①Photovoltaic principle
Photovoltaics (PV) is a solid-state semiconductor technology that can directly convert light energy into electrical energy, without moving parts, noise and emissions.
From the 1950s to the beginning of the 21st century, the most common form of photovoltaic equipment was polysilicon. Polysilicon has a high conversion efficiency. In addition, silicon resources are relatively abundant and the technology is relatively mature. Although its physical properties are not the best match, it is close to the visible spectrum. Other technologies are based on amorphous silicon (a-Si), copper indium selenium (CuInSe2 or CIS), dilute cadmium (CdTe), arsenic image (GaAs), organic solar cells (using titanium oxide and organic dyes) and their This is the result of mutual choice between scientific research and the market today.
Semiconductor-based technology (regardless of the current organic solar cells) works on the same principle: photons excite electrons on photovoltaic devices, thereby providing enough energy to move some of them through the semiconductor junction and building electrical “pressure”. This situation occurs at the electronic imbalance, where there are excess electrons (negative charge) on one side of the semiconductor junction (PN junction, or PIN junction), and excess “holes” (positive charge) on the other side. In order to release this voltage, through the surface grid and cell interconnection, electrons flow from one cell area with too many electrons to another cell area with less electrons.
②Photovoltaic technology
Today, there are many photovoltaic technologies, some of which have been applied to the commercial market, some are about to be commercialized, and some are in the early stages of commercial research. Photovoltaic technologies are generally divided into two categories: flat panel and concentrating (there should be a “other” category, which will include organic solar cells and other novel or exotic technologies, such as polymers, which are not included here) . The flat panel type is the most common on the market; while the concentrating system uses more expensive photovoltaic materials and relies on cheap plastic lenses or reflectors to gather more light, but it has not yet formed an important impact in the commercial market.
At present, flat-panel photovoltaic technology plays a leading role in the market. Although it is subdivided into crystals and thin films, there is a great overlap between these technologies. Crystals can be simply divided into single crystals and polycrystals. Single crystals are easier to explain. Polycrystals usually slice the ingot material and leave many crystals in each unit. Another subcategory of crystals is sheet or ribbon technology, where photovoltaic materials are extracted from the melt (such as EFG ribbon, dendritic web and sheet technology), varying from smectic to highly polycrystalline.
The advantages of crystallization technologies are that they have relatively high conversion efficiency and a large installed base of production equipment. However, they also have the disadvantages of labor-intensive and material-intensive, and are limited by their physical form (rigid unit slices obtained from fragile, larger pieces of material).
Thin-film technologies are so named because they usually deposit very thin films on less expensive substrates (such as glass, stainless steel, plastics, ceramics, etc.). Such technologies include amorphous silicon, copper-steel selenide, and cadmium. They have the ideal advantages of automated manufacturing and use low-quality materials. And they can also be deposited on a series of materials with uniform and unique shapes. The disadvantage is the lack of manufacturing experience and low conversion efficiency (until recently, CIS and CdTe technologies have begun to approach the conversion efficiency of crystallization technology).
③Type of photovoltaic system (DC, AC, hybrid)
Photovoltaic systems are almost suitable and used in any aspect of today’s power applications, from consumer products, remote signaling, water pumping, home furnishing, public grid support, and space satellites. To support such a wide range of applications, photovoltaic systems are designed and suitable for operation in DC (PV cells and modules naturally output DC) or AC systems (using inverters to convert the DC output of photovoltaic modules into AC). These systems can be directly connected from a photovoltaic module to a single load (such as a water pump), can also be applied to a household photovoltaic system, including a module, a battery, a charging control device and a compact fluorescent lamp, or can be connected to a grid-connected System or hybrid power generation system. There are many power sources for power generation in the system (such as wind generators, diesel generators or micro-hydrogenerators).
