Solar-thermal power plants

1. Tower technology + heliostats

Our concept is that there is a need, in many regions of the earth, for "mini" power plants, for the purpose of autonomous supply of villages and small towns with electrical energy independently of the grid, for example.

A rational size for such a plant could, for example, be a field for the generation of 1 MWe. This, on a European calculation base, would probably involve investment of around 3.5 million Euro.

Such pricing can be only achieved, however, provided all components are standardized and can be produced in large numbers.

For various reasons, which are discussed in the "Solarthermal systems" section, we propose a hydraulically actuated and controlled type of heliostat for concentration of solar radiation onto a receiver in a tower.

A further proposal concerns the installation of the heliostats in groups. Six heliostats, for example, can be supplied from a centrally located hydraulic unit. The supply lines would be routed in covered ducts. The hydraulic and electronic control system would then be located in the control cabinet of each individual heliostat.

1.1 Heliostat

The heliostat is composed of the following modules: the Pylon (1), consisting of sectional steel with a top-mounted Pivot (5), a Transverse Support (2), also consisting of steel section, the Support Frame (3) of shaped steel plates, four Mirror Mountings (4), consisting of reinforced sandwich plates with bonded-on thin-glass mirrors, and the Control Cabinet (8) with flexibly connected Cylinders (6 and 7) and the integrated hydraulic and electronic control system for the heliostat.

All components are dimensioned in such a way that they can be transported in standard containers. Assembly is by means of simple bolting together of the prefabricated components.

A prototype has been assembled and tested.

(please click on the drawing to enlarge it)

1.2 Tower

The tower onto which the solar radiation is focussed by the heliostats consists, firstly, of the tower head, taking the form of a prefabricated component, and the tower frame, consisting of bolted sectional-steel elements.

The tower head contains one or two receivers. These consist of a honeycomb-like porous ceramic material which is heated up by the incident radiation, causing the ambient air in it to be heated to around 800 degrees C.

The hot air is then routed through a conventional heat-exchanger, generating steam, which is then used, via the turbine connected, to drive a generator and thus produce electrical power.

To cover periods without sunshine, a side stream of the hot air is routed into a thermal accumulator, from which it can be fed again to the heat-exchanger when needed.

The accumulator consists of an insulated steel vessel with a ceramic bulk packing in its interior. To permit bridging of longer periods without sunshine, a gas burner could be installed inside the vessel in order to keep the packing at a certain minimum temperature, thus resulting in a hybrid design.

New developments include the receiver (DLR, Cologne) and the accumulator (Solar Institut, Jülich). All other components are known technology.

The great advantage of this so-called "tower technology" is the use of atmospheric air as the heat-bearer. The process is simple, safe and reliable. Air is available without limitation, nontoxic and free-of-charge. It can be routed in a hot-gas circuit virtually without pressure, with absolute technical safety and reliability. Start-up and shut-times are short, and no harmful or pollutant substances are produced at any point during purely solar-based operation. In the case of hybrid-mode operation, the CO2 output can at least be balanced via the use of biogas.

A standardized power-generating plant unit as described above can simply be multiplied in case of greater energy demand.

(please click on the drawing to enlarge it)

The target must be that of generating power with no emissions, safely and reliably, and at the lowest possible cost, across a period of thirty years; depreciation of the investment costs across this period must constitute only an acceptable level of burden for users.

LEHLE GmbH Technik & Design  robert.lehle@lehle-gmbh.de fax: +49 (0) 7034 26661 Teckstrasse 37 D-71116 Gärtringen Germany Registered: HRB 3902 Amtsgericht Böblingen VAT-Nr.: DE811926159