ITRM20090113A1 - CONCENTRATOR OF LIGHT AND PARABOLIC GEOMETRY FOR THE CONVERSION OF LIGHT IN ELECTRICAL AND OR THERMAL ENERGY OR THERE IS CATHEDRAL CONDENSER WITH SOURCE TRACKING SYSTEM - Google Patents

Description

Title

Light concentrator with parabolic geometry for the conversion of light into electrical and / or thermal energy, or "retroreflective condenser with source tracking system"

Description

This invention introduces significant innovations in the exploitation of solar energy for the production of energy.

In optics a capacitor can be defined as a convergent system intended to concentrate the light radiations of a source on an object, giving rise to a very intense light beam with a considerable aperture. Capacitors are divided into two categories: diopters and retractors; the former are made up of lenses, the latter of mirrors.

Basic concepts

The electromagnetic radiation that reaches the Earth from the Sun is at the basis of both climatic processes and life itself on our planet. This radiation derives from the emission of radiant energy generated by the nuclear fusion processes that occur on the Sun, and at the average distance the Earth is from the Sun its intensity is conventionally assumed to be about 1.3 Kw / m2 (Kilowatt per square meter of area normal to the radial direction between Earth and Sun)

The electromagnetic radiation coming from the Sun, by means of suitable technological systems, deriving from technical-scientific knowledge, can be used and converted into other forms of energy suitable for obtaining "work" (with "work" we mean the physical concept of the same )

State of the art

For the exploitation of solar energy there are "flat" systems, consisting of systems that, when exposed to the sun, heat a fluid (thermal collectors) or that generate electricity by means of a series of photovoltaic cells electrically connected to each other (photovoltaic panels). There are also focusing or concentration systems, where by means of optical systems (appropriately oriented and / or shaped mirrors) the light is concentrated on a target (or target), obtaining an increase in the incident power per unit of surface. In this way, a significant increase in temperature is obtained in the event that the conversion system uses a fluid in a thermodynamic cycle (for example a steam engine), and a significant increase in the electrical energy produced, per unit area, if as a system conversion is done using one or more photovoltaic cells, since, per unit of surface exposed to light, the production of electricity is directly proportional to the intensity of the luminous flux.

The concentration of light, in both cases, involves the emergence of various problems (physical, chemical, optical) that each researcher tries to solve in the best possible way to obtain a system that is on the whole economically competitive with the costs of other forms of energy, in an infinity of shapes, geometries, solutions. The present invention is a system with a concentration of parabolic geometry where, thanks to the laws of optics, sunlight is concentrated on a target, obtaining an increase in the temperature of the target and at the same time the transformation of light into heat, which, when transferred to a fluid, can be used for various purposes, from powering a heat engine to space heating, to the activation of thermochemical processes and any other factor that is deemed useful.

Description of the invention

This solar energy conversion system consists of four parts:

the concentrator (A)

the target (B)

the support (C)

the aiming (or tracking) system (D)

It is illustrated, as a whole, in the attached drawing Table 01;

The cited drawing is indicative of the concepts and operating principles of the invention, descriptive of a possible construction architecture, but not descriptive of all the possible construction architectures applicable to the same concepts and operating principles. In fact, a feature of this invention is the flexibility of use and therefore the dimensions, the base, the target, are part of the originality of the invention itself, and allow it to adapt to different construction, economic, climatic, meteorological and territorial needs.

A) Concentrator

(see drawings Tav.02; Tav.03;)

The concentrator "A" is composed of a central support "A2" (in this case of steel, but any material suitable for the purpose can be used) on which a series of ribs "Al" with radial positioning with respect to the center of the system are fixed optical.

These ribs (in this case of plastic material, but any material suitable for the purpose can be used) are worked in such a way as to bring back in the concave upper part facing the center of the optical system a parabolic profile deriving from the calculation of a typical equation of the parabola Y = aX2 (y = a for X squared) whose parameters “Y” and “a” define the dimensions and the focal length of the parabolic optical system.

Each rib "Al" supports a mirror "A3" so that by placing the mirror on the rib it copies the parabolic profile and therefore reflects the incident light on the center of the optical system, and therefore on Target "B"

The mirrors can be made differently since both the flexible support and the reflective deposit can be made with the materials that will be considered most suitable for the purpose.

The concept of operation is always the same, what changes are the efficiency and costs defined by the reflectance / cost / duration ratios of the mirror, and therefore the most convenient mirrors in all respects can gradually be adopted.

In this case, the solution adopted is that of mirrors made of flexible plastic material on which a light-reflecting layer is deposited, capable of adapting to the parabolic profile of the rib by elastic deformation of the mirror itself. By way of example, the aluminate Mylar of suitable thickness is indicated, which is a mirror made by means of a light reflecting deposit on a sheet of flexible plastic material.

The mirrors are fixed to the ribs by mechanical means (screws, rivets, brackets, etc.) so that they can be easily replaced if they degrade over time due to the action of atmospheric agents or the action of sunlight itself.

On one or both sides of the flexible mirrors, on the orthogonal of the radial axis "AR", a "fold" is made, that is, a plastic deformation of the mirror obtained by thermoforming or cold molding, with the function of stiffening the mirror flexible to bending stresses on the orthogonal of the radial axis "AR", as illustrated in the drawing Tav.02;

Between the rib and the mirror a sheet, indicated with "A4", suitably shaped, of flexible material (for example plastic material but also any other material suitable for the purpose) can be interposed with the function of supporting and protecting the mirror "A3"

In the drawing Tab.03 we have the vision of the concentrator “A” in plan.

This solution is considered the most convenient from the point of view of cost-effectiveness of construction and maintenance and therefore is an integral part of the novelty of the invention.

Since the concentrator must necessarily be positioned outdoors, and therefore exposed not only to bad weather but also to mechanical stresses due to weather conditions, such as wind, snow, hail, etc., appropriate measures have been taken to minimize these loads, with the aim to contain structure costs and ensure that the object was protected from damage due to excessive stress. This is achieved by the solution adopted by flexible mirrors.

In fact, if the pressure due to the wind or the pressure due to the snow load exceeds a certain value (indicatively about 5Kg per square meter, corresponding to about 8 meters per second (29 km / h) of wind speed or to about 2-4 centimeters of snow deposit) this pressure exerted on the mirrors determines their elastic deformation, so that in the case of wind the total resistant section automatically decreases, and in the case of snow it falls to the ground by gravity.

The "resilience" property of the material adopted. For the realization of the mirrors ensures that the mirrors return to their original geometric shape determined by the parabolic profile of the ribs once the wind or snow load has ceased. The "resilience" is the property of materials to undergo elastic deformations and to regain their original shape once the load has ceased.

The mirror cleaning system

Since the concentrator must necessarily be positioned outdoors, it is exposed to pollutants present in the atmosphere and non-polluting substances (dust, salt), which can be harmful to the efficiency of the concentrator itself.

This is mainly because the solar light collection efficiency depends on the optical surfaces of the mirrors (light reflection) and the Target (light absorption).

It is intuitive to understand that the mirrors, facing upwards and having a large surface, are the element that can be most affected by the accumulation of substances on their surface, causing a degradation of their reflectance over time (ratio between incident light and reflected), and therefore should be periodically cleaned in order to keep the drop in optical efficiency of the same within admissible values and in accordance with what was defined in the design.

The efficiency of the mirrors over time is therefore a maintenance problem typical of all concentrating solar systems, maintenance that can become very expensive to the point of making the use of concentrating solar energy systems uneconomical. The pollutants that are deposited on the mirrors over time are of various kinds, and largely depend on the typicality of the place. For example, we will have chemical type pollutants if the concentrator is exposed in an “industrial” atmosphere (characterized by mainly industrial emissions), or physical, such as dust or salt, or a set of pollutants.

To remove these pollutants, special detergents dissolved in aqueous solution can be used periodically, but with two serious drawbacks:

The cost of the operation. In fact, it involves the periodic intervention of an operator who, equipped with the appropriate materials and equipment, carries out the cleaning operations.

The need to use distilled water as a base for the detergent, with significant increases in costs due to the cost of the same and its transport to the site.

The need to use distilled water is due to the fact that water in its natural state contains dissolved limestone that would remain deposited on the mirrors after washing. In fact, unless you carefully dry the mirrors after washing (practically impossible because it would make the management of the concentrator uneconomical) the washing water, evaporating from the surface of the mirrors, would leave a deposit of limescale on them as harmful as the pollutants removed. Deposit that would be added to each wash, putting the system out of service and forcing the replacement of the mirrors. For these reasons, in cleaning operations, it is necessary to use distilled water, which does not contain limescale, as a base for the detergent.

If substances other than distilled water were to be used as the basis of the detergent, there would be problems of another nature, such as the disposal of waste that is not biodegradable with a serious increase in costs.

To overcome these problems, the concentrator is equipped with an automatic and programmable cleaning system, which is fed by distilled water produced on site by a commercially available distilled water production system. These systems are based on the use of osmotic membranes and suitable filters, and are able to eliminate from the mains water the large part of the substances that would, in our case, damage the mirrors of the concentrator. <-> Connected to this system for the production of distilled water a tank is inserted containing a suitable detergent, chosen among those commonly available on the market.

At the time of washing (which as mentioned can take place periodically according to convenience and need) a metering pump introduces the detergent into the distilled water circuit, and a hydraulic pump starts the liquid thus mixed to a series of nozzles placed in an appropriate position on the concentrator and spray the cleaning mixture on the mirrors. Subsequently, only distilled water will be sprayed through the same circuit for the definitive elimination of pollutants from the surface of the mirrors.

This washing system is fully automatic, easily programmable, and reduces the maintenance costs of the concentrator.

B) Target "B"

See drawing Table 04;

The Target (or target) is that element on which the light collected by the concentrator is concentrated.

It is anchored to the central support (the same to which the radial supports of the mirrors, or ribs are anchored) by means of metal bars or pipes "B2" (or other material) of suitable length and rigidity, which also have the function of hold the Target in the most appropriate position, in the optical center of the system.

It will be made in such a way as to "absorb" as much as possible of the incident solar radiation and then naturally transform it into heat. In this case, a carrier fluid (air, water or other) will flow into the target, which will be suitably hollow, which will transfer the heat to a storage tank or to use.

The maximum "absorption" of solar radiation occurs according to the physical principle of the "black body", and therefore of an object capable of being completely opaque to the wavelengths of light that it is interested in converting into heat. This can be achieved by using materials with suitable physical and optical characteristics and with shapes that minimize the re-emission of heat by convection and radiation.

Since the problem is only apparently simple but in reality it involves various problems of a technological nature, particular measures and solutions have been adopted to optimize the yield of the Target according to the purposes for which it is made, which are:

1) maximum absorption of the incident light, therefore with minimum reflection of the same

2) Minimum "irradiation" (*) at typical working temperatures; 3) minimum losses due to convection and conduction towards the outside; 4) maximum efficiency in the heat exchange to the carrier fluid; (*) note: for "irradiation, means the physical phenomenon whereby any body that is at a temperature higher than that defined as "absolute zero" (-273.14 degrees centigrade) emits energy in the form of electromagnetic radiation. The amount of energy emitted in this way depends on the temperature of the object and its size, and therefore the Target must be constructed taking into account all the factors to optimize its energy yield (i.e. the ratio between the incident energy of visible light and that reissued by radiation).

Description of the Target, as per the drawing already indicated Table 04;

TI Target looks like a closed hemisphere "B 1" built in steel sheet in which a fluid flows by means of suitable channels, placed in the appropriate way to make the geometric center of the same hemisphere coincide with the optical center of the parabolic system. The flowing fluid absorbs heat by conduction from the internal walls of the Target. The hemispherical shape was chosen because, as is evident from the graphics, the incident light from the sun is reflected towards the center of the optical system.

One of the factors that optimizes the performance is that the incident light hits the Target with an angle close to the orthogonal one with respect to the Target surface, as this minimizes the reflection phenomena of the light itself.

For what has already been explained (minimizing losses due to radiation and convection) it would be convenient to make the target as small as possible, but it must be considered that the energy absorbed by the target and transformed into heat must then be transferred to the vector fluid flowing to the inside, and therefore there is the need to have an adequate heat exchange surface between the Target and the fluid. Therefore the geometric dimension of the Target is a compromise between two different needs, and may vary according to various factors such as the working temperature, the nature and speed of the fluid that passes through it, etc.

The external surface of the Target is made in such a way as to optimize the absorption of light, and this is achieved by means of a first deposit of transparent ceramic "B4" in which the fine powder of a material having the appropriate optical characteristics is previously dispersed ( which is therefore as close as possible to a "black body"). In the case in question, cobalt oxide is used, which has the desired optical characteristics.

We therefore have, on the external surface "B4" of the Target, a first deposit of transparent ceramic in which the cobalt oxide in a fine powder with pigment functions is dispersed. This layer will be about 0.2 / 0.3 mm thick (but the thickness can vary according to convenience and need). A second layer of transparent ceramic “B5” is then applied to the first layer, again with a thickness of about 0.2 / 0.3 millimeters.

The surface thus created takes the name of "selective surface", as it is a surface designed and built to let through and absorb the maximum of solar radiation and minimize the electromagnetic radiation re-emitted by radiation from the Target. In fact, the light (electromagnetic radiation on the band of the "visible to the human eye", included in a wavelength between 0.4 and 0.7 microns (millionths of a meter) freely crosses the first transparent layer "B5" and enters depth meets the “B4” layer which contains the pigment formed by cobalt oxide.

Cobalt oxide, which acts as a black body, absorbs visible light, transforming it into heat which it transfers by conduction to the ceramic mass, which in turn transfers it by conduction to the steel wall which yields it in turn by conduction to the vector fluid flowing inside the Target. The emission of energy by radiation takes place instead through the "B5" layer of transparent ceramic, which however is transparent only at the wavelengths in the visible band, but "black" at the wavelengths emitted on the infrared band. In this way the infrared radiation is retained within the system and the energy lost by radiation is minimized.

The hemispherical target can be contained in a transparent glass hemisphere "B3", suitable for resisting the heat generated by the concentration of sunlight, and with the functions of minimizing losses by convection and conduction with the outside air. This glass hemisphere can be mounted on the system or not according to the working temperatures of the system or the climatic conditions of the place of installation. Basically it will be used in cases where there will be an economic advantage in the cost / efficiency ratio.

D) Aiming system (Tracking)

The "pointing system" appropriately activates the movements in Azimuth and Zenith (horizontal and vertical) in order to keep the concentrator always "pointed" towards the Sun, following the apparent motion that the Sun described in the sky.

To say that the pointing system always maintains the optical axis of the parabola orthogonal to the radial of the Sun.

Any pointing error affects, if it exceeds certain limits, the functionality of the concentrator itself.

This concentrator has been conceived with a geometric configuration such as to maintain its complete functionality with an aiming error of up to 2 degrees, considering the overall cost / effectiveness ratio in the design.

But we want to point out that while claiming the originality and specificity of this pointing and tracking system (which we will describe below), pointing and tracking systems have been on the market for years applicable to systems for the use of solar energy that could also be used on the present found as an accessory.

Description of the aiming system - See drawing Tav.05;

The aiming system is based on four electro-optical sensors placed on the quadrants of the dish (on the peripheral circle of the dish, at 90 degrees from each other). So two are intended to command the azimuth movement (rotation on the horizontal plane) and two to command the zenith movement (rotation on the vertical plane). The function of the sensors is to detect the moment in which the optical axis of the parabola moves away from the solar radial, and then provide an electric signal, through the actuation of a relay, to an electric motor which, upon entering into action, brings back the axis of the parabola to coincide with the solar radial.

By solar radial we mean the optical axis that connects the optical center of the parabola with the center of the solar disc. Then the sensors, as per drawing Table 05, are mounted and fixed at the ends of the ribs. They are made of material with suitable optical characteristics, in this case of PMMA (polymethylmethacrylate)

See drawing Table 06;

The sensors (fig. 1) have a cylindrical shape with sections of different diameters

-Section D2_is black so as not to let light through, and of a larger diameter than the underlying section DI

Section DI is transparent to visible light, but for an arc of 180 degrees (D1.1) it is blackened by painting so as not to let light through. The blackened section is always oriented towards the optical axis of the parabola (see drawing table 5 "AS" position)

The lower section DI.2 is of smaller diameter and inserted in the support D4 in pos. 2

An electrical sensor capable of reacting to light is mounted on the lower end, in this case a photoresistor.

The photoresistor is glued to the sensor with an adhesive with suitable optical characteristics, in this case a transparent acrylic adhesive. The photoresistor is an electrical sensor that varies its resistance to the passage of electrical current in a manner proportional to the intensity of the light that affects it. When the photoresistor is not hit by light, the resistance is maximum and does not allow electric current to pass. When the photoresistor is hit by light, the resistance is minimal and allows the electric current to pass. Then through two electric cables D6 pos. 2 the sensor sends its electrical signals to a realis which in turn activates an electric motor which moves the concentrator.

The operation of the aiming system and the sensors is described as follows.

“S” indicates the apparent position of the sun with respect to the sensor. From a perspective, the sun is considered "to infinity" and therefore the rays of light it sends are considered parallel.

See Pos. 1 - when the sun is perpendicular to the optical axis of the parabola, the upper part D2, black and with a larger diameter than the lower part D1, prevents light from entering the sensor through the part of the transparent surface. So the system is immobile and oriented towards the sun

See pos. 2 - When the apparent motion of the sun moves it with respect to the optical axis of the parabola, the light will be able to enter the sensor through the transparent part.

Illuminated in this way, the photoresistor will let the electric current pass, and then through a realis activate an electric motor that will bring the dish back to its previous position.

See pos. 3 - When the apparent motion of the sun is in the opposite direction, the blackened sector D1. 1 of the sensor prevents the light from entering.

In this way, each sensor is activated only in one direction, and therefore a movement controlled by one of the four sensors follows each shift of the apparent position of the sun.

Claims (8)

Claims Claim n. 1) Parabolic concentrator of sunlight where a series of ribs placed on the radials of the optical system are shaped with a parabolic profile and the mirrors made of flexible material adapt by copying the parabolic profile, thus concentrating the light on the optical center of the system (focus). Claim n. 2) Parabolic concentrator of sunlight where the mirrors made of flexible material are worked in such a way as to obtain, on the sides orthogonal to the radial axis of the system, one or more folds with the purpose of strengthening the mirror itself to the bending stresses on the orthogonal of the radial axis. Claim n. 3) Parabolic concentrator of sunlight where a sheet of flexible material, suitably shaped, is interposed between the rib and the flexible mirror, with the function of supporting and protecting the mirror. Claim n. 4) Parabolic concentrator of sunlight where mirrors made of flexible material are able to deform elastically under stresses due to atmospheric or other conditions, and to resume their primitive geometric shape when the stress ceases. Claim n. 5) Parabolic concentrator of sunlight equipped with an automatic mirror washing system. Claim n. 6) Parabolic concentrator of sunlight where in the center of the optical system there is a "Target" intended to convert light into heat, suitably treated with a double layer of ceramic, one of which is transparent and pigmented with a suitable material having the functions of black body and one completely transparent to visible light. Claim n. 7) Parabolic concentrator of sunlight where a tracking system equipped with electro-optical sensors as described keeps the concentrator pointed towards the center of the solar disk. Claim n. 8) Electro-optical sensor for pointing towards the sun of an apparatus for the use of solar energy, as described, capable of varying the accuracy of the minimum acceptable deviation with the variation of the diameters of its cylindrical sections.