Th.3. Means of solar energy conversion/TITLE>
SEMICONDUCTOR NON-TRADITIONAL ENERGY SOURCES

MEANS OF SOLAR ENERGY CONVERSION TO ELECTRICETY

The ways of solare energy transformation

Solar energy can be transfered to heat, electricity, chemical energy, mechanical and others .  

TRANSFORMATION TO HEAT
Heat generation - one of the most ancient and the most effective means of solar conversion. There are a lot of effective converers solar energy in heat in the market (see picture at the bottom).Conversion solar energy to heat is used in projects of modern eco-houses (see picture above on the left), for cooking, for water heating (pictures below).

Солнечная плита для подограва пищи Тепловые коллекторы. Производство КНР.

The collector is the main element of all solar energy converters to heat. The main destination of the collector is heating of heat carrier. As rule the heat carrier is fluid or gase. The most common carriers are water and air. If we mark Tin input temperature of the carrieer and Tout output temperature ( Тout > Тin). Than higher Тout - Тin , than higher effectiveness of solar converter. Effectiveness:

Eff = Q / (H·A)%,

where Q - heat power in the load, H - density of input solar power , A - area of the collector.

Диаграмма эффективности

The above picture shows the main losses and their influence on effeciency of the converter.

The price of heat supply equipment may be 15-35% of the object price.
Technical design may be: once-through, single-tuned, double-tuned, multy-tuned. Some examples are shown below..

Прямоточная схема

Прямоточная схема с аккумулятором

Замкнутая схема с теплообменником

BIOCONVERSION

The solar energy is reserved as chemical energy in biomass formed during photosynthesis. All plants use this way of solar energy transformations. All modern bio fuel appeared as a result of bioconversion of energy of solar radiation, reaching the Earth.The vegetative cover of ground makes of 1800 billions tons of dry substance. The energy equivalent of it is 3·1022J.Annually photosynthesis produces approximately 173 billion tons of dry substance. Approximately twentieth part of this amount is used in power and the one two-100-th part is used in food.

THERMODINAMOC CONVERSION OF SOLAR ENERGY

At thermodynamic transformation of a solar energy at first the energy is converted to heated steam ener Tower thermodinamic solar atation , then in mechanical and then in electrical is used. In the majority of installations the collectors, concentrating solar radiation, are used for heating water steam or air up to temperatures about several hundreds of degrees. Heated up steam or air are applied then in order to get work according to a thermodynamic cycle. Thus, from a solar energy by a method of thermodynamic transformation it is possible to receive an electricity practically the same as and from other sources of energy. For reception of high temperature in solar power stations with thermodynamic transformation a basic element are the concentrators of a solar energy. The degree of concentration up to 1000 times is used.In a solar power station of a tower type the transformation of energy is carried out by a so-called open cycle of Brighton submitted on the circuit on the right. In this cycle the chamber of combustion is replaced with the receiver of the concentrated radiation, located on a tower. On an the compressor input air acts at Т= 299oК, on an the receiver output temperature of air Т=1023°К529°K>According to efficiency of an ideal cycle of Brighton makes 1 - TinpТвых = 48%. The advantage of a tower type station consists in that it is not necessary to carry out transportation of working gas on the large distances from the receiver up to the turbine. However system of radiation concentration is expensive. And it is not enough effective, because of errors tracking errors, factor of concentration. The efficiency equals e approximately 1/3 from theoretical calculated. 

The stations with the allocated energy receiver are more perspective. For them degree of concentration about 100 times is reached at use of reflecting surfaces concentrating energy at any of solar beams arrival direction. The system of Sun trackingis carried out in this case with the help of the simplified control system.

For parabolic reflector axis is horizontal (right figure), or is perpendicular to movement of the Sun. Such installations react only to change of the Sun position within day. The change of a of the Sun within the year is not taken into account. The measures are accepted only, that the focal image did not fall outside t of the receiver surface he limits.  The oil is used in it as heat carrier. The station of this type has some hundreds mirrors (1), directing radiation on a thin pipe from corrosion-proof steel (2), with a black covering. The overheated oil (390oС) in heat exchanger (3) gives back heat to water, transforming it in steam. The exhaust steam goes condenser (4). Overheated steam actuates turbo generator of a usual type (5). Gas heater (2) is used for heating of the carrier in the case of low solar radiation.
The appearance of a machine hall of a solar power station such as "Luz" is shown in figure on the right. Some stations of a similar type with the general established power in some hundreds MW were constructed. The size of the energy, produced by them, exceeds 1010 Wh.

There are two approaches to creation of solar stations working on a thermodynamic cycle. First - use of the small-centralized stations for the remote areas. Second - creation of large solar power installations with power in some tens Wh, designed on work in the centralized network.The solar power stations of a parabolic type have appeared cheaper, than power station of a tower type. A number of firms on their designing and installation was created, that has allowed to carry out their gradual perfection and decrease initial expenses and accordingly cost of the made energy (see forecast in figure on the right).

 

 


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