Considering Heatstore and PV Diverter

[Ferdinand]

I am looking at adding a Heatstore and an Immersion type device whilst I am redoing my two bathrooms this summer.

 

The position is:

 

• Currently I have a big solar array (10kWh, generating approx 550 kWh per year due to E/W alignment and a measure of shading)
• No Immersion diverter as I have no convenient heat sink.
• Big combi boiler (Worcester Bosch Classic Range - the biggest model). Not relevant, but modulates down to 35C. The boiler is quite new - 2-3 years.
• Combined UFH/radiator downstairs/upstairs heating driven from the combi. But no buffer tank in the heating system.
• 2 x elecric shower, 1 x shower, bath etc driven off the gas.
• No problems on space in the Consumer Unit etc.
• Most of the plumbing is in the right places, and I do not plan t be digging too many holes in walls apart from the bathrooms.
• Current bills are more or less £1000-1200 a year - half gas, half electric.
• Showers are used everyday, bath several times a week. Mainly use the gas powered shower.

 

I am thinking about:

 

• Adding a heatstore and immersion or i-Boost, to make better use of the solar.
• Putting in provision for a buffer in the ufh, which willrequire inserting a couples of pipe runs in one of the bathroom refurbs.
• I can see that in the future I may wish to replace the boiler with a ASHP - space is available for that.

 

Questions:

 

• Can I use a heat store in a straightforward way in this arrangement? eg can one be used to preheat water to the combi like a Sunamp?
• I am aware that a Divert-device will be about £500 installed, and should potentially give me £150-200 of electricity a year (perhaps), which would replace perhaps £60-75 of gas.
• What bill am I facing for a potential heat store? I estimate I would want one that would do 1-2 days usage. There are currently 2 here but it is potentially a house with 3-4 or a family.
• Am I missing any tricks? Really I am trying to think about what can usefully be done at the same time as bathrooms.

 

All comments will be gratefully received, as thus is not an area where I have good gut-feel?

 

(Potentially I can move some solar to the South to get better performance, but that requires me to get a car-port past the authorities - which will not happen any time very soon)

Cheers

 

Ferdinand

Edited May 19, 2019 by Ferdinand

[ragg987]

26 minutes ago, Ferdinand said:

Currently I have a big solar array (10kWh, generating approx 550 kWh per year due to E/W alignment and a measure of shading)

I believe you have dropped a zero here - 1kWp of PV has the potential of delivering about 1MWh per year in optimum conditions, England.

 

Not clear what problem you are trying to solve here.

 

Is it: I want maximise my use of generated solar?

• As you have mains gas / combi, as you say you will need a water store if you go that route, seems counter to the gas combi capability, plus your savings will be small compared to investment
• An option might be to get battery storage, you would need to do the calculations on return, but prices seem to be dropping

Is it: I want to future-proof and think about ASHP?

• An ASHP will require a DHW store, so maybe install it now and use the immersion diverter as a stepping-stone to a future ASHP. But see above, it will not pay back on its own merits. And presumably your combi is good for another 10+ years so why bother now?
• I guess you could use the solar-heated water as input to the combi, maybe others can comment here
• Another option might be to have a cold-water coil in the tank that pre-heats the water to supply the combi

Edited May 19, 2019 by ragg987

[Alexphd1]

I remember something about the worcester cdi's didnt like preheated water but this was years ago. 

A esbe 1 inch solar diverter is approx £120, £500 installed seams a bit high.

[Ferdinand]

Indeed 10kWp of solar and 5500kWh of energy.

 

I am doing bathrooms, so I am thinking about what else would be appropriate at the same time.

 

It may be that I in fact do nothing now about from a little provisioning.

 

Ferdinand

Edited May 19, 2019 by Ferdinand

[Ed Davies]

1 hour ago, ragg987 said:

2 hours ago, Ferdinand said:

Currently I have a big solar array (10kWh, generating approx 550 kWh per year due to E/W alignment and a measure of shading)

I believe you have dropped a zero here - 1kWp of PV has the potential of delivering about 1MWh per year in optimum conditions, England.

 

I, too, hope you've dropped a zero here. Typically you'd expect something like 800 to a 1000 hours worth of generation per year in the UK for a decent installation depending on location and orientation. For a somewhat sub-optimal one to get 550 hours (so giving 5500 kWh) might be reasonable; 55 hours would be stunningly awful.

[Ferdinand]

3 hours ago, ragg987 said:

I believe you have dropped a zero here - 1kWp of PV has the potential of delivering about 1MWh per year in optimum conditions, England.

 

Not clear what problem you are trying to solve here.

 

Is it: I want maximise my use of generated solar?

• As you have mains gas / combi, as you say you will need a water store if you go that route, seems counter to the gas combi capability, plus your savings will be small compared to investment
• An option might be to get battery storage, you would need to do the calculations on return, but prices seem to be dropping

Is it: I want to future-proof and think about ASHP?

• An ASHP will require a DHW store, so maybe install it now and use the immersion diverter as a stepping-stone to a future ASHP. But see above, it will not pay back on its own merits. And presumably your combi is good for another 10+ years so why bother now?
• I guess you could use the solar-heated water as input to the combi, maybe others can comment here
• Another option might be to have a cold-water coil in the tank that pre-heats the water to supply the combi

 

Excellent focusing question - thanks. It is more exploring whether there is an opportunity for me at this point, rather than trying to solve a problem. It is really - can I reduce my bills further at this point, in a way which is at least marginally justifiable on the numbers (I am always happy to take a slight hit for energy economy)?

 

(Bills have just gone back up again as I am now running heating more for a parent who is heading towards mid-80s. When we moved in in 2013 I knocked them down by a 35-40% by various usual means, but got a small shock over the last 2 quarters as extra usage has taken them part way back again.)

 

I do not think batteries are anywhee near viable for me yet - especially as I do not get eg power cuts and so on, and I am wedded to diesel for my car for some years (towing) - just having bought a new one.

 

For now, it would be a 24 hr capacity (ish) heat store linked to the hot water only, with the water preheating done via a heat exchanger. That is it would have at least one coil plus an immersion heater or two, and the mixing valve, boiling prevention gubbins and the rest.

 

Reflecting, I think I would be happy to lay out perhaps £1000 for the type of saving I mentioned including the Immersun equivalent, and I do not think that will happen unless a suitable Heat Store comes up for a couple of hundred.

So I think it is probably futureproof and wait until one is taken out by a Sunamp Enthusiast, and have it on the "ebay swoop" or "returned to seller" list, and provision where necessary. I will also take a look at Shower Waste HR devices, but these may be tight for my setting, and still seem to be seriously overpriced.

 

I also need to provision for a buffer tank, which does not currently I think exist in my ufh system, unless it is in hiding.

 

 

Cheers all.

 

Ferdinand

 

 

 

 

 

 

 

 

[PeterW]

20 minutes ago, Ferdinand said:

Reflecting, I think I would be happy to lay out perhaps £1000 for the type of saving I mentioned including the Immersun equivalent, and I do not think that will happen unless a suitable Heat Store comes up for a couple of hundred.

 

Unlikely however .... in your situation I would use 3 or 4 smaller cylinders such as pretty standard 140 litre hot water tanks. You can get these pretty cheap, but you can daisy chain these - and their immersions - to an immersun or similar. Also easier to source and to plumb in and locate. 

[Ferdinand]

Thanks for tecpomments, all.

 

It looks like provision for the future and watch this space, for now, then.

 

Ferdinand