Things could change but for now many people who had the cash sitting around and invested in solar roofs are saying they are getting better returns than from the banks which in of it self is a remarkable state of affairs.
Are you sure?
Put Capital in a bank account, and you can get v100% of the Capital back.
Invest Capital in Solar Panels, how do you get your Capital back? You need more than a better "interest rate" to make this comparison work.
What's the business case?
I did say returns, meaning income on the capital, but lets look at some numbers which necessarily involves all manner of approximations and long time scales which I discuss later and I may have got some of the sums wrong so please correct if so.
A 2019 4kW system costs, according to the article below, around £6800 and with Feed in Tariffs (FIT) returns about 6.5% per year, giving a break even in about 13 years, but as FIT has been replaced with the Smart Export Guarantee with lower payments this given a break even of 17 years and a return of 4.58%https://greenbusinesswatch.co.uk/uk-dom ... turns-2019
So for 4 kW systems at £6800 with a life of 30 years, beyond year 17 the system is paid for so that the buyer has their £6800 back, and then the income comes to the owner of the system. If this is compounded over the remaining life of the system of 13 years, then the final amount after 30 years is 6800x(1.0485)**13 = £12,171, or a gain of £5371.
iF however, the money was invested at 0.5% over 30 years, then the return would be 6800x(1.005)**30 = £7898, or a gain of £1097.0
Clearly there are huge assumptions here over interest rates, Export Guarantees, electric bills etc etc ...
Folk have suggested that installers are desperate and are offering incentives which could reduce the initial costs or spread it interest free over a few years etc.
Still unless my sums are wrong the returns are better than what one can typically get on deposit and in some cases returns are negative, in other accounts larger. One can chase ones tail trying to think through all options, but as it is, roof top solar looks attractive compared to bank interest for someone intending to live in the same house for 30 years, or as an additional value added if it is proposed to sell the property.