Solar - economist technology quarterly

Thought this was quite useful- www.economist.com/printedition/displaystory.cfm?story_id=E1_RSGGDQV

"At present, solar power is at least two to three times as expensive as the typical electricity generated in America for retail customers."

but

"Decades of research have improved the efficiency of silicon-based solar cells from 6% to an average of 15% today, whereas improvements in manufacturing have reduced the price of modules from about $200 per watt in the 1950s to $2.70 in 2004"

"Cleantech Venture Network, an umbrella organisation based in Ann Arbor, Michigan, says VCs invested $2.9 billion in North American clean-technology start-ups in 2006"

Nice simple summary of the basics:

"The photoelectric effect was not discovered until 1839, when Alexandre Becquerel, a French physicist, observed that light could generate an electric current between two metal electrodes immersed in a conductive liquid. About 40 years later Charles Fritts, an American inventor, built the first solar cell. Made with selenium and a thin layer of gold, the device was less than 1% efficient. At the birthplace of the transistor, the now legendary Bell Laboratories, a team of scientists invented the first practical solar cell in 1954. The core of the invention was a semiconductor device"

"It is composed of two layers of semiconductor material, typically silicon, that are sandwiched together between metal contacts. One layer, of n-type material, contains lots of negatively charged free electrons; the other, of p-type material, contains an abundance of positively charged “holes”, which are spaces that can accept electrons. At the junction where the two layers meet, electrons pair up with holes, establishing an electric field that prevents electrons from moving from the n-type material to the p-type. When light of an appropriate wavelength strikes the solar cell, the individual packets of energy, called photons, knock some paired-up electrons free from their holes. The electric field then coaxes these free electrons and holes to move in opposite directions. The result is a build-up of free electrons in the n-type material, and a build-up of holes (that is, a shortage of electrons) in the p-type material. An external circuit provides a path for the electrons to return to the p-type material, producing an electric current along the way that continues as long as light strikes the solar cell."


annual reduction in manufacturing costs of about 5%; average crystalline silicon cell 13% efficient approx $3 per watt

silicon based solar cells still 90% of market - leading to silicon shortage and increase raw materials costs

"thin film" solar cells use little or no silicon (1% of 'regular cell') - high volume production difficult
e.g Amorphous Silicon cells (easier to produce) - example United Solar Ovonic
e.g. cadmium-telluride (less efficient - 9% - but cheaper to produce) example First Solar: $1.40 per watt; but additional space needed because less efficient
e.g. CIGS (copper indium gallium diselenide) very efficient (19.5%) but hard to produce
example - Nanosolar "nanoparticle ink"; Miasole- flexible encapsulants

Another alternative- lens/mirrors to focus sunlight onto cells (quoted efficiencies of 40%)- SolFocus