GB2476981A

GB2476981A - Spectrally selective solar panel

Info

Publication number: GB2476981A
Application number: GB1000787A
Authority: GB
Inventors: Andrew Clifford Pate
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-01-19
Filing date: 2010-01-19
Publication date: 2011-07-20
Also published as: GB201010073D0; GB201000787D0; GB2477001A

Abstract

A spectrally selective panel 7 comprises a spectrally selective fluid which is mechanically bound to a solar transparent covering 2. Preferably, the liquid is water, or a similar fluid with hydrogen bonds, which absorbs infrared heat. The spectrally selective fluid 1 may be bound to the covering by mixing it with a gelling agent or resin. Alternatively, the spectrally selective fluid (3, fig.4) may first be bound within a sphere (4, fig.4) which is then bonded by resin or gel (5, fig.4) to the covering. Advantageously, the spectrally selective fluid may be quilted between two coverings (see figures 5 and 6). The spectrally selective panel may be combined with an absorber to form a solar collector, where the absorber preferably comprises an oil bed 9 flowing over a black surface 10 contained by a neoprene rubber membrane 11. Preferably, the spectrally selective panel is held in tension, or separated from other components of the solar collector, or otherwise made rigid, by the use of a pressurised gas, such that the solar collector may be inflated.

Description

INTELLECTUAL

. .... PROPERTY OFFICE Application No. GB 1000787.0 RTM Date:18 February 2010 The following terms are registered trademarks and should be read as such wherever they occur in this document: V Cool [sic]; (V-Kool) Mylar Intellectual Property Office is an operating name of the Patent Office www.ipo.gov.uk Spectrally selective composite panel for thermal solar collection

Description

The principle of collecting light from the sun and using it to heat a gas or liquid has been around for several decades and many technologies exist to convert this heat into electrical power, such as organic Rankine cycle (OCR) and sterling engines. However solar power production generally remains economic due to the high cost of conventional thermal solar collection panels and the high cost of alternative more complex systems that track the sun and focus the sunlight onto a small absorbing surface.

To produce an efficient thermal solar collector requires a panel component that allows the majority of sunlight (with wavelengths around 600 nanometres) to pass through it while also heat radiated from the collectors light absorbing surface to escape into the environment. Typically this radiated heat has wavelengths around 16,000 nanometres.

Materials possessing this property are referred to as spectrally selective.

According to the current state of the art there exist many spectrally selective materials and coatings (for example V Cool 70) that have excellent spectrally selective characteristics and typically reflect around half of heat radiated from an absorber back to it while letting 70% of the sunlight through. These are generally based on interference filter technologies wherein several partially reflective layers are separated by a thin film. Unfortunately these materials are costly to manufacture (around £60 per square metre).

There also exists another type of spectrally selective material that allows sunlight to pass through but absorb radiated heat. In the absence of convective heat loss this absorbed heat gradually warms the material so that it begins to emit heat radiation itself. The material then effectively becomes opaque to heat radiation and approximately half of the re-radiated heat will return back to its source (Figure 1).

An example of this second type of material is glass which is usually used in several layers separated by an insulating gas which further enhances the blocking of radiated heat (Figure 2). Glass, Polycarbonate and Mylar all have the desired spectrally selective light absorption characteristic but they need to be several millimetres thick in order to achieve this and are relatively expensive resulting in collector costs in excess of 11 per square metre.

There are several solar transparent coverings that are cheap to manufacture that are only slightly spectrally selective, for example polyethylene sheet at less than £ 0.50 per square metre. Such a covering could be combined with liquid water (or other similar fluids that exhibit strong spectrally selective properties) to produce a high-performance low-cost spectrally selective composite. Water is strongly spectrally selective because it possesses multiple hydrogen bonds which absorb heat. A layer of water 30 millionth of a metre thick is sufficient to completely absorb heat radiation.

According to the present invention liquid water (or a similar fluid) is mechanically bound to a solar transparent covering in order to form a spectrally selective panel or sheet. The spectrally selective panel may be held in tension or separated from other components of a solar collector, or otherwise made rigid, by the use of a pressurised gas; in other words the solar collector assembly may be designed to be inflated. The solar collector assembly may have reflectors situated around it in order to improve its performance.

The present invention does NOT lay claim to the prior-art where sun-tracking solar collector designs employ a pressurised gas in order to produce a rigid concave reflector.

Several embodiments of the invention will now be described by way of example with reference to accompanying drawings.

Figure 3 shows in cross-section a spectrally selective panel where the spectrally selective fluid 1 is bound to the covering 2 by mixing it with a gelling agent or resin to the spectrally selective fluid. The refractive index of the resin may be deliberately close to that of the spectrally selective fluid in order to reduce scattering of the incoming sunlight.

Figure 4 shows in cross-section a spectrally selective panel where the spectrally selective fluid 3 is first bound witbin a Sol-gel sphere 4 (not shown to scale) which is then bonded by resin or gel 5 to the covering 2. The Sol-gel capsule may prevent the bonding 5 effecting characteristics of the spectrally selective fluid 3, or extend the lifetime of the panel.

Figure 5 shows in cross-section a spectrally selective panel where the spectrally selective fluid 3 is quilted between two coverings 2.

Figure 6 shows an illustration of a spectrally selective panel where the spectrally selective fluid has been quilted between two coverings.

Figure 7 shows in cross-section a solar collector design where pressurised gas 6 separates the spectrally selective panels 7 from each other and the absorber which may be comprised of an oil bed 9 flowing over a black surface 10 contained by a neoprene rubber membrane 11.

Figure 8 shows in cross-section a solar collector design as described in Figure 7 which possesses radial symmetry about a central axis 12. The resulting solar collector formed would be dome-like or geodesic in structure. Such a structure is likely to be significantly more rigid and wind-resistant than that described in Figure 7.

Figure 9 shows in cross-section a solar collector design as in Figure 7 which uses a vertically mounted reflector to increase the amount of light captured when the sun is low.

Claims

Claims I A spectrally selective panel where a spectrally selective liquid is mechanically bound to a solar transparent covering.
2 A spectrally selective panel as claimed in any preceding claim where the spectrally selective liquid is water.
3 A spectrally selective panel as claimed in any preceding claim where the spectrally selective liquid contains one or more hydrogen bonds.
4 A spectrally selective panel as claimed in any preceding claim where the spectrally selective liquid contains additives to prevent freezing or microbes forming.
A spectrally selective panel as claimed in any preceding claim where the spectrally selective liquid contains a gelling agent.
6 A spectrally selective panel as claimed in any preceding claim where the spectrally selective liquid is encapsulated within a Sol-gel.
7 A spectrally selective panel as claimed in any preceding claim where the spectrally selective liquid or Sot-gel is mechanically bound to the solar transparent covering by use of an adhesive, gel or resin.
8 A spectrally selective panel as claimed in claim 6 where the spectrally selective liquid is mechanically bound to the solar transparent covering by use of a second solar transparent covering to form a layered or quilted structure.
9 A spectrally selective panel as claimed in any preceding claim where the solar transparent covering is glass or one of the following polymers Polyethylene, Acrylic, Polycarbonate, Mylar, FEP, PVF, PMMA, PETP or FRP.
A spectrally selective panel as claimed in any preceding claim where the solar transparent covering or spectrally selective liquid could be devised by someone reasonably skilled in the art.
11 A solar collector assembly that uses a spectrally selective panel as claimed in any preceding claim that could be devised by someone reasonably skilled in the art.
12 A solar collector assembly as claimed in any preceding claim wherein the spectrally selective panel is held in tension or separated from other components of the solar collector, or otherwise made rigid, by the use of a pressurised gas; in other words the solar collector assembly is designed to be inflated.
13 A solar collector assembly as shown in any of the accompanying drawings.
14 A solar collector assembly as claimed in any preceding claim where a reflector is used to increase the amount of light captured.A solar collector assembly as claimed in any preceding claim where the pressurised gas, is a greenhouse' gas for example carbon dioxide.