Concentrated Solar Power: overview of the types of systems

Photovoltaics is the most used technology worldwide for the conversion of solar radiation into electricity. Signs of a possible change we have already learned, however, already in 2011, when the sector has accused the first difficulties. And the thermodynamic (Concentrated Solar Power, CSP), however, did boom, with growth of over 160% compared to 2010 in terms of new installed capacity.

This technology is able to convert solar radiation into thermal energy, through a concentrator formed by reflective surfaces which focus the sunlight onto a receiver tube highly absorbent. The set of concentrator and receiver is called the solar collector and, thanks to a handling system, is able to constantly chasing the Sun in its motion across the sky.

In practice, if we exclude the particular case of the collector disc, with the different models of the radiation collectors is not converted directly into electricity but is collected in the form of thermal energy and, as such, can be easily stored in storage systems ( generally tanks), to then be used thereafter.

The ability to modulate the delivery of the collected energy is a characteristic of the technology Csp: makes it particularly advantageous compared with intermittent renewable energy (wind, photovoltaics), which are dependent on the availability at a given time of the energy source (sun, wind , etc.). The thermal energy collection and available at high temperatures can be bound to many applications, among which the main one is obviously the conversion into electrical energy.

Behind the common name of CSP, in reality they hide four different systems, ie solutions Parabolic Troughs (parabolic trough), Linear Fresnel (linear Fresnel collectors), Dish Stirling (parabolic dish collectors) and Tower (tower systems with central receiver), which differ in their geometry and the arrangement of the concentrator respect to the receiver.

The system consists of Parabolic Troughs long linear rows of parabolic mirrors in whose focal point is placed a tube receiver, integral with the reflective surface. This, by concentrating the sun's rays onto a receiver tube, heat the heat transfer fluid flowing within it, bringing it to the desired temperature in the subsequent use.

The system Parabolic Troughs is the most widespread among CSP technologies currently productive, holding 90.9% of the power currently installed globally (over 1.5 GW). This supremacy is guaranteed by the state of maturation of this technology, which is already very competitive: in the Mediterranean area (where in the coming years are expected very large investments) equipment Parabolic Throughs ensure manufacturability than 2,700 hours a year, or more than double a photovoltaic installation placed in the same conditions.

The second step of the podium (about 7% of installed worldwide) belongs instead to the "Tower", or tower, consisting of a series of flat mirrors (heliostats), large up to 100 m², which track the sun on two axes . The only limitation of this technology is given by the maximum distance of the heliostats with respect to the tower, an element that limits the installed power for each plant. Observers expect, however, a strong growth of this solution, particularly in large American desert areas.

Another technology of Csp is that of the Fresnel collectors, which can be seen as a simplification of the plants parabolic: the parabola is segmented into several rows of mirrors much narrower and half-planes, placed flat and moved in remote starting from corners of positioning different for each row. The solar radiation is concentrated in a fixed linear absorber tube placed at a height of about 8 meters with respect to the surfaces captanti, while the slight curvature of the mirrors is defined elastically from the supporting structure of the same. On the development of this technology, however, the reduced weight average efficiency of operations, in the order of 8 to 10% of the total annual solar radiation, compared to values ​​of the order of 15% of Parabolic Throughs.

Finally, the market is the Dish Stirling systems technology, is still little known despite high efficiency of conversion of solar energy into electricity. It is a modular system which allows to achieve both small plants that gigantic, installing hundreds or thousands of records in a single solar park.

Whatever the solution adopted, the current one is undoubtedly a very favorable to the development of solar thermal power. According to the report Solar Energy Energy & Strategy Group of the Politecnico di Milano, in the past year have been installed all over the planet longer than 545 MW of new capacity. The combined power of the overall thermodynamic world thus reached 1,655 MW at the end of 2011, to which we must add another 66 MW became operational in early 2012.

The leadership of the CSP is in the hands of Spain, just in 2011, has clearly overtaken the United States: the Iberian country now boasts as many as 66% of installed capacity worldwide, compared to 29% American. Overtaking is determined largely by the operation of the plants planned from 2009, while the large U.S. projects have remained only on paper.

 

05/09/2012

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Translated via software

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Source:

Italian version of CercaGeometra.it

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