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Using Immersun with PV Solar

I have a 4kW PV solar system ......... it has been suggested that I install an Immersun unit ...

If I understand the concept right, it monitors any unused PV power (i.e. that would be exported to the grid) Using that to power an immersion heater, being sold as a from of using HW storage in effect a storage battery for PV energy.

It would be slightly more complex as I have a thermal store and underfloor heating not a DHW tank, but ultimately it is heating water.

Anybody used such a device ........ my thermal store is set with no timer - nice and simple if stat on store call for heat then boiler fires heating up entire contents on the. So in basic terms store is always kept up to temp.

I would need some way of stopping boiler operating if there is capability of using PV power. Perhaps as simple as putting immersion heater on it's own stat set to higher kick-in temp compared to boiler stat ... so immersion would operate first.

The problem would be overnight the boiler would (due to no PV) heat up store on boiler ... so may not be much drop during day to be gained form immersion.

Anyone use such a unit ?

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Reply to
rick
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The idea is that the input to the immersion heater us controlled so it is s lightly less than the output of the PV panels.

So on a dull day if your panels are generating say 1500w then the device en sures that the immersion heater only takes 1500w. Not 1500w from the PV and the remaining 1500w from the mains.

Naturally the it takes longer to heat the water up but it's all done on fr ee electricity.

Last time I looked they cost around £200 installed. Dunno how much they a re to fit yourself.

They go into the immersion heater circuit with a sensor clipped onto the AC output from the inverter.

Reply to
harry

Because there is no such thing as 'free electricity' (unless you happen to be using a kite in a thunderstorm of course)?

You certainly can't be talking about 'free' from a UK FIT subsidised PV system because I'm paying towards that (not that anyone asked me if that was ok)?

Oh, I take a solar panel camping (where such things make some sense as I generally only go camping in the summer) and it cost me 50 quid. I worked out your share of that is about 2p so could you post that to me straight away please. ;-)

Cheers, T i m

Reply to
T i m

Yes they work very well indeed. The cost payback calculations are not good however if you buy and pay for installation so decide more on grounds of technical interest rather than money saving. I built my own unit based on online designs and so cost was minimal and technical interest very high.

You will need to modify your DHW boiler timings If my thermal store is below the thermostatic mixer setting ie 50 degrees first thing in the morning, I let boiler run for 20 minutes for morning ablutions. At around 5pm when we will need water for the evening meal etc then if the temperature is less than 50C I will let the boiler run for up to 30 minutes.

In practise the boiler rarely runs from late March until October. On good days my store gets up to 93 degrees when I bottle out and switch on a heat dump system.

Reply to
Bob Minchin

You'd be using the most expensive energy to do a job that can be done by very cheap energy. There lies the issue. Spend the 200 on some solarthermal kit instead.

NT

Reply to
tabbypurr

I have an older version of one of these:

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Today it has put 2.15Kw into the immersion heater. This is the third full year that I've had it. Usually it generates enough hot water that I don't need the gas on for hot water from the beginning of May until the beginning of September. This year it's given me hot water most days in September as well. It cost me £295 fitted and I reckon it saves about £100 a year. Results would be different for a larger household. In theory I should get some benefit during the winter, when some of the hot water used for the central heating is provided by the solar but I can't quantify that.

Reply to
Peter Johnson

Very True NT. I've just looked at my logs for the last few days. I have

16sqm of PV and about 2sqm of solar thermal. The excess PV diverted to the tank is within a few % of the capture from the ST system. PV is fundamentally far far less efficient than ST.
Reply to
Bob Minchin

Bob care to share your info & design ? (direct if easier)

I have no DHW timings .... it is currently set fairly simply ......... Thermal store stat calls for heat ... boiler burns ... so store always at full temp - no off period.

Only real extra bit is that once you start DHW draw off boiler pump runs (without boiler fire up) to provide de-stratification function within the store.

When I first installed system and just hooked up temporary I could not figure out how water would go cold after only a few minutes ... was due to no de-stratification pump run.

Would need to monitor 'unused' power 'export' ..(which thankfully Tim is already funding) If the power is being used would not want immersion to be taking any mains power.

Be good to know how you achieved this.

Reply to
rick

Ahh no ... you would be using Solar PV energy .. which is free

Reply to
rick

did you just use standard 1 x immersion in a DHW tank. ?

I'm looking today .. for several Hrs my array was putting up more than

2.5kW at a time we were not using it, so heating the water might be a good idea.
Reply to
rick

I don't want to go down Solar Thermal direction ... too difficult to include in with existing house design.

Reply to
rick

Thiefing B's are actually paid for the electricity they nominally export even if they never export a mWHr by selfishly using it all themselves.

Reply to
Dave Liquorice

On Thursday, 1 October 2015 19:36:35 UTC+1, rick wrote: NT:

perhaps you jest

NT

Reply to
tabbypurr

replied directly to your email addy Rick

Reply to
Bob Minchin

Still pontificating/drivelling on about a topic you know FA about? It's not actually possible to use all the PV power generated oneself. Especially if you are working away from home.

One can only use so much hot water. Which is why these devices are not economical to fit. (Except possibly as a DIY thing)

Often they are used as an inducement to buy the PV installation in the first place. I'll get one when the price falls sufficiently to make it worthwhile.

Reply to
harry

All forms of electricity production are subsidised shit-fer-brains. I can see your fixation is affecting you mentally. You may need medication, go and see the quack.

Reply to
harry

PV price to install had dropped by almost 30% ... plus panel efficiency now much better and guaranteed for 25 years ........ also I usd 330W panels to get full 4kW install

Reply to
rick

And charge so many electric cars?

Only because the extra paid for the deemed export is only a few more per unit on top of the the 40 odd pence/unit you get paid for actual generation.

So over the last couple of years how much have you been deemed to have exported and how much have you actually exported?

Reply to
Dave Liquorice

It's getting there then.

At what final efficiency do we know IIO?

Any idea what the predicted payback time would be on a straight 'electricity saved' calculation, rather than some FIT compensated version (that I didn't get a say over). ;-(

Cheers, T i m

Reply to
T i m

Yes. I should have said that my PV is 4Kw.

Reply to
Peter Johnson

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