each unit of electricity was worth about £1 in round terms when used in this way.
Unlikely - even if he is on the first tier of fits at 45p/unit and he uses every last drop of power to offset other electricity purchases (I.e. not the immersion heater thing which in the post above is displacing gas at 4.5p) he will be making/saving the equivalent of 60p unit. If he has more than 4kw, then he will be on a max of 32 or 38 p, less if he installed recently.
Solar panels still make sense if you have the right roof with no shade and don't pay over the top for the system AND you can afford to lose access to the cash for the time it takes to pay them back. Typical payback for a domestic system vary between 6-10 years depending on how much of the power you can use at the time it is being made.
Anyone who thinks domestic electricity bills aren't going to rise above inflation is kidding themselves IMO, same with oil/gas. I was talking to the MD of a large oil drilling company last week and he reckons the cost of drilling west of Shetland is up to 6 times that in the North Sea.
As for The technology involved becoming obsolete, it's a fair point but we don't know what is around the corner so you have to make your own mind up. Typical crystalline silicon panel efficiencies are 14-16% with the next level being 18% for hybrid panels but they aren't cost effective at uk tariff/production levels. After that you get into gallium arsenide (space station type panels) that are 100s of times more expensive and unlikely to be cost effective anytime soon at 25% efficient.
Inverters are 96% efficient so even a halving of the losses won't mean a huge leap forward in yield.
My advice, as an installer of renewables inc PV is to go for it, but I'm biased!