1. System Composition
A photovoltaic (PV) power generation system consists of solar cell arrays, battery banks, charge/discharge controllers, inverters, AC distribution cabinets, and solar tracking control systems. The functions of some of these components are:
Battery array
When illuminated (whether by sunlight or other light sources), a solar cell absorbs light energy, causing an accumulation of opposite charges at its terminals, resulting in a "photovoltaic voltage." Under the influence of the photovoltaic effect, an electromotive force is generated at the terminals of the solar cell, converting light energy into electrical energy; it is an energy conversion device. Solar cells are generally silicon cells, and are classified into three types: monocrystalline silicon solar cells, polycrystalline silicon solar cells, and amorphous silicon solar cells.
Battery pack
Its function is to store the electrical energy generated by the solar cell array when exposed to sunlight and to supply power to the load at any time. The basic requirements for the battery pack used in solar power generation are: a. low self-discharge rate; b. long service life; c. strong deep discharge capability; d. high charging efficiency; e. low maintenance or no maintenance required; f. wide operating temperature range; g. low price.
controller
It is a device that can automatically prevent overcharging and over-discharging of batteries. Since the number of charge-discharge cycles and the depth of discharge of a battery are important factors that determine its lifespan, a charge-discharge controller that can control overcharging or over-discharging of the battery pack is an essential device.
Inverter
An inverter is a device that converts direct current (DC) to alternating current (AC). Since solar cells and batteries are DC power sources, and the load is an AC load, an inverter is essential. Inverters can be classified by operating mode into stand-alone inverters and grid-connected inverters. Stand-alone inverters are used in stand-alone solar power systems to supply power to independent loads. Grid-connected inverters are used in solar power systems connected to the grid. Inverters can also be classified by output waveform into square wave inverters and sine wave inverters. Square wave inverters have simple circuits and low cost, but high harmonic content, and are generally used in systems below a few hundred watts and where harmonic requirements are not high. Sine wave inverters are more expensive, but can be used with various loads.
2. System Classification
Photovoltaic power generation systems are divided into stand-alone photovoltaic power generation systems, grid-connected photovoltaic power generation systems, and distributed photovoltaic power generation systems.
① Stand-alone photovoltaic (PV) power generation, also known as off-grid PV power generation, mainly consists of solar cell modules, a controller, and a battery. If it needs to supply power to AC loads, an AC inverter is also required. Stand-alone PV power stations include village power supply systems in remote areas, solar household power systems, communication signal power supplies, cathodic protection, solar streetlights, and various other PV power generation systems equipped with batteries that can operate independently.
② Grid-connected photovoltaic power generation is the process where the direct current generated by solar panels is converted into alternating current that meets the requirements of the municipal power grid by a grid-connected inverter and then directly connected to the public power grid.
Grid-connected photovoltaic (PV) power generation systems can be categorized into those with and without batteries. Systems with batteries offer dispatchability, allowing them to connect to or disconnect from the grid as needed, and also serve as backup power, providing emergency power when the grid experiences a power outage. Grid-connected PV systems with batteries are often installed in residential buildings. Systems without batteries lack dispatchability and backup power capabilities and are typically installed in larger systems. Centralized large-scale grid-connected PV power plants are generally national-level power plants, characterized by directly transmitting generated energy to the grid for unified distribution to users. However, these plants require large investments, have long construction periods, and occupy large areas, limiting their development. Distributed small-scale grid-connected PV, especially building-integrated photovoltaics (BIPV), is the mainstream of grid-connected PV power generation due to its advantages such as lower investment, faster construction, smaller footprint, and stronger policy support.
③ Distributed photovoltaic (PV) power generation systems, also known as decentralized power generation or distributed energy supply, refer to small-scale PV power generation systems configured at or near user sites to meet the needs of specific users, support the economic operation of existing power distribution networks, or simultaneously meet both requirements. The basic equipment of a distributed PV power generation system includes PV modules, PV array supports, DC combiner boxes, DC distribution cabinets, grid-connected inverters, AC distribution cabinets, and other equipment, as well as power supply system monitoring devices and environmental monitoring devices. Its operating mode is as follows: under solar radiation conditions, the PV system's solar cell array converts solar energy into electrical energy, which is then centrally fed into the DC distribution cabinet via the DC combiner box. The grid-connected inverter then converts this electrical energy into AC power to supply the building's own load. Excess or insufficient power is regulated by connecting to the power grid.
3. Advantages and disadvantages
Compared with commonly used power generation systems, the advantages of solar photovoltaic power generation are mainly reflected in:
Solar power generation is considered the most ideal new energy source. ① It has no risk of depletion; ② It is safe and reliable, with no noise or pollution emissions, and is absolutely clean (pollution-free); ③ It is not limited by the geographical distribution of resources and can utilize the advantages of building rooftops; ④ It can generate and supply electricity locally without consuming fuel or erecting transmission lines; ⑤ It has high energy quality; ⑥ It is easily accepted by users emotionally; ⑦ It has a short construction period and a short time to obtain energy.
shortcoming:
① The energy distribution density of solar radiation is low, requiring a large area; ② The energy obtained is related to the seasons, day and night, and weather conditions. Solar power generation is expensive, and the utilization rate of solar energy is low, limiting its widespread application. It is mainly used in special environments, such as satellites.
4. Application Areas
I. User solar power supply: (1) Small power supply ranging from 10 to 100W, used for electricity for military and civilian life in remote areas without electricity, such as plateaus, islands, pastoral areas, and border outposts, such as lighting, television, radios, etc.; (2) 3-5KW household rooftop grid-connected power generation system; (3) Photovoltaic water pump: solve the problem of drinking water and irrigation from deep wells in areas without electricity.
II. Transportation sector, such as navigation lights, traffic/railway signal lights, traffic warning/sign lights, Yuxiang streetlights, high-altitude obstruction lights, highway/railway wireless telephone booths, and unattended track maintenance station power supply, etc.
III. Communications/Telecommunications Field: Solar-powered unattended microwave relay stations, optical cable maintenance stations, broadcasting/communication/paging power systems; rural carrier telephone photovoltaic systems, small communication devices, and GPS power supply for soldiers, etc.
IV. Petroleum, marine, and meteorological fields: solar power systems for cathodic protection of oil pipelines and reservoir gates, living and emergency power supplies for oil drilling platforms, marine detection equipment, meteorological/hydrological observation equipment, etc.
V. Power supplies for household lighting fixtures: such as garden lights, street lights, portable lights, camping lights, mountaineering lights, fishing lights, black lights, rubber tapping lights, energy-saving lights, etc.
VI. Photovoltaic power stations: 10KW-50MW independent photovoltaic power stations, wind-solar (diesel) hybrid power stations, and various large parking lot charging stations, etc.
VII. Solar buildings combine solar power generation with building materials, enabling large-scale buildings to achieve self-sufficiency in electricity in the future, which is a major development direction for the future.
VIII. Other fields include: (1) Automotive-related: solar-powered cars/electric vehicles, battery charging equipment, car air conditioners, ventilation fans, cold drink boxes, etc.; (2) Solar hydrogen production and fuel cell regenerative power generation systems; (3) Seawater desalination equipment power supply; (4) Satellites, spacecraft, space solar power stations, etc.
