thermal store and solar panels

[safronsue]

does anyone have this combination? I am thinking this may be the ideal set up for us. I believe it could be used i.n conjunction with a stove with a back boiler. I would be interested to hear what people have to say about what they paid for their thermal store and how big it is and how it actually works out.

[safronsue]

thanks for your detailed and interesting response.
We really need to talk to an engineer about ins and outs and sizes and all but i am guessing we are ideally set up as our wood burner is semi basement and we have a huge roof with plenty of storage space nearby.
PV systems are expensive here. about 25,000 euros for our setup. maybe more now. greek government in no position to offer grants...although tbf there was one before the crunch.
We are wondering if a locally made thermal store would be possible to cut costs so may well take you up on the offer of advice from your hands on hubby!
Also thinking of a locally made clip in boiler for the hunter herald stove, How complicated can they be??! ....but that's another post :)
thanks again. sue

[Zech]

Having picked the brains of SusieGee's husband, we have a system very similar to theirs, i.e. solar panels and wood burning stove both heating a thermal store, which provides heat for both underfloor heating and hot water

There's one point where I went against conventional wisdom, though, and that's on "bigger is better." The bigger the store, the more energy you can store in it, but the more energy it will take to get it up to temperature. For some systems, e.g. underfloor heating, it may not matter if the water is only lukewarm, but for others, e.g. hot water to the taps, you'll probably want it hotter. Stores are usually designed to 'stratify' so that you get hotter water at the top and cooler water lower down, but I've heard that this can be a bit temperamental, so I didn't want to rely on it.

I calculated the size of our store based on what we need to get out of it: Heat the house for a couple of hours in the morning, plus one shower. After that, we can light the fire to heat it up again. Our store is 350 litres and, though the system is only half finished (we don't have the solar panels installed yet, which reduces the effective size of the store because there's a solar loop full of air. On the other hand, the shower is not yet connected to the hot water system and still runs on electricity), it works pretty much as designed.

The main reason, as far as I can tell, for having the biggest store possible, is to absorb all the heat being generated without overheating. This isn't really an issue for us but with solar panels in Greece, you could easily get too much heat. It is essential that you have somewhere for the heat to escape to. We have a radiator in the bathroom - it's supposed to be on all the time, but our plumber was kind enough to fit valves so it doesn't shed heat constantly.

There are decisions to be made with this type of system about whether each heat exchange (water being heated up or giving heat off) is direct or indirect. We have four exchanges: Stove and solar providing heat, and underfloor heating and hot water taking it out. Our stove heats the water in the store directly, which means that it's the same water in the store as in the boiler on the back of the stove. The solar panels will heat indirectly, meaning there's a coil in the store through which water from the panels will flow. The underfloor heating is heated directly, i.e. same water in the store as in the underfloor pipes (except that there's a clever bit to send the water round and round the pipes if it's too hot, until in cools down then more hot is added in) and the hot water to the taps is heated indirectly, by sending mains water through a coil in the store. This means that we get mains pressure hot water and we don't have to worry about having lukewarm water sitting around breeding Legionnaires disease then coming out of the taps.

A note on thermosyphoning systems: Even if this wasn't a requirement (and I'm not sure it is in the UK - one plumber certainly tried to persuade us to have a pumped system), I wouldn't be happy relying on a pump to take heat from the stove to the store. If you have a power cut, you have to put the fire out! We have a thermosyphoned system with the store on the same level as the stove. I was surprised that this would work, but if you have a roughly circular pipe run, the hot water will rise up out of the back of the stove creating a current round the loop, with cooler water sinking out of the bottom of the store and returning along the lower pipe to the stove. It does work. The only downside is that it also goes backwards. When there's hot water in the store and the stove is cold, the hot water heads from store to stove. Regulations apparently prohibit any kind of obstruction in this system at all (in which case I'm not entirely sure how pumped systems are allowed. Very confusing) so we can't have a valve to stop the water flowing backwards. You might want to consider this sort of arrangement especially if you go for a very large store. The larger the store, the stronger the floor supporting it needs to be, so you might be happier with it on the ground floor.

[The Riff-Raff Element]

This is basically the set up we have - 300 litre store combined with solar panels and a back boiler on the stove. It does require a bit of management to get best results. As I type, all the heat from the back-boiler is going into the tank to make hot water for showers: in a little while I'll go and open one valve and close another to keep that water in the tank and put the stove into the rads. When & if it brightens up enough for the panels to make a meaningful contribution, I'll feed that into the rads. In other words, this is a good arrangement for those who are around the house!

[Zech]

Ours is more automated than Jon's in terms of where the heat goes (no need to open and close valves manually) but we do have to tend the fire a lot of the time, especially when it's really cold (at the moment we're not lighting it until about 6pm) so as he said, it is necessary to be around the house quite a lot.

A thought about back boilers that may not have occurred to you: They reduce the amount of heat that the stove puts into the room. This struck me yesterday when we visited our neighbours. They have a small stove with no back boiler that heats the room much more than our big stove with boiler, because the boiler takes most of the heat away into the tank. A clip-in boiler probably wouldn't make as much difference, but I expect you'd still notice it.

[The Riff-Raff Element]

Rachel's point is a very good one. I leave the stove turned into the tank with the radiators closed overnight. When I get up I stoke up the fire to make sure there is hot water for the kiddies, then isolate the tank and open up the rads. There's a temperature gauge on the front of the oven and that craters when I do this.

[safronsue]

with these snippets i am gleaning more and more info. It's striking me more and more how this country NEEDS this knowledge so desperately it's not true. how is all this stuff just not generally implemented??! astounding when you think about it.

[Odsox]

Another item to add to the mix
If you live in a windy part of the world you can get a wind turbine to power an immersion heater in your thermal store.
All you need is the turbine and a DC immersion heater, nothing else, no controllers, and on a windy day you could be injecting a kilowatt or so of free heat into the system.

[red]

the set up we plan on at the end is a wood fired esse, contributing to a thermal store, with solar tubes also adding their bit. and a gas boiler for the times we have flu etc and dont have the energy to fill up the stove with logs.


so far we have the thermal store , the economical gas boiler, the old gas rayburn plumbed into the system and are getting quotes for a new roof as it seems sensible to replace that first.

[solarwind]

Another item to add to the mix
If you live in a windy part of the world you can get a wind turbine to power an immersion heater in your thermal store.
All you need is the turbine and a DC immersion heater, nothing else, no controllers, and on a windy day you could be injecting a kilowatt or so of free heat into the system.

Not sure it's quite as simple as that, an immersion heater of useful wattage permanently connected to a wind turbine is likely to prevent the rotor from starting and achieving it's design speed. (electromagnetic braking)

[safronsue]

the mechanics may or may not be simple but variations of the theme have to be the way to go for greece. when it gets its thinking head back on.

[velacreations]

we have a big thermal store for our hot water system. It's 1300 l, and it stays around 130F year round. We use it for domestic hot water and for radiant floor heating in the winter. We have the tank is a large insulted box, with r-60 insulation all the way around. For the panels, we have 2 big panels, 8 ft by 4 ft each. Everyone once in a while (maybe 2 times per year) we get a stretch of cloudy days, and the temp of the tank will slowly drop to about 100F, after a week or so without sun. It typically recovers in 2 days.

For the wind option, you want a dump-load controller. It basically diverts the power form the wind generator to the heating element once your batteries are full. Very easy to set up.