A Method and apparatus for generating energy The invention relates to a method and apparatus for generat ^¬ ing electrical energy using natural resources of the environ ^¬ ment, in particular in a desert.

Most of the world' s current energy resources have been formed by the conversion of sunrays in fossil materials such as oil, gas or coal. However, the available amount of available fos ^¬ sil materials is limited. Furthermore, the burning of fossil materials leads to emissions which in turn cause global warm ^¬ ing. Global warming emissions deriving from energy production is a serious environmental problem.

Consequently, more and more renewable energy sources are used for energy production. Renewable energy can come from natural resources such as sunlight, wind, rain, tides and geothermal heat which are renewable, i.e. naturally replenished. How ^¬ ever, most conventional renewable energy resources are trans ^¬ formed in other energy forms, in particular electrical energy, by means of complex technical systems such as solar plants or wind turbine plants. These conventional power gen- eration systems are complex systems and require high invest ^¬ ments into infrastructure. Moreover, these conventional sys ^¬ tems are difficult to maintain because of their technical complexity and prone to misfunctions . Accordingly, it is an object of the present invention to pro ^¬ vide a method and an apparatus for generating in an efficient manner electrical energy from natural resources and being easy to maintain. This object is achieved by an energy generation system comprising the features of claim 1. Accordingly, the invention provides an energy generation system comprising at least one underground chamber surrounded at least partially by soil which is warmed up by solar and/or geothermal energy to heat up fluid within said underground chamber, and a turbine driven by the heated up fluid to gen ^¬ erate electrical energy.

An advantage of the energy generation system according to the present invention resides in that it is comparatively easy to construct and uses natural resources which are available in the environment in abundance to generate electrical energy.

The energy generation system according to the present invention exploits the temperature difference between day and night to generate electrical energy.

In a possible embodiment of the energy generation system ac ^¬ cording to the present invention the underground chamber comprises a chamber inlet adapted to receive said air from the environment, and a chamber outlet adapted to output said fluid to the environment.

In a possible implementation of the energy generation system according to the present invention the chamber outlet com- prises a tube through which the heated up fluid passes to drive the turbine of the energy generation system.

In a still further possible embodiment of the energy genera ^¬ tion system according to the present invention tube is ar- ranged in a vertical direction with respect to ground level and has a predetermined height.

In a still further possible embodiment of the energy genera ^¬ tion system according to the present invention the chamber inlet and the chamber outlet both comprise a gate.

In a possible embodiment of the energy generation system ac ^¬ cording to the present invention both gates of the chamber inlet and the chamber outlet are opened during a night pe ^¬ riod. The windows are opened after fluid (F) trapped in cham ^¬ ber 2, gets the maximum heat from hot soil surrounding the chamber 2 and when there is no solar energy heats up the soil surrounding the underground chamber and both gates are closed during a day period when solar energy heats up the soil surrounding the underground chamber.

In a still further possible embodiment of the energy genera- tion system according to the present invention a heat insulation unit is provided adapted to insulate the soil surround ^¬ ing the underground chamber during the night period from the environment to prevent a cooling of the surrounding soil warmed up by solar energy during the day period.

This embodiment has the advantage that the efficiency of gen ^¬ erating electrical energy is increased.

In a still further possible embodiment of the energy genera- tion system according to the present invention the energy generation system further comprises a water evaporation unit which is provided within said underground chamber.

In a possible embodiment the water evaporation unit is adapted to evaporate sea water supplied to said water evapo ^¬ ration unit.

In an alternative embodiment the water evaporation unit is adapted to evaporate underground water supplied to the water evaporation unit.

In a possible embodiment of the energy generation system ac ^¬ cording to the present invention the supplied sea or under ^¬ ground water is evaporated in the evaporation unit to provide steam which drives a turbine of said energy generation sys ^¬ tem. In an alternative embodiment of the energy generation system according to the present invention the supplied sea or under ^¬ ground water is evaporated in the evaporation unit to provide steam which condenses at a sloping surface to provide clean drinkable water collected in a water transport channel.

In a still further possible embodiment of the energy genera ^¬ tion system according to the present invention a solar energy focussing unit is provided.

In a possible embodiment of the energy generation system ac ^¬ cording to the present invention the solar energy focussing unit is adapted to focus the sunrays transporting the solar energy on soil surrounding said underground chamber during a day period.

In a still further possible embodiment of the energy genera ^¬ tion system according to the present invention the solar energy focussing unit comprises a dome structure.

In a possible embodiment of the energy generation system the dome structure comprises optical lenses which are adapted to concentrate sunrays on the soil surrounding said underground chamber during the day period.

In a still further possible embodiment of the energy genera ^¬ tion system according to the present invention the energy generation system further comprises a wastewater evaporation unit .

In a possible embodiment of the energy generation system ac ^¬ cording to the present invention the wastewater evaporation unit is provided within said underground chamber adapted to evaporate wastewater supplied to said wastewater evaporation unit.

In a further possible embodiment of the energy generation system the inlet area of the chamber inlet of said under- ground chamber is bigger than the outlet area of the chamber outlet of said underground chamber.

In a still further possible embodiment of the energy genera- tion system according to the present invention the fluid heated up in said underground chamber comprises air and/or water .

In a further possible embodiment of the energy generation system according to the present invention the energy generation system further comprises a control unit.

In a possible embodiment this control unit is provided and adapted to control the gates of the chamber inlets and the chamber outlets depending on sensor data provided by sensors connected to the control unit.

In a still further possible embodiment of the energy genera ^¬ tion system according to the present invention the sensors are adapted to measure an inside temperature of said fluid within said underground chamber, a soil temperature of the soil surrounding said underground chamber, and a surrounding temperature of the surrounding air. The invention further provides a method for generating energy comprising the steps of claim 15.

Accordingly, the invention provides a method for generating energy comprising the steps of

heating up a fluid within an underground chamber by soil sur ^¬ rounding said underground chamber warmed up by solar and/or geothermal energy, and

driving at least one turbine by the heated up fluid to gener ^¬ ate electrical energy.

In the following possible embodiments of the apparatus and the method for generating electrical energy according to the present invention are described with reference to the en ^¬ closed figures in more detail.

Fig. 1 shows a cross-section view of a possible embodiment of an energy generation system according to the present invention ;

Fig. 2, 3 illustrate a possible embodiment of an energy gen ^¬ eration system comprising a heat insulation unit according to a possible implementation of the present invention; (above the chamber 2)

Fig. 4, 5 illustrate a possible implementation of a heat in ^¬ sulation unit as employed by a possible embodiment of an en- ergy generation system according to the present invention (under the structure and beneath the soil)

Fig. 6, 7 show a top view and a cross-section view of a possible embodiment of an energy generation system according to the present invention;

Fig. 8 shows a further top view on a possible embodiment of an energy generation system according to the present invention ;

Fig. 9 shows a cross-section view through the embodiment shown in Fig. 8;

Fig. 10 shows a further cross-section view through the em- bodiment of Fig. 8;

Fig. 11 shows a further cross-section view through the embodiment of Fig. 8; Fig.l2-A shows detailed layout of the combination between energy unit A-B and water desalination unit Fig. 12-B shows a cross-section view of an alternative implementation of the embodiment shown in Fig. 8 ;

Fig. 12-C shows more details for cross section through the water desalination unit and the energy generation unit using hot air.

Fig. 13 shows a cross-section view of a further possible embodiment of a possible implementation of the embodiment shown in Fig. 8 ;

Fig. 14 shows a further possible embodiment of an energy generation system according to the present invention having a wastewater treatment unit;

Fig. 15 shows a cross-section view of a further possible embodiment of an energy generation system according to the present invention; Fig. 16 shows a diagram for illustrating the use of an energy generation system according to the present invention.

Fig. 1 shows a cross-section through a possible embodiment of an energy generation system 1 according to the present inven- tion. The energy generation system 1 according to the present invention comprises at least one underground chamber 2 sur ^¬ rounded at least partially by soil 3. The underground chamber 2 comprises a chamber inlet 4 and a chamber outlet 5 to which a tube 6 can be connected. In the embodiment shown in Fig. 1 the underground chamber 2 is located under ground level and is completely covered by soil 3. In a possible embodiment the surrounding soil 3 is formed by sand such as desert sand. This sand can cover the underground chamber 2 completely as shown in the embodiment of Fig. 1. The underground chamber 2 comprises a chamber wall 7 which is formed by a material which can conduct heat. This material can be a natural mate ^¬ rial from the surrounding environment with a high specific heat capacity such as stones. In a possible embodiment the chamber wall 7 is formed by concrete. In an alternative em ^¬ bodiment the underground chamber 7 is formed by another heat conducting material such as a metal. In the embodiment shown in Fig. 1 a turbine or an electrical generator 8 is provided on top of the tube 6. In the embodiment of Fig. 1 the tube 6 is arranged in a vertical direction with respect to ground level and can comprise a predetermined height H.

The underground chamber 2 is embedded in the soil 3 wherein soil 3 is warmed up by sunrays S transporting solar energy during the day period. This heat is conducted through the chamber wall 7 so that a fluid F within the underground cham ^¬ ber is heated up by the surrounding soil 3. The heated up fluid F' such as heated up air passes through the tube 6 and drives the turbine 8 to generate an electrical current which can be provided to an electrical grid. The fluid F' after having passed the turbine 8 exits the energy generation sys ^¬ tem 1 via an outlet 9 as shown in Fig. 1. The upward movement of the heated fluid F' within the tube 6 is caused by the fact that heated fluid F' such as heated air has a lower den ^¬ sity than a cold fluid F. As can be seen in Fig. 1 the chamber inlet 4 can suck in fluid F from the environment such as air via an inlet 10 at ground level. The outlet 9 of the en ^¬ ergy generation system 1 is at a predetermined height H above ground level. For instance, the tube 6 can pass through a tube within a tower having a height H of more than 10 meters. In the embodiment shown in Fig. 1 the electrical generator or turbine 8 is located on the top of the tower. In an alterna ^¬ tive embodiment the electrical generator 8 can be located anywhere within the tower as long as the heated up fluid F' passes through the electrical generator 8. In a possible em ^¬ bodiment the chamber inlet 4 and the chamber outlet 5 both comprise a gate. In a possible embodiment both gates are opened during a night period when no solar energy heats up the soil 3 surrounding the underground chamber 2. During a day period when the sun shines on the soil 3 both gates are closed so that the solar energy of the solar rays having an impact on the soil 3 heat up the soil 3 surrounding the un ^¬ derground chamber 2.

In a possible embodiment the soil 3 surrounding the under- ground chamber 2 is heated up by solar energy. In an alterna ^¬ tive embodiment the underground chamber 2 is heated up by geothermal energy. In a still further embodiment the under ^¬ ground chamber 2 is warmed by solar and geothermal energy. In a possible embodiment the inlet 10 is built such that it is directed towards a general direction of air, i.e. wind direc ^¬ tion, so that surrounding air can easily enter the underground chamber 2 when the chamber inlet gate is open, for instance during a night period. In a possible implementation the inlet 10 of the energy generation system 1 is movable and can be turned towards the direction of the wind. In a possi ^¬ ble implementation the inlet area of the inlet 10 is bigger than the outlet area of the outlet 9. In a possible implemen ^¬ tation the ratio between the inlet area and the outlet area is significant and can be more than ten.

In a possible embodiment the gates of the chamber inlet 4 and the chamber outlet 5 are controlled by a control unit. In a possible embodiment the control unit controls the gates de ^¬ pending on sensor data provided by sensors connected to the control unit. In a possible embodiment these sensors comprise temperature sensors. In a possible embodiment the temperature sensors are adapted to measure an inside temperature of the fluid such as air within the underground chamber 2. In a further possible embodiment the sensors are adapted to measure a soil temperature of the soil 3 surrounding the underground chamber 2. In a still further possible embodiment the sensors also measure a surrounding temperature of the surrounding air . The energy generation system 1 according to the present invention exploits in a possible embodiment a temperature dif ^¬ ference between a day period and a night period to generate electrical energy and/or to obtain clean drinkable water from salty sea water. The electrical generator or turbine 8 con ^¬ verts the movement of the fluid stream into electrical en ^¬ ergy. During the day period the soil 3 covering the underground chamber 2 absorbs the solar energy heating up the soil 3 and the gates of the underground chamber 2 are closed such that a fluid F such as air is trapped in the chamber 2. Dur ^¬ ing the night period the gates of the underground chamber 2 are opened so that the heated up fluid F' drives the electri ^¬ cal generator 8. The energy generation system 1 as shown in Fig. 1 can, for example, be placed in a sand desert. The sand surrounding the underground chamber 2 absorbs the heat all day and this solar energy is transported through the wall 7 of the underground chamber 2 and heats up the fluid such as air within the chamber. The heated up fluid F' in turn drives the turbine 8 to generate electrical energy. During the night period, especially in a desert, the temperature drops sig ^¬ nificantly by, for example, 30 to 40 Kelvin. Accordingly, in a preferred embodiment the energy generation system 1 of the present invention further comprises a heat insulation unit which is adapted to insulate the soil 3 surrounding the un ^¬ derground chamber 2 during the night period from the environ ^¬ ment to prevent a cooling of the surrounding soil 3 warmed up by the solar energy during the day period. The energy generation system 1 according to the present invention uses the heated up fluid or hot air to generate elec ^¬ trical energy since the heated up air is lighter than cold air to cause an upward movement of the fluid within the tube 6. Moreover, the energy generation system 1 according to the present invention uses wind in a desert at night, wherein the moving air is caught by the inlet of the energy generation system 1 and moves through the underground chamber 2 up through the tube 6 and passes via the electrical generator 8 through the outlet 9 of the energy generation system 1. Ac- cordingly, in a preferred embodiment the energy generation system 1 according to the present invention does not only transform the solar or geothermal energy absorbed from the surrounding soil 3 but also energy transported by the sur- rounding wind. Accordingly, in this embodiment there are two sources of energy to drive the electrical generator 8 of the energy generation system 1. The wind movement at night plus the absorbed solar energy and/or geothermal energy stored within the surrounding soil 3 is used to generate electrical energy .

In a desert the temperature difference between day and night is big. The cold air has a higher density than hot air thus it exists in lower height. Hot air with its low density al ^¬ ways moves up to higher height.

When both gates are opened at night, this allows cold air and wind to enter the hot chamber. The hot air trapped in the chamber 2 moves up because of its lower density. The cold wind (high density) enters from inlet 4 with a certain speed, and then this cold air gains energy from the hot chamber 2 and it becomes itself hot. Its density becomes lower and it moves up to the turbine 8. The air movement cycle creates electrical energy by means of the turbine 8.

The system 1 uses the big temperature difference

between day and night in a desert. At the beginning of the night, the gates are closed until the fluid or air trapped in the chamber 2 reaches a maximum temperature. When air temperature increases, the gates of the system are opened again. Hot air with low density moves up from the chamber 2, this attracts cold wind to enter the chamber 2 with a certain speed. The cold air from outside the chamber 2 has a high density (due to the low temperature at night in the desert) . It gains heat energy beside its kinetic energy. It becomes lighter and moves up. This air/wind movement can be used to generate energy by the turbine 8 which is located on the out ^¬ let .

The efficiency of the electrical energy generation is in ^¬ creased by using in a possible embodiment a heat insulation unit. This heat insulation unit insulates the soil 3 sur ^¬ rounding the underground chamber 2 during the night period from the environment to prevent a cooling of the surrounding soil 3. Fig. 2, 3 show a possible implementation of such a heat insulation unit. Fig. 2 shows soil 3 covering an underground chamber 2 of the energy generation system 1 and being heated up by the sunrays during the day period. The soil 3 is sur ^¬ rounded by a channel 11. The channel 11 of the heat insula ^¬ tion unit can circumvent the soil volume on top of the under ^¬ ground chamber 2 in a ring structure as shown in Fig. 2. The walls of the channel 11 can, for example, be formed by con- crete. In the channel 11 a heat insulation plane 12 can be moved around, for example by roller means 13A, 13B, 13C, 13D placed in the corners of the rectangular channel ring. Fig. 2 shows a position of the insulation plane 12 where the insula ^¬ tion plane is located such that the sunrays can heat up the soil 3 surrounding the underground chamber 2.

Fig. 3 shows a state of the heat insulation unit where the heat insulation plane 12 within the channel 11 insulates the soil 3 from the air during the night period to prevent a cooling of the soil 3 warmed up by the solar energy during the day period. In a possible implementation the insulation plane 12 can be moved by an insulation chain within the channel 11 wherein the walls of the channel 11 are either made of metal or concrete. The roller means 13A, 13B, 13C, 13D can in a possible implementation also be controlled by the control unit of the energy generation system 1. This control unit can, for instance, receive sensor data from sensors measuring the temperature of the surrounding air, the temperature of the fluid within the underground chamber 2 and the tempera- ture of the soil 3. If the temperature of the surrounding air drops under a predetermined threshold value, the control unit can control the heat insulation unit as shown in Fig. 2 such that the insulation plane 12 is moved to be located above the soil 3 to insulate it from the cold air as shown in Fig. 3. Accordingly, the heat insulation unit comprises at least one heat insulation plane 12 which is moved in a built-up chan ^¬ nel. In the morning the insulation plane 12 is moved such that the sunrays can directly impact the surface of the soil 3. At night, the insulation plane 12 covers the soil to trap the absorbed energy stored in the soil 3.

Fig. 4, 5 show an alternative implementation of the heat in- sulation unit provided to insulate the soil 3 surrounding the underground chamber 2 during the night period. In this em ^¬ bodiment the heat insulation unit comprises not a ring struc ^¬ ture but peripheral channels in which different heat insula ^¬ tion planes can be located during the daytime as shown in Fig. 4. In the shown embodiment there are several peripheral channels where heat insulation planes 12A, 12B, 12C, 12D, 12E can be located or placed during daytime. In this way, the soil 3 can be heated up directly by the impacting sunrays during the daytime as shown in Fig. 4. In the evening the different insulation planes are moved from the peripheral channels to insulate a soil volume 3 from the remaining de ^¬ sert D (in case the soil around the system loses heat because of the low temperature at night) as shown in Fig. 5. The heat insulation unit as shown in Fig. 2, 3 can be combined with the heat insulation units as shown in Fig. 4, 5, wherein the heat insulation units as shown in Figs. 2, 3 can be used mainly to insulate the soil 3 from the surrounding air, whereas heat insulation units as shown in Figs. 4, 5 are mainly used to insulate the soil 3 from the surrounding soil of the desert during the night period. The insulation of the soil 3 during the night period from the environment can in a possible embodiment be performed under the control of a con ^¬ trol unit automatically. In an alternative embodiment the in- sulation of the soil 3 during the night period can be per ^¬ formed manually.

Fig. 6, 7 show a possible embodiment of the energy generation system 1 according to the present invention. Fig. 6 shows a top view on the underground chamber 2 and its in- and outlets whereas Fig. 7 shows a cross-section view A-A through the energy generation system 1. In the embodiment shown in Fig. 6, 7 the energy generation system 1 comprises only one under- ground chamber 2. In an alternative embodiment the energy generation system 1 can comprise several underground chambers 2 which can be used for different purposes. Fig. 8 shows an embodiment of the energy generation system 1 comprising three underground chambers 2-1, 2-2, 2-3. Each un ^¬ derground chamber 2-i can comprise a chamber inlet and a chamber outlet. Fig. 8 shows a top view on the three under ^¬ ground chambers 2-i of the energy generation system 1. In the shown example the inlets of the energy generation system 1 are placed to the right hand, whereas the outlets are placed to the left hand. In the shown embodiment of Fig. 8 the wind direction is from right to left so that the fluid, i.e. sur ^¬ rounding air, can enter the underground chambers 2-i during the night period easily when the gates are open. At the out ^¬ lets three different electrical generators 8-i are provided. The electrical generators 8-i can be connected to an electric grid and can in a possible embodiment generate an AC cur ^¬ rent I. The different underground chambers 2-i can be sepa- rated from each other by means of walls or gates formed by concrete or other materials. Each subsystem or underground chamber 2-i can function differently based on the applica ^¬ tion. Each underground chamber 2-i can in a possible embodi ^¬ ment comprise its own heat insulation unit. Different heat insulation units can be controlled in a different manner dur ^¬ ing day or night depending on the function of the respective underground chamber 2-i.

Fig. 9 shows a cross-section view A-A through the underground chamber 2-1 of the energy generation system 1 as shown in

Fig. 8. This underground chamber 2-1 is formed in a similar manner as the underground chamber 2 shown in Fig. 1. It comprises a chamber inlet and a chamber outlet connected to a tube 6 through which heated up fluid F' drives an electrical generator 8-1 as shown in Fig. 9.

Fig. 10 shows a cross-section view B-B through the second underground chamber 2-2 of the energy generation system 1 shown in Fig. 8. As can be seen in Fig. 10 the energy generation system 1 comprising the second underground chamber 2-2 comprises in this implementation a water evaporation unit 13. The water evaporation unit 13 is provided within the under- ground chamber 2-2 and is adapted to evaporate sea and/or un ^¬ derground water supplied to the water evaporation unit 13. The water evaporation unit 13 comprises a water supply channel 14 which supplies underground or sea water W to the water evaporation unit 13. The bottom of the water W supply channel 14 can have a curved form as shown in Fig. 10. If the sup ^¬ plied water is salty sea water the energy absorbed in the surrounding soil 3 heats up the supplied water so that water evaporates and can condense at a sloping surface 15 of the water evaporation unit 13. The condensed water CW is col- lected by a clean water transport channel 16 and output by the energy generation system 1. The remaining salt of the evaporated salty seawater is collected in side channels 17-1, 17-2 which can be cleaned from time to time to collect the remaining salt. Accordingly, the energy generation system 1 outputs in the shown embodiment not only electrical energy but also clean drinkable water CW. Moreover, the energy generation system 1 further provides usable salt. In the embodi ^¬ ment of Fig. 10 the energy generation system 1 can also comprise two electrical generators 8-2a, 8-2b in the second un- derground chamber 2-2. Further, in the shown embodiment there are two gates 18, 19, wherein one gate 18 separates the evaporation unit 13 from the remaining underground chamber 2- 2. The other gate 19 can be placed at the inlet of the under ^¬ ground chamber 2-2 as shown in Fig. 10. During daytime the gates can be closed so that the trapped air can be heated up by the surrounding soil 3. At night both gates are opened so that the air can pass through both electrical generators 8- 2a, 8-2b to generate electrical energy. The air trapped in a chamber 20 of the water evaporation unit 13 during daytime is also heated up by the surrounding soil 3 and helps to evapo ^¬ rate the supplied underground or seawater. In the embodiment shown in Fig. 10 the clean water is generated mostly during daytime when the surrounding soil 3 is heated up. Fig. 11 shows cross-section views C-C through the third underground chamber 2-3 of the energy generation system 1 as shown in Fig. 8. In the third underground chamber 2-3 sea or underground water is supplied to the underground chamber in a supply channel 14. The sea or underground water W is used to cool the air within the chamber during the day period. Ac ^¬ cordingly, the third underground chamber 2-3 of the energy generation system 1 is used to generate electrical energy by means of the driven turbine 8 but no clean water is obtained.

Figure. 12-A shows layout of the combination between energy unit A-B and water desalination unit (C-D) . They are perpendicular to each others. The water desalination unit gets wa- ter directly from the sea.

Fig. 12-B shows a further embodiment of an energy generation system 1 according to the present invention. In the embodiment shown in Fig. 12 the chamber 2 is placed within a water tank 20 to which water is supplied via a water supply channel 21. The soil volume 3 can be heated up during the day period and is insulated during nighttime by using a heat insulation plane of a heat insulation unit as shown in Fig. 12. A water layer can be formed between the hot soil 3 and the air void 2 that contains the heated air. When the air is heated it is trapped between two layers of water as shown in Fig. 12. The water between the heated up soil 3 and the chamber 2 containing the hot air does evaporate and can move up within a tower 22 until it reaches a sloping surface of the tower where it can condense. The condensed steam is collected in a clean wa ^¬ ter transport channel 23 similar to the clean water transport channel 16 shown in Fig. 10. In the embodiment shown in

Fig. 12 there are also two separate insulation systems wherein one insulation system is provided for insulating the soil 3 covering the water tank 20 from the environment during the night and one insulation system is provided for insulat ^¬ ing the surrounding soil 3 surrounding the water tank 20 from the remaining soil of the desert during nighttime. In the em- bodiment shown in Fig. 12 the chamber 2 within the water tank 20 is provided for generating desalinated water from the wa ^¬ ter supplied to the water tank 20 via the water supply chan ^¬ nel 21. The system 1 shown in Fig. 12 allows hot air to heat and evaporate water to generate clean drinkable water CW at nighttime. The arrangement shown in Fig. 12 can be combined with the underground chambers 2-1 shown in the other embodi ^¬ ments . Fig. 12-C shows more details for cross section through the water desalination unit and the energy generation unit using hot air.

Fig. 13 shows a further possible implementation for a subsys- tern for generating clean drinkable water. In the shown embodiment the underground chamber 2 comprises a water tank to which water as a fluid is supplied to. The water W or fluid F is heated up and evaporates to generate clean drinkable water CW collected in a clean water transport channel 23. In a pos- sible embodiment the steam or evaporated water further drives an electrical generator or turbine 8 to generate electrical energy at the same time. In an alternative embodiment the heated up evaporated water W or steam does drive only an electrical generator or turbine 8 as shown in Fig. 14.

The supplied water W can be underground water or seawater. In a still further possible embodiment the supplied water W can also be wastewater. In this embodiment the evaporated water is mainly used to generate electrical energy and not to gen- erate clean drinkable water. Accordingly, in a possible embodiment the energy generation system 1 according to the present invention can comprise a wastewater evaporation unit adapted to evaporate wastewater supplied to the wastewater evaporation unit. This wastewater evaporation unit can be im- plemented as shown in Fig. 14. Accordingly, in this embodiment wastewater coming from a private household or a plant can be used to generate electrical energy by means of elec ^¬ trical generator 8 as shown in Fig. 14. Accordingly, in this embodiment the energy generation system 1 according to the present invention can be attached to a wastewater treatment plant. The vapour energy can be used to generate electrical energy and the sludge of the remaining wastewater can be re- moved automatically in a possible implementation.

Fig. 15 shows a further possible embodiment of the energy generation system 1 according to the present invention. In this embodiment the energy generation system 1 further com- prises a solar energy focussing unit 24 which is adapted to focus the solar energy on soil 3 surrounding the underground chamber 2 during the day period. In a possible embodiment the solar energy focussing unit 3 can comprise a dome structure. This dome structure can comprise optical lenses 25-i as shown in Fig. 15 which are adapted to concentrate sunrays S on the soil 3 surrounding the underground chamber 2 during the day period. These optical lenses 25-i can be integrated in a glass structure carried by the dome structure. Moreover, the glass surrounding the soil 3 additionally traps solar energy within the dome chamber 26 as shown in Fig. 15. Accordingly, in a possible embodiment the dome structure can also work as a greenhouse which helps to keep the soil 3 surrounding the underground chamber 2 warm during the night period. The dome chamber 26 can be a great space which can be used for other purposes as well. For instance, it can be used to grow plants. Moreover, the dome can be used as a room for other activities such as art gallery, exhibitions, parties, science festivals or recreation. In a possible embodiment the dome structure comprises glass elements carried by a steel struc- ture . Lenses 25 integrated in the glass structure can be used to collect the parallel sunrays and concentrate the sunrays to the soil 3 as shown in Fig. 15 to heat up the soil 3 cov ^¬ ering the underground chamber 2 during daytime. Fig. 16 shows a diagram for illustrating the distribution of energy and clean water by the energy generation system 1 according to the present invention. The energy generation system 1 is supplied with solar and/or geothermal energy as well as with sea or underground water W as shown in Fig. 16. The system 1 generates electrical energy E which can be supplied to different buildings B. Moreover, the system 1 is able to supply buildings B with clean drinkable water CW as shown in Fig. 16. Wastewater output by buildings B can be recycled within the system 1 by a wastewater evaporation unit.

The invention provides a method for generating energy and/or clean drinkable water by using four main elements which are provided in high quantities in specific environments such as a desert. These main elements comprise a large area, sun en ^¬ ergy, soil or sand as well as seawater. By efficiently using these elements the method according to the present invention does not only generate energy E but also other usable prod- ucts such as clean drinkable water CW and/or salt. No energy besides solar energy and/or geothermal energy must be sup ^¬ plied to the system 1. With the method according to the pre ^¬ sent invention a fluid within an underground chamber 2 is heated up by soil or sand surrounding the underground chamber 2 using solar and/or geothermal energy. At least one electrical generator or turbine 8 is driven by the heated up fluid F' such as air or water W' to generate electrical energy. In a further embodiment the energy generation system 1 can be constructed beneath a dome structure having structural ele- ments formed by steel in which glass panels are embedded and having additional optical lenses to focus light on a specific area beneath the dome structure where soil 3 surrounding the underground chamber 2 is located. The energy generation system 1 according to the present invention can be implemented inside a city as an internal en ^¬ ergy generator. The dome covering the energy generation system 1 can be used for different purposes or activities by people living in the city. The energy generation system 1 ac- cording to the present invention requires few workers for maintenance and produces green energy. Moreover, the energy generation system 1 has the advantage that it does not gener ^¬ ate any waste. The substance storing the solar energy can be formed by desert sand where it is provided in abundance. In a possible embodiment the energy generation system 1 according to the present invention does not only generate electrical energy but supplies a city or buildings of the city also with clean drinkable water at the same time. Moreover, the supply of the buildings B with clean drinkable water CW and electri ^¬ cal energy E is achieved without any energy input to the en ^¬ ergy generation system 1. The energy generation system 1 can consist of different subsystems depending on the needs of the city and each subsystem can comprise one or several under ^¬ ground chambers 2-i. For instance, one subsystem can be pro ^¬ vided for generating electrical energy whereas another sub ^¬ system is provided for generating clean drinkable water CW. The energy generation system 1 according to the present in- vention can be easily built in a desert and can be easily maintained. The energy generation system 1 according to the present invention can be formed by a central structure within the city and/or by decentralized energy generation subsystems in different buildings B of the city. If the surrounding soil 3 is heated up by geothermal energy it is possible to place the energy generation system 1 according to the present invention beneath a building B such as a house. The size and geometry of the underground chamber 2 can vary. In a preferred embodiment the chamber 2 has a geometry where the sur- face of the chamber 2 has a maximum area attached to the heated up soil 3. Accordingly, the underground chamber 2 is in a preferred embodiment relatively flat so that the surface of the soil 3 covering the chamber 2 is a large area to col ^¬ lect a maximum of solar energy. The energy generation system 1 operates best in an environment where the temperature dif ^¬ ference is high between the day and night period. This is typically the case in a desert. In a possible embodiment the energy generation system 1 can be located at a beach comprising sand surrounding the underground chamber 2 and being close to the ocean to supply the system 1 with seawater. In a possible embodiment the energy generation system 1 can provide a house built at the beach with electrical energy as well as with clean drinkable water by exploiting the tempera ^¬ ture difference between day and night.