Often known as PV panels, photovoltaics covert light into electricity, and have been about for many years. In recent years the prices have come down, the efficiencies have gone up and probably the most significant change is the introduction of Feed In Tariffs (FIT) which means that you get money into your bank for every watt you generate. So, even if you have no interest in the environment, PV panels are an excellent investment.
There are even companies that will install PV on your house, for free, give you the generated electricity, and they collect the FIT. You need a south facing roof, a flat roof will do (see above), and although strong sunlight works best, they do give some output on most days.