Dave W,
In 2012 I had 2.2kW of solar PV panels fitted to my house in Hertfordshire – I only had room for 8 panels, on a south facing roof. A delay in fitting them (whilst the local council messed about re planning permission) meant I got a reduced return (as the government assistance paid to generators reduced in the interim).
When I moved in 2016 I was getting 17.4p per unit generated and roughly 5p per unit for half of the total generated. The return I received all came to the grand total of around £250 per annum.
I looked on it as money which offset my fuel bills, but as to whether it was a good return on the capital investment, I think your wife is quite correct (even if there isn't something she's not telling you)!
Regards Tom