Photosynthesis, solar, ...
Power is power wherever it comes from. The same laws of physics always apply. The thing that matters is the cost - which is not always easy to convert into money. Gas is cheapest right now because new supplies have been found (and sometimes taxed out of existence). France has far cheaper electricity bills than the UK because they are 80% nuclear, and we are 10% wind (in the record breaking month). Photovoltaic is profitable when large populations live near a desert. Perhaps the price of the panels will fall enough to make them profitable in the UK one day. You still need a huge area to generate a significant amount of power (10-20W/square meter).
Photosynthesis is solar power. Plants are one or two percent efficient at converting sunlight, CO2 and water into sugar and oxygen. Make sure you include all the costs - transport and distribution of fertiliser to maintain soil quality. Irrigation. Transport and conversion of plants into biofuel. Starving hordes setting fire to your local MP because using all the farmland to make biofuel has sent food prices rocketing. There are theories about dumping minerals into barren oceans so phytoplankton can grow. The good news is that it does not use up all the farmland and might create a fishing industry. As far as I know, there have been no large scale tests (because they would be illegal).
All the information you need to understand the scale of sustainable energy can be found at: http://www.withouthotair.com/