by australsolarier » Wed Jul 20, 2016 3:49 pm
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.)