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At the International Conference on Climate Change in Copenhagen 2009 it was suggested that the sun and wind at the Sahara could supply all the energy for Europe. In practice a mix of different systems will be the best answer of which the deserts could provide a substantial proportion.
Theoretically 1/10,000 (0.01%) of all suns energy reaching the earth could provide all the energy consumed on earth and eliminate the need for oil, gas, coal & nuclear. Solar power uses the suns radiation and various ways of doing so are being developed. However to be available at night as well as day, means of energy storage and/or cross world transmission is needed.
Parabolic trough reflectors
Parabolic reflectors focus the suns rays onto a heat collector containing fluid (water or oil at 400 C) which in turn raises steam in a heat exchanger. The steam powers turbine driven generator/s. Banks of trough mirrors track the sun automatically.The basic energy cost (excluding transmission and storage) is currently the same as that from a $50 a barrel of oil and this could reduce possibly to $20 in the future (ref 142).
Heat storage near to the site (in nitrates of Sodium or Potassium) helps diversity and night demand.
Near to Las Vegas, 'Nevada Solar One' pipes oil through the reflectors to run a 64 MWe steam generator (ref 203):-
Power could be transmitted long distances by HV DC (High Voltage direct current), including under sea, losses being 3% per 1000 km probably. A further feature in the future is that the shaded areas under the reflectors could be used for crops watered by local desalination plants.
Dish/Sterling engine
A parabolic dish focuses sunlight onto a point to heat a gas or fluid (water) to 1500 C to drive a sterling engine which in turn drives an electric generator. Each dish is dual axis controlled to track the sun.
Solar Power Tower
Hundreds of dual axis controlled flat mirrors (heliostats) in a circular array focus energy onto a power tower. A fluid (eg moltern salts) is used as a heat collector (eg up to 1000 C) and used to generate steam in a heat exchanger to drive a turbo alternator. Liquid Sodium may be used in larger arrays as a heat collector. (example PlataformaSolucar, Andalusia, 11 MWe 115m high tower 624 mirrors.)
A refinement is the Multi Tower Solar Array (MTSA) (proposed by D R Mills & P Schramek) to reduce ground area. Several smaller towers receive radiation from a reduced number of heliostats per tower. This arrangement uses areas otherwise blocked or shaded.
Solar induced draft tower
In NSW Australia a large 1000m tower in the desert air is induced by being heated under glass at ground level to flow and drive wind turbines. This design is based on a smaller 50 kw tower experiment in Spain. It is planned to build of five more.
At night the air under the transparent roof area remains warm and electricity continues to be generated. It is claimed therefore that the cost is competitive to other forms of energy production.
The area under the transparent roof produces condensation at night and thus conditions for plant growth.
NASA idea for Solar collectors in space where sun is (more) continuous.
The idea is to place solar collectors at a geo stationary orbit 20km high where sun is more continuous than on the earths surface and transmit power down by laser. Costs for placing equipment in space is high thus a further idea is that equipment could be transmitted up on a solar powered buggy/elevator on a cable.
Solar Photo voltaics (PV) (ref 127) electricity source of the future?
Solar Grid Parity (SGP) is when the lifetime cost of Photovoltaics meets the electricity house or industrial tariff.
Photovoltaic cells will be a significant green source of electricity in the future with obvious local application in buildings at the point of use. Power storage would require batteries and diversification obtained from the grid(s.) However massive arrays of cells are needed to provide power on a large scale.
Photons (sunlight) absorbed by semiconductor material (eg silicon p-n semiconductor junctions) cause electrons to be emitted producing direct current (DC). Voltaic cells consist of a thin film of crystalline semiconductor attached to glass. The glass faces the sun to provide protection from the elements.
The original single junction devices were only 33% efficient. These are being superceded by thin film materials on glass or ceramics. Cells can be made wafer thin and printed on aluminum foil. Use of low cost materials and production techniques will pull costs down and increase efficiency.
The world production of electricity by Photovoltaics is around 0.4%. There are several installations of 10 to 20 MW in Europe and a 130 MW installation planned in Spain. A 154 MW installation of photovoltaic panel heliostats, which track the sun in both axes, is planned in Victoria Australia by 2013. Light is also being magnified onto the cells eg using Fresnel lenses (light weight lens with wide aperture used in lighthouses.)
AbuDhabi is building a 6 sq km city for 50,000 residents and 1500 businesses entirely powered by the solar photovoltaics, which should be complete by 2012. Thin film polysilicon rubber will be applied to the surface of buildings and on canopies. A feature will be travel by bike and light rail with no cars. Design by Foster and partners.
The 550 MW Topaz Solar Farm project will use thin film PV panels by OptiSolar, producing electricilty direct. The panels swivel in 2 dimensions to track the sun. These installations could soon be competitive with CSP and wind but in future may be several times as effective which could enable them to be a major contibution to enabling zero carbon homes, including older dwellings, in addition to large scale arrays / power plants. (ref 187.)
Thin film solar generators.
Solar generators will in future be made up from Polycrystaline thin film (1 to 10 micrometres reduced from 100 t0 300 micrometres). These could be incorporated in flexible materials which could be used as canopies or become cladding for buildings.
Dye sensitised solar cell (DSSC), notably the Gratzel cell, promise a low cost system which is simple to construct. (ref 209.) Sheets are flexible and mechanically robust.
In future windows may consist of layers of electrolyte, photosensitive dye and semiconductor sandwiched between layers of glass to produce electriccity.
Solar panels for buildings
Domestic installations convert the heat collected from suns rays on roof panels which in turn heat water fed into a cylinder to heat water. The first systems of panels of tubes in which water circulates are now superceded by metal elements in vacuum tubes transferring heat to water at a header. Designs need to consider storage volume to carry over from day to day and loss through insulation and (heat) conduction along pipes entering water cylinders.
Solar Catermaran Project 'Planet Solar.'
A 31 m X 15 m catermaran powered by 500 sq metres of black solar panels is due to be sailed (driven) around the equator. Top speed 15 knots (17 mph) and accomodation for 50 people. A joint project built in Kiel, Germany with Nippon Oil.
Solar Car project - Endeavour- race Darwin to Adelaide
25 cars completed the race. Endeavour came 15th.
Solar round the world flight 2011 (ref185)
Round the world flight is to be piloted by Bertrand Picard and Andre Borschberg to demonstrate solar flight. It will fly at 25,000 feet at day using power from solar cells and fall to 5000 feet at night gliding and using lithium battery power.
