Photosynthesis in plants converts solar energy to chemical energy by splitting water to release hydrogen.

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Dye-sensitized solar cells


"The equation for photosynthesis is a deceptivey simple summary of a very complex process. Actually, photosynthesis is not a single process, but two processes, each with multiple steps. These two stages of photosynthesis are known as the light reactions (the photo part of photosynthesis) and the Calvin cycle (the synthesis part).

"The light reactions are the steps of photosynthesis that convert solar energy to chemical energy. Water is split, providing a source of electrons and protons (hydrogen ions, H) and giving off O2 as a by-product. Light absorbed by chlorophyll drives a transfer of the electrons and hydrogen ions from water to an acceptor called NADP+  (nicotinamide adenine dinucleotide phosphate), where they are temporarily stored. The electron acceptor NADP+ is first cousin to NAD+, which functions as an electron carrier in cellular respiration; the two molecules differ only by the presence of an extra phosphate group in the NADP+ molecule. The light reactions use solar power to reduce NADP+ to NADPH by adding a pair of electrons along with an H+. The light reactions also generate ATP, using chemiosmosis to power the addition of a phosphate group to ADP, a process called photophosphorylation. Thus, light energy is initially converted to chemical energy in the form of two compounds: NADPH, a source of electrons as 'reducing power' that can be passed along to an electron acceptor, reducing it, and ATP, the versatile energy currency of cells. Notice that the light reactions produce no sugar; that happens in the second stage of photosynthesis, the Calvin cycle." (Campbell 2008:188-189)

Plant-inspired solar cells mimic photosynthetic dyes and processes to generate solar energy many times more cheaply than silicon-based photovoltaics, while having the flexibility to be integrated with a building skin. Conventional silicon-based solar panels capture, separate, and transport light energy in one highly-purified material whose manufacture requires large amounts of energy, toxic solvents, and bulky infrastructure to support rigid panels. Alternatively, dye-sensitive solar cells use a variety of photo-sensitive dyes and common, flexible materials that can be incorporated into architectural elements such as window panes, building paints, or textiles. Although traditional silicon-based photovoltaic solar cells currently have higher solar energy conversion ratios, dye-sensitive solar cells have higher overall power collection potential due to low-cost operability under a wider range of light and temperature conditions, and flexible application.