The RETScreen Clean Energy Project Analysis Software is a unique decision support tool developed with the contribution of numerous experts from government, industry, and academia. The free software can be used worldwide to evaluate the energy production and savings, costs, emission reductions, financial viability and risk for various types of clean energy technologies. The software (available in 36 languages) also includes product, project, hydrology and climate databases, a detailed user manual, and a case study based college/university-level training course, including an engineering e-textbook.
RETScreen is a very useful tool, covering all renewable energy types, and energy efficiency. It allows you to quickly interpret the main opportunities, as well as providing LCA and financing information. The textbook is also of an extremely high quality. For a freely available tool it's hard to fault; my only criticism would be that it needs MS Excel in order to work, though I understand that will be addressed in future releases.