Harvesting Solar Energy through Natural or Artificial Photosynthesis: Scientific, Social, Political and Economic Implications

Abstract

Natural photosynthesis is an inherently inefficient process that developed millions or even billions of years ago. Thus present systems for harvesting solar energy in the form of organic carbon are inefficient compared with solar photovoltaic cells. The highest productivities are about 1% compared with ∼10% for solar cells. Somewhat higher rates can be envisaged in the future but only through the use of a high solar footprint (the area of the Earth's surface needed to sustain a certain energy output), i.e. by using extra energy, which in a long-term sustainable world can come only from solar energy. While bioenergy production from algae may be lead to even greater efficiencies in the future it seems that this will only come about by an even higher solar footprint. Additionally, while bioenergy production may seem to be favourable in terms of carbon footprint, in practice there are several unfavourable outcomes. Further, bioenergy production immediately conflicts with use of the Earth's surface for food production and/or the need to maintain biodiversity. Thus artificial photosynthesis with very much higher expected efficiencies than natural photosynthesis is a worthwhile goal, in that it could potentially compete in efficiency with energy production by photovoltaic cells.