Solar heating/ combi boiler

[kenco]

Hi, new member Kenco here with a few queries!!
I'm building a house in the south of France and trying to decide the best (cheapest to install and run??) heating option(s)
My intention is to place solar collectors (evacuated tubes) on the roof as it seems a shame not to reap the free energy provided by the sun. Temperatures are typically 35 degrees in the summer months and I have a large south facing roof. The temp also drops to around minus 10 in winter so antifreze is a must.
I intend to run this through the coil of an unvented indirect cylinder. the system I favour is to run the hot water outlet to the input of a combi boiler (obviously one that accepts hot input) with a bypass valve if the tank temp is hot enough to go straight to the taps, or through the boiler to pep it up if not.
The combi would also run the central heating side of things (underfloor heating down stairs and radiators up stairs.
There is no mains gas where I am so LPG would be the prefered fuel.
My question is, does this sound like a viable set up?? or is there an easier/cheaper way of doing things??
Also if I had a 2 coil tank could I couple the coils together to get one large surface area coil in the tank as this plan doesn't use the second coil in the traditional way??
Phew!! sorry that was a bit long winded.
Any advice/suggestions would be greatly appreciated.
Thanks in antipitation.

 

[Toddyplumb]

You are limited as to which combi s can take pre heated inlet .
Why not run combi hot to 1 outlet , say kitchen sink. Then 'S' plan heating(rads up underfloor down) and second coil in solar cylinder (3 zone valves). Thats what I would do

 

[kenco]

Thanks for your reply,
Yeah, I kinda see where you're coming from.
I was trying to keep the advantage of a comb,i ie not using it to heat a tank of water, only heat what is used, whilst using only the free solar energy to heat the tank,just not sure if this would save me any money compared to the system you recomend. In your system woul another type of boiler be more suitable?
Sorry if I'm missing some impotant point here but please bear in mind I'm not a plumber and not fully familiar with all the systems out there!!
Thanks for your patience.

 

[Toddyplumb]

You can do it with a system boiler. The combi would give you hot to kitchen 24/7 . With system boiler you need either sun to heat cylinder or boiler to heat cylinder

 

[kenco]

Thanks for the reply, another querie I have is;
I understand the importance of automated shut down of the heating coil in the unvented tank so as not to raise the temp too high!! and that this is easilly done if using a boiler as the primary heat source. However how is this controlled if using solar energy as the prime heat source?? It is easy to electronically disable the pump in the solar collector loop but what happens to the fluid (water/antifreeze) in that loop?? does it require a dump radiator or some such device??