Sunlight is converted to electricity in three ways: (i) by making steam that drives a turbine which turns an electricity generator; (ii) by taking advantage of the photo-excited electrons that power photosynthesis and make biofuels, which can be stored and burned to make steam; or (iii) in solar cells, which extract the photo-excited electrons directly as electric power. I will briefly survey the first two technologies, and then focus on solar cells. The ones that have reached application were invented 60 to 40 years ago. The oldest, silicon solar cells, are commercially most mature and have been in continuous rooftop operation for 30 years – see Bunn Intercultural Center Solar Array at http://sustainability.georgetown.edu/initiatives/carbonfootprint/ .
While expensive to install, the cost of operation and maintenance of photovoltaic systems is low – see Table 1 at http://www.eia.gov/forecasts/capitalcost/ . The science, technology, manufacturing, and financing of photovoltaic electricity has been focused largely on bringing its cost down to that of conventionally generated electricity. After evaluating the electric energy available from sunlight, I will illustrate some important factors of photovoltaic electricity: energy efficiency, materials and manufacturing, and systems integration.