solar chinmeys, Solar updraft tower

Solar      updraft towers, also known as solar chimneys, are a relatively new concept      of renewable energy power plant that may become widespread in the future. 
    They would combine three old and proven technologies: the chimney effect,      the greenhouse effect, and the wind turbine. Air would be heated by      sunshine and contained in a very large greenhouse-like structure around      the base of a tall chimney; the resulting convection would cause air      to rise up the updraft tower. This airflow would drive turbines, producing      electricity.          A first              research prototype operated in Spain in the 1980s.
 
 Many modelling studies              have since been published as to their optimisation, scale and economic              feasibility. Some proposals have involved mega-structures reaching up              to a kilometre in height.* A small operating plant is reported to have been built in Jinshawan,              China, as of 2011. The solar updraft tower (SUT) is a renewable-energy power plant for generating electricity from solar power.  Sunshine heats the air beneath a very wide greenhouse-like roofed  collector structure surrounding the central base of a very tall chimney tower.
 
The resulting convection causes a hot air updraft in the tower by the chimney effect. This airflow drives wind turbines placed in the chimney updraft or around the chimney base to produce electricity.  Plans for scaled-up versions of demonstration models will allow  significant power generation, and may allow development of other  applications, such as water extraction or distillation, and agriculture  or horticulture.

As a solar chimney power plant (SCPP) proposal for electrical power  generation, commercial investment is discouraged by the high initial  cost of building a very large novel structure, and by the risk of  investment in a feasible but unproven application of even proven  component technology for long-term returns on investment—especially when  compared to the proven and demonstrated greater short-term returns on  lesser investment in coal-fired or nuclear power plants. Likewise, the  benefits of 'clean' or solar power technologies are shared, and the  widely shared harmful pollution of existing power generation  technologies is not applied as a cost for private commercial investment.
 
 This is a well-described economic trade-off between private benefit and shared cost,  versus shared benefit and private cost. If it is in the public  interest, then some form of public investment or subsidy to share cost  and risk will be required to demonstrate SCPP feasibility at scale. Power output depends primarily on two factors: collector area and  chimney height. A larger area collects and warms a greater volume of air  to flow up the chimney; collector areas as large as 7 kilometres  (4.3 mi) in diameter have been discussed.
 
 A larger chimney height  increases the pressure difference via the stack effect;  chimneys as tall as 1,000 metres (3,281 ft) have been discussed. Due to  variations in design, climate, local geography and latitude, a  standardised model for comparisons between design features and outputs  is needed and proposed Heat can be stored inside the collector area. The ground beneath the solar collector, water in bags or tubes, or a saltwater thermal sink in the collector could add thermal capacity and inertia to the  collector. Humidity of the updraft and condensation in the chimney could  increase the energy flux of the system