Oh yeh. I would never advocate investing in something with that long of a pay off but I also think it depends a lot on individual circumstances. Costs are often higher to add to an existing property that to include in a new build.

Of course the cheapest of all are panels installed in vast arrays on the ground. Realistically for electricity generation the real solution is not home based. Most places are moving towards a situation where wind+solar+hydro will make up the majority of the electricity anyway.

The real home based cost savers / pollution reducers will be in the areas of transport and heating. Where I live currently the transport bit is easy (town centre with rail station) but the heating bit is hard (currently completely reliant on gas boiler).