Patent Application
20120192946
The present invention relates to use of calcium oxide as a water scavenger in edge sealant formulations for solar modules.
Photovoltaic solar panels or modules generally include a photovoltaic device that is laminated and/or sandwiched between a plurality of layers. The majority of photovoltaic devices are rigid wafer-based crystalline silicon cells or thin film modules having cadmium telluride (Cd—Te), amorphous silicon, or copper-indium-diselenide (CuInSe2) deposited on a substrate. The thin film solar modules may be either rigid or flexible. Flexible thin film cells and modules are created by depositing the photoactive layer and any other necessary substance on a flexible substrate. Photovoltaic devices are connected electrically to one another and to other solar panels or modules to form an integrated system.
The efficiency of photovoltaic solar panels is lessened by intrusion of moisture. One effective method of lessening this transfer of moisture from the environment to the interior, moisture sensitive portion of the solar module is to use edge sealants. These edge sealants have the property of having a low rate of moisture vapor transmission, or MVT.
An additional method for reducing the rate of moisture transmission is through use of a desiccant material. One such class of desiccant materials is molecular sieves. Molecular sieves are comprised of materials containing tiny pores of a precise and uniform size that are used as an adsorbent. Molecules of water are small enough to pass through the pores and are adsorbed within the molecular sieve material. A typical molecular sieve can adsorb water up to 22% of its own weight. Examples of molecular sieves include, but are not limited to, aluminosilicate minerals, clays, porous glasses, microporous charcoals, zeolites, active carbons, or synthetic compounds that have open structures through which small molecules, such as water can diffuse.
However, the absorption of moisture by molecular sieves is reversible. That is, moisture held within a molecular sieve can be released. Some versions of molecular sieves attempt to better trap moisture by including additional compounds or elements that react with the water.
Other materials can be used as desiccants. These include silica gel, calcium sulfate (offered for sale as Drierite™), and calcium chloride. These desiccants react with water, but in a reversible way. Thus some of the moisture can be released after being absorbed, adsorbed or reacted.
Another class of materials that can remove moisture from surroundings include water scavengers. Unlike standard desiccants, water scavengers react with water in a manner that is not reversible under the conditions that the product experiences in its normal lifetime. However, water scavengers are caustic compounds that are corrosive. Accordingly, water scavengers have not been used in solar module applications due to the caustic nature of the compound. Therefore, there is a need in the art for a sealant in solar modules that incorporates a water scavenger that does not release water and that does not corrode the sealant over the lifetime of the solar module and that provides improved water absorption over desiccant materials.
The present invention provides a photovoltaic solar module with an edge seal. The edge sealant incorporates calcium oxide as a water scavenger in place of a desiccant, such as a molecular sieve. The calcium oxide within the edge sealant has improved water absorption characteristics over conventional desiccants. In addition, the calcium oxide does not corrode or reduce the effectiveness of the edge sealant over time.
In one example of the present invention, a sealant composition includes an olefinic polymer, a silane modified polyolefin, at least one filler, a carbon black, a calcium oxide included in an amount greater than about 2.5% by weight of the total composition, and at least one aging resistor.
In another example of the present invention, the sealant composition further includes a molecular sieve in an amount greater than about 2.5% by weight of the total composition.
In another example of the present invention, the sealant composition exhibits a water break through time of greater than 5 hr and a steady state moisture vapor transmission rate of less than 40 g·m2/day for a 0.030 inch thick sample of the sealant composition tested at 85 C and 100% relative humidity.
In another example of the present invention, the sealant composition exhibits a water break through time of greater than 10 hr and a steady state moisture vapor transmission rate of less than 30 g·m2/day for a 0.030 inch thick sample of the sealant composition tested at 85 C and 100% relative humidity.
In another example of the present invention, a combination of the calcium oxide and the molecular sieve is included in an amount greater than about 10% by weight and the sealant composition exhibits a water break through time of greater than 5 hr and a steady state moisture vapor transmission rate of less than 40 g·m2/day for a 0.030 inch thick sample of the sealant composition tested at 85 C and 100% relative humidity.
In another example of the present invention, a combination of the calcium oxide and the molecular sieve is included in an amount greater than about 10% by weight and the sealant composition exhibits a water break through time of greater than 10 hr and steady state moisture vapor transmission rate of less than 30 g·m2/day for a 0.030 inch thick sample of the sealant composition tested at 85 C and 100% relative humidity.
In another example of the present invention, the sealant composition further includes at least one of a clay, a calcium sulfate, and a silica gel. The sealant composition exhibits exhibit a water break through time of greater than 5 hr and a steady state moisture vapor transmission rate of less than 40 g·m2/day for a 0.030 inch thick sample of the sealant composition tested at 85 C and 100% relative humidity.
In another example of the present invention, the sealant composition further includes at least one of a clay, a calcium sulfate, and a silica gel. A combination of the calcium oxide, the molecular sieve, and the sealant composition exhibits a water break through time of greater than 10 hr and steady state moisture vapor transmission rate of less than 30 g·m2/day for a 0.030 inch thick sample of the sealant composition tested at 85 C and 100% relative humidity.
In yet another example of the present invention, a combination of the calcium oxide and the molecular sieve is included in an amount from about 10% to about 40% by weight of the total composition.
In yet another example of the present invention, a combination of the calcium oxide and the molecular sieve is included in an amount from about 20% to about 40% by weight of the total composition.
In yet another example of the present invention, combination of the calcium oxide and the molecular sieve is included in an amount from about 25% to about 35% by weight of the total composition.
In yet another example of the present invention, the olefinic polymer is included in an amount from about 30% to about 60% by weight of the total composition, the silane modified polyolefin is included in an amount from about 10% to about 25% by weight of the total composition, the carbon black is included in an amount from about 2% to about 20% by weight of the total composition, the filler is included in an amount from about 20% to about 60% by weight of the total composition, the calcium oxide is included in an amount from about 2.5% to about 25% by weight of the total composition, and the aging resistor is included in an amount from 0% to about 2% by weight of the total composition.
In yet another example of the present invention, the olefinic polymer is included in an amount from about 20% to about 40% by weight of the total composition, the silane modified polyolefin is included in an amount from about 10% to about 20% by weight of the total composition, a combination of the carbon black and the filler is included in an amount from about 30% to about 40% by weight of the total composition, the calcium oxide is included in an amount from about 10% to about 30% by weight of the total composition, and the aging resistor is included in an amount from 0% to about 2% by weight of the total composition.
In yet another example of the present invention, the sealant composition further includes a molecular sieve included in an amount from about 2.5% to about 25% by weight of the total composition.
In yet another example of the present invention, the sealant composition exhibits less than about 15 gm/((m̂2)*day) moisture vapor transmission rate at steady state for a 0.030 inch thick sample of the sealant composition tested at 85 C and 100% relative humidity.
In yet another example of the present invention, the sealant includes balanced properties that keep swelling of the sealant to a predetermined amount upon reaction of the calcium oxide with water.
In yet another example of the present invention, the calcium oxide does not substantially react with or corrode other components of the sealant.
In yet another example of the present invention, the olefinic polymer includes at least one of a polyethylene, a polypropylene, a polybutene, a polyisobutene, a butyl rubber (polyisobutene-isoprene), styrene block copolymers, and modified forms of styrene block copolymers, wherein the olefinic polymers have a Number average molecular weight of 100-700,000 Da. The silane modified polyolefins include at least one of an amorphous poly alpha olefin, a silane grafted PE, a moisture curing catalyst, an alkoxy silane, and an amino silane. The fillers include at least one of a ground chalk, a precipitated chalk, a silicate, a silicon oxide, CaCO3, Ca(OH)2, and titanium dioxide. The silicate is selected from the group comprising talc, kaolin, mica, silicon oxide, silicas, and calcium or magnesium silicates. The aging resistors include at least one of hindered phenols, hindered amines, thioethers, mercapto compounds, phosphorous esters, benzotriazoles, benzophenones, and antizonants.
The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.
With reference to
The photovoltaic cell 12 is operable to generate an electrical current from sunlight striking the photovoltaic cell 12. Accordingly, the photovoltaic cell 12 may take various forms without departing from the scope of the present invention. For example, the photovoltaic cell 12 may be a thin film cell with a layer of cadmium telluride (Cd—Te), amorphous silicon, or copper-indium-diselenide (CuInSe2). Alternatively, the photovoltaic cell 12 may be a crystalline silicon wafer embedded in a laminating film or gallium arsenide deposited on germanium or another substrate. Other types of photovoltaic devices 12 that may be employed include organic semiconductor cells having conjugate polymers as well as dye-sensitized metal oxides including wet metal oxides and solid metal oxides. The photovoltaic device 12 may be either rigid or flexible. The photovoltaic cells 12 are linked either in series or in parallel or combinations thereof. The current produced by the photovoltaic cells 12 are communicated via bus bars or other conductive materials or layers to wires or lead lines 15 that exit the solar module 10. The lead lines 15 communicate with a junction box 17 in order to distribute the electrical current generated by the solar module 10 to a power circuit.
The first substrate 14, or front panel, is formed from a material operable to allow wavelengths of sunlight to pass therethrough. For example, the first substrate 14 is glass or a plastic film such as polyvinylflouride. The second substrate 16, or back panel, is selected to provide additional strength to the solar module 10. For example, the second substrate 16 is a plastic such as fluorinated ethylene-propylene copolymer (FEP), poly(ethylene-co-tetrafluoroethylene) (ETFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), poly(tetrafluoroethylene) (PTFE) and combinations of these with other polymeric materials.
The photovoltaic cells 12 are encapsulated by a laminate layer 19 that is preferably a cross-linkable ethyl vinyl acetate (EVA). However, it should be appreciated that other laminates or encapsulants may be employed without departing from the scope of the present invention. The laminate layer 19 is used to partially encapsulate the photovoltaic device 12 to protect the photovoltaic device 12 from contamination and from the environment.
A border or edge seal 18 is located near an edge of the solar module 10 between the first substrate 14 and the second substrate 16. The border seal 18 may have various widths. In addition, a second border seal (not shown) may also be included. The second border seal may be comprised of, for example, for example, a silicone, a MS polymer, a Silanated Polyurethane, a butyl, or a polysulfide. The border seal 18 is operable to seal the laminate layer 19 and photovoltaic devices 12. The border seal 18 must have sufficient weatherability to withstand exposure to outside environments including prolonged ultra-violet radiation exposure, have low moisture vapor transmission (MVT), and have low conductivity. The border seal 20 is comprised of a sealant composition having the unique characteristics of high weatherability with low conductivity and MVT, as well as the ability to permanently absorb and react with water during normal operating conditions of the solar module 10.
The sealant composition of the border seal 18 includes an unsaturated reactive polyolefin, an olefinic polymer, a silane modified polyolefin, inert fillers, calcium oxide, and aging resistors. These components are balanced to produce a sealant having desirable sealing characteristics, high weatherability, desired rheology, low conductivity, and good water absorption.
Calcium oxide reacts with water to form calcium hydroxide, according to the equation:
CaO+H2O→Ca(OH)2 (1)
When heated to 512° C., the partial pressure of water in equilibrium with calcium hydroxide reaches 101 kPa and decomposes into calcium oxide and water. Since solar modules do not experience such high temperature conditions, this reverse reaction does not occur to any appreciable extent.
The calcium oxide adsorbs a much greater amount of water vapor at a very low relative humidity than other materials. Calcium oxide is most effective where a low critical relative humidity is necessary, and where there is a high concentration of water vapor present. Calcium oxide removes water from the environment very slowly, often taking days to reach its maximum capacity. In addition, calcium oxide has a low water capacity at room temperature and humidity. As the calcium oxide adsorbs moisture, it swells. Accordingly, the sealant composition must have balanced properties to account for any swelling during use. The properties are balanced by, for example, adjusting the amount of calcium oxide in the composition. The density of calcium oxide is 3.25-3.38 g/mL, and the density of calcium hydroxide is 2.24 g/mL, according to the CRC Handbook of Chemistry and Physics, 60th edition. Therefore, theoretically, there is a limit as to how much calcium oxide may be incorporated into an edge sealant formulation. However, no difficulties have been observed over the incorporation range tested.
The use of calcium oxide having about a three micron median particle size results in less free volume as compared to the typically larger particle sizes of other desiccants. As a result, the steady state moisture vapor transmission rate (after about 150 hours in
In addition to steady state MVTR,
In addition, one liter of water combines with approximately 3.1 kg of calcium oxide to give calcium hydroxide plus 3.54 MJ of energy. The level of heat generated by the exothermic reaction between calcium oxide and water discourages the use of calcium oxide as a water scavenger in edge seals. However, since the reaction occurs so slowly, the heat generation is imperceptible during use in an edge seal, and thus calcium oxide is a satisfactory edge seal water scavenger.
Calcium oxide is corrosive and can theoretically react with other components within an edge seal and within a solar module. However, within edge seals in solar modules with the present composition, no corrosive effects manifest.
In addition, calcium oxide can be combined with molecular sieves to further increase the moisture trapping ability of the edge sealant.
In order that the invention may be more readily understood, reference is made to the following example which is intended to illustrate the invention, but not limit the scope thereof:
The olefinic polymers may include, for example, polyethylene, polypropylene, polybutene, polyisobutene, butyl rubber (polyisobutene-isoprene), styrene block copolymers, and modified forms of styrene block copolymers. The olefinic polymers have number average molecular weights of 100-700,000 Da, and preferably have number average molecular weights of 100-300,000 Da.
The silanes may include, for example, DFDA-5451NT (silane grafted PE available from Dow Chemical of Midland, Mich.), DFDA-5481 NT (moisture curing catalyst from Dow Chemical of Midland, Mich.), amorphous poly alpha olefins (such as but not restricted to VESTOPLAST 206 and VESTOPLAST 2412 available from Evonik Degussa GmbH of Marl, Germany), alkoxy silanes, and amino silanes.
The inert fillers may include, for example, ground and precipitated chalks, silicates, silicon oxides, C black, CaCO3, Ca(OH)2, and titanium dioxide. The silicates may include, for example, talc, kaolin, mica, silicon oxide, silicas, and calcium or magnesium silicates. The aging resistors may include, for example, hindered phenols, hindered amines, thioethers, mercapto compounds, phosphorous esters, benzotriazoles, benzophenones, and antizonants.
The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 045 104.2 | Sep 2007 | DE | national |
This patent application claims the benefit of U.S. Provisional Patent Application No. 61/251,527, filed on Oct. 14, 2009, and is a continuation-in-part of co-pending U.S. patent application Ser. No. 12,679,250, filed on Mar. 19, 2010, which claims priority to International Application No. PCT/DE/2008/001564, filed on Sep. 22, 2008, which claims priority to German priority document DE/10 2007 045 104.2, filed on Sep. 20, 2007. The contents of the above applications are incorporated herein by reference in their entirety.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US10/52726 | 10/14/2010 | WO | 00 | 4/13/2012 |
| Number | Date | Country | |
|---|---|---|---|
| 61251527 | Oct 2009 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12679250 | Oct 2010 | US |
| Child | 13501923 | US |
