Reading up whether solar PV is a good investment, seems there is a payback period of at least 15 years. What I am unsure of is do those calculations take into account running a heat pump? I guess the time they are generating most output is when you are using least electricity. If it could heat the water in summer you could use more of the produced energy, have read about diverters. Has anyone got experience of retrofitting to existing system? We have ecodan packaged cylinder running 14kw ecodan ho with ufh throughout