WO2002002463A1

WO2002002463A1 - Methods of utilising solar energy

Info

Publication number: WO2002002463A1
Application number: PCT/GB2001/002873
Authority: WO
Inventors: Christopher Peter White
Original assignee: Christopher Peter White
Priority date: 2000-06-30
Filing date: 2001-06-28
Publication date: 2002-01-10
Also published as: AU2001266195A1; GB0015907D0

Abstract

A method of utilising solar energy includes providing a first solar panel (10), which is contained within a second solar panel (11) which, in turn, is contained within a third solar panel (12). Salt water can be introduced into the interior of the first solar panel (10) and steam discharged thereform. Condensation of the steam then produces potable water.

Description

METHODS OF UTILISING SOLAR ENERGY

Field of the Invention

This invention relates to methods of utilising solar energy, desalination systems, water treatment systems and the like.

Access to drinking water and the provision of water for agricultural purposes is one of the most important issues in the world today. It is a recurrent problem for many areas in the "sun belt" and, in particular, for many of the poorest countries in the world.

In many cases, there is ready access to sea water, but the high costs associated with desalination prohibit its large-scale use.

There are also often major problems with water contamination following flooding and there is thus an increasing requirement for means for making water safe for drinking. At present, desalination of sea water to produce potable water is achieved using two main systems, i.e. reverse osmosis and distillation, and sometimes a combination of the two.

Reverse osmosis utilises membranes which do not permit the sodium and other metal ions to pass through, i.e. they effectively sieve out the salt. Reverse osmosis systems are, however, technically complex and high in energy requirements and running costs.

Distillation systems involve collecting and condensing water vapour. Some systems heat the water using conventional energy sources, such as gas or electricity, whilst others use solar energy. Systems using solar power may use the solar energy either directly or indirectly. The indirect methods include the use of silicon panels or heat transfer systems, while the direct methods utilise either concentration-type technologies (such as reflecting the solar energy onto a reduced area) or simple compartments, relying on the solar energy to increase the natural levels of evaporation.

The existing simple compartment systems for the solar desalination of water need to cover large areas in order to produce significant quantities of water. Thus, current units measuring approximately 1 m. X 2 m. are capable of producing around 15 litres per day during the summer months in the "sun belt".

These systems use a single compartment covered in transparent glass and the temperature within the compartment is raised to a level of the order of 75° C. Raising the temperature of the water to this level increases the rate of evaporation of the water; and the water of evaporation rises and then condenses and is collected.

The fundamental problem with these simple compartment systems is that the temperature of the water cannot rise sufficiently for the water to boil. If boiling could be achieved, then the amount of condensation, i.e. the output rate, would be significantly increased.

The existing multiple compartment systems have included a heat transfer arrangement and have been inefficient.

At present, boiling of the water has been achieved in two ways, the first of which has been to create a vacuum above the water. This reduces the boiling point of the water. The second approach has been to use an electrical heating element for heating the water to 100° C. or more.

It is an object of the present invention to provide an improved method of utilising solar energy.

It is a more specific object of the present invention to provide an improved form of desalination system which utilises solar energy more effectively than existing solar energy desalination systems.

Summary of the Invention According to a first aspect of the present invention there is provided a method of utilising solar energy, the method comprising providing a first solar panel, which is contained within a second solar panel which, in turn, is contained within a third solar panel, and supplying a controlled flow of a liquid to the first solar panel.

The arrangement is preferably such that the temperature within the second solar panel is in excess of 100° C.

According to a second aspect of the present invention there is provided a system comprising a first solar panel to which water is fed and from which steam is discharged, said first solar panel being arranged to receive solar energy and being itself contained within a second solar panel which, in turn, is contained within a third solar panel.

The second solar panel preferably contains air and a desiccant, while the third solar panel may contain a vacuum and a desiccant.

The steam discharged from the first solar panel is preferably fed to a turbine (for the generation of electricity) and then to a condenser.

Each of the solar panels preferably comprises a base and side walls formed of a light-impervious material, such as aluminium or steel, and a transparent cover. The solar panels are preferably of rectangular form in plan view with the bases of the panels superposed and insulating spacers located between the bases of adjacent panels. The base and the side walls of the outermost panel are preferably covered by means of an insulation material.

The transparent covers of the solar panels are preferably formed of high clarity glass.

The condenser may include a chamber which is disposed in heat exchange relationship with a tank through which water is supplied to the first panel so that pre-heating of the water supplied to the first panel is effected.

Brief Description of the Drawing

The single figure of the accompanying drawing illustrates the construction and mode of operation of a solar-powered desalination system.

Description of the Preferred Embodiment

The desalination system shown in the drawing includes three solar panels 10, 11 and 12 arranged one within the other. The first solar panel 10 is contained within the second solar panel 11 and the second solar panel 11 is, in turn, contained within the third solar panel 12. The second solar panel 11 is in the form of a sealed unit containing air and a desiccant, the third solar panel 12 is in the form of a sealed unit containing a vacuum and a desiccant while the first solar panel 10 is connected by a stainless steel pipe 13 to a tank 14 to which sea water is supplied. A pump (not shown) may be provided for pumping sea water into the tank 14 and a float- controlled valve 15 is provided for controlling the flow of water from the tank 14 into the interior of the first solar panel 10, thereby maintaining a substantially constant level of water in the first solar panel 10. As shown, the interior of the first solar panel 10 includes a receiving portion 16, into which water flows from the tank 14, and an exit portion 17, from which steam is discharged into a turbine chamber 18 and thence into a condenser 19. The depth of the receiving portion 16 is less than the depth of the exit portion 17, this being achieved by the provision of a barrier 20 which has sealed connections to the base and side walls of the first solar panel 10.

The tops of the solar panels 10, 11 and 12 are of high clarity glass. The interior of the first solar panel 10 functions as a boiling compartment and the temperature within the interior of the second solar panel 11 is in excess of 100° C. so that no condensation takes place on the undersurface of the glass top of the first solar panel 10.

The bases and walls of the second and third solar panels 11 and 12 are of aluminium or steel painted black, to maximise the amount of heat which is absorbed, while the base and walls of the first solar panel 10 are of aluminium or steel with a matt black enamel or other resistant finish. The enamel or other resistant finish is to ensure that there is no tainting of the water. The solar panels 10, 11 and 12 are of rectangular form in plan view, with the third solar panel 12 typically having dimensions of 1 metre by 1.5 metres.

The water content of the second and third solar panels 11 and 12 can be minimised by manufacturing them in a low humidity environment and then adding a desiccant, such as silicate granules. If any water vapour were present in the second and third solar panels 11 and 12, this would reduce the transmission of light and heat to the boiling chamber contained within the first solar panel 10. The glass is sealed in place using a sealant which is resistant to the high temperatures which are encountered and, for the first solar panel 10, the sealant which is used is resistant to boiling salt water.

The salt water from the tank 14 is fed into the receiving portion 16 of the boiling chamber contained within the first solar panel 10 and is topped up under the control of the float valve 15.

Steam exits from the boiling chamber via a stainless steel pipe 21 and enters the turbine chamber 18. The steam turns the turbine to produce electricity and passes from the turbine chamber 18 into the condenser 19. A filter (not shown) may be interposed between the turbine chamber 18 and the condenser 19 to ensure that small oil droplets from the turbine do not enter the condenser 19. The condenser 19 may contain a large number of glass balls (not shown) which provide a substantial surface area on which condensation takes place. Water from the condenser 19 typically passes to a fresh water tank (not shown) from which it can be withdrawn for domestic, agricultural or other use.

The boiling compartment within the first solar panel 10 needs to be flushed out at regular intervals, typically at the end of each day, to remove the salts remaining in the boiling compartment following distillation.

If the salts are required for sea salt, or if there are environmental objections to discharging the high salinity effluent, the water flushed from the boiling compartment may be collected in salt pans and the water evaporated using conventional means. If the high salinity effluent is not required, it can be returned to the sea.

The entry of solar energy into the boiling compartment in the first solar panel 10 provides direct heating and increases the temperature of the water within the boiling compartment to temperatures far in excess of 100° C. even if the external temperature is only of the order of 25° C. This is as a result of the effective insulation of the boiling compartment in the first solar panel 10 from the atmosphere by the second and third and solar panels 11 and 12, and the resulting temperature gradient, which ensures that relatively little thermal energy is lost.

Insulating pads can be located beneath the bases of panels 11 and 12 to reduce the loss of heat through conduction. The base and the walls of the third solar panel 12 can be enclosed in a layer of insulation material. The arrangement will typically be such that air can circulate in the gap between the walls of the third solar panel 12 and the second solar panel 11. This allows the interior of the second solar panel 11 to become heated and there will normally be no insulation between the first solar panel 10 and the second solar panel 11. This is to allow the transfer of heat from the second solar panel 11 to the first solar panel 10 to replace the heat used in boiling the water in the first solar panel 10.

The desalination and electricity generation system is intended primarily for use in the "sun belt" areas such as the southern areas of the United States, the Middle East, Central and Western Australia and North Africa. Sea water is distilled using solar energy to provide fresh water and electricity. The resulting salts can either be returned to the sea or crystallised and sold as sea salt.

The desalination system may, however, be used in other areas with high solar radiation and may be employed, with or without the accompanying generation of electricity, to provide distilled water or to sterilise or pasteurise water following floods.

The system may also be used to kill pathogens in water supplies. Thus the water in the first solar panel 10 can be brought to boiling point and kept there for a sufficient length of time to kill any contaminants. The system can also be used for waste treatment, for example, plant waste which, when treated, can be used as animal feed. The plant waste is macerated, has water added to it and is then heat treated in apparatus substantially as described above. This serves to break down any complex molecules and cell structures. The heat-treated waste is then cooled and fermented. This produces ethanol and a mixture that is suitable for animal food, thereby avoiding the requirement for disposal of the plant waste by either landfill or incineration procedures.

If water having a high metal content is treated, the metals within the water are gradually concentrated and the system can thus be used to remove heavy metals from effluent produced by commercial processes. The system of the present invention thus offers substantial advantages as compared with current systems of mineral extraction, which are highly environmentally destructive.

Chemical processes that are tolerant to sunlight and involve heating substrates can also be carried out in a unit similar to that shown in the drawing.

Claims

Claims:-

1. A method of utilising solar energy, the method comprising providing a first solar panel, which is contained within a second solar panel which, in turn, is contained within a third solar panel, and supplying a controlled flow of a liquid to the first solar panel.

2. A method as claimed in Claim 1 , in which the arrangement is such that the temperature within the second solar panel is in excess of 100° C.

3. A method as claimed in either of the preceding claims, in which the liquid is water containing salt or other impurities.

4. A system comprising a first solar panel to which water is fed and from which steam is discharged, said first solar panel being arranged to receive solar energy and being itself contained within a second solar panel which, in turn, is contained within a third solar panel.

5. A system as claimed in Claim 4, in which the second solar panel contains air and a desiccant.

6. A system as claimed in Claim 4 or Claim 5, in which the third solar panel contains a vacuum.

7. A system as claimed in Claim 4, in which the steam discharged from the first solar panel is fed to a turbine (for the generation of electricity) and then to a condenser.

8. A system as claimed in Claim 4, in which each of the solar panels comprises a base and side walls formed of a light- impervious material and a transparent cover.

9. A system as claimed in Claim 8, in which the solar panels are of rectangular form in plan view with the bases of the panels superposed and insulating spacers located between the bases of adjacent panels.

10. A system as claimed in Claim 9, in which the transparent covers of the solar panels are formed of high clarity glass.

11. A system as claimed in any one of Claims 4 to 10, in which the arrangement is such that the solar energy received by the solar panels is such as to increase the temperature within the first solar panel to a temperature substantially in excess of 100° C. and the temperature within the second solar panel to a temperature in excess of 100° C.