence the resistance of the 240V 3kW immersion gets you close to the 'max power point' of the panels.

 

ETA if it's a BIG upright cylinder, a shorter element MAY work better days with limited sun.

 

cheers, Pete.

~smpt~

And you could add the solar water panels on later.

[bobbingabout]

Thanks for the feedback I've had a hunt around and found a guy that makes custom elements in varying voltages and watts so the options are put the panels in parallel so they stay 36 volts with 300 watt element or repair third pannel and put them in series and have a 120 volt element 500 watt or put a solar controller in the mix and go for 12 volts sooooooo many options.

I found a water heating calculator on the interweb. I had to guess water tank size of 40 litres which I would imagine should not be to far away I will check when I can get under the bed.

Using a 300 element to heat 40 litres of water from 8c to 60c would take 8 hours which is actually better then I hoped as on long summer days this should be easily achievable add to it that the tank will never really be run out of all hot water then it will have a higher starting temp in the morning so greater temps should be achievable so on the sums and our great British summers it all looks viable.

 

Pete you blew my mind on the 240 volt element my brain just could not cope any chance you could explain it for me as if you would to a cave man so I can understand cheers fella

 

Gary

[peterboat]

Been here done this one not really worth the effort then someone reminded me of legenaires disease from not heating the water hot enough. I had a 12v 300w element run from 300w of spare panels (I have 1200w of panels for battery charging) I think you would do better with an instant water heater

 

Peter

[bobbingabout]

Thanks peterboat would you mind telling me how you wired up your system and were your panels flat or tilted and what sort of results did you find many thank

 

Gary

[peterboat]

For the hot water it was 3 100w 18v open circuit palels wired in parallel straight to the immersion heater panels tilted into the sun. It produced warm water enough for a quick shower wasnt worth the effort to be honest Next year its back to 240v immersion heater and all power diverted to this after charging of batteries completed

 

Peter

[Paul's Nulife4-2]

Hi gang,

I love ideas & innovations,but at present i am firmly of the opinion that at this latitude,a solar water heating system will not be a low cost,efficient,practical or therefor viable way to provide sufficient hot water in any useful quantities, if one wher available for year round use,or even 8 month use,say beginning of March to end of September,I would be happy to get one.

It's a shame,but I believe its as much a geographical problem as a material problem. At the moment !. But one day it might happen.

Edited December 7, 2013 by Paul's Nulife4-2

[smileypete]

Pete you blew my mind on the 240 volt element my brain just could not cope any chance you could explain it for me as if you would to a cave man so I can understand cheers fella

Only a modern caveman that knows a bit about volts, amps and ohms There's some excellent info about it in the online course notes of the Tony Brooks training web site:

 

http://www.tb-training.co.uk/MarineE01.html#BASIC%20ELECTRICS

 

Very roughly speaking the 240V is like a high pressure that pushes a greater flow of current through the immersion element giving 3000W of power.

 

But the solar panel voltage is like a much lower pressure which pushes a much lesser flow of current through the immersion element giving about 350W of power.

 

Needless to say when connecting a mains immersion element to solar panels, the element must be completely disconnected from any mains voltage connection whatsoever.

 

If you'd like try an experiment, on a sunny day connect the solar panels in series to the L and N plug pins of a 2kW or 3kW electric kettle with croc clips, then see how well it heats up.

 

cheers, Pete.

~smpt~

Edited December 7, 2013 by smileypete