IF GREEN plants can capture 95 per cent of the total energy from sunlight through the process of photosynthesis, why can't the solar photo-voltaic cells (SPV)? The best SPVS are able to absorb only 25 per cent of the solar energy available on the surface of the Earth -- a fact that has puzzled solar energy advocates for quite sometime.

A team of British researchers have identified the details of the atomic structure of the "light harvesting system" -- the place in the leaf where energy from sunlight is absorbed in a strain of purple bacteria. The findings could help in designing more effective spv cells.

Green plants and photosyntheic bacteria employ an extremely sensitive and effective molecular-antennae system that absorbs individual photons and quickly passes on the energy to the "reaction centre" -- the place where photosynthesis proper, or the splitting of water molecules begin.

The research team from the University of Glasgow and Daresbury Laboratory, Cheshire, used 3-dimensional x-ray crystallography -- a technique used for studying the structure of the "reaction centre". They observed two concentric cylinders, a couple of millionth of a millimetre across, of a spiralling protein molecule, enclosing a ring of chlorophyll (a chemical pigment that initially absorbs sunlight). When a photon excites 1 of the chlorophyll molecules, the energy is transferred quickly around the ring to a point near the reaction centre.

Now that 1 biochemical structure that efficiently captures solar energy is available as a guide, it can become an ingredient in a more efficient future solar cell, they argue.