Abstract:
The invention relates to a solar energy collection system that uses linear parabolic concentrators designed on a small scale and with a modular configuration that allows optimum usage of solar collection surface area in places such as the roofs or flat roofs of factories or shops where space is generally small or irregular. The solar collector is coupled in rows actuated by a fully autonomous system for electronically controlling solar tracking, the operation of which is based on an algorithm programmed in a microcontroller. An autonomous solar tracking system can efficiently control two parallel rows with a pre-defined number of solar concentrators, as well as automatically detecting the presence of impurities on a reflecting radiation surface for the maintenance thereof. The thermal energy produced is harnessed by a heat exchanger, the operation of which is based on conduction, convection and radiation for dehydration uses.

Description:
OBJECT OF THE INVENTION 
       [0001]    Energy is one foundation in developed countries, and factories and stores in industrialized societies typically generate energy based on fossil fuels to obtain process heat. Diesel, LPG and natural gas are fuels used in these sectors where companies shall withstand their constant increases and cost volatility. 
         [0002]    There are technologies in marketplace for solar energy application within a generation range from 50 to 90° C. with flat-type collectors and vacuum pipes, commonly used for household water heating use. Within a range from 300 to 750° C. or above, solar concentration technologies commonly used for electric power generation through thermal solar plants may be found, located in large and open spaces such as desserts. Within a range from 100 to 300° C. there are limited options for solar energy supply, and this range is typically used by factories or stores in processes such as water heating, steam generation, product and foodstuff dehydration and the like. Said temperature range may be reached by parabolic-linear concentrators which collect solar energy transforming it into useful heat. A special interest application at reported temperature levels (100-300° C.) is solar energy foodstuff dehydration, allowing conservation of vegetables, fruits, grains and other crops in a practical and economical way by not using fossil fuels thereto. 
         [0003]    The invention disclosed in this document is a solar concentrator with flexible and modular features allowing easy installation, better usage of available solar collection area, lower costs in logistics and transportation and great flexibility to be installed on roofs or factory and shop areas at ground level. Combined with above mentioned invention, the invention of a highly efficient system for product dehydration provided by application of solar thermal energy and collected by a small scale linear parabolic concentrator is also introduced such as that above disclosed, which transfers energy by three heat transfer modes: convection, radiation and conduction towards a dehydration exchanger. The dehydration system has a high operation temperature and industrial scale production capacity, which is not currently commercially offered by current solar energy products. 
       BACKGROUND OF INVENTION 
       [0004]    There are currently parabolic-linear concentrators for a number of applications in the market, with an operation based on a linear parabolic mirror moving along a shift axis, tracking the sun path during the day in a North-South or East-West orientation. A thermal receiver is coupled to the concentrator focal line which is typically a tubular element manufactured of coated stainless steel with a selective surface for direct normal irradiation, this receiver pipe is further coated with a glass concentric cylinder which prevents losses by thermal convection. Said collectors are installed in row and column arrangements depending on the power calculated for the generation plant. A high thermal transfer fluid or water is circulated within the receiver, which absorbs the heat power coming from the sun which is reflected by the parabolic mirror, thus transporting energy to a conventional thermodynamic cycle for applications such as electric power generation, process heat, refrigeration or a combination of several processes. The cycle has elements such as hydraulic pumps, turbines, condensers, cooling towers and other devices. 
         [0005]    There are currently solar concentration systems for thermal energy generation with process heat applications, however, their use is often restricted for developing countries or for those not having government incentives in terms of renewable energies, which in turn leads to high installation and commissioning costs for the companies. In addition to above problems, manufacturers of these systems impose restrictive demands such as: high costs of engineering, supervision, logistics and maintenance. Quite important to note is that solar concentration technologies currently in the market do not show sufficient flexibility and adaptability in their energy production capacities for a wide range of user requirements; this means that finding a technology with all its features (collector, solar tracking controller and thermodynamic elements) easily adapted to the roofs or installation spaces and to energy demand of several users is complicated. One important limitation regarding to currently available parabolic-linear mirror concentrator systems is that most of them are difficult to install in reduced spaces such as flat-roofs in factories and stores. Usually, it is very common to find installation spaces with little adapted orientations for solar path in small and medium-size companies, and irregularities which make even more difficult to install equipment and a better usage of installation area due to a lack of flexibility and modularity of current technologies in marketplace having already defined physical measures. 
         [0006]    Based on above paragraph explanation, it has been identified a need in factories and stores to have a reliable, flexible, modular and low-cost solution for thermal energy generation useful in processes, without suffering the constant cost fluctuation of fossil fuels. 
         [0007]    One application of special interest is food product dehydration based on solar energy, allowing conservation of vegetable, fruit, coffee and many other types of crops in a practical and economical way. 
         [0008]    Solar concentration technologies have a number of applications due to their efficiency at a high temperature range, where conventional flat collectors do not achieve a proper performance. There are dehydration systems currently using solar energy, which are classified in two types: passive, operating by natural circulation or convection and active, using forced convection for functioning. Both technologies offer a sustainable, hygienic alternative and with sanitary conditions under international standards for food processing, without representing a high cost compared to fossil fuel systems. However, said systems do not have sufficient dehydration capacity for large industrial stocks and their operative temperature hardly reaches 100° C., which results in a lower product dehydration speed and therefore, lower production rates. Coupling of a parabolic-linear mirror concentrator system, suitable for industry installation, for industrial dehydration processes is a feasible solution by supplying suitable temperature ranges for this process by solar energy. It is worth to mention that most of the product dehydration systems, whether by solar energy or fossil fuels, transfer heat to the products to be dehydrated by natural or forced convection, which is not an efficient method of thermal energy use. 
     
    
     
       BRIEF DESCRIPTION OF FIGURES 
         [0009]      FIG. 1  is an isometric view of a linear parabolic solar concentrator  1 , for energy and dehydration generation, comprising a reflective surface  2 , a reflecting mirror support structure  19 , an electronic control solar tracking system  3 , an electromechanical actuator  5 , a solar position sensor  4 , rear support arcs  7 , support masts for each module  10  and a solar irradiation receiver  6 . 
           [0010]      FIG. 2  is a rear view of the parabolic solar concentrator  1 , where stress support traverse bars  11  and stiffness rear ribs  7  are shown. 
           [0011]      FIG. 3  shows a side view of the linear parabolic solar concentrator. 
           [0012]      FIG. 4  shows a detailed view of the reflective surface  2 , sectioned in equal and symmetrical parts  20  in addition to a support rear structure  19  of the reflective surface. 
           [0013]      FIG. 5  shows an isometric view of the linear parabolic solar concentrator structural elements consisting of parabolic curve stiffness arcs  7  and transverse stress supports  11 . 
           [0014]      FIG. 6  shows a detailed view of the structural element assembly components consisting of threaded bolts in both sides  13  and inner thread nuts  12 . 
           [0015]      FIG. 7  shows an isometric view of a row of serial assembled collectors  15  coupled by spin pivot bearings  9  and alignment pins  18 . 
           [0016]      FIG. 8  is a view of several collector rows  15  installed on a building roof  47 , the rows consisting of full modules  1  and halves of each module  14 . 
           [0017]      FIG. 9  shows an upper view of the collector rows  15  installed on a building roof or flat roof  17  and surrounded by safety walls  16  used in construction. 
           [0018]      FIG. 10  is an isometric view of a half-section of the linear parabolic collector. 
           [0019]      FIG. 11  is a sectioned front view of a tunnel-type modular solar dehydrator  22 , whereby a thermal fluid is introduced in a zigzag inlet piping  23 , having a fluid outlet  33 , a bottom  24  and an upper plate  25  each other transmitting thermal energy by heat conductor bars  27  towards an assorted nature product  34  and heat is insulated from outside by an inner protective surface  32  in contact with a thermal insulator  26  and an outer surface  33 . Ventilators  30  are also shown as thermal convection actuators, thermoelectric cells as heat-to-electricity transducers  29  and heat sinks  31 . 
           [0020]      FIG. 12  is another section view of the tunnel-type solar dehydrator  22 , with schematic drawings of the heat flows involved in product dehydration. Convection heat flow  37 , radiation between plates  38 , radiation from conductor bars  27  towards surroundings  39  and a heat inlet  35  together with its respective outlet  36  are shown. 
           [0021]      FIG. 13  is a scheme of a thermodynamic circuit comprising a solar collector field  40  in rows and columns coupled to a backup heater  41  using any fossil fuel, a tunnel-type solar dehydrator  22 , a condenser  43  and a recycle pump  42 . A low-temperature thermal transfer fluid  44  is circulated through the components, providing high temperature heat  45  within the dehydrator  22 . 
           [0022]      FIG. 14  shows an arrangement wherein a boiler or fuel heater  41  functions as pre-heated fluid superheater by solar collector field  41 . 
           [0023]      FIG. 15  shows a component assembly for the solar tracking actuator system  51 , where an electronic control module  3  may be seen which receives luminosity signals proceeding from a photoelectric sensor  4 . The electronic control module  3  calculates the required positions of the electromechanical actuator  5  and sends control signals to this last element, therefore the joint mechanism of serial solar collectors ( FIG. 7 ) may rotate by making a solar tracking over a horizontal rotation axis. 
           [0024]      FIG. 16  shows a flow diagram of the algorithm  52  used for solar tracking electronic control. 
           [0025]      FIG. 17  shows an arrangement of two solar concentrator rows  61  together with a solar tracking electronic control central module  3 . 
           [0026]      FIG. 18  shows an arrangement of two detection elements or temperature sensors which may be also solar luminosity sensors  65  and  66 , detecting light intensity or energy amount incident on its surface and sending a notice signal to the user, so that he may provide a proper cleaning to the reflective surface  2  of the solar concentrator. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Linear Parabolic Solar Concentrator 
       [0027]    The present invention consists of a small scale parabolic-linear solar concentrator. Its size and design have been created to be used by a number of factories and stores, providing the easiness to be installed on roofs or company&#39;s open areas, allowing adaptability to energy user requirements because of an integral and modular arrangement of the solar tracking collector-controller. Moreover, its flexible design provides a possibility of more usage of installation area thus providing a higher solar energy collection in reduced spaces, without representing a risk for the users due to inclement weather which may be present at the location. 
         [0028]    The solar collector performance is based on the parabolic curve principle: 
         [0000]    
       
         
           
             y 
             = 
             
               
                 x 
                 2 
               
               
                 4 
                  
                 
                     
                 
                  
                 f 
               
             
           
         
       
     
         [0029]    wherein: 
         [0030]    f=Parabolic curve focus point. 
         [0031]    x=Horizontal distance from center. 
         [0032]    y=Vertical distance. 
         [0033]    The parabolic curve is extruded to create a channel or concave shape surface sectioned in symmetrical panels  20 , assembled by aluminum or steel metallic profiles (but not limited to these materials) which limit the panel outline and comprise structural crossbars providing higher stiffness to each piece  19 . A reflective surface based on aluminum sheet (not restricted to this material)  2  with a highly reflective sunlight mirrored finish is adhered to the panel frame by fastening elements such as screws, rivets or special adhesives. A suitable reflective material consists of a mirrored-finishing aluminum sheet coated with an anodized surface suitable to support weather exposure during extended periods. It is also possible to use a polymeric film reflective material with silver coating, laminated with pressure-sensitive adhesive over a metallic or plastic sheet. There is also a possibility to use an acrylic-base reflective material coated with a reflective coating, which allows to be molded according to the intended geometric shape. 
         [0034]    In order for the concentrator to be capable of supporting wind loads which have an impact on its surface without showing any deformation, the concentrator has elements providing stiffness upon compression and further upon stress being present during weather phenomena, then a curved-rib base structure  7  is included, providing high compressive strength and parabolic curve mechanical expansion and attached each other by several transverse tubular elements  11 , providing excellent tensile strength and transverse compression to the solar collector. Crossbars  11  are fastened with ribs  7  by two-side threaded nuts  12  and screws  13  for easy assembly. 
         [0035]    One of the main properties of the solar concentrator is its modularity for system design and installation with a number of power generation capacities, serially coupled, where one to eight modules in a row  15  may be arranged attached each other by rounded spin axes supported over bearings  9  allowing solar tracking spin motion throughout a day in a North-South or East-West axis. A power transmission comprising a direct current electric motor (not restricted to this type)  5  coupled to an endless screw arrangement and a helical gear allows torque increase and motion interlock when the motor is not energized. The transmission system also includes a set of coupled pinions  8  increasing the transmission ratio, thus achieving a slower and more accurate solar tracking motion. 
         [0036]    A receiver element  6  which collects parabolic mirror thermal energy is positioned in the parabolic curve focal point, which is capable of absorbing said energy by a copper or stainless steel cylindrical pipe (not limited to these materials) with a highly absorbent selective surface for solar irradiation; a second borosilicate or glass pipe is concentrically arranged to the metallic pipe with a high transmissivity index and low reflectivity to solar radiation, thus lowering those convection losses caused by wind. 
       Solar Tracking Electronic Control System. 
       [0037]    A smart electronic control unit  3  actuates an electric motor  5  (this unit being expansible to a second motor) and achieves keeping the solar concentrator orientation throughout the day towards the maximum possible irradiation amount. The solar monitoring or tracking system operates on alternating current basis at 120V (not restricted to this voltage), which may be directly supplied by the utility company or by any solar to electric power conversion system such as photovoltaic panels. The electronic controller uses a position control algorithm  50  programmed in a semiconductor element called microcontroller, which is capable of performing calculations to compensate system position based on voltage difference readings, provided by the pyramidal-array photoelectric sensor  4 . The algorithm has been specially conceived for functioning with the disclosed mechanical system and is the element which provides intelligence and solar energy collection autonomy to the system, on the opposite side, the mechanical system is useless without this control algorithm. The tracking system  3  together with its components; photoelectric sensor  4 , control card with microcontroller and supply and measurement connections comprise a single component integrating a solar tracking module  51  which is easy to install, calibrate and arrange in a small size parabolic-linear solar collector  1  (not restricted to this type of collector, dish-type solar collectors or photovoltaic systems may be adapted among applications requiring a high accuracy and automatic active solar monitoring). 
         [0038]    The solar tracking electronic control smart unit  3  may be installed in a two-row solar collector arrangement  61  as shown in  FIG. 17 , the control module  3  has the capacity to receive signals proceeding from a row of up to ten solar concentrators  62  and another equally in parallel  63 , each with a solar luminosity sensor  4  indicating an ideal position in a determined time of the day for each of the rows. Once the solar tracking module  3  calculates the ideal position of each of the two collector rows, transmits electric control signals to the electromechanical actuators  5  located in the motion transmission system  8  of each collector row. This dual arrangement of solar tracking control allows reducing system&#39;s manufacturing costs and cutting installation and commissioning time for the solar concentration system. 
         [0039]    The solar tracking control system includes two temperature or luminosity sensors  65  and  66 , located on the solar radiation receiver  6 , these sensors detect a temperature or light intensity difference and they send signals as a second feedback towards the solar tracking electronic control  3 . The sensors located in the solar receiver  65  and  66  also act as soil or impurity detection instruments on the reflective surface  2  of the linear parabolic concentrator  1 , this function allows correct detection when system demands maintenance and cleaning on the reflective surface  2  and thus system performance is optimal during useful life with a lower maintenance cost. 
       Solar Tracking Electronic Control Algorithm 
       [0040]    The system starts in a rest state performing solar luminosity measurements  53 . When the system detects that light intensity is sufficient to start conducting an alignment routine  54  it then goes into a first alignment stage, or the solar position control  55  is turned on. Once that the system is aligned by carrying the position error at zero level, the algorithm enters into a continuous alignment error measurement cycle  57  and controls the solar collector position throughout the day. As sun&#39;s apparent motion reaches sunset and nighttime luminosity level  59  is detected, the algorithm leaves the control cycle and enters into a return status to the solar collector  60  initial position where kept ready and in a rest state  53  starting again the following day with the control routine  52 . 
       Solar Dehydration System 
       [0041]    The solar dehydration system consists of an exchanger operating in three available heat transfer modes: conduction, convection and radiation. Said exchanger consists of a thermal chamber manufactured with metallic materials  32  (not limited to these materials) and coated with a refractory or insulating material  26  preventing heat losses outside. An arrangement of zigzag piping is located within this chamber  28  said piping made of copper or stainless steel (not restricted to this material) wherein steam or a high thermal transfer oil is circulated, the piping arrangement conducts heat to a metallic sheet made of copper, carbon steel or stainless steel (not limited to these materials)  24 , which in turn is interconnected to a parallel plate  25  located in the opposite side of the exchanger by a high thermal transfer material such as copper, steel or graphite bars (not limited to these materials)  27 . The dehydrator or exchanger has also ventilators  30  producing a forced outside-to-inside air convection, causing in this way a hot air regular flow  37  with an outlet in system&#39;s upper section. The operation principle of this dehydrator consists of heat transfer by thermal conduction from piping to parallel plates, which in turn transfer heat to the product to be dehydrated by convection produced by ventilators  37 , and radiation heat transfer between the two plates  38  caused by a temperature difference among them and also radiation between the conductor bars and their surroundings  39 . The use of electric power is required in order to lead to a forced convection with the ventilators, which often is not easily available in and agricultural environment, then the system has thermoelectric cells  29  located on the lower temperature plate side which in turn is connected to the outer side by heat sinks  31 . Cell performance consists of absorbing the heat from said plate, transforming it into electric power due to a temperature difference between dehydrator inner and outer sides, so that electric power is used and ventilators which produce forced convection are actuated. The dehydration system is modular and may be serially interconnected with identical systems until reaching the required thermal capacity for dehydration. 
         [0042]    In order to achieve high temperatures within the dehydrator chamber, this is interconnected with an arrangement of solar concentrators  40  which heat the thermal fluid and optionally further to a heating backup system with any fossil fuel  41  such as diesel, LPG, natural gas, and the like, thus supplying sufficient energy according to the required operative conditions.