Solar PV, hot water, combi boilers and storage heaters

[minimutly]

The KISS in me says all these valves could be trouble. I am wondering whether a stand alone system would be better - ie mixer taps for cold and boiler heated water, and a seperate tap for electrically heated. Shower would be a problem though.
Binning the combi is also an option....

 

[waddycall]

Why not use a cylinder that’s heated by the solar and also the heating side of the combi boiler. Use the hot outlet from the combi boiler to supply a draw off close to the combi and supply the other draw offs with water from the cylinder.
I’m a heating engineer and often come across over complicated systems that someone’s dreamt up 10 or years ago and is now falling to bits, not working properly and potentially dangerous either due to legionella or risk of overheating/bursting. Stick with your KISS approach!
Keeping it simple will also aid any engineer in the future who may need to fault find/repair.

 

[minimutly]

Why not use a cylinder that’s heated by the solar and also the heating side of the combi boiler. Use the hot outlet from the combi boiler to supply a draw off close to the combi and supply the other draw offs with water from the cylinder.
I’m a heating engineer and often come across over complicated systems that someone’s dreamt up 10 or years ago and is now falling to bits, not working properly and potentially dangerous either due to legionella or risk of overheating/bursting. Stick with your KISS approach!
Keeping it simple will also aid any engineer in the future who may need to fault find/repair.

Now this has been suggested by a local plumber, but really, untill now I didn't know you could "ignore" the Dhw outlet on a combi. It has become option 2. Option 1 is to install an unvented stainless tank on the feed to the dhw inlet on the boiler. All the issues about legionaires are moot, since the solar pv in summer, and a timed override in the winter will boost the tank temperature. The boiler is a wooster bosch, I'll check the inlet pipework to the heat exchanger, if it's not plastic then I think this is doable. I may fit a new stat on the tank to bring the boiler on below 40 deg on dhw, but this could bena manual operation I think.

 

[Gareth J]

Regarding the diverters, if you too want a secondary output like your daughter's, get a normally open thermostat (other way round to the usual) you can then flip diverted power away to a second dump load when the tank is up to temp.

Regarding storage heaters, you could probably bodge a modern unit to let it's digital controls and gubbins be fed by a proper 220V supply but feed the element with divertered power. Not sure on the safety of such surgery though!

Now, it gets to the point where you really don't want more heat in the house but sensible in shoulder months

 

[minimutly]

Regarding the diverters, if you too want a secondary output like your daughter's, get a normally open thermostat (other way round to the usual) you can then flip diverted power away to a second dump load when the tank is up to temp.

Regarding storage heaters, you could probably bodge a modern unit to let it's digital controls and gubbins be fed by a proper 220V supply but feed the element with divertered power. Not sure on the safety of such surgery though!

Now, it gets to the point where you really don't want more heat in the house but sensible in shoulder months

Summer months you want hot water, shoulder months you want hot water and heat, winter you get scraps - except for cold clear days.

I have toyed with buying a modern controllable storage heater and taking it to bits - but surely to god you'd think the suppliers would be on to this? It seems not though, no more than the boiler suppliers.

 

[waddycall]

Unless you’ve done so already you might find it interesting to calculate the actual cost of heating the actual amount of hot water you use by different methods/fuels and compare that to installation, maintenance, repair costs etc.

 

[waddycall]

untill now I didn't know you could "ignore" the Dhw outlet on a combi.

I’ve seen a few installations with combis not connected to the hot water. I’ve seen one gas combi with a tap below it for testing and nothing’s else!

 

[minimutly]

Unless you’ve done so already you might find it interesting to calculate the actual cost of heating the actual amount of hot water you use by different methods/fuels and compare that to installation, maintenance, repair costs etc.

The tank is free, nearly new unit removed, foc. Maintenance? As in what? Repair? Well that includes what as an extra? An immersion heater? Everything else she has.

 

[waddycall]

The tank is free, nearly new unit removed, foc. Maintenance? As in what? Repair? Well that includes what as an extra? An immersion heater? Everything else she has.

Well if it’s unvented then it “should” be serviced annually by an unvented qualified engineer. They rarely are though.
Recently calculated costs of solar hot water for a a friends new build. They decided it wasn’t worth the additional installation costs.

 

[Gareth J]

Summer months you want hot water, shoulder months you want hot water and heat, winter you get scraps - except for cold clear days.

I have toyed with buying a modern controllable storage heater and taking it to bits - but surely to god you'd think the suppliers would be on to this? It seems not though, no more than the boiler suppliers.

I think it's because the market would be pretty small and the returns not that great. Especially if trying to displace fossil fuel heating.

 

[minimutly]

Well if it’s unvented then it “should” be serviced annually by an unvented qualified engineer. They rarely are though.
Recently calculated costs of solar hot water for a a friends new build. They decided it wasn’t worth the additional installation costs.

That's interesting. How do you service an unvented cylinder?

 

[minimutly]

I think it's because the market would be pretty small and the returns not that great. Especially if trying to displace fossil fuel heating.

Well how many people with pv would maybe make the choice - if it was there and they knew about it? I would buy one, plus 1 for my daughter. That's 100% of people I know. You have to understand how poor the payment you get for export Vs the cost of import - 10p a unit difference.
And yes - displacing oil @40p a litre at "old prices"

 

[waddycall]

That's interesting. How do you service an unvented cylinder?

Check the pressure relief valve and temp and pressure relief valve. Check the discharge pipe is clear, runs ok etc. Check water pressure and flow, check working and limit stats, check expansion vessel and recharge/replace as required. Check immersion, check operation of two port limit valve. Only ever checked commercial installations myself. Don’t think many domestic ones get done.

 

[minimutly]

I stand to be corrected, but none I know of. Some of those checks would be apparent in operation, but appreciate the safety stuff should be done.

 

[Matchless]

I have some new, unused solar hot water panels for sale, cannot remember how many, Wolf, German I think, actually sold them to a mate to heat his pool in France but decided he did not need the extra heat, they are still in Essex, I kept six to heat my pool but life keeps getting in the way!

 

[gaz1]

Check the pressure relief valve and temp and pressure relief valve. Check the discharge pipe is clear, runs ok etc. Check water pressure and flow, check working and limit stats, check expansion vessel and recharge/replace as required. Check immersion, check operation of two port limit valve. Only ever checked commercial installations myself. Don’t think many domestic ones get done.

first 2 points is check them but replace them if faulty they are the main items to stop that tank exploding apart

as goes for extra heating wood stoves or oil stoves do produce the heat as a top up to any system out there

domestic ones should be checked yearly but owners dont want to pay the yearly charge had one recently not even serviced in 14 years of running it since it was installed

 

[Wedg1e]

I keep thinking about panelling my garage roof with solar HW units; as I'm not overlooked the 30' x 10' flat roof can spend almost all day sunlit. Some kind of diverter to let the rads keep the house warm while I'm at work in the winter would stop the combi kicking in and wasting gas heating an empty house.
I perused a couple of 'DIY' solar energy websites that suggested how to build panels using 8x4 alloy sheeting and small-bore hose as a start but never took it any further.

 

[minimutly]

first 2 points is check them but replace them if faulty they are the main items to stop that tank exploding apart

as goes for extra heating wood stoves or oil stoves do produce the heat as a top up to any system out there

domestic ones should be checked yearly but owners dont want to pay the yearly charge had one recently not even serviced in 14 years of running it since it was installed

I'm surprised the insurace companies don't ask for records?

 

[waddycall]

I'm surprised the insurace companies don't ask for records?

I’m sure they would if it went pop.

 

[Gareth J]

Well how many people with pv would maybe make the choice - if it was there and they knew about it? I would buy one, plus 1 for my daughter. That's 100% of people I know. You have to understand how poor the payment you get for export Vs the cost of import - 10p a unit difference.
And yes - displacing oil @40p a litre at "old prices"

Do a back of the envelope calculation. Think you might find it'd take a long time to pay back a £400?? Heater. Oil at old prices used to work out at about 6ppkwh. You get about the same for export if you're on the octopus agile tarriff.

Even if you don't get anything for export, it's hard to justify. Worth messing about with second hand stuff and some cheap relays but a bigger upfront cost would put most off in what is not a huge market anyway.

If you have wet heating anyway, a thermal store is the way to go.

Alternatively, if you have anything that can only use proper 220v AC, if you can get that to come on only when it's sunny to displace ~15ppkwh electric, there are bigger savings.

You can get alternative diverters like your (iboost?) That fire a relay if export exceeds a set value. Good for air conditioners dehumidifiers, pumps, motors, electronics etc.

Consider putting fridges/freezers on a smart plug so they turn off for a few hours in the morning/evening and push their usage into middle of day and off-peak nighttime.

If you're really keen on utilising own generation and not too worried about the economics, battery storage might be worth looking into.

P.S; I'm not anti your idea. I currently have 3x diverters and a combination of heat loads which all work quite nicely.