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Solar hot water systems with a wetback

PostPosted: Mon Jul 18, 2016 10:32 pm
by offgridCBR
Hi everyone,

I've been trawling the forums and have found a wide mix of systems that people use for shw and was recently recommended to go down the path of a wetback.

I can't find any independent info or reviews on red circle solar: they seem very similar to what we saw on on most roofs in Vietnam and they say they are made in China.

It also appears that they distribute through ultimate solar, whose address is next door in vic.

We are thinking of pairing it with a yunca monte wetback fireplace.

I've always found this forum to be a great place to bounce ideas or to learn from others' experience and am keen to find out what your thoughts are?


Re: Solar hot water systems with a wetback

PostPosted: Wed Jul 20, 2016 10:02 am
by australsolarier
that system that you linked has vacuum tubes that have water from the tank directly in them. that means if one tubes break, or the seal leaks or you pull a tube out, all the water in the tank (or more) will run out.
also the heat exchanger typically will lose about 10 degrees.
but will be easier to connect to your water jacket as the water in the tank is low pressure/ open vented.

that system is not very common here in australia. another disadvantage with that system, in the summer is that it might overheat and boil and use cold water from the inlet to cool it. the same if you heat the house with your wood stove, at some point the water will be boiling.

i myself have a solahart on low pressure with a small header tank above the hot water tank. the flat solar panels cool the heat generated from the wood stove down so it never boils. all is thermosyphoned. so no pumps etc. it has been going for more than 25 years. though the hot water is much lower pressure than the cold. but in practice it is not a problem.
(the cooling via the solar panels typically takes places at temps over 60 degrees or so)

Re: Solar hot water systems with a wetback

PostPosted: Wed Jul 20, 2016 2:45 pm
by offgridCBR
Thanks for the info australsolarier!

Do you know of any evacuated tube systems that would work well with a wet back that don't use the same approach add the red circle or run on sun systems?

Our builder was initially going to go with a kelvinator gas boosted system but I have friends using a wetback and they love it

Re: Solar hot water systems with a wetback

PostPosted: Wed Jul 20, 2016 3:03 pm
by Gordon-Loomberah
RunOnSun also have systems with tubes that are not water-filled, the hot bulb inserts into a manifold. I have both types, fortunately the tube that got broken by hail was one of the non water filled ones.

Re: Solar hot water systems with a wetback

PostPosted: Wed Jul 20, 2016 3:49 pm
by australsolarier
well any solar hot water system works well with a wetback system. it is just a matter of tying in the pipes. the correct way of course if you bank on thermosyphoning the system.
systems using circulation pumps just turn off the pump if the water in the tank gets too hot. the manifold of the heat pipes get hot (140 degrees or more)(or the flat panels), but that seems to be alright. if the heat pipes connect directly to the tank, you cannot turn off heating, unless you cover the heat pipes. that is the reason you do not see those direct into the tank going systems on the roofs much. also some seller of solar systems told me that was the reason those direct systems did not get australian certifications, what ever he meant by that i am not quite clear, but that's why they were not selling them anymore.
being in your shoes i would go with flat panels, having a largish tank inside the roof space, if you have the room there. so the tank is higher than the flat panels and the would stove. leave it at gravity pressure and open vented. you can always add a booster pressure pump if you think the pressure of the hot water is too low. but it is not a problem for me.
at high temperatures vacuum heat pipes are much more efficient than flat panels. so as the temperature goes up the flat panel is less efficient. how ever at low temperatures flat panels generally are more efficient. heat pipes also work much better in windy and or cold days.
i have a space heating system powered by 100 heat pipes. well for about half the year there is not enough hot water for heating. then in the summer you do not heat anymore there is 3000l of 80 degrees water. when it reaches the programmed temperature (78degrees in my case) the circulating water is diverted to another tank standing in the open air via a copper spiral. the water gets cooled down to 50degrees or so before entering the manifold with the 100 pipes to be heated up to 78 degrees again. i did not want to have the manifold at high temperatures months at a time. that is the reason i added the cooling system. but that is just my preference. (i was also thinking something like a garage roller door to cover the heat pipes automatically. but, just worried the wind ripping it off. plus the matter with the weight, electrical motors and controlls etc.)

Re: Solar hot water systems with a wetback

PostPosted: Wed Jul 20, 2016 3:56 pm
by Gordon-Loomberah
I manually cover my evacuated tubes with shade cloth when required. Being ground mounted it is quick and easy to do. One of these days I might get around to automating it, but that is a low priority, since manually doing it is no problem.

Re: Solar hot water systems with a wetback

PostPosted: Wed Jul 20, 2016 4:05 pm
by offgridCBR
I will have to put the system on the roof as we have too many wombats and roos running around.

Do the circulating pumps use much power? Also isn't it better to use a heat exchanger to prevent possible legionaires?

Re: Solar hot water systems with a wetback

PostPosted: Wed Jul 20, 2016 4:14 pm
by Gordon-Loomberah
The pumps use anything from about 10W to maybe 50 or 60W, depending on capacity, AC or DC etc. I have a little Topsflow pump here that operates directly from a small PV panel (6-24VDC).

IMO, I don't think there is any risk from Legionaires if the water gets to over 65C at least once per week. I've had an occasional longer period of minimal sun, but never had any problems, and the water doesn't smell, like it does in evaporative air conditioned buildings at the start of summer ... I often wonder what sort of bacteria is associated with that horrible smell.

Re: Solar hot water systems with a wetback

PostPosted: Wed Jul 20, 2016 5:02 pm
by australsolarier
you might also look at this here:

sounds interesting. the wiring certainly beats the plumbing.

Re: Solar hot water systems with a wetback

PostPosted: Wed Jul 20, 2016 5:36 pm
by 34by151
Thats my setup

It beats thermal systems including evac tubes

I have had rheem solar, with gas and electric boost as well as evac tubes (aprecus)
Sooner or latter issues arise in the collection, plumbing or pump

Ive had gas and electric as well

My tank is 400L and ive never needed any boost from the grid in the 8 months it been installed
It works on as little as 2 panels, nice and simple
One element/thermostat ison the grid
The other is run from the solar panels via DC
The temp of the grid connected thermostat is set lower then the solar so it only can come on if the solar needs a boost