Electrical generators which convert or transform solar radiation into electrical energy typically include a photovoltaic device which usually is mounted on a support. Said photovoltaic device is also referred in the art as a solar cell, Energy conversion occurs as a result of what is known as a photovoltaic effect, i.e. solar radiation impinging on the solar cell generates electricity when absorbed by an active region thereof. The active region usually contains a semiconductor material, which may be made of a rigid single-crystal silicon, poly-crystal silicon or glass. Solar cells having a rigid active region are usually referred to in the art as rigid solar cells. Although rigid solar cells offer a clean and efficient source of energy, the rigid substrates thereof have several drawbacks in that they are fragile, bulky and minimize the acceptability of solar cells in many applications.
To alleviate the above mentioned drawbacks, solar cells on flexible substrates were developed, an example thereof being mentioned in U.S. Pat. No. 6,548,751. Such solar cells on flexible substrates are usually referred to in the art as flexible solar cells. U.S. Pat. No. 6,548,751 describes a thin-film flexible solar cell built on a plastic substrate which comprises a cadmium telluride p-type layer and a cadmium sulfide n-type layer sputter deposited onto a plastic substrate at a temperature sufficiently low to avoid damaging or melting the plastic and to minimize crystallization of the cadmium telluride. A transparent conductive oxide layer overlaid by a bus bar network is deposited over the n-type layer. A back contact layer of conductive metal is deposited underneath the p-type layer and completes the current collection circuit. The semiconductor layers may be amorphous or polycrystalline in structure.
A flexible electrical generator is also known from CN2838046, whereas CN101132031 describes a method for making the same. CN2838046 describes a plurality of rigid solar cells which are connected to a flexible bottom material, i.e. a flexible support. The flexible support may comprise textile fabrics or plastic films. A gap is left between the adjacent edges of every two solar cells and the solar cells are connected in series to form a larger foldable electrical generator. Each solar cell comprises an upper and a lower adhesive layer and an upper and a lower outer layer of a transparent polytetrafluoroethylene composite material, wherein the upper outer layer is larger than other layers to form a hanging circumference. Connecting holes can be distributed on said hanging circumference for affixing the solar cell to the flexible substrate. The solar cells are flat arranged on the flexible substrate and glued or stitched through a line with the flexible bottom material through the circumference of the upper outer layer. The electrical generator of CN2838046 has the advantages of a good flexibility and folding property and can be used for example in garments.
A vehicle roof having a main part covered with organic type solar cells for capturing solar energy and transforming it into electric energy to power a part of electrical equipments of a vehicle is known from FR2934206. The roof is flexible and foldable and can be opened or closed. The solar cells are fixed on a polymer strip fixed on the roof and protected externally by a transparent synthetic layer.
It was observed however that in the known flexible electrical generators such as the ones disclosed above, the plastic substrate of the solar cells used therein is fragile and can be easily damaged or broken. Also the electrical generators comprising flexible supports onto which rigid or flexible solar cells are affixed have the above mentioned disadvantages, i.e. they are fragile and have a rather short lifetime. In particular it was observed that large sized flexible solar cells must be supported on rigid supports such as rigid roofs or rigid panels. If not supported, large sized flexible solar cells are susceptible to break under their own weight or under external forces generated by hostile environmental factors such as winds, impacts from debris carried by the wind, accumulated rain water and the like. These drawbacks were partially alleviated by the flexible solar cell disclosed in US 2010/239797.
US 2010/239797 discloses a flexible solar cell wherein a layered material is used, said layered material comprising a layer of ultrahigh molecular weight polyethylene fibers which is surrounded on each of the sides by a film made of polyethylene or polypropylene. According to US 2010/239797 the layered material is lightweight and has high stability or tear resistance and a high modulus of elasticity.
It was observed however that the flexible solar cells of US 2010/239797 have a reduced mechanical stability in that the textile fabric support elongates and/or shrinks during utilization in hostile environments. Due to its pronounced mechanical instability, the textile fabric used as support induces mechanical loads on the solar cells mounted thereon. These mechanical loads negatively influence the durability of the solar cells and may lead to damages or even complete failure thereof.
An aim of the present invention may therefore be to provide a flexible electrical generator which presents the above mentioned disadvantages to a lesser extent. A particular aim of the invention may be to provide a flexible electrical generator which has a better durability than the known electrical generators. A further aim of the present invention is to provide a self-supporting, large sized, flexible electrical generator which has a good mechanical stability, e.g. a reduced elongation and/or shrinkage during its lifetime.