Immersun vs solar thermal

[BruceB]

I am being asked to quote for some solar pv, solar thermal and gshp on a listed building. The solar pv will be a TIC of 10kW. There is no requirement for baths/showers, just hot water for a kitchen. Although I will of course quote and probably fit whatever they want, with the advent of Immersun and the like I am inclined to suggest that they should save their money rather than install solar thermal, install a couple of extra pv panels instead in the space and just use electricity to heat the water. It will save the visual intrusion of solar thermal pipes on the external of the listed building or cutting through the historic fabric on the internal of the building. Even x3 immersuns for a 3 phase setup will be cheaper and simpler than a solar thermal system. Anyone else been through a similar thought process?

 

[Gavin A]

for water heating alone you'd only need 1 x immersun, as you'd just use the single phase that the immersion is connected to.

worth checking the balancing of the phases first, and potentially pulling the immersion out and onto a different phase if that phase is significantly more heavily loaded without the Immersion.

 

[BruceB]

The PV will generate on all 3 phases so a 3 phase immersion heater is probably best to make best use of the generation. I have one at home I use as a backup.

 

[yellowvanman]

Had a customer looking at this for a 3 phase system but there is nothing suitable yet.

Consider the following:
3kW being generated and exported on each phase - so each Immersun on each phase will divert 3kW to its relevant immersion. So the 9kW excess is being used up.
Now if the cooker/hob is on 1 of the phases and takes 6kW.
Immersun on the cooker phase turns off, but the other 2 keep going , so now you have 9kW generated but 12 kW being used, so you have to start using power from the grid - something you're trying to avoid!

So a real 3-phase solution is required - as opposed to 3 single phase solutions.

 

[BruceB]

If you have a 6kW cooker you may find it is capable of being wired to more than one phase by changing jumpers internally.

 

[yellowvanman]

The situation I was considering, is that the customer had a 10kW wind turbine and 7kW PV. Turbine came first and he had to get 3 phase installed, hence the fact that the house is only single phase.

I've have seen houses with 3 phase supplies but never seen any internal supply in 3 phase.

Figures used were only hypothical (?) anyway!

 

[Worcester]

Had a customer looking at this for a 3 phase system but there is nothing suitable yet.

Consider the following:
3kW being generated and exported on each phase - so each Immersun on each phase will divert 3kW to its relevant immersion. So the 9kW excess is being used up.
Now if the cooker/hob is on 1 of the phases and takes 6kW.
Immersun on the cooker phase turns off, but the other 2 keep going , so now you have 9kW generated but 12 kW being used, so you have to start using power from the grid - something you're trying to avoid!

So a real 3-phase solution is required - as opposed to 3 single phase solutions.

Even if the other phases are exporting, in your scenario with the 6kW load on a single phase, would they not be being charged for the 3kW import anyway? ....

 

[yellowvanman]

Even if the other phases are exporting, in your scenario with the 6kW load on a single phase, would they not be being charged for the 3kW import anyway? ....

Not if the Immersun was 3 phase and there was a 3 phase meter, as far as I understand!

 

[Worcester]

Time for some input from Andy at Sibert - I'll give him a call

 

[Gavin A]

Not if the Immersun was 3 phase and there was a 3 phase meter, as far as I understand!

I don't see how this is going to be right. The meter will read the import on the other 2 phases, and ignore any export on the phase that's exporting on most 3 phase meters I can think of.

possibly on an old rotary 3 phase meter that might not be the case, but tbh I'm struggling to think of situations I've seen these in place, I can only think of seeing 3 x single phase rotary meters for some reason, though I'm sure the 3 phase versions must have existed.

 

[Worcester]

Nor can I - i'm sure he'll be charged for the 3 kw he's importing on the single phase for the oven and it will 'ignore' the other two that are exporting.

Andy's recovering from a flight back from Singapore, claims it was work .... I'll speak to him over the weekend

 

[yellowvanman]

I don't see how this is going to be right. The meter will read the import on the other 2 phases, and ignore any export on the phase that's exporting on most 3 phase meters I can think of.

possibly on an old rotary 3 phase meter that might not be the case, but tbh I'm struggling to think of situations I've seen these in place, I can only think of seeing 3 x single phase rotary meters for some reason, though I'm sure the 3 phase versions must have existed.

Have been in contact with Lee (@ 4eco) and he 'sees' the problem with 3 individual Immersuns on each of the phases!

 

[Energetic]

Back to the OP, we are accredited for thermal and currently advising that the immersion control and PV is a better option than thermal.

Less servicing, less to go wrong, less intrusive and far better payback atm.

Can only really see thermal making sense at big commercial level at the proposed rhi tariff for domestic.

 

[Energetic]

Have been in contact with Lee (@ 4eco) and he 'sees' the problem with 3 individual Immersuns on each of the phases!

You need a 3phase cooker, the immersuns would work fine individually managing their phases and shouldn't affect the metering. With a 6kw 1pahse cooker you would import only on that phase the other two would be neutral-diverting to tank. The phases are metered individually.

Are you after a 3phase immersun with a single output?

 

[BruceB]

........ and currently advising that the immersion control and PV is a better option than thermal.

Less servicing, less to go wrong, less intrusive and far better payback atm.

Yes, that is my thinking.