WO2016178056A1

WO2016178056A1 - A system that uses greenhouse gases to increase the receiver efficiency of concentrated solar power systems

Info

Publication number: WO2016178056A1
Application number: PCT/IB2015/053221
Authority: WO
Inventors: Janaka WIJEWICKRAMA
Original assignee: Wijewickrama Janaka
Priority date: 2015-05-02
Filing date: 2015-05-02
Publication date: 2016-11-10

Abstract

The invention can be integrated to all existing Concentrated Solar Power (CSP) systems. It is inspired by the greenhouse effect where a group of atmospheric gases, called Greenhouse Gases (GHGs) allow sunlight to pass through to the surface of a planet but traps some of the heat (Infrared) escaping from the planet's surface within its atmosphere. However, there are certain GHGs that can trap several thousands of times more heat than an equivalent mass of carbon dioxide. In a CSP system, a massive amount of energy is wasted at the receiver and at temperatures such as those of a CSP receiver, the primary mode of energy wastage is through Infrared radiation. This invention surrounds the central receiver (2) of a CSP system with a powerful GHG, held in place by a strong transparent casing (1) around the central receiver, which is sealed from the outside environment. This creates a powerful artificial greenhouse effect around the receiver that lets sunlight in, but traps a portion of the escaping infrared radiation (otherwise wasted energy).

Description

A system that uses Greenhouse gases to increase the receiver efficiency of Concentrated Solar Power systems.

Summary of Invention

An invention that creates an artificial greenhouse effect around the central receiver of a CSP system by surrounding it with a potent greenhouse gas held in place by a fully or partly transparent casing. Can be integrated to all existing Concentrated Solar Power (CSP) systems, simply by using a casing and the suitable GHG that optimizes the receiver efficiency. A gas inlet and outlet is fixed into the casing so that the GHG concentrations can be controlled when necessary. Reduces the energy wasted at the central receiver by trapping Infrared radiation.

DESCRIPTION

Technical Field

This invention relates mainly to Concentrated Solar Power as it is a system that increases the efficiency of technologies in the said field. It is also applicable to certain other fields where solar thermal energy is used. This invention is inspired by the Greenhouse effect that is a prominent topic in climate sciences.

Background and Related art

Concentrated Solar Power (CSP) systems collect the sun's energy over a large area using reflectors and focus it on to a central receiver. Despite the difference in scale, this system is somewhat similar to concentrating sunlight with a lens to light a matchstick, the head of the matchstick representing the central receiver. The central receiver absorbs this solar energy which is converted into heat energy, absorbed by a work fluid and used to do mechanical work to generate electricity. Even though CSP systems have various designs, this basic principle where sunlight is concentrated to a central receiver, is common to every single one of those variations. The main kinds of CSP systems are

(1) Solar Power Tower

(2) Parabolic Trough

(3) Dish Sterling

(4) Compact Linear Fresnel Reflector

As mentioned before, all these systems have a common basic principle, namely, a large amount of sunlight is concentrated to a central receiver. And therefore all the different existing designs have a common weakness. That is, they lose a massive amount of energy at the receiver resulting in the decrease in the overall efficiency.

This invention is inspired by the greenhouse effect. The greenhouse effect is a process by which certain gases in a planetary atmosphere let sunlight in, but absorb thermal radiation escaping from a planet's surface and re-radiates some of this energy flux back towards the surface. This results in an overall increase in the temperature of the planet. This effect is caused by a unique group of gases known as Greenhouse gases (GHG's). The greenhouse effect is what maintains earth at a temperature that can sustain life. The enhancement of this effect due to anthropogenic emission of greenhouse gases (such as Carbon dioxide), resulting in an increase in the concentration of such gases in the atmosphere, is the primary the cause of global warming. In planets such as Venus, a tremendously powerful greenhouse effect takes place, and is responsible for making the planet the hottest in our solar system, despite being the second from the sun.

Technical Problems:

There is a certain problem that affects all CSP systems. When sunlight hits the receiver it assumes a certain thermodynamic temperature and radiates a large amount of energy outwards. (According to the Stephan-Boltzmann law, considering the temperature of CSP receivers, the vast majority of this energy radiated from the receiver is in the form of infrared radiation). All of this energy is unfortunately, wasted energy. This means that the efficiency of the overall system is reduced greatly. In certain methods of CSP systems such as the parabolic trough, the receiver tube (central receiver) is enforced with a vacuum surrounding it, in an attempt to reduce escaping heat. Even though a vacuum is effective in preventing heat loss through convection, it does not prevent heat loss through radiation. Because the CSP receiver loses energy mainly through radiation of heat, a vacuum does no good in preventing the energy lost in this form.

Technical Solution:

In this invention, the central receiver of a CSP system is surrounded with a potent

Greenhouse gas, enclosed in a strong, transparent casing. All Greenhouse gases are transparent to electromagnetic radiation of the visible light frequency range but opaque to those in the infrared range. Almost all of the energy arriving at earth's surface from the sun is visible light. Therefore, the solar energy that is concentrated at the receiver will not be disturbed by the GHG when reaching the central receiver, as it is visible light. However, part of the energy escaping the receiver as Infrared will be absorbed and re-radiated towards the receiver to be absorbed. The application of this invention will result in a dramatic increase in overall efficiency of any CSP system. (It should be mentioned that incoming solar energy consists of Infrared as well. But this Infrared is categorized as near Infrared as its frequency is very high. The Infrared escaping the receiver is mid Infrared and has a much lower frequency than that of near infrared. Greenhouse gases are in fact very opaque mostly to the mid-range infrared and will allow the near infrared to pass through without

disturbance). Description of drawings

Figure 1 shows the fundamental structure of the invention.

Figure 2A shows a Solar Power Tower in current condition.

Figure 2B shows an improved Solar Power Tower after the invention is applied.

Figure 2C shows the base of transparent casing, made of 6 sectors.

Figure 2D shows a sixth of the curved surface of the cylindrical casing.

Figure 2E shows the cross section of the invention after integrated to a Solar Power Tower.

Figure 3 shows the invention whose structure is adjusted to fit into a Parabolic Trough system.

Figure 4 shows the invention whose structure is adjusted to fit into a Dish Stirling system.

Figure 5A shows the cross section of the receiver of a Compact Linear Fresnel Lens reflector after the invention is applied.

Figure 5B shows the invention whose structure is adjusted to fit into a Compact Linear Fresnel reflector system.

Detailed description of invention

This invention is designed to boost the efficiency of all the existing methods of CSP. It is very simple and although its structure and materials may differ in various CSP systems, the basic principle underlying the design is exactly the same. That is as follows; a strong, transparent casing (1) is built around the receiver (2) so that the receiver is completely surrounded by the casing and sealed from the outside environment. Since it is transparent, it will not disturb the sunlight hitting the receiver. It is built with an inlet (3) and an outlet (4) consisting of valves. This is to allow air inside to be pumped out and once the air is drawn out of the casing, to allow the space to be replaced by a powerful greenhouse gas. This whole structure can be compared to two concentric cylinders where the inner cylinder is solid and the outer one is hollow. The solid inner cylinder would be the receiver and the outer hollow cylinder would be the casing. It is in the space between the two cylinders that the greenhouse gas will be put into place (5). This simple design is modified in shape and size so that it best suits the type of CSP system used. The exact greenhouse gas to be used around a certain CSP system and the amount of the said gas to be used can be calculated through experiment only, since different greenhouse gases have different potentials in its capacity to trap heat as well as different densities. In some systems, it is possible to use a strong heat insulating material (6), instead of a transparent material, for the parts of the casing that do not stand in the way of incoming sunlight. Sunlight is focused by a variety of designs of reflective surfaces (7). It is important to mention that in much of this patent report, CSP systems for electricity generation are discussed for the ease of explanation. However, the system can be applied to a broad range of existing technologies that use a central receiver to absorb solar thermal energy as mentioned under Claims, (e.g. - Solar powered water distillation methods).

A few examples of the various embodiments of the invention are given below.

Integrated with the receiver of Solar Power Tower systems.

In existing solar power tower systems (Figure A), the central receiver (2) is exposed to air and the Infrared energy can escape without any obstruction. However this invention can easily be integrated to fit existing Solar Power Towers. First, above the receiver, a solid cylindrical structure made of a heat insulating material is built into the tower (6). The casing which is made of a strong, transparent material will be attached to, and held in place by this structure and will form a cylindrical shape outside the receiver. The casing will slightly exceed the height of the receiver equally in both directions. The base of the casing (8) is made of 6 separate sectors for the ease of assembly. Each sector (9) will support a sixth of the vertical curved surface of the cylinder (10). The base of the casing will contain the inlet (3) and outlet (4). Once these separate components are assembled together, it must be made sure that the casing is sealed. Then, the air can be pumped out and replaced with the greenhouse gas. The insulator serves not only as a support to the casing, but also to prevent any convectional currents that may occur in the gas body and result in heat loss through the upper part of the structure. Since all the incoming solar energy comes from below the horizontal plane of the receiver, it is unnecessary for the uppermost portion of the structure to be made of a transparent material. Therefore, it is best to insulate it well.

Integrated with the receiver of Parabolic Trough systems.

In a parabolic trough system consisting of trough shaped reflective surfaces (7), the transparent casing (1) and the receiver (2) will form two concentric cylinders, as in the solar power tower system. This is very similar in shape to the glass casing used to maintain a vacuum surrounding the receiver, which is used at present in parabolic trough systems. Except, instead of a vacuum there will be a strong greenhouse gas (5) within the casing. The size of the casing will vary depending on what greenhouse gas is used as they have different capacities in trapping heat. Under present conditions, individual receiver tubes are connected together to form the final receiver that allows the work fluid to be pumped through the entire length of the trough. The casings of the each receiver would individually contain an inlet and an outlet. If the proper greenhouse gas is used, existing receiver tubes may be used directly by simply replacing the vacuum with the gas but the increase in efficiency may not be optimum in that case.

Integrgted with the receiver of Dish Stirling systems

In a Dish Stirling system the reflective surface is in the shape of a dish (7) the receiver is different from the other systems. To prevent IR from escaping from this receiver surface, a casing in the form of a frustum of a cone is used (1). The frustum can be made entirely of a transparent material, or else, the base can be made transparent while the curved surface of

Claims

the cone can be heavily insulated (7). In the latter case, the cone will be wider since all the sunlight must pass through the base. In both cases, the receiver is located at the upper circular face of the frustum. This casing is fixed to the component of the Dish Sterling that contains the Stirling engine (11). The casing is of course sealed and contains a gas inlet (3) and outlet (4).

Integrated with the receiver of Compact Linear Fresnel Reflector systems

There are two types of compact linear Fresnel reflector systems. One with a secondary reflector (7), and the other without it. In systems where there is no secondary reflector, the same process of the parabolic trough system is applied. In Fresnel reflectors where a secondary reflector is present, a casing in the shape of a frustum of a hollow triangular prism is used. The casing will not have an upper face. The inlet (3) and outlet (4) is at the side of the prism. The rectangular upper edge of the casing is attached to the secondary reflector (7) and the reflector acts as the top face of the casing. This combined structure encloses the receiver tube around which the gas is to be filled.

Intended use:

The invention described in this patent can immediately be applied to any existing

Concentrated Solar Power system. To do so requires a slight modification in the receiver of existing CSP technologies. Its size, structure and material can be changed so that it can be applied in the most effective method to each individual CSP system to attain the optimum efficiency of the chosen system. By using more of the energy that would otherwise have been wasted, from the invention described in this patent, all CSP systems around the world will be able boost their efficiency with only a small, simple addition to its central receiver. That in turn would help in strengthening renewable power generation throughout the world to a great degree.

Other than Concentrated Solar Power systems that are used to generate electricity, this invention can be applied to a broad variety of other systems. If a system requires sunlight to be concentrated to a central receiver, then there will most definitely be a wastage of energy in the form of thermal radiation (IR) escaping outward from the receiver. Then the said receiver of that system can be integrated with this invention so that the escaping thermal radiation is minimized, resulting in an increase in efficiency, (e.g. - Desalination of water using concentrated solar power). CLAIMS

I claim as my invention:

1) A system that boosts the efficiency of any Concentrated Solar Power system,

consisting of one or more greenhouse gases fully or partly surrounding the solar receiver.

2) A system as claimed in claim 1 where the said greenhouse gas in held in place

around the receiver by a transparent casing.

3) A system as claimed in claim 1 where the greenhouse gas is held in place by/ made to move inside of/ made to move into and out of the volume created by the said transparent casing.

4) A system as claimed in claim 1, where the said transparent casing is only partly

transparent to allow sunlight in and the rest of its body is built with an opaque material, such as a heat insulator.

5) A system as claimed in claim 1, where an outlet and inlet consisting of valves are built into the casing to draw out/ pump in air or a greenhouse gas.

6) A system as claimed in claim 1 that can be integrated into,

The central receivers of all Concentrated Solar Power systems of electricity generation or energy storage.

Systems of water distillation and/or desalination that use concentrated solar power.

Engines that rely on concentrated solar power to do mechanical work. Low and mid temperature solar thermal systems that use solar energy but do not normally do not require it to be concentrated, (e.g.- water heating systems) Solar cookers.