Basic principles of solar systems: solar thermal
INTRODUCTION TO SOLAR THERMODYNAMIC
The guiding principle of this solution is rather simple, and is based on the idea of replacing in a normal thermal power plant steam the steam generator with a solar system capable of producing steam to be sent to the turbine.
The steam turbine for power work needs to steam at appropriate pressure and temperature, and the efficiency of the thermodynamic cycle is a function of these parameters.
The system for heating the fluid is made up of parabolic concentrators, in which focus is placed a conduit where the fluid flows.
The solar rays, focused at the duct manage to raise the temperature of the fluid at adequate levels in the expansion turbine, which then is connected to an electric generator connected to the network.
E 'is therefore clear that the most critical part of the entire system is constituted by the system of its own production and distribution of such heat, or by the system of parabolic mirrors, from pipelines, from the heat transfer fluid and from any of the heat accumulation systems.
The first thermodynamic plants in the world were made in the 80s in the United States, and initially the fluid was made up of fuel oil, the danger of which in the case of incendione has seen the rapid replacement with other fluids capable of good thermal performance and the same time able to ensure the safety in case of leakage of fluid.
DIAGRAM
A solar thermal power plant has a development similar to a large photovoltaic field on the ground, with the addition of the building that houses the turbine and the condenser.
For the cooling of the condenser is necessary to have a water or a solution to the cooling tower or unit heaters, similarly to what happens in a normal thermal power plant traditional steam.
There are two different plant solutions, the first involves a large number of collectors to the ground (usually file parabolic collectors), which concentrate the sun's rays on the conduit where it passes the heat transfer fluid, which then is sent to a steam turbine to produce electricity .
A second solution involves the construction on the ground of an expanse of mirrors (heliostats) which are oriented so as to reflect towards a tower properly positioned with the rays of the sun
In the tower there is a "receiver" that allows you to collect the sun's rays to heat the heat transfer fluid, which then expands in a steam turbine similar to the previous case.
A steam system, although of reduced power, has difficulties to operate in non-stationary conditions, both in terms of current supply on the network, both in terms of flow rate and temperature of the steam is not constant, therefore the use of thermal accumulators provides help in the regularization of plant operation, also you have the opportunity to accumulate any excess heat during maximum insolation, then to be able to use when radiation is not enough or is completely absent (evening and night).
E 'obvious that this excess heat must be produced during the insolation, therefore if the demands of the network are such as to consume the entire production, you can not have any energy reserve.
EXAMPLES OF EXISTING FACILITIES
The technology thermodynamics today is experiencing a remarkable expansion and interest, and there are several plants in operation in the world that can be examined to better understand this technology.
As an example of system with solar tower we can refer to a plant built in Spain, called PS10.
This plant is credited with a maximum power equal to 11MW electrical and uses a solar tower 100 meters high.
This plant operates with saturated steam in a cycle with two levels of pressure and temperature and maximum pressure of the steam respectively equal to 250 ° C and 40bar, and manufacturability annual electricity is assessed in 23GWh/anno, and the surface occupied by the heliostats is 55 hectares.
This plant has a storage system capable equal to 20MWh, capable of providing a 50-minute duration at 50% load.
The cost of this facility was € 16.65 million, with an EU contribution of EUR 5 mln €.
An example of a system equipped with a parabolic panels instead Andasol, facility which has maximum power of 50MW electrical, for an annual production of electricity equal to 179GWh.
This system uses as the medium of molten salts and has a range of A7.4 hours, also declares a number of hours per year equivalent to the maximum output of 3589.
The area occupied by the mirrors is 200 hectares, and the costs for building the plant totaled € 14.3 million, with an EC contribution amounts to € 5ml.
CONSIDERATIONS
From the two examples just presented, and without wanting to enter into discussions particularly complex, I think it is fair to develop some considerations on this technology, I find it particularly important to contrast the advantages in terms of pollutant emissions that this solution entails, what are its limits technicians, in particular must take into account that such facilities, although subject to continuous technological improvements, free surfaces require extremely high in relation to the production of electricity, so it can be installed anywhere and in the presence of activities that require the use of the land for other purposes, also the possibility of producing in conditions of absence of insolation is subject to a higher production placing on the network, that is the energy that the plant is capable of accumulating is energy that has been previously produced but not consumed, and therefore it can be used lazily.
Appears on the other hand evident that large-scale use of this technology as a replacement for traditional technologies appears rather complex and problematic as the energy consumption are of extremely different orders of magnitude with the production capacity of this technology, while the need for territory becomes difficult to meet unless you have uninhabited areas with adequate insolation conditions, provided of course not present in a diffuse manner.
All you simply want to encourage readers to critically evaluate each ad sensationalized on energy and the environment, as each technology and solution has its strengths and weaknesses, and their application requires therefore always trade-offs that make the valid 'use.
05/10/2009
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Translated via software
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Source:
Italian version of ReteIngegneri.it