In my calculations of our 3500 Kw system, I only use the FIT payments, that's probably why it took 12 yrs, to repay the investment, because, in the real world, the free
solar electricity generation, was available completely free, without spending a penny.
i.e. There are
solar companies, out there, who will install systems for free. In these cases, they receive the FIT payments, and the householder has the electricity
that is generated. Several houses, in my local area took advantage of these schemes, but , IF I had included the free electricity, in my calculations, I would have been fooling myself. Only the FIT payments are relevant !
I researched doing the installation, myself, but, the stumbling block was obtaining the necessary accreditation, to claim FIT payments. It wasn't really possible.
I did, however, go up onto the roof, to take down a disused chimney, to allow an extra
solar panel to be fitted.
I am quite happy with our
solar system , because it generates between £600 - £700, in FIT payments, per year, so, now that it's payed off the original investment, it's money in our pockets, for the next 8 yrs, completely tax free, and the taxpayer subsidises this.
The only downsides are problems with pigeons, and regular cleaning, of the panels.
Obviously, when the motorhome is parked at home ( most of the time ), the batteries receive a free charge, from out domestic system.
P.S. When making my calculations, I also included what I might reasonably have expected, in interest, If I had made a financial investment, with the money, instead of buying
solar panels. This too, is the reality, living in the real world.