Abstract:
A solar power arrangement for converting solar energy into electricity comprising; a solar chimney, the chimney having a flared base spaced from the ground the chimney including a transparent surface to allow solar energy to heat air within the solar chimney. A first air turbine drives a first generator, and the chimney including an exhaust. The first air turbine drives an air compressor and wherein the compressor includes an ambient air intake and a plurality of pipes for receiving compressed attached to the solar chimney. A plurality of heliostats focus solar energy on the pipes to heat the compressed air contained therein and a second turbine driven by expansion of the compressed air wherein the second turbine drives a second generator.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     None 
     STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to deriving power from solar sources. 
     2. Brief Description of Prior Art 
     U.S. Pat. No. 5,300,817 is one prior art attempt to collect solar power using a chimney effect. The housing of the device is constructed partially of glass such that air heated by the sun rises within a chimney. As the air rises in the chimney it can drive a turbine. A problem with the prior art is that these large solar collectors are expensive to build and must take up a large section of land. Therefore it is important to derive the maximum amount of energy from as compact and economical structure as possible, power interruption is also an important consideration. It is also important that a solar generator be able to produce energy in a range of conditions that might include cloudy days, sunny days and days that fluctuate between cloudy and sunny. Often times the prior art requires an expensive buffer such as a battery bank to even out energy flow between sunny and cloudy days, or a thermal storage such as a molten salt tank to even out the energy flow during intermittent cloudiness within a day. 
     In prior art pure solar thermal chimney towers such as U.S. Pat. No. 5,300,817, all electrical power generation is derived from the mass flow and the pressure differential of the updraft to drive a wind turbine and electrical generator. For a given electrical power generation rate, the diameter of a pure solar thermal chimney tower structure needs to be large to allow for adequate volume of air flow. The pure solar thermal chimney tower structure needs to be high enough to generate adequate buoyancy (pressure differential) in the updraft. The diameter of the flared portion of the pure solar chimney also needs to be large to collect enough solar energy to heat up a large volume of air to generate adequate amount of updraft. Thus a large tall structure is required and the cost of construction makes the arrangement impractical. 
     It is also known to use a field of heliostats (solar mirrors) to focus solar energy. When the solar input into the solar thermal receiver fluctuates such as from temporary misalignment of heliostats (control or mechanical glitches), or intermittent cloudiness, or rapidly varying grid electrical power demand, a single spool (mechanically coupled compressor and turbine) pure solar Brayton cycle is susceptible to turbine instability or receiver burnout. Thus heliostat arrangements typically require special safety consideration to avoid damaging equipment with the intense focused solar energy. As a result, in practice, heliostats are often taken off line, generating no energy, when conditions are less than optimal. This make many prior art arrangements either expensive to operate or unreliable. Heliostats have to be situated at certain minimum distances from the central receiving tower to prevent the reflected sun rays striking the solar receiver at unfavorable angles, and to avoid the shadow cast by the central receiving tower. The land area adjacent to the central receiving tower in a heliostat field is thus wasted. 
     Prior art arrangements have failed to be able to provide enough energy benefit to offset the cost of the land used and the structure required. 
     SUMMARY OF THE INVENTION 
     The invention includes a solar power arrangement for converting solar energy into electricity comprising; a solar chimney having a flared base spaced from the ground, and the chimney including a plurality of windows to allow solar energy to heat air within the solar chimney. A first air turbine driven by heated air rising in the chimney. The first air turbine drives a first generator to create electrical power to drive a load. The chimney includes a flared upper exhaust. The first air turbine drives an air compressor and the compressor includes an ambient air intake and a plurality of coils containing compressed air looped around an upper portion of the solar chimney. A plurality of heliostats focusing solar energy on the coils to heat the compressed air contained therein and a second turbine driven by expansion of the compressed air wherein the second turbine drives a second generator and wherein a controller controls the speed of the compressor in response to the energy load and in response to the amount of solar energy available. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view of the system; 
         FIG. 2  is a view of details of the system; 
         FIG. 3  is a flow chart of the control of the system. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows an overall view of the system  100 . The system  100  includes a chimney shell  102 . The chimney includes a large flared base  104  that is held off the ground to allow for intake air to flow in. Air flow is indicated by arrows ‘A’. Air flows upward through the chimney shell  102  driven by solar heating that occurs within the chimney shell  102 . Within the chimney shell  102  air can be heated by solar energy ‘S’ part of which can pass through window portions  108  of the chimney shell  102 . Ideally the chimney shell  102  will primarily be glass or similar material that will allow for a maximum amount of net energy transfer into the chimney shell  102 . The flared base portion  104  should ideally be almost entirely transparent. Air travels up through the chimney shell  102  and as it does so it powers the wind turbine  110  located within the chimney shell  102 . The air then passes out the top end  112  of the chimney shell  102 . 
     The first energy system of the chimney shell  102  is powered by the wind turbine  110 . The blade  112  of the wind turbine is horizontal and the diameter of the blade approximately fills the inside diameter of the chimney shell  102 . The wind turbine  110  can include a stabilizer  114  connected to the ground. The wind turbine  110  also includes a power shaft  118 . A hollow cylindrical housing  120  has a bullet shaped nose portion  122  and contains some of the equipment to transfer power from the shaft  118  to a load  150 .  FIG. 2  shows details of the equipment within the cylindrical housing  120 . 
       FIG. 1  shows that the system  100  has a second way to capture solar energy, a Brayton like cycle. A plurality of heliostat mirrors  130  track the sun and focus the sun&#39;s rays onto a solar receiver  132  on the upper portion of the chimney shell  112 . A pipe inlet  134  brings ambient air into the receiver  132 . The receiver  132  includes an air compressor that compresses air to be heated by the receiver  132 . A plurality of pipe coils  136  carry compressed air in circular paths around the upper portion of the chimney shell  112 . The pipe coils  136  form a band, the surface of which is at an advantageous angle to receive solar rays reflected and/or focused by the heliostats. The pipe coils  136  are heated by heliostats  130  along the entire path of the coils  136  heating the air to a very high temperature. The compressed hot air is expanded to spin an air turbine contained within the cylindrical housing  120  details of which are shown in  FIG. 2 . 
       FIG. 1  shows that a controller  140  controls the operation of system  100  to optimize power flow to an electrical load  150 . The system  100  derives electrical power both from the wind turbine  110  and from the solar heliostats  130  and solar receiver  132 . Details of the equipment are shown in  FIG. 2  and a flowchart of the operation is shown in  FIG. 3 . 
       FIG. 2  shows details of the equipment in the upper portion of the chimney shell  112  including the cylindrical housing  120 . The wind turbine power shaft  118  brings rotational power from the wind turbine blade  110  and powers an electrical motor/generator  124 . The controller  140  determines how much energy is taken off from the generator by electrical load  150 . The shaft  118  also provides power to clutch/transmission  126 . If the controller engages the clutch  126 , then the shaft  118  is also connected to power the air compressor  138  which supplies air flow to the solar receiver  132 . The solar receiver  132  includes an air inlet  134  that provides cool atmospheric air to the compressor  138 . The compressor  138  compresses the air and provides it to solar receiver pipe  136  where the air is heated by heliostats  130  as it flows circular loops around the chimney shell  112 . The hot compressed air flows to a turbine  142  where it expands and cools and drives a second generator  144 . 
       FIG. 3  shows a flow chart of the operation  300  of the system  100 . The system  100  starts and focuses the heliostat field  301  and starts the system in chimney mode  309 A. In chimney mode  309 , the clutch  126  is disengaged  311  such that turbine  138  is not operating. When there is only diffused sunlight available the system  100  operates in chimney mode  309 , such as on overcast or cloudy days, the air inside the tower shell structure is heated by the green house effect through the transparent windows. Diffuse light condition is detected by the absence of direct sun light using small sensors for that purpose and/or the absence of high air temperature in the receiver tube. The Hybrid Solar Thermal Chimney system  100  operates as a pure solar thermal chimney on days with only diffused sunlight. The controller  140  commands the clutch/transmission to disengage  322 . The thermal updraft spins the wind turbine which drives only the motor/generator to generate electricity feeding the electrical load. The controller  140  then checks for direct sunlight  313  if no sunlight is present, the controller returns to timer loop  315 . Time loop provides a dwell time between each condition check such that the system will not rapidly change between modes of operation. Dwell time can be set to optimize operation and might be a few minutes. If direct sunlight is present, then the controller  140  checks that the receiver temperature  315  is above a first minimum temperature, the first minimum temperature would be that which would allow a change to the hybrid mode  320  A. 
     The solar energy transmitted through the transparent windows  108  heats not only the air within the tower chimney shell  112 , but also the ground underneath the tower chimney shell  112 , including the ground under the flared portion  104 . Thus the ground under the tower chimney shell  112  can act as a short term thermal buffer storage to enable the wind turbine  110  to operate at a fairly even speed level when the solar input fluctuates. 
     When there is direct sunlight reflected to the solar thermal receiver  132  by the heliostats  130 , the following hybrid operation  320  (indicated by dashed box) happens: 
     The controller  140  commands the clutch/transmission  330  to engage so that the wind turbine  110  can also spin the air compressor  138 . The air compressor  138  takes in ambient air from inlet  134  outside the tower chimney shell  112  and compresses the air to a higher pressure. The air compressor  138  pushes the compressed air through the solar thermal receiver  132 . The controller  140  can then check  313  for direct sunlight. If there is no direct sunlight then the controller will change to chimney mode  309  to be effective after the next 8 dwell time  315 . In hybrid mode  320  the controller  140  then checks if temperature exceeds a second minimum temperature  333 . If not, then the controller  140  maintains operation in hybrid mode. If the temperature does exceed the second minimum temperature then the controller checks that the wind turbine speed is above a first minimum  336 , if the speed is not above a first minimum speed then the controller  140  will reduce the load on the generator  338  so that the turbine speed will increase. So long as the load on the motor/generator is greater than 0 the controller  140  will continue to cycle back to step  336  to check if the wind turbine speed has reached its first minimum speed. When the wind turbine speed at step  336  is above the first minimum speed then the controller  140  checks that the receiver temperature is above a certain preset maximum  350 . This preset maximum temperature indicates that the receiver is over heating indicating a need to maximize air flow. The load on the motor generator is further reduced  352  and if it reduces to zero  354  then the controller changes operation to boost mode  360 A. In step  350  if the temperature is not above the max 2  temperature then the controller  140  will check that the receiver temperature is below a third minimum temperature min 3  in step  362 , if not the system will stay in hybrid mode  320  and return to dwell timer loop  315 . If the temperature is below the third minimum this indicates a cool condition at the receiver that can be improved by reducing airflow through the chimney so the controller  140  increases load on the motor generator  364 . The controller  140  can then cycle checking the receiver temperature  365  compared to min  3  temperature and increasing the load  366  until a more ideal temperature is obtained. 
     In boost mode  360  the clutch is engaged and the motor/generator is offloaded  370 . The controller  140  checks that the receiver temperature is above Max  2  in step  372 . If the temperature at the receiver is above Max  2  then the controller  140  increases the power  374  to the motor/generator to increase air flow through the chimney and to reduce the temperature at the receiver. The controller  140  then checks the temperature at the receiver is below min  3  at step  376 . If the temperature is below min  3  then the controller changes back to hybrid mode  320 A. If the receiver temperature is above Max  2  at step  372  and power input to the motor is increased at step  374  then the controller  140  checks that the power input to the motor generator is below its limit, if so the controller  140  checks again the receiver temperature again at step  372 . If the power to the motor generator is maximum at step  380 , this indicates an unsafe condition where the receiver temperature may go higher and damage the receiver  132 , so heliostats  130  are defocused  382  and the system goes into chimney mode and sounds a warning. 
     Min 1  temperature should be around 450-600 deg. C. to indicate that direct sunlight is present. There is no Max 1  temperature. Min 2  temperature is around 550-700 deg. C. and is the threshold for a positive turbine power output (more mechanical shaft power is being extracted than spent on compressing the air, given the turbo-machinery efficiencies). Max 2  temp should be around 1000-1150 deg. C. for non-exotic receiver materials and low cost turbine and more air circulation (boosting) should start. Min 3  temp should be in the range of 900-1050 deg. C. Max 3  temp. 1200-1250 deg. C., the material limit of low cost turbine, reaching this maximum temperature shows an operational fault or unusual ambient condition. The control  140  should revert to chimney mode only (greenhouse heating alone can&#39;t cause overheating) until a manual reset by an operator. The overlapped ranges between modes provide the system hysteresis for a stable operation with less frequent mode switches. 
     In the solar thermal receiver  132 , the compressed air is heated by the solar energy reflected from the heliostats  130  to a higher temperature. Exiting the solar thermal receiver  132 , the heated compressed air is routed to and allowed to expand through the air turbine  142 . The expansion of the heated compressed air spins the air turbine  142  which in turn drives the main electrical generator  144  to produce electricity to be fed to the electrical load  150 . The operation of the Hybrid Solar Thermal Chimney  100  from the air compressor  138  onward is similar to an open air solar Brayton cycle. 
     The integral motor/generator  124  on the wind turbine shaft  118  may continue producing electricity in conjunction with the main electrical generator  144  if there is enough updraft for the wind turbine  110  to drive both the motor/generator  124  and the air compressor  138  (hybrid mode). The motor/generator  124  is one of the many unique features of Hybrid Solar Thermal Chimney  100 . The motor/generator  124  serves three functions. 
     First the motor/generator  124  together with the disengaged clutch/transmission  126  lets the Hybrid Solar Thermal Chimney  100  operate as a pure solar thermal chimney power generator on days with only diffused sunlight. The first function of the motor/generator  124  is as a pure electrical generator. On days with both diffused and reasonable quantity of direct sunlight, the motor/generator  124  generates electricity to supplement the main generator  144 . The amount of generated electricity to be taken out of the motor/generator  124  is determined by the controller  140  depending on the relative availability ratio of diffused versus direct sunlight. If the updraft is only enough for the wind turbine  110  to drive only the air compressor  138  to compress air to the desired pressure, the motor/generator  124  may be completely offloaded to lessen the drag on the wind turbine  110 . If there is updraft available in excess of what is required to drive the compressor  138  to compress air to the designed pressure, the controller  140  lets the motor/generator  124  generate electricity. The controller  140  regulates the amount of electricity taken out of the motor/generator  124  so that the resultant electromotive drag torque keeps the (wind turbine) compressor  138  in the desired speed range. This regulated compressor speed is designed to move the appropriate amount of air flow through the solar thermal receiver  132  to be heated to the optimal designed temperature. Too much air flow through the pipe  136  without adequate direct sunlight input to heat the air to an appropriate temperature may decrease the net power output of the solar thermal receiver  132 . 
     The second function of the motor/generator  124  is both as a supplemental electrical generator and as an electromotive speed governor for the air compressor  138 . When the availability of direct sunlight is too high, there is a danger of overheating the air in the solar thermal receiver  132 . The danger may be the result of not enough updraft to spin the wind turbine  110  faster or the wind turbine  110  may already operate at its aerodynamic design speed limit and cannot spin faster from the force imparted by the updraft to move more air flow through the solar thermal receiver  132 . In this case some electricity may be diverted from the main electrical generator  144  output to drive the motor/generator  124  (as a motor) to spin the wind turbine  110  and the air compressor  138  faster. The aerodynamic design speed limit of the wind turbine  110  does not inhibit the wind turbine  110  from spinning faster by the additional force imparted to it by the motor/generator  124 . The faster spinning air compressor  138  can move more air through the solar receiver  132 , thus keeping the air temperature from getting too high. A small amount of electric power is diverted from the output of the main electrical generator  144  but the higher mass of air flow will enable the Hybrid Solar Thermal Chimney  100  to generate more net electrical power. Since the motor/generator  124  can regulate the wind turbine and compressor speed regardless of the level of direct sunlight input, the Hybrid Solar Thermal Chimney system  100  can operate at near optimum efficiency on majority of the solar energy days. Thus more electricity may be generated from solar energy and transferred to load  150  to do useful work. 
     The third function of the motor/generator  124  is as a supplement motive force to increase the air flow through the system to not only avoid the over-temperature problem but also generate more net electricity generation on days with very high direct sunlight. Electrical power can be supplied to the motor/generator at startup if required to start the wind turbine  110  turning. 
     Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. 
     It would be obvious to those skilled in the art that modifications be made to the embodiments described above without departing from the scope of the present invention. Thus the scope of the invention should be determined by the appended claims in the formal application and their legal equivalents rather than by the examples given.