Batteries: thermoelectric and photoelectric – Photoelectric – Panel or array
Reexamination Certificate
2001-09-10
2002-10-29
Diamond, Alan (Department: 1753)
Batteries: thermoelectric and photoelectric
Photoelectric
Panel or array
C136S246000, C136S259000, C136S291000, C126S622000, C126S623000, C126S621000, C126S625000, C126S626000, C126S634000, C126S643000, C052S173300
Reexamination Certificate
active
06472593
ABSTRACT:
The invention pertains to a hybrid roof covering element comprising a thin film solar cell sheet. Hybrid roof covering elements are elements which can suitably be mounted on or in roof structures or otherwise integrated into buildings or, if so desired, in stand-alone systems, in which solar energy is employed in two ways. On the one hand, solar energy is converted into electricity by a thin film solar cell sheet. On the other hand, solar energy is used to heat a gaseous and/or liquid medium, such as air and/or water.
Hybrid roof covering elements comprising a thin film solar cell sheet are known. They are described, e.g., in U.S. Pat. No. 5,589,006 and EP 0 820 105. U.S. Pat. No. 5,849,006 describes a hybrid roof covering element comprising, from top to bottom, a top layer composed of, preferably, a transparent coating, a thin film solar cell sheet cast in a filler, a back insulating member, a filler layer, and a roofing sheet. Air is passed underneath the roofing sheet. EP 0 820 105 describes a system where a thin film solar cell sheet is provided on a back plate of high load bearing capacity and high processability, so that the plate can be freely bent into any desired shape, more specifically into a trapezoidal shape. The air is passed underneath the back plate and over the thin film solar cell sheet.
Although these hybrid roof covering elements function adequately, they are open to improvement, especially as regards heat generation efficiency.
It has now been found that an improvement can easily be effected in this field by directly contacting a thin film solar cell sheet with low heat capacity with the medium to be heated. This will result in higher efficiency on the part of the roof covering element, as less energy is required to heat the thin film solar cell sheet itself, leaving more energy for useful processing. This leads to a higher response speed on the part of the hybrid roof covering element.
The invention thus pertains to a hybrid roof covering element comprising a thin film solar cell sheet that is characterized in that it has a heat capacity of less than 3.5 kJ/m
2
·K, preferably less than 600 J/m
2
·K.
The thin film solar cell sheet used in the hybrid roof covering element according to the invention is a flexible thin film solar cell sheet. The flexibility of the film is attractive for a number of reasons. First of all, said flexibility makes it possible to transport the thin film solar cell sheet in rolled-up form to the place where the roof covering elements are assembled. Secondly, it is easier to divide flexible thin film solar cells up into sections of the desired size than rigid thin film solar cells on, say, a glass carrier. Thirdly, the flexibility of the thin film solar cell sheet makes it possible for the film to be integrated into the roof covering element in different ways if so desired, as a result of which the position of the film vis-à-vis the sun can be optimized and any desired aesthetic effects may be obtained. Thus a flexible thin film solar cell sheet can not only be made into a flat sheet as is most common, but also bent into, say, a trapezoidal or some other desired shape. Thin film solar cell sheets manufactured by means of a roll-to-roll process are particularly attractive, as they very fully satisfy the desired properties of easy transportation and easy dividing up into sections of the desired size.
The thin film solar cell sheet used in the hybrid roof covering element according to the invention generally is composed of a flexible carrier, a back electrode, a photovoltaic layer, and a transparent front electrode. If so desired, the thin film solar cell sheet may be provided with one or more protective layers or other top layers. The heat capacity of such a thin film solar cell sheet is determined principally by the nature of the carrier and any protective and top layers present. In selecting these materials care has to be taken to ensure that the desired properties as regards heat capacity are obtained.
The thin film solar cell sheet employed in the hybrid roof covering element according to the invention preferably has an overall thickness of less than 1000 &mgr;m, more preferably of less than 500 &mgr;m, most preferably of less than 300 &mgr;m. Generally speaking, the thinner the thin film solar cell sheet, the lower its heat capacity will be.
The thin film solar cell sheet employed in the hybrid roof covering element according to the invention preferably has a weight per surface area of less than 1400 g/m
2
, more preferably of less than 700 g/m
2
. Generally speaking, the lighter the thin film solar cell sheet, the lower its heat capacity will be. Furthermore, lighter sheets may result in simpler and less costly transportation and processing.
Suitable materials for the carrier layer of the thin film solar cell sheet include thermoplastic or thermosetting polymer films, combinations thereof, and, optionally, fibre-reinforced variations thereon. Suitable thermosetting materials include polyimides, unsaturated polyesters, vinyl esters, SI, etc. The thermoplastic materials may be amorphous as well as semi-crystalline. Examples of suitable amorphous thermoplastics are PEI, PSU, PC, PPO, PES, PMMA, SI, PVC, PVDC, FEP, and various other fluorine-containing polymers. Examples of suitable semi-crystalline materials are PET, PEN, PEEK, PEKK, PP, and PTFE. Examples of suitable liquid-crystalline materials are PPTA (Twaron, Aramica, Kevlar (all trade marks)). Use may be made of melt-extruded films as well as solution-, emulsion- or suspension-cast films. Biaxially drawn films as a rule will have superior mechanical properties. Metal films on which an insulating (dielectric) top layer has been provided, or compositions of polymer and fiber reinforcement like glass fiber reinforced epoxy-may also serve as a carrier layer if so desired.
Polymeric “co-extruded” films provided with a thermoplastic adhesive layer with a softening point below that of the carrier itself are preferred. Optionally, the coextruded film is provided with an anti-diffusion layer of, e.g., aluminium or SiOx.
At present, preference is given to biaxially drawn polyesters, preferably ones provided with an inorganic anti-diffusion coating.
The thickness of the carrier preferably is 75 &mgr;m to 1 mm. Preferred ranges are 100 &mgr;m to 600 &mgr;m and 150 &mgr;m to 300 &mgr;m. As indicated above, the use of a thin film solar cell sheet manufactured by means of a roll-to-roll process is attractive. An attractive roll-to-roll process for the manufacture of a flexible thin film solar cell sheet comprises the following steps:
a. providing a temporary substrate
b. applying the transparent conductive electrode onto said substrate
c. applying the photovoltaic layer
d. applying the back electrode
e. applying a permanent carrier onto the back electrode
f. removing the temporary substrate.
g. optionally applying a transparent protective layer
The reason why this process is so attractive for manufacturing thin film solar cell sheets for use in hybrid roof covering elements is that the use of the temporary substrate makes it possible for the front electrode of the transparent conductive oxide, the photovoltaic layer, and the back electrode to be applied under such conditions as will produce a solar cell of good quality. The permanent carrier which is applied onto the thin film solar cell sheet at a later stage can be selected such that it will readily satisfy the conditions imposed by specific use in a hybrid roof covering element. However, there is no need for the permanent substrate to be resistant to the conditions, e.g., the high temperature conditions, prevailing during the application of the front electrode, the photovoltaic layer, and the back electrode, as a result of which there is greater freedom of choice when it comes to selecting the permanent carrier.
For that reason the invention also pertains to hybrid roof covering element comprising a thin film solar cell sheet manufactured by a process comprising the aforesaid steps a-g. Examples of suitable processes are those described
Andel Van Eleonoor
Middelman Erik
Akzo Nobel N.V.
Diamond Alan
Fennelly Richard P.
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