What kind of flow rates do you achieve tho?
dependant on solar element, not as much as you seem to need, I still treat the whole system as a one tap design, but there is no sense of inadequacy with one tap (28kw combi usually fed water above 15 degrees C so delta T result more effective), and when their is a lot of solar heat or only solar heat it has the flow rate of any unvented hot water supply. what is important is that very few days in the year have absolutely zero solar input, so whatever the output would have been for the combi is always increased by the fact the supply water to the combi is pre-heated.
The idea behind the HW buffer is so i have a high flow rate/fast recovery. I suppose it would also be very simple to build a simple controller that recognises what the stored temp is at a set time, then if the Solar hasnt provided enough HW hen it would simply turn the HW circulator on and top the buffer up.
you loose efficiency for the benefit of comfort doing that. To benefit from solar you have to have a cold store of water waiting to benefit whenever it is available. Your method would heat that store so later when the sun comes out you can't benefit from it.
works for me.Would you think i would be better off using the existing primaries for solar or the fabricated ones?
If you want economy and comfort then you have to have a two coil cylinder and always leave the bottom strata for solar, heat the top strata only for comfort, or have two cylinders one for solar one for comfort feed the output of the solar into the comfort so that at least you always utilise what is heated by solar. the downside is you require double the storage space.
What i find from solar is that you have a low level warm up available to your all year and far too much solar power for a very short part of the year. Really you could export the over capacity to your neighbours as it is simply wasted. if you went for the two cylinder method during hot days you could switch over the comfort cylinder to a second solar store. A sort of weather compensation system in reverse.