Solar PV for heating

You don't need batteries or expensive gadget. The solar is producing electricity which is fed into your consumer unit to power anything electrical as normal, be mad not to be using it for anything else.

Have you thought about PV and thermal combined

I know nothing about them myself, but if you have either a plumbing or electrical background it could be an exciting DIY project.

Wow - that's a pretty unique and interesting problem DTP. I'd echo what Jonathan and graememk have mentioned, but I'd also come at it with a slight different viewpoint for you to think about. It sounds naff, but ultimately you need to decide what the goals/priorities are. Is it in heating the water, saving energy or cutting down on your fuel bill - or a mixture of all three :-)

If the "only" thing that you care about is heating the water then you can't beat those evacuated tubes. They capture as mentioned about 50% of the suns energy, meaning that per sq meter on your roof they'll do a better job than the panels (~20%). You being a plumber you can sort most of that work yourself.

The reason why you don't see them installed much anymore is that over the past 10 years, the prices of panels has gone through the floor where a 5Kwp system would have cost €20K a decade ago....it now cost 1/3 of that. So people then started to think, why heat just water when you can slap a load of these lower efficient (but reasonably cheap now) PV panels on your roof and power your xBox and Sky TV box .... in addition to heating the immersion.

Failing that.....with your problem I'd be thinking some form of heat pump is the way to go. You get 2-3x times the heating power from a heat pump from the energy put in, meaning if you need 100Kwhr to heat the tank, then with a HP you could cut that down to 40-50Kwhr. Ok, now that's still not a trivial problem to power, but you've made some serious inroads into the problem

Some other thoughts. Most inverters max out at 6Kw, so if you had a few immersion coils, you'd only be able to run 2 x 3kw which would max out a inverter. You could also go 3 phase bringing you to 11Kw, but that's a whole different ball game.

I don't know about them (the evacuated tubes) as I don't have them installed, so I can't say definitively how they perform in dull cloudy days, but if you get a good sunny day, you could heat that tank up pretty well. Then it will be a question of the insulation that you have on the tank. If it's top notch, you'll be able to hold that heat/energy for 24 hrs with only minimal losses (maybe 20-30%)?

The comment about 10-15 panels barely making a dent. 10 panels would be about 3.7Kwp and 15 would be about 5.5Kwp. I guess it goes back to the "why heat 2000L of water"? What's its use? If it's solely for heating, then it's unlikely you need it in summer - where solar PV energy is best, and that brings us back to the original thoughts I have myself about the goals here. Ultimately whatever you capture on the roof via PV should be seen in the context of the whole house, including the 2000L tank. If the PV electricity is going into the tank or going into the house, it's energy that your not having to pay for which goes towards paying back the solar installation.

Still reckon your heating solution of the 2000L is best served by a solar PV installation possibly driving a Heat pump. It's the "best" way to cut down on the energy required. You may still have to use the boiler/stove, but it would have substantially less work to do. Maybe heating from 40C to it's final temp rather than 20C to the final temp.

Unfortunately, it's a question that comes up (fairly regularly) on the forums and it's just not really possible for solar PV to supply enough energy to heat your house in winter, unless you spent north of €20-30K I reckon on panels and have a mini-solar farm out your back yard. To give you some context of why this is true.... here is my actual generation of 14 panels (5.3Kwp) for November, December and January just gone.

You can see in December I generated 58 units. Or approx 2 units a day on average. To heat your 2000L tank, you would be taking somewhere in the region of 50-80Kwhr a day. (depending on the starting/ending temps). So you can see the shortfall. You might be able to get the temperature up a bit from it's 15C-20C starting point, but you'll never have enough power captured from the sun in the dark months to fully heat it.

In March and to take this specific march which is outstanding, then yes, you could make a serious dent into that heating requirement with Solar, but then we are getting into the time of the year where heating is less likely to be needed, so your actual benifit is minimalized.

I know that's not the answer that you/most people (including myself) want to hear. I was also thinking similar that solar PV could get me some heating in the winter, but heating lots of water takes a huge amount of energy.

That said, solar PV is still a great way in reducing your energy needs, I'd encourage you to have a think about it even for non-heating reasons.