Device for direct conversion of solar energy by rectennas

Abstract

 Object of the present invention is a new nanorectenna based device for high efficiency conversion of sunlight in electric energy to be used for example in solar concentrators.

Description

[0001] The present invention relates to a new nanorectenna based device for high efficiency conversion of sunlight in electric energy to be used for example in solar concentrators.

[0002] The direct conversion of solar energy in electricity usually occurs by using photovoltaic cells. At the state of the art the photovoltaic effect is quite known and depends essentially on photons interaction, the energy being equal or greater than the energy of the photovoltaic material range.

[0003] The concept of using rectennas for solar energy conversion is based on the fact that the solar radiation is actually an electromagnetic wave. In other words, it can be described as a series of electric and magnetic waves propagating from Sun to Earth. Using rectennas for transmitting and receiving power and signals in the microwave range is a mature technology today. The idea of using a rectenna for converting solar energy was first proposed in 1973 by Dr. R. Bayley, but only recently it has been re-examined for the remarkable progress in the nanotechnologies, which make possible the design of structures with dimensions in the order of nanometers. Said idea was formulated also by Gustafson and Billman in 1974. After, in 1984 Brown presented a critical study on the state of the art of rectennas in the microwave spectral range. Most of the first works was carried out using microwaves at frequency 2,45 GHz.

[0004] Moreover, the traditional photovoltaic cell has still many disadvantages, among which the low efficiency in conversion from solar to electric energy, at the state of the art, is between 20% for single cell and 30% for multi-junction cells. Therefore, rectennas can represent the best alternative with respect to classic photovoltaic cells to convert solar radiation energy.

[0005] To achieve the prefixed aims, the present invention proposes to convert the visible solar energy in infrared energy (by means of high temperature heating an absorber element) to be irradiated on the nanorectenna for the conversion in electric energy. Therefore, aim of the present invention is a solar concentration system comprising an optical body for receiving the solar radiation and a receiving element characterized in that said receiver is provided with at least an absorber element associated to a rectenna matrix for direct conversion of solar energy in electric energy.

[0006] The present invention will refer to the following drawings 1/2 and 2/2, which show an absolutely not limiting preferred embodiment of the invention. In particular:

• Fig. 1 shows a base scheme of the main elements constituting a rectenna;
• Fig. 2 shows a general scheme of a possible embodiment of the device object of the present invention in case of a parabolic solar collector;
• Fig. 3 shows a detailed view of the receiver with the device object of the present invention therein.

[0007] Fig. 1 shows a base scheme of a rectenna with its main characteristic elements. As yet said, a rectenna is a device for converting the electromagnetic energy propagating in the free space in direct current and it is usually made up of many elements, as for example: an antenna 1, a diode 2 as rectifier element, two filters 3 and 4, respectively arranged upstream and downstream of the diode 2. The input filter 3 between antenna and rectifier has to:

• adapt the impedance between the antenna and the downstream circuit;
• guarantee a continuous current flow for the power flux produced by the antenna;
• avoid the energy re-irradiation by the antenna owing to the greater harmonics produced by the non linear load (rectifier).

[0008] The output filter 4 is needed for smoothing and rectifying the current produced. The just described scheme in fig. 1 has many problems of realization in the hypothesis of converting an electromagnetic radiation with visible wave length in electric energy. Therefore in order to solve the technologic problems connected to what just described, the present invention proposes to introduce a frequency adapter from the visible to the infrared range.

[0009] Fig. 2 shows a possible, absolutely not limiting, preferred embodiment of the object of the present invention, in which a solar concentrator 6 allows to concentrate the solar radiation on the surface of a receiver 7 which, in this particular case, is arranged on the focal axis of the parabolic mirror 6.

[0010] Fig. 3, instead, shows the detail of the receiver 7 which, at its ends, is constituted by a glass cover 8 and by a rectenna matrix 9; between said ends being arranged an absorber element 10 mounted on supports of thermally insulating material 11. In this way, the solar concentrator 6 allows to concentrate, by means of parabolic mirrors, the solar radiation so that the power density arriving on the surface of the receiver 7, increases. Therefore, the solar radiation crosses the glass cover 8 and arrives to the absorber 10 where the conversion of the solar radiation in infrared radiation occurs (energy down-converter). Still in the receiver 7, after the transformation in the absorber 10, the infrared radiation is converted directly in electric energy by a rectenna matrix 9 through an outer load.

[0011] The just described system is only a representative example of a possible embodiment of the new device concentrator-absorber object of the present invention. In this preferred embodiment there have been used rectennas matrices, but similar results, though with lower efficiency, can be obtained with other types of photovoltaic cells as well. Similarly, the shape and the material for the realization of the receiver (7) can be different as long as the principle of the solar radiation absorbing by the absorber element (10) is maintained.

[0012] As yet previously stated, the rectennas can surely be considered as one of the best alternatives with respect to the traditional photovoltaic cells to convert solar radiation energy, since they are an excellent transducer of the radiations propagating in the free space.

[0013] Considering the rectennas functioning principle, which is completely different from the one of photovoltaic cells, an array of rectennas can theoretically reach a 100% efficiency (for a realistic system it was expected a 96% efficiency). This, if confirmed by the experimental results, could represent a very important technologic break-through in the field of solar energy direct conversion systems, thus making the current photovoltaic systems obsolete.

Claims

1. Solar concentration system comprising an optical body (6) receiving the solar radiation and a receiving element (7) characterized in that said receiver (7) is provided with at least an absorber element (10) and a rectenna matrix (9) for direct solar energy conversion in electric energy.

2. Solar concentration system according to claim 1, characterized in that said absorber element (10) is made up of a frequency adapter from the visible to the infrared range.

3. Solar concentration system according to claim 1 and 2, characterized in that the absorber element (10) in the receiver (7) is interposed between at least a glass cover (8) and the rectenna matrix (9).

4. Solar concentration system according to any one of claims 1 to 3, characterized in that the absorber (10) is mounted on supports (11) of thermally insulating material.

5. Solar concentration system according to any one of claims 1 to 4, characterized in that the shape and material for the realization of the receiver (7) can be different as long as the principle of the solar radiation absorbing by the absorber element (10) is maintained.

Drawing