So it costs £400 and can shave up to £100 a year - how it was calculated? In best case scenario you'll have to hang this thing off balcony for 4 years to break even. Will it be good after 4 years? I cannot see the economics of that. If it shaves £50, then it's 8 years.

How long do they last? How much maintenance costs (cleaning etc.)

Sounds like a way to stuff the poor with copium device. The rich will get minted and government doesn't have to resolve the problem of expensive electricity for another election cycle.

4 years is a pretty good payback time, it's a pretty obvious investment if you can afford it, and it's pretty affordable (with the added bonus that if you're renting, you can take it with you). Solar panels tend to last a pretty long time, really the only worry is whether the manufacturer has cheaped out on the electronics (cleaning is literally going to be wiping it with a sponge once a year or so).

(Insulating your house or getting double glazing, for example, takes a lot longer to pay itself back, and these are pretty popular home improvements despite that and the higher outlay)

I see it more as a way for relatively well off people to do a little bit for the environment rather than any sort of solution of high energy prices for the poor. The nice thing, of course, is that the more people buy them, the cheaper electricity is for everyone else, so you're doing everyone else a small favour by having one.

I'll certainly be buying one, not because of the ROI/payback calculation, but just because it's fun to talk about with my kids and a nice thing to do.

Similarly, plug in batteries are on the way (see recently Octopus announcement). I'll probably buy one for the same reasons.

That said, the payback time also looks very favourable, especially relative to a full rooftop install, so you don't even need to be alturistic!

Panels have 25+ year lives. Anything after the break even is free energy. There is no material maintenance cost.

You think a balcony solar panel is going to die after 4 years? Why? What makes it different from any other solar panel? They have lives in decades.

You're spouting tired anti-solar talking points. Again, why?