Hi all, I am a long time watcher and now new poster.

I am looking to link a wood burner (with back boiler), an oil boiler and solar. A Heat store is attractive and even more so with a passive internal coil for DHW.

My worry is in the summer, will a south facing evacuated tube Solar system really heat a 250L \ 300L tank enough to get usable DHW. I understand that the heat store needs to be 10 or so degrees hotter than the DHW water you want out, but solar doesnt heat very hot.

If we went with this would we (my wife) end up dissatisfied. I really want green but without compromising too much (afterall we could get used to cold showers).

Does anyone have experiences of this type of setup that the could share.

many thanks

Andrew

andrew - evacuated tube systems have no trouble heating water nice and hot. For a conventional tank with bottom-mounted solar coil then rule of thumb is 5l per tube, and that should supply all your hot water from may to october. However the right answer does depend on how much hot water you use. I understand you should get more like a 5C temp diff between store and DHW output, but I don't have one myself (yet), and it does depends on the design details. It is easy to set up your system to run the boiler for a bit if the solar has not got things quite hot enough, so you will never get cold showers. If you can have showers in the afternoon/early evening rather than 1st thing in the morning then that works better witha solar system, as that's when they are hottest (without boiler assistance).

There are plenty of people with systems just like what you propose on the navitron.org.uk forum. I suggest you ask there.

I was about to post the same question - the only difference is that I already have one installed.

I have a 1400l Akvaterm thermal store, with is heated by an 18KW Atmos log boiler and 2 Greenskies FK240 Solar Panels. We had them all installed about April.

I know it's been a poor summer, but the panels don't seem to have contributed to the heating of the store at all. The problem seems to be that the panels don't get that hot, and as the feed it at the bottom of the Akvaterm tank, by the time the heat has risen to the top the benefit is lost

Yesterday, for example was a very sunny afternoon, and the solar was pumping for about 6 hours. In this time it raised the temp of the bottom of the tank 5 degrees (60 to 65), but this did nothing for the top of the tank, which stayed at 63 degrees.

Does anyone have such a system working effectively?

Thanks,

Aled

You need more area of panels or better panels

Hi,
I assume at the moment this is used just for DHW, although here this summer you’d probably want some heat.
That amount of energy will raise the temp of the water only by that amount whatever the starting point, or as pointed out above a smaller volume by more. The energy must balance out.
To get more space heating support you’d need more panels. I would guess the coil in the bottom could support about 10m2 of panels.
If the water at the bottom of the store were cooler then the power transfer would be better (slightly quicker) because of the better temp difference, but the energy would again be the same.
60+deg is quite warm for the lower section of the store which suggests you are doing a full burn then using this only for DHW over a period of days. Try a smaller burn which will push hot water no so far down the accumulator, leaving the bottom cooler to absorb the solar.
There is a device (Laddomat) at the bottom of the tank that raises the temp of the boiler feed to about that temperature (60deg), so your burn will easily raise the temp to 80deg. When you are using more heating the lower temp is likely to be less anyway.
A lot does depend on usage patterns. In the winter if you were out to work all day you could burn in the early evening and use the stored energy that night and morning, leaving the accumulator very cooler to absorb any solar before the next evening burn. But if you were in all day (and it was sunny) and you wanted to do a boiler burn it would be much harder to ensure the accumulator was cool enough to absorb any solar gain.
Cheers, Mike up North

Posted By: AledSomebody on here mentioned that the hotter the store is, the better it retains the heat.

A possible misunderstanding there. The hotter the store is the greater the rate of heat loss, although the difference between 70 and 80 degrees won't be much. However a hotter store is storing more energy, so it should go a bit longer between top ups.