Solar Chimney Power Plant

Contents

Summary

1. Introduction

2. Glass Roof - The Collector
2.1. Absorbing Medium - Hothouse Effect
2.2. Warm Air Collector (a kind of a flat collector)

3. Chimney
3.1. Cold and Warm Air - Ascending Force
3.2. Measurements and Efficiency

4. Turbines, Generator and Gearing
4.1. Wind Turbines in Solar Chimney Power Plants and Adjustable Airscrews
4.2. Position and Alternatives for Wind Turbines
4.3. Generator and Gearing

5. Conclusion and Outlook
5.1. The Plant Itself with View to the Life Span
5.2. A Successful Test and Big Plans
5.3. The EXPO 2000 and the Solar Chimney Power Plant

References

Summary

Advantages, Disadvantages and just Political Realisation Problems of the Solar Chimney Power Plant

The report ‘Solar Chimney Power Plant’ points out reasons and advantages for such a power plant. It starts with the main principle in short

Than the text gives the main parts of the plant to show the separate advantages and the simplicity of building them. First the collector and the used hothouse effect. Belonging to that are the glass roof (absorber), natural ground (accumulator) and the operating medium (air) explaind. Also mentioned are possibilities to increase the efficiency. Further the chimney with the suction effect and the problem of its efficiency. As third part the turbine is mentioned with its principle drive and its possibilities of different positioning. In addition to the third part generator and gearing to get current power are within the report. At least the report contents a compact view to the whole plant

The text goes on to introduce a successfull operated test plant. As well as to inform about actual plans for building solar chimney power plants. Finally it draws the readers attention to political strange activities to avoid promotions for solar chimney power plants

1. Introduction

The solar chimney power plant has been developed twenty years ago. Against the conventional alternative energy sources it has two advantages. Firstly it is not technically difficult to realise and secondly it nearly needs nothing of natural materials. Conventional solar cells have the disadvantage of an expensive current and a not environmentally friendly manufacturing and waste disposal. But the assumptions for an solar chimney power plant are a big enough amount of space and a big enough amount of insolation. Especially in countries with desert regions are these assumption in existence. Also the needed building materials as glas and concrete are no problem in those regions. So these power plants are most interresting for developing countries for which they have been developed. The energy can be produced without using fossil or radioactive combustibles and no injurious waste products emerge. And compared with other power stations the costs for operating the solar chimney power plant are on a low level

The solar chimney power plant basically operates like a hydroelectric power plant, but instead of water it uses hot air. The principle is a relative simple one. A round ascending glass roof with a diameter of several thousand metres is used as a collector. A chimney in the middle sucks the ascending heated air and the air ascends with a velocity about fifteen metres per second. The arising air suction is driving wind turbines which are placed in the chimney. The turbines are used together with a generator and a gearing to produce current

The present report points out the basically parts of the solar chimney power plant. In order to make clear which well known principles are used for this power plant and that the realisation is not a matter of special materials or constructions what would be very expensive or would need further developments. Finally it gives a short overview about the facts and a view on happened enterprises as well as on future plans

2. Glass Roof - The Collector

2.1. Absorbing Medium - Hothouse Effect

To get energy from the sun for the solar chimney power plant is the same effect used like it is used for hothouses. All bodies absorbs the insolation at least partly. The absorbed insolation of short wave length is going to be changed from the bodies into radiations of long wave length, so to be changed into warmth. And in general transparent material like glas or foil, the typical material for hothouses, has also the ability of reflecting the radiations of long wave length. So such material is impervious for long wave radiations (‘elamination of radiation casualties’), which gives the material a good efficiency. Beside that there is the advantage of the mentioned kind of material that it also absorbs diffuse light. That means that the solar chimney power plant also operates with overcast sky, what is importand to tropical regions in addition to the regions mentioned in the introduction

2.2. Warm Air Collector (a kind of a flat collector)

The absorber is the mean part of the collector. In the case of the solar chimney power plant large glass roofs are needed. These power plants have an output of 50 to 400 MW each. A 200 MW plant will produce about 1.500 GWh/year at 2.300 kWh/square(m) radiation. For such measurements is it now important to have proceedings against casualties because of convection (due to wind outside the absorber) and transmission (due to the contact with colder materials like steel wich supports the glass roof). But just in the closer area of the roof to the chimney is to adjust thermal covering and translucer for the air temperature which is high at the biggest diameter and decreases with decreasing diameter. The costs for a panelling at the sides and the support places with material that thermal covers or a vaccum insulation of the complete absorber (glass or foil) would not been useful with a view to the efficiency

Than there is natural ground as an accumulator for warmth. Over the day the ground gets heated and over the night it gives its warmth to the ascending collector air. This effect can be supported with black tubes placed on the ground under the glass roof. The tubes are filled with water only once (no further water is needed) to increase the effect. Black coloured bodies have best abilities to absorb radiations of long wave length at day to heat the water and at night to heat the air

All in all the warm air collector. A collector which is robust , not difficult to realise and to operate 24 hours a day. Its glass roof ascends to the middle (in two to six metres over the ground and with up to 10m x 10m big glass segments) , so that the heated air can accelerate on the way up to the middle where the chimney is

3. Chimney

3.1. Cold and Warm Air - Ascending Force

The ascending force emerges due to the fact that hot air is not as heavy as cold air. The only way for the hot air from the collector is along the glass roof up to the middle through the chimney. In the chemney exists a suction in cause of the small and cold (compared to the heated air) surface of the chimney. The hot air likes to get upper the cold air and if the space for the air gets smaller the air accelerates. Further the air accelerating depends to the temperature difference between inside the plant (mainly inside the chimney) and outside the plant. In case of the mentioned plant approximately 35 degrees. As higher the chimney is as higher is the suction effect

At this point it is to recognize that the effect of the ascending glass roof and the suction effect are superimposed

3.2. Measurements and Efficiency

The chimney is basically the thermal engine of the solar chimney power plant. Due to the optimized proportion of surface and volume the chimney is a low loss and low friction pressure pipe. Compareable with the pressure pipe of a water power plant.