We're investigating fitting solar PV to our large guesthouse in the UK. We can fit around a dozen panels on the south-facing roof (sadly this is one of the smaller roofs). Some installers are advocating higher-efficiency panels (say 18% rather than the more common 14%).
The price of these panels is higher than the increase in efficiency would seem to warrant (say and increase cost of 40% for an energy improvement of 30%). There are other subtle differences in the specs but nothing that even in the installer's figures suggest any significant financial logic in buying the more expensive panels.
It looks like a no-brainer to get the lower-efficiency panels that pay back in the same timeframe, and indeed more profitably; but are we missing something?