Things to remember when getting a ST system?

BigGeorge

Looking for any key things to remember when buying a solar thermal system which will feed a large buffer tank.

Are there any recommended controls, levels of insulation, standard for tank pressure etc....?

quentingargan

BigGeorge wrote: »

Looking for any key things to remember when buying a solar thermal system which will feed a large buffer tank.

Are there any recommended controls, levels of insulation, standard for tank pressure etc....?

Well, yes. There are, but quite numerous.

Insulation is straightforward enough. Unlike central heating or an immersion, your cylinder and pipework will be hot for a lot of the time, so insulation is key. The solar loop should have insulation that is capable of taking temperatures up to about 150 to 160 degrees. You should use additional insulation over all connectors so none of the circuit is visible. Generally insulation thickness should be roughly the same as the pipe diameter.

The pressure in the solar circuit must be matched to the maximum temperature set in the controller. I see a lot of systems filled to 1 bar (which will boil at 120C approx) matched to the default max panel temp setting of the controller at 140C. If you fill the solar loop to 3 bar, then 140 is OK, but make sure the expansion vessel is pre-charged to suit this pressure.

I assume that the solar will feed a domestic hot water cylinder first, and then dump to the buffer tank? Most controllers have a facility to accommodate this. What size buffer are you looking at? Is it being used with a log gassifying stove or some other heating system, or are you trying to use solar for space heating? (I have my doubts about this but there are other threads on that subject...).

I also assume that the solar will feed a coil in the buffer tank, rather than the actual fluid in the buffer? Otherwise you'll need an awful lot of anti-freeze. I have seen systems where there was no coil for the solar, and antifreeze therefore couldn't be used. That's OK with tubes, and the controller should have a defrost function set in that case. However, if you get a power cut during a frost, you will get damage, unless you have a UPS on the circuit, which ONLY works for antifreeze. That's complicated to set up, but it can be done.

I'm sure other posters here will have a few ideas I haven't considered..

Q

Evergreen

One more to add to Quentins list.

* Make sure that you size the solar system and buffer tank size to suit each other.

I have seen a guy try to heat a 1600 L buffer tank with 6 square meters of flat plate. He called me out to see why he was getting no heat in his buffer tank......

Rule of thumb for flat plate is 50 L of storage for every square meter (aperture) of solar panel.

Rule of thumb for evacuated tube systems will vary depending on what system you install. Having said that the system we use requires 80L of storage for every square meter (aperture) of solar panel.

Buffer....Flat.......Tubes
500L......10 sm...6.25 sm
750L......15 sm....9.37 sm
1000L....20 sm....12.5 sm
1500L....30 sm....18.75 sm
2000L....40 sm....25 sm

Hope this helps?

quentingargan

Eh... it depens on what the buffer tank is for.

If the buffer tank is serving as a heat dump for surplus heat when the cylinder is satisfied, you certainly don't want 20 sq m on it. Otherwise you will have to empty that heat out of the buffer tank each day in the summer time (or have your system in stagnation). Its a bit more nuanced than that. Q