Review-Research Needs for Photovoltaics in the 21st Century

By 2050, the scale of installed solar panels must reach about 100 TWp in order to make a tangible impact on our energy mix and carbon emissions. Thin-film amorphous silicon panels are the only technology today capable of 100 TWp installation. Wafer silicon panels could reach 100 TWp if the silver in silicon panels is replaced with copper or aluminum. Cadmium telluride and copper indium gallium selenide would become technologies of insignificance in the big picture. For energy-efficient production of silicon panels, research is needed in energy-efficient purification of silicon, low kerf loss wafering of silicon, and an Earth-abundant top cell on silicon. Alternatively we can pursue a new cell technology which is more energy efficient than silicon and utilizes only Earth-abundant materials. For any cell technology, research is needed to improve the cost, efficiency, and sustainability including storage technologies for daily to multiyear storage and for regional and global trade of solar electricity, recycling technologies to minimize cost and maximize revenue from waste panels, and systems and applications for real-time and in situ consumption of solar electricity.