solar heating and second cylinder

[LeoMagill]

Possibly a daft question but what the hell...
I am considering fitting thermal solar panels for hot water but being out at work during daylight hours it seems to me that once the tank is hot the rest goes to waste, is there any reason why a second cylinder couldn't be plumbed inline with the inlet to the gas boiler so when it does kick in it has a heat store already there so uses less gas, my idea is solar heat into main water tank upstairs then out to second cylinder downstairs then back to solar collector, if the main cylinder is cold it won't heat the second one (which wont be any colder than house temp anyway), when main cylinder is hot the water coming out from the coil will be hot and heat the secondary one giving the boiler a free heat store, effectively the closed system will just be higher capacity.
The extra heat store could be utilised for either re-heating the main tank after a bath or pumped round the heating system, will be used with a new condenser boiler.
Am I on to something or just about to piddle on an elecric fence???

 

[ALEC1]

solar can supply hot water in peak summer, but the rest of the year it just raises the water temperature from which the boiler has to do the rest of the work..

thats why the best system is one tank with two coils, solar doing the bottom of the tank...the boiler the rest..

 

[dcawkwell]

Solar thermal hot water is a complete waste of money in this country
and will never pay for itself.

Might be worth it if you are rigging up something yourself from an old
radiator but otherwise forget the idea.

Save your money and buy more insulation.

 

[Agile]

Solar has no payback unless energy continues to rise at 15% or more each year.

But its a nice feeling to have hot water for free during the summer.

Two tanks are the cheapest way to implement solar but rarely used as they are so much cheaper than an over priced twin coil tank.

Put "Solar" on to anything and it increases the cost by about 50%!

Tony

 

[ALEC1]

the fact is that solar is only worth it if you use alot of hotwater....so think young families, gyms, hotels etc...

for singles/couples its not really worth the investment...


the extra it cost in most cases would be better spent on insulation in my opinion...

 

[LeoMagill]

the fact is that solar is only worth it if you use alot of hotwater....so think young families, gyms, hotels etc...

for singles/couples its not really worth the investment...


the extra it cost in most cases would be better spent on insulation in my opinion...

Thats why I'm thinking of ways to store the spare and feed it back into the system somewhere.

 

[ALEC1]

well a solar contribution to heating has no place in the UK

its a good idea but not very practical the reason is that solar collectors are more efficient when the temperature difference between the collectors and the water at the bottom of the tank is greatest...so unless you make a corresponding investment in panels you won't really gain anything..storing luke warm water has limited use...

 

[RigidRaider]

They are probably right but that doesn't mean you shouldn't do it and enjoy the project. Read about mine here:

www.diynot.com/forums/viewtopic.php?t=255833

 

[ALEC1]

Its a difficult one for people to get their heads round... but a system working almost al the time and rarely getting the cylinder up to temperature can be contributing more that one that shuts down and dumps heat. In terms of ROI you want the system working all the time, once shut down because the cylinder is at temperature it earns nothing....

of court other inefficiencies need to be removed, such as having two tanks...which has higher heat losses to make a system effective...

 

[LeoMagill]

Thanks for all the input, I am talking about proper glass vacuum tube collectors here and not a black painted radiator by the way , the second tank wouldn't be a heat loss as it would be out of the system until the main tank is hot so any losses from it would be from what would otherwise be wasted anyway by the system not running.(thermostat & motorised valve in mind)
Surely even a tankfull of lukewarm water uses less gas to heat up than a tankfull of cold mains temperature water, likewise if the gas boiler draws in luke warm water instead of cold for the radiators it still uses less gas to get going.

 

[ALEC1]

solar can be used to raise the return temperature to a gas boiler...but with condensing boilers there is little point...and if you haven't got a condensing boiler that would be the better investment.

If you have compensation controls you may get returns of around 25-30c, but with on-of controls you won't have that sort of return temperature except at start up


two separate tanks have much higher losses than one twin coil one.. for obvious reasons..

 

[Norcon]

solar can be used to raise the return temperature to a gas boiler...but with condensing boilers there is little point

Less gas will be burned if solar has done part of the job and that will be more efficient than a boiler retreiving a small amount of heat through condensing.
Heated far enough and the boiler stays OFF which I think is the most efficient you can get.
Apart from never having the boiler manufactured in the first place.

 

[DeltaT2]

Solar thermal hot water is a complete waste of money in this country
and will never pay for itself.

Might be worth it if you are rigging up something yourself from an old
radiator but otherwise forget the idea.

Save your money and buy more insulation.

What a load of rubbish!! We've been fitting Thermal Solar for the last 25 years here in Scotland, most of these systems have never, ever needed any repair of any kind!! Unlike your £13K+ PV systems pish poor performance & an inverter that'll pack in 5 years. Many homes with TS systems do not heat any water during Summer months and will pre-heat hot water all year round.

EV tube panels can be bought for under £400, it's as cheap as chips to install & a system that'll last a lifetime..............ROI is the best of any of the Greenwash products.

A thermal siphoning system has no moving parts, so nothing to break done, so only a poorly informed idoit would say 'it's a waste of money in this country'!!

 

[dcawkwell]

£400 pounds for the tubes alone before any installation.

Ouch that's an awful lot of hot water to pay that back.

It will never happen.

 

[Modokon]

Solar thermal hot water is a complete waste of money in this country
and will never pay for itself.

Might be worth it if you are rigging up something yourself from an old
radiator but otherwise forget the idea.

Save your money and buy more insulation.

What a load of rubbish!! We've been fitting Thermal Solar for the last 25 years here in Scotland, most of these systems have never, ever needed any repair of any kind!! Unlike your £13K+ PV systems pish poor performance & an inverter that'll pack in 5 years. Many homes with TS systems do not heat any water during Summer months and will pre-heat hot water all year round.

EV tube panels can be bought for under £400, it's as cheap as chips to install & a system that'll last a lifetime..............ROI is the best of any of the Greenwash products.

A thermal siphoning system has no moving parts, so nothing to break done, so only a poorly informed idoit would say 'it's a waste of money in this country'!!

So how much would your average installation into an unvented (with solar coil pre-plumbed already) be?