Solar power: learning from the experts

Challenge: harness the sun's powerMan sunbathing © Mátyás Huszár, www.sxc.hu

Natural inspiration: plants

 

 

Every square metre of the earth receives an average of 340 joules of energy per second from the sun – approximately the amount of energy used per second by a large plasma screen TV.  About 29% of this is reflected back into space and 23% is absorbed by the atmosphere, leaving about 160 joules per second to reach each square metre of the earth’s surface. This energy not only makes life on earth possible, but is a potential source of power for human technology.

 

Solar photovoltaic (PV) technology uses the energy in sunlight to generate electricity. The amount of solar energy received by the earth is much greater than global human energy use, and PV could in theory provide all of our electricity needs.3   However, at present only about 0.004% of total world power is from solar generation. 4  The barriers to increasing use of PV include cost, space and the difficulties of storing energy for when it is needed. 4  Although PV technology is around 40 years old, improvements have been slow. 5 Research to improve efficiency and bring down the cost of solar panels is ongoing.2

 

ivy © Dora Pete, http://www.sxc.hu

 

 

 

Nature has been using sunlight for about 2.5 billion years. 6 The process is called photosynthesis, and the most familiar group of organisms to use it is plants.  In photosynthesis, the energy of the sunlight hitting the leaves is used to convert carbon dioxide and water into glucose and oxygen.  The glucose is effectively a way of storing the sun’s energy until the plant needs to use it. 7 PV is already more efficient than photosynthesis at converting energy: plants capture about 6% of the sunlight falling on them,8 compared to about 15% for solar panels. 5  However, plants may have lessons to teach photovoltaic technicians.Solar Ivy. © SMIT, http://www.s-m-i-t.com/

 

 

 

 

 

 

An important way to increase the efficiency of PV panels is to increase the proportion of light they absorb.  One research team 9 has created PV panels covered with microscopic bumps, mimicking plant leaves.  These bumps serve the same two purposes as in plants: focusing the sunlight onto the active parts of the surface 10 and helping keep the surface clean by preventing dirt from sticking 11.  Another researcher has developed a product inspired by ivy leaves, which uses a series of small, flexible solar cells rather than one large panel.  12 This means it can be modified for different situations, and if one ‘leaf’ fails it can easily be replaced: just like an ivy plant growing up a wall and adapting to the space available. 
 
cactus © Eva Schuster, www.sxc.hu

 

 

 

Biodiversity survives using photosynthesis in a huge range of environments, including in the cold of Arctic snow 13, the heat and pressure of deep-sea thermal vents 14 and in the scorching days and freezing nights of deserts.15  There are about 400,000 species of plants, most of which use photosynthesis, and uncounted numbers of photosynthetic microscopic creatures. 16 New species, and new variations on photosynthesis, continue to be discovered.  By comparison, human attempts at capturing the energy from sunlight are in their infancy.

 
 
 
 
 
 
 
 
 
 
 
 
 
References
1. NASA Earth Observatory.  Accessed February 2010.
2. Carbon Trust: emerging technologies.  Accessed February 2010.
4. IPCC, 2007: Climate change 2007: mitigation of climate change.  Contribution of Working Group III to the Fourth Assessment Report of the IPCC, p279.
5. How to live a low-carbon life, Chris Goodall (2007).  Earthscan, London, UK.
6. Buick, R. (2008) When did oxygenic photosynthesis evolve? Philos Trans R Soc Lond B Biol Sci. 363:2731-43.
7. Royal Society of Chemistry: photosynthesis.  Accessed February 2010. 
8. Food and Agriculture Organisation. Accessed March 2010.
9. Zhu, J. et al. (2009) Nanodome Solar Cells with Efficient Light Management and Self-Cleaning. Nano Letters
DOI: 10.1021/nl9034237.  See also New Scientist, December 2009.  Accessed February 2010.
10. Govaerts, Y.M. et al. (1996) Three-dimensional radiation transfer modeling in a dicotyledon leaf.  Applied Optics 35: 6585-6598       
11. Neinhuis, C. et al (1996) Characterization and distribution of water-repellent, self-cleaning plant surfaces.  Annals of Botany 79: 667 – 677
12. Solar Ivy by Sustainably Minded Interactive Technology.  Accessed February 2010.
13. Starr, G. et al. (2003) Photosynthesis of Arctic evergreens under snow: Implications for tundra ecosystem carbon balance.  Ecology 84: 1415-1420
14. Beatty, J.T. et al. (2005) An obligately photosynthetic bacterial anaerobe from a deep-sea hydrothermal vent.  PNAS 102: 9306-9310
15. Seemann, J.R. et al. (1984) Photosynthetic Response and Adaptation to High Temperature in Desert Plants.  Plant Physiol. 75: 364–368.
16. Botanic Gardens conservation international. Accessed March 2010.