Materials for photovoltaic, solar-power generators, with excellent weather resistance

Solar power generation exploits the photovoltaic effect, in which sunlight energy is converted directly into electrical energy by semiconductor devices known as photovoltaic cells. This method, which harvests power from the fully renewable resource of solar energy, promises to slash energy costs and accelerate progress toward the United Nation’s Sustainable Development Goals—and, for these reasons, has grown explosively in recent years.

According to the International Energy Agency (IEA), the total power produced by photovoltaic installations grew at an average annual rate of 24% between 2010 and 2020. Within IEA forecasts predicting trends in global power-generation capacity under various future scenarios, solar energy consistently ranks among the most promising of the various available power sources, and the market for photovoltaics is widely expected to continue growing rapidly in the years to come.

Photovoltaic generators may be classified into two categories by size : megasolar generators, capable of producing one megawatt of power or more, and smaller dispersed generators like those installed on the roofs of buildings. According to the IEA, some 60% of all photovoltaic generators are megasolar-scale, with the remainder being dispersed generators.

Megasolar stations are large-scale operations commonly located near bodies of water or on land formerly used to grow crops; the power they generate is not used on-site, but is transmitted elsewhere through the power grid.

One recent innovation, adopted for both megasolar and dispersed generators, is the use of batteries to store power generated during daylight hours, thus achieving greater flexibility in how and when the power is used.

At present, many countries around the world are expanding solar energy as a strategy for decreasing greenhouse-gas emissions. One consequence is that the energy policies adopted by various nations have become important factors affecting the global photovoltaic market.

Two particularly important examples of such policies are feed-in tariffs (FITs) and conventional government subsidies. FITs attempt to promote growth in renewable energy by offering special treatment to power-plant operators in the form of legally mandated minimal purchase prices for renewable energy, while subsidies directly offset the cost of building and operating plants.

Going forward, policy support for solar power is expected to remain robust in many countries, while investments in megasolar-scale facilities are forecast to continue their recent growth trajectory.

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Solar power generators comprise photovoltaic elements and other components. The simplest functional unit is the photovoltaic cell (or solar cell). Groups of cells may be combined to form a module. Each module consists of several tens of cells arranged in a planar grid configuration and packaged together with a frame, glass, encapsulants, a backsheet, and a junction box. Two or more modules may be connected in series to yield a string. Two or more strings can be arranged in parallel to form an array.

The power generated by each module is collected by a junction box installed on the back of the module and delivered via connectors and cables to the outside world. These junction boxes incorporate bypass diodes that play an important role in avoiding energy losses by routing power flows around cells that may be malfunctioning due to damaged or dirty surfaces.

Photovoltaic generators produce direct-current (DC) power, which may be converted to alternating-current (AC) power using power conditioners (inverters) to furnish standard household AC power supplies.

To ensure the safety and performance of commercial photovoltaic products, photovoltaic modules are tested and certified by third-party certification bodies, such as the internationally recognized UL, TÜV Rheinland or JET in Japan and similar bodies in the world. For a module to receive certification, the materials from which it is fabricated must pass a variety of safety tests.

Photovoltaic generators operate in harsh environments that place stringent demands on their component materials. In particular, generators intended for installation in farm areas, near bodies of water, or on steep mountain grades must withstand severe storms, frigid temperatures, and intense ultraviolet radiation, necessitating materials with excellent weather resistance and cold-impact resistance. Moreover, the 20-year service lifetimes expected for these systems demand materials of extraordinary long term property, while the safe generation and transmission of electric power imposes constraints on heat resistance, flame retardance, tracking resistance, among others. All of these material-property requirements are reflected in the testing methods—and in the numerical values of performance criteria—used by certification bodies like UL and TÜV Rheinland, and the best way to ensure compliance for photovoltaic systems is to use only materials that have been certified to satisfy all of these rigorous specifications.