Is it worth having them installed now?The cost benefit isn't as simple as it appears, there's also the difference / cost of global warming in the longer term to take into account.
I have 2.4kwh of solar, installed when the fit scheme started. Costs were twice what they are now, fit was higher. They've now paid for themselves and are earning a tax free profit way better than the same money in the bank over the period. Circa 8%. 25 Yr estimated lifespan.