The present invention relates to a solar energy generator, and in particular a generator which can be easily transported and installed for producing thermal and/or electric energy. The present invention also relates to a system and a process which can be employed for controlling said generator. Known solar energy generators with large sizes comprise a multiplicity of concave mirrors which are mounted in a rotating manner on a support structure for being rotated by an electric motor around a substantially horizontal axis for converging the solar rays toward a collector fixed in front of the concave mirrors. However, these known generators are installed in a stable manner on the territory, so that they require complex and expensive installation and maintenance, they cannot be moved and have a relatively low efficiency with respect to the area occupied by the concave mirrors. It is therefore an object of the present invention to provide a generator free from said disadvantages. Said object is achieved with a control system, a control process and a generator, the main features of which are disclosed in claims 1, 4 and 9, respectively, while other features are discloses in the remaining claims. Thanks to its relatively simple and compact structure, the generator according to the present invention can be easily transported and has low purchase and maintenance costs. Furthermore, the concave mirrors are mounted on particular modular frames and/or are manufactured with flexible reflecting sheets, so as to reduce their weight for making their carriage easy and for reducing the energy required for their orientation toward the sun. Thanks to the particular control system and process, the generator according to the present invention can work automatically, so as to be employed also by an untrained user without relevant additional costs. Finally, thanks to the particular precision in the orientation toward the sun and to the particular structure of the collectors, the generator according to the present - 9 _

invention has a high efficiency in the production of thermal and/or electric energy, when compared to the area occupied by the generator itself. Further advantages and features of the generator, the control system and process according to the present invention will become clear to those skilled in the art from the following detailed and non-limiting description of an embodiment thereof with reference to the attached drawings, wherein: - figure 1 shows a front view of said embodiment of the generator; - figure 2 shows a side view of the generator of figure 1 ; - figure 3 shows a top view of the generator of figure 1; - figure 4 shows a perspective view of the generator of figure 1 ; - figure 5 shows a perspective view of a collector of the generator of figure 1 ; - figure 6 shows a cross-sectioned view of the collector of figure 5; - figure 7 shows an enlarged view of a detail of figure 6; and - figure 8 shows a block scheme of the control system according to the present invention. Referring to figures 1 to 4, it is seen that the generator according to the present invention comprises in a known way one or more concave mirrors 1 which are mounted in a rotating manner on a support structure 2 for being rotated around a substantially horizontal axis by a first electric motor 3 in the direction of the arrow of figure 2, so as to change their zenithal angle. The concave mirrors 1 can converge the solar rays toward one or more collectors 4 fixed by means of support members 5, for example section bars, in front of the concave mirrors 1 for being rotated by the first motor 3 together with these mirrors. According to the invention, the support structure 2 of the concave mirrors 1 can be rotated around a substantially vertical axis by a second electric motor 6 on a fixed base 7 in the direction of the arrow of figure 3 so as to change their azimuthal angle. In particular, the support structure 2 comprises a substantially cylindrical-shaped upright on which the first motor 3 and the relevant transmission system are fixed. Said upright can rotate in a corresponding seat 8 of base 7 by means of a further transmission system 9, for example with a toothed belt or a chain, connected with the second motor 6 fixed on base 7. The latter comprises a plurality of feet, in particular three feet, which can be folded beside the support structure 2 for reducing the overall size during the carriage. The concave mirrors 1 are preferably made up of flexible reflecting sheets which are fixed to a modular frame mechanically connected to the transmission system of the first motor 3 through at least one horizontal bar 10. Each modular frame comprises two or more ribs 11 mutually connected by two or more crossbars 12. The rear edge of ribs 11 is convex so as to arch said reflecting sheets and obtain the concave mirrors 1. The support members 5 of collectors 4 are fixed to the horizontal bar 10. The present embodiment comprises two modular frames which are fixed onto the horizontal bar 10 with the support structure 2 in the middle. The number and/or the size of the modular frames mounted on the support structure 2 may therefore change according to the required configurations. Referring to figures 5 to 7, it is seen that collectors 4 comprise an elongated housing 13 having a substantially parallelepiped shape. Wall 14 of the elongated housing 13 suitable for being turned toward the concave mirrors 1 is transparent so as to let the solar rays pass into the same housing. One or more delivery 15 and/or outlet 16 ducts, also having a substantially parallelepiped cross-section, are arranged side by side in the elongated housing 13 for circulating a cooling liquid or a liquid to be heated by means of solar energy. An insulating material 17 can be arranged between the elongated housing 13 and ducts 15, 16, while one or more photovoltaic cells 18 can be arranged between the transparent wall 14 and ducts 15, 16, so as to be cooled by the liquid circulating therein. The photovoltaic cells 18 output the electric energy by means of conductors 19 made of strip pairs of a conductive material which are arranged one on the other at the sides of cells 18 between the transparent wall 14 and ducts 15, 16 and are separated by a strip of an insulating material. An insulating film 20 is arranged between cells 18 and ducts 15, 16, while a sealing strip 21 is arranged between conductors 19 and the insulating material 17. For this purpose, ducts 15, 16 are connected to inlet fittings 22 and/or outlet fittings 23, respectively, which lead to one or both ends of the elongated housing 13 for connecting collectors 4 to external tubes for the cooling liquid or the liquid to be heated. Referring to figure 8, it is seen that the generator according to the present invention is provided with a control system comprising an electronic control unit CU, in particular based on a microprocessor, which is connected to at least one digital memory DM, to at least on output interface OI for controlling motors 3 and/or 6, to one or more temperature sensors TS for measuring the temperature in collectors 4, to a clock CK for measuring time and/or date, to input means IM, for example a keyboard or an interface, and/or to one or more photocells PC suitable for detecting the position of the sun. When the generator is turned on, the control unit CU requires the user to input through the input means IM the coordinates of the geographic position of the generator, which are stored in the digital memory DM, after which the control unit CU tries to detect the position of the sun through photocells PC. If the signal sent to photocells PC indicates that the generator is not oriented toward the sun, the control unit CU drives the first motor 3 and/or the second motor 6 for orienting the concave mirrors 1 toward the position of the sun determined by photocells PC. When photocells PC signal that the concave mirrors 1 are correctly oriented toward the sun, the control unit CU stores into the digital memory DM the current azimuthal and/or zenithal angles together with the current time and/or date output by clock CK. If instead photocells PC do not output any useful signal, for example because the sun is obscured, the control unit CU recalls from the digital memory DM the stored azimuthal and/or zenithal angles and the corresponding times and/or dates stored in the above described way and calculates by means of a first pointing algorithm, also of a known kind, the estimated position of the sun according to these stored angles, to the corresponding stored times and/or dates and to the current time and/or date output by clock CK, after which it drives the first motor 3 and/or the second motor 6 for orienting the concave mirrors 1 toward this estimated position: If the digital memory DM does not comprise any data sufficient for calculating this estimated position, the control unit CU recalls from memory DM the coordinates stored at the beginning and calculates by means of a second pointing algorithm, also of a known kind, the estimated position of the sun according to the stored coordinates, as well as to the current time and/or date output by clock CK, after which it drives the first motor 3 and/or the second motor 6 for orienting the concave mirrors 1 toward this estimated position. Finally, if the temperature of a collector 4 measured by the temperature sensors TS exceeds a threshold value stored in the digital memory DM, the control unit CU drives the first motor 3 and/or the second motor 6 for getting out of the sun and thus cooling collectors 4, after which it orients again concave mirrors 1 toward the sun when the temperature measured by sensors TS returns under said threshold value, hi another embodiment of the invention the coordinates stored in memory DM may also be obtained by the control unit CU by means of a calculation algorithm according to the sun position data obtained from photocells PC and stored in the digital memory DM. Possible modifications and/or additions may be made by those skilled in the art to the embodiment of the invention hereinabove described and illustrated while remaining within the scope of the same invention.