Immersun (or other) cylinder/thermal store suggestion?

[Sumilkra]

Hi folks,

I know this is the Electricians forum and this may be more relevant to a plumbers forum, but I wondered if I could get some advice or suggestions from you guys.

We`ve recently had a 3.5KW solar PV system fitted and it's working a treat, and I spent a considerable amount of time on here reading the various threads regarding taking the export energy and using that for an immersion heater which sounds like a good idea as (at the moment) we`ll get 50% of generation as export payments anyway. The actual product choice I don't know yet, and burst fire vs phase angle stuff whilst very interesting is not something I have any expertise in so I won't comment on that until I`ve done some more research into what those differences actually mean

So to my question, unfortunately I don't have a hot water cylinder in the house - all our hot water is provided by a combi-boiler which (I`m pretty sure) means I need an unvented *something*. I`ve been looking around at cylinders and thermal stores, but wondered what you guys have found most efficient for heating in this way (if any... maybe it's just the principal)?

I`m leaning towards a thermal store (accumulator) at the moment with backup from the combi so it can do hot water and maybe preheat the central heating somehow too, but a lot I have seen are more geared toward solar thermal rather than PV. I`m more interested in what would work better with something like an immersun or similar if you folks have any suggestions?

Cheers,

Matt

 

[oliver s]

Hi Matt

I think the best thing to do would be to install a unvented cylinder to pre heat your hot water from the PV / immersun unit. You will need to check the spec of your combi as only a few accept pre heated water. They need to be able to modulate depending on the temp of the incoming water

Oliver

 

[Worcester]

Some combi's can take preheated water, so you could simply add a small electric direct unvented cylinder before the combi and use a controller to mix / blend. - The Grant CombiSOL is your solution, Solar Water Heating. Combine Your Existing Heating With A Grant Solar Heating Solution | Grant UK it is specifically designed to work with Solar Thermal systems and hydraulically this is no different.

If your combi can't take preheated water, your other ooption is to effectively convert your combi to a system boiler.

Very simple when you know what you;re doing, you'll need a G3 certified heating engineer to supply and install it.

 

[Sumilkra]

Thanks guys, appreciate your time. I`m liking the look of that CombiSOL - will do some reading up on that and see what it's capable of.

Next job, work out where the hell I can put a cylinder :-D

Cheers,

Matt

 

[The Solar King]

Also have a look at this as a solution.
Simple solar heating with solar heat store
Can be purchased without the solar coil and just an immersion element specifically for use with a device such as the Immersun.

One caveat in all this is economics and payback. If you are on mains gas, you will only save the cost of the gas you would have used to heat the water, no more than £0.05/kwh. If you are on oil or LPG, the savings are greater. If your boiler is relatively new and to the latest efficiency levels you would be ill advised to swap it out for a system boiler, you won't make your money back. If it is an old inefficient combi, it may be worthwhile. You have also got to factor in the cost of the hot water cylinder and fitment. If it is unvented, the person fitting needs to hold qualification in this. Again the savings you make may not justify the expenditure.

One other thought. If and when you end up with a smart meter, you may well be paid for the exact amount of energy exported rather than a deemed amount. The current export tariff is £0.0477/kWh or about what you pay for mains gas. This being the case, there is then no benefit in fitting a device like an Immersun.

Also be aware that viable storage of PV power is on the horizon, certainly within the life of your equipment. At a cost of £0.15/kWh for electricity, there is no way you would want to divert it to heat water where you save less than £0.05/kWh.

Make sure you do your sums.

 

[Sumilkra]

Thanks for that - solid advice there. My boiler is only 3 years old so plenty of life in the old girl yet, and you make a good point about the cost of gas so I`ll need to work things out.

I suppose my main purpose was to make as much use of the PV system as possible - to be fair they`ve only been up a couple of weeks and I have developed an unhealthy obsession with pvoutput.org so may not be thinking as clearly as I should yet

I did look at battery systems but at present they are expensive and space hungry, plus I`d have to swap out my spanking new inverter for one that can couple with a charging unit so I was thinking a water "battery" might be a good idea... that said unvented cylinders don't come cheap and as you point out the returns will take a considerable time to recoup the investment, then when smart meters come along and the legislation changes around export rates I would end up potentially worse off in the long run.

Food for thought indeed - some maths and patience required methinks - thanks again

 

[digital48]

...when smart meters come along and the legislation changes around export rates I would end up potentially worse off in the long run.

But, presumably, those already with PV and already receiving FiT payments will continue to receive the 50% assumed export payment as our contracts are fixed for 25 years?

 

[The Solar King]

With a 4kW system, you are unlikely to use much more than 35% of generated energy you may be better off being metered. With a smaller system you will use proportionally more, but it is unusual to get above 50%, unless you have lots of strategies in place to be able to optimise self use during the day.

 

[Worcester]

But, presumably, those already with PV and already receiving FiT payments will continue to receive the 50% assumed export payment as our contracts are fixed for 25 years?

Yes, and your contract says that it is deemed only whilst they aren't measuring export.... there is no need for any legislative change this has been there from the beginning - deemed isn't a right.

You cannot be forced to have a Smart meter - they are optional, hence you can opt out - there is a whole thread that I started on this about 12 months ago.