Using solar (and attached direct) cylinders as heat stores

[chris watkins]

Water as a storage medium is good but not good enough I am afraid, you would just need to store to much of it.
They are looking at gas to liquid (& back) systems as I understand it, as changing state you can store much more.

 

[Sparkgap]

Looks similar to a wet (heating only) system I installed years ago at an outdoor centre. Place was off-grid and previously relied on a generator which had been replaced by a wind turbine and solar PV feeding battery storage & inverters with the genny as backup. Existing turbine controls dumped excess energy into a large resistor heating up the locality once the batteries were charged. We fitted a 1000L buffer tank with 4kW immersion heaters (8x500W) switched by the existing controls so instead of wasting energy it was used to preheat the tank. Heating was weather compensated with 3-way valve. According to the site manager the boiler hardly ran at times in spring and autumn.
Water might not be the best material for thermal storage but it's the easiest to install without getting expensive.

 

[OffshoreGas]

Hi Greg,

The problem with your idea of storing energy as heat is basic thermodynamics and efficiencies.

No process is 100% efficient, every time you convert one form of energy to another there are losses, think of your car for example. You put fuel in the tank and want to convert it to movement, but you also get waste energy such as heat/noise. Your proposed system has lots of heat exchanges which would be inefficient.

The other problem is heat loss, if you stand a cup of tea on your desk it would cool in say 2 hrs to be the same temperature as the room. If you store hot water in a tank you've got the same problem. You can add insulation it suffers from diminishing returns, the first 50mm may reduce heat flow by 75% but if you want to reduce it by another 15% you may have to have 20mm of insulation.

Litium ion batteries work well for energy storage in the medium term due to low self discharge. This may be worth looking at instead of heat?

 

[oz-plumber]

The solar on the system you have shown will have very minimal impact on heating the cylinder.
Generally the solar pump will only switch on when the temperature of the water in the collectors is 2 degrees above the stored water temperature in the cylinder.
It may come on in winter, but it will be switching on and off all the time.
As for running the radiator panels off a coil in the cylinder, that would also be very hit and miss also.

You could introduce more refrigeration principles into your desired system, but as soon as you introduce refrigeration ( heat pump ) systems, costs start exploding.

I understand what you are trying to do, I have been looking into environmental system for years - can't find anything that will return the outlay before some of the system components die.
eg: 10 years - you would never see a financial benefit out of installing the system

 

[Stigster]

If you are saying that storing heat in water for later use in heating then fine. Why? What is wrong with the idea? If you are saying that there is a problem with the execution, what?
You're pros.
Can you please specify what the issue is?
Thank-you.

Long post alert!

Here in Guernsey a local company used make a product called Ecostor. They are no longer available after they never achieved popularity and had some performance issues in day to day use.

It was a large unvented cylinder with a six kilowatt immersion, a coil for connecting either an oil boiler or heat pump and a second coil for solar. There was a heat exchanger mounted on the outside of the unit to provide hot water. The cylinder was heated by the solar coil when conditions were right with the immersion as a backup and also as I mentioned connected to a boiler or heat pump.

The water in the cylinder was not what came out of your taps, but rather a thermal store. This stored water was pumped both through the heat exchanger for on demand hot water and through the rads to do the central heating.

The problem was that you more or less had to choose whether you have a warm house or hot water. If you came home from work and put the heating on, good luck getting enough hot water for a family to use in the evening as the heat was lost too quickly to the room heating. Likewise, long showers or big baths would deplete the heat store and your heating would not perform adequately. If used very carefully and in a specific way with timings it would work. Likewise for very small properties like flats, it worked ok.

There was never enough stored heat to do both jobs and the immersions ended up being used most of the time which kind of defeated the purpose of the system. Sorry for the long post but these things were never liked here and are no longer available as far as I know. I've got one here in the workshop as a demo model but I've just finished ripping it out as our apprentices really don't work on them enough to dedicate the space any longer.

 

[chris watkins]

Thermal stores are still available & still have there place but as said before the amount of hot water (heat energy) you would need to store to provide for domestic heating & HW often means they are impractical.

 

[Sharp Point]

Great products, in behemoth sizes. Akvaterm thermal stores.

:: In English

 

[GregKaye]

Long post alert!

Here in Guernsey a local company used make a product called Ecostor. They are no longer available after they never achieved popularity and had some performance issues in day to day use.

It was a large unvented cylinder with a six kilowatt immersion, a coil for connecting either an oil boiler or heat pump and a second coil for solar. There was a heat exchanger mounted on the outside of the unit to provide hot water. The cylinder was heated by the solar coil when conditions were right with the immersion as a backup and also as I mentioned connected to a boiler or heat pump.

The water in the cylinder was not what came out of your taps, but rather a thermal store. This stored water was pumped both through the heat exchanger for on demand hot water and through the rads to do the central heating.

The problem was that you more or less had to choose whether you have a warm house or hot water. If you came home from work and put the heating on, good luck getting enough hot water for a family to use in the evening as the heat was lost too quickly to the room heating. Likewise, long showers or big baths would deplete the heat store and your heating would not perform adequately. If used very carefully and in a specific way with timings it would work. Likewise for very small properties like flats, it worked ok.

There was never enough stored heat to do both jobs and the immersions ended up being used most of the time which kind of defeated the purpose of the system. Sorry for the long post but these things were never liked here and are no longer available as far as I know. I've got one here in the workshop as a demo model but I've just finished ripping it out as our apprentices really don't work on them enough to dedicate the space any longer.

I'd imagine the people developing it thought this will change everything. At this stage I think things like some buffer tank use and use of thermal stores are mainly for people with real ecological commitment.
I'd imagine that a conventional design of system with one of those devices added in would work.
If people actually stopped using energy when renewables were in short supply then the government might think again about all its expensive non renewable investment.
Thanks for th einfo

 

[Welder]

So you’re trying to build an inter-seasonal thermal store?
You’ll see some on that forum, that are behemoth and buried in the ground with differing types of heat exchangers to heat ufh/ rads/ greenhouses

And hot water.

THere are plenty of people who are doing similar things. One thing I would say to you now is that having pressurised solar panels is a nightmare. THere are plenty of examples now of open vented solar systems are they prove far more reliable than closed systems. Google a guy called Eric Hawkins (he's on Twitter I know). He'll be a good resource as he has an open vented heat recovery system for cooling PV panels so they are more effecient.

 

[chris watkins]

Dave, can I ask why they are a problem & are we talking about directly filled or heat pipes?
I teach solar but must confess haven't got a much practical experience, so always interested.

 

[Sharp Point]

Yes, why are they problematic?

 

[Welder]

Dave, can I ask why they are a problem & are we talking about directly filled or heat pipes?
I teach solar but must confess haven't got a much practical experience, so always interested.

My honest answer is I dont know. My experience of solar has only been to ultimately rip em out as they have leaked like sieves. Three instances of calling designers/maintainers back to check, service & refill again and again. Custs all got fed up & ripped em out (including p1ss poorly insulated thermal stores) and instead put in well insulated & controlled UVCs. Last one has halved her gas bill.

From what I know, the pressurisation is a pivotal problem. Ive had vessels fail so they obvs cause leaks as systems go mental. Ive heard vessels don't last too long in such agressive & hostile environs. Thinking about it, no std rubber diaphragm will stand 120c for too long and each was a std htg type vessel.

 

[Welder]

Thermal stores are still available & still have there place but as said before the amount of hot water (heat energy) you would need to store to provide for domestic heating & HW often means they are impractical.

Remember water is actually a rubbish medium for heat transfer as it's shc is so high. We'd be better off using a different medium but it'd be more expensive and less 'simple' to service.

 

[Sharp Point]

Thinking about it, no std rubber diaphragm will stand 120c for too long and each was a std htg type vessel.

If the vessel was installed in a non stagnation area, the vessel would see no more heat than a standard vessel. Poor installers screwing it up for the customer

 

[Welder]

If the vessel was installed in a non stagnation area, the vessel would see no more heat than a standard vessel. Poor installers screwing it up for the customer

What's a non stagnation area? #IgnoranceIsBliss

 

[Sharp Point]

What's a non stagnation area? #IgnoranceIsBliss

Lol, I’m sure I don’t need to tell you😉

 

[chris watkins]

Or use intermediate vessel, but it is more likely no maintenance on the vessel caused problems.

 

[Welder]

Lol, I’m sure I don’t need to tell you😉

Oh yes you do - please.

 

[Welder]

Or use intermediate vessel, but it is more likely no maintenance on the vessel caused problems.

Thing is, with an open vented system there are no vessels to cause those problems! Regardless, even for systems just ten years old the energy they consumed via their thermal store aspect was simply huge as they were all so poorly controlled.

I do see the benefit of solar but I'd never entertain a thermal store neither would I entertain a sealed/pressurised system. Of course what I do not understand is how one would 'lose' the heat if it wasn't a thermal store. Perhaps it needs to be, is a bigger metalic thermal mass heated using solar but designed more like nuclear fuel rods calculated to absorb huge amounts which can then be lowered into a medium to heat our water. Then we go back full circle to the shc of water and it being a b1tch to heat up...

I need a beer!

 

[chris watkins]

I need a beer!

Your overheating Dave😀