Martin Brown wrote:
What is the payback period for your thermal solar tubes?


Without RHI the payback calculations would make it a total non starter.
My basic capital costs of the solar thermal are covered by the RHI. I
did a one day training course for around £200 enabling me to do the
installation myself and get it MCS certified - mandatory in order to get
RHI.
I did it as an interesting retirement project together with a PV dumping
diverter - home made. The overall project has covered its costs over 6
years and now is in profit after all my household energy has been paid for.

Presumably one of the variants that uses a heat pipe in a glass tube
silvered on the back half and plugged into a manifold.

Yes exactly that. An array of 30 vacuum tubes each with a water based
heat pipe.