Hello from the West Midlands

[cojmh]

The system is about 15 years old, and it does have a twin-coil cylinder, although we bought it so long ago that the bottom coil is just like the top one. I think nowadays twin-coil cylinders have the bottom one split into 4 parallel tubes to increase the heat transfer. The gas boiler heats the top coil when or if needed (normal cylinder stat near the bottom of the cylinder coil.) It often doesn't cut in for weeks on end in the summer.

There is an over-heat sensor near the top of the cylinder (1/3 of the way down the top boiler-fed coil.) It has only ever run 8 hours in anger (one time when we were away on holiday) and if needed the controller turns on the central heating (water circuit) pump but isolates the boiler power supply. Heat therefore is taken to the boiler, which works "backwards" and hot air convects up the flue. Some people have a motorised valve to open a heat-dump radiator but my experience is that motorised valves are the one thing that dies on our system. The last thing you want is for it not to work the one day the tank is getting near boiling...

I have put a by-passable thermostatic mixing valve on the bathroom taps for when the grandchildren are here in the summer, as between the equinoxes a day of full sun but little draw-off gets the water dangerously hot. I could set the upper temperature limit lower, but it would mean paying for electricity to throw away heat!
A

That all makes sense. Do you mind me asking the following:

1. How big is your solar water tank and how many people would it cover for average use?
2. How much of the year do you think the solar thermal works?

I have been trying to work out how much PV I would need to heat the water tank - currently using a a 300 litre tank (for 5 people) and temperature raise of 70 degrees (so that I can roughly equate it to a solar thermal setup getting to 90 degrees on warm days) - my calculations are coming out at circa 25KWh ..... which I would need to double my existing setup to get that much regularly during the summer .....

So I am still a bit torn. I do believe the PV will be easier and more reliable which is a positive in its own right .... possibly cheaper too .... but I am also mindful of the absolute limit I have for roof space .... so need to make sure it all counts for as much as possible.

So the jury is still out at the moment ..... need to think about it more!

[cojmh]

If I were you here is what I'd do:
- Solar Diverter for DHW/Hot Tub. I'd go for an Eddi.
- More Batteries.
- PV on extension directly charging batteries via charge-controller.
- PV on garage directly charging batteries via charge-controller.

Eddi, hub and Harvi ordered this morning.

My house is getting rewired in May - so this is very fortunate I found out about all of this, this month! I am able to get the additional wiring put in place for the two immersion heaters.

Reading up on what people are managing to do with the storage heaters I am now beginning to wonder if I should have an additional 2.5mm cable run to each room - so in the future I can put in storage heaters without having to try and retrofit it to the house!

[Countrypaul]

...

Reading up on what people are managing to do with the storage heaters I am now beginning to wonder if I should have an additional 2.5mm cable run to each room - so in the future I can put in storage heaters without having to try and retrofit it to the house!

Definitely imho - I had several "spares" installed when we renovated (including full rewire) but somehow most of them have already been used. leave them labelled both ends and not connected to anything if need be (not sure if ho that wrks out with a different electrician).

[Stinsy]

If I were you here is what I'd do:
- Solar Diverter for DHW/Hot Tub. I'd go for an Eddi.
- More Batteries.
- PV on extension directly charging batteries via charge-controller.
- PV on garage directly charging batteries via charge-controller.

Eddi, hub and Harvi ordered this morning.

My house is getting rewired in May - so this is very fortunate I found out about all of this, this month! I am able to get the additional wiring put in place for the two immersion heaters.

Reading up on what people are managing to do with the storage heaters I am now beginning to wonder if I should have an additional 2.5mm cable run to each room - so in the future I can put in storage heaters without having to try and retrofit it to the house!

Definitely worth doing the wiring for a SH or two while you're doing the rewire. A 20A radial in 2.5 wired from CU to where the Eddi might go then to where the SH might go is a good idea. Think also about electric UFH in the kitchen/bathroom, this can also be controlled by a diverter. If you have a total of over 10kWp of solar then there'll be plenty of occasions where you'll be generating a decent amount of power at the same time as you are requiring saceheating. Good also for using/storing cheap overnight electric.

[cojmh]

Definitely imho - I had several "spares" installed when we renovated (including full rewire) but somehow most of them have already been used. leave them labelled both ends and not connected to anything if need be (not sure if ho that wrks out with a different electrician).

Thankfully my friend is an electrician ... So an initial chat with him when I can get hold of him should solve the issue ...

Something I am trying to work out is whether each storage heater needs 1 cable or 2. I don't have experience of these sorts of heaters and there seems to be conflicting info online.

Are there any benefits to the more modern storage heaters or should I look to get older second hand units and refurbish them?

Thanks for all the help

[cojmh]

Definitely worth doing the wiring for a SH or two while you're doing the rewire. A 20A radial in 2.5 wired from CU to where the Eddi might go then to where the SH might go is a good idea. Think also about electric UFH in the kitchen/bathroom, this can also be controlled by a diverter. If you have a total of over 10kWp of solar then there'll be plenty of occasions where you'll be generating a decent amount of power at the same time as you are requiring saceheating. Good also for using/storing cheap overnight electric.

Electric underfloor for the bathroom is an interesting thought.

How do you work out space heater requirements? Is it a case of having one per traditional radiator?

Sorry if the questions are basic .... If there are useful resources that cover this then I would be grateful for a link.

Thanks

[Stig]

Something I am trying to work out is whether each storage heater needs 1 cable or 2. I don't have experience of these sorts of heaters and there seems to be conflicting info online.

Are there any benefits to the more modern storage heaters or should I look to get older second hand units and refurbish them?

Thanks for all the help

I guess two cables would be one for Economy7 and one for daytime? I've just wired one to my storage heater (old one from Ebay). Beware of modern storage heaters that have so-called 'smart' controls, if you're wiring it up to a PV diverter then you want something basic with no electronics in it.

[Stinsy]

Re storage heaters, no need to make it complicated! So long as you have a TRV in the room with the storage heater the radiator on the central heating will adjust for the additional heat source. This can be a basic "analogue" one such as a TRV4 or a smart system such as Tado/Hive.

There are several ways to wire up a SH. IMO the best way is to site the solar diverter next to your CU (or somewhere else unobtrusive) then run a wire from there to the heating side of the SH and connect up the control side of the SH to your normal sockets circuit. You can connect the SH to a single power supply and rely on the onboard timer for traditional Ecconomy7 usage, but that isn't what we're doing here!

[Joeboy]

Something I am trying to work out is whether each storage heater needs 1 cable or 2. I don't have experience of these sorts of heaters and there seems to be conflicting info online.

Are there any benefits to the more modern storage heaters or should I look to get older second hand units and refurbish them?

Thanks for all the help

I guess two cables would be one for Economy7 and one for daytime? I've just wired one to my storage heater (old one from Ebay). Beware of modern storage heaters that have so-called 'smart' controls, if you're wiring it up to a PV diverter then you want something basic with no electronics in it.

As stig says, one cable is to the 24hr peak rate and the other is to the off peak storage. Essentially an on demand resistive heater or a set of 850W storage elements.

I have both types with our without the 24hr resistive elements. I have also found that 2x850W storage elements is good to bring the background temp up. Three elements and you Really feel the rise in a room. Welcome onboard!

All my storage heaters are on Hive smart plugs so I can set timers to coincide with TOU tariff low cost window or I can manual override specific heaters and bring them on if we have a huge solar day. Works well along with the woodstove and the GCH remains off.

[cojmh]

I guess two cables would be one for Economy7 and one for daytime? I've just wired one to my storage heater (old one from Ebay). Beware of modern storage heaters that have so-called 'smart' controls, if you're wiring it up to a PV diverter then you want something basic with no electronics in it.

Thanks - that makes sense .... So I would just need a single cable as I expect to use Storage Heaters once I can get onto a cheap / cheaper than gas over night tariff.

I need to play with the solar diverter but I imagine that the primary output of the Eddi will be to the HWT and the secondary output will switchable between the hot tub in the summer and a storage heater in the winter .... But just what I am thinking at the moment.

I intend to install the Eddi right under the consumer units .... Looks like I am going to potentially have three (main house with heavy loads, EPS load and then storage heaters)

But all of that is subject to change as I get my head around everything a little more