That's true now, but wasn't true when those panels were installed. There were subsidies available to get the market kick-started.

They consist of an extra payment for every kwh you generate on top of the payment for delivering the power to the grid. The amount varied depending on when you signed up to the scheme, but at certain points it was as much as 50p/kwh (+ inflation, so more than that now).

At grid scale, yes.

For the house, not so much.

The feed in tariff was at one point 41 pence per kwhr which is probably £10 a day in summer.

but at 12p a kwhr it drops to £3.6

However, 10kwp of panels is ~£1800, but the micro inverters needed to drive them are >£3k (as its outside you can probably use two larger inverters.) Then mounting system is probably a good 800 quid too.

I think he is describing a subside that some governments gave years ago: you installed for example 5K, and get paid for whatever they generate at 300% market price, for a long time (25 years?). Today you find out that upgrading panels would made perfect financial sense, if you were selling at 100% and are going to sell electricity at 100% (you will be doubling the output for a tenth of the inversion 15 years ago), but as the subsides of 300% no longer exist, you will be actually losing money by upgrading.