Solar cell square array and storage battery in solar photovoltaic system
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The characteristic of solar power technology is that solar energy is an inexhaustible renewable energy source, and the initial energy cost is extremely low; the power of solar photovoltaic power supply or photovoltaic power station can be configured from a few milliwatts to tens of megawatts according to the needs. The system construction period is short, convenient and flexible; as a semiconductor device that directly converts light energy into electric energy, a crystalline silicon solar cell can be used for more than 20 years, and the whole system has no rotating device, and the system has a long life, high reliability and easy use.
Although the current cost of solar photovoltaic power generation is still higher than the cost of conventional energy generation, with the gradual exhaustion of global fossil energy and the rapid development of photovoltaic power generation technology, the cost of solar photovoltaic power generation will continue to decline, taking into account the external cost of thermal power generation In the near future, the cost of photovoltaic power generation and thermal power generation will be equal, and then lower than the cost of thermal power generation. According to the “Global Photovoltaic Market Analysis and 2020 Outlook” report, by 2030, photovoltaic power generation systems will provide 2,600 TW/h of electricity, accounting for 14% of the global electricity demand. By the end of the 21st century, renewable energy will account for more than 80% of the energy structure, of which solar power will account for more than 60%.
Solar photovoltaic system directly converts solar energy into DC or AC power for users to use. Therefore, to form a solar photovoltaic power generation system, it needs to include solar cell components (square array), energy storage device (battery pack), controller and Components such as inverters.
Solar cell phalanx
The function of the solar cell is to directly convert sunlight energy into electrical energy, and its working principle is based on the photovoltaic effect based on the semiconductor PN junction. Since a single solar cell can only produce a voltage of about 0.45V, it is necessary to connect the single cells in series (and in parallel) as required to form a solar cell module to meet the requirements of the rated charging voltage of the matching battery. If you want to charge a battery with a rated voltage of 12V, the general number of series connection is 33 or 36. According to the user’s load requirements (voltage, power), the solar cell components are connected in series/parallel to form a solar cell array.
The open circuit voltage of the solar cell has a negative temperature coefficient, about 2~3mV/℃. Therefore, when selecting the number of battery modules in series, the environmental temperature of the application site should be considered. If it is used in high-temperature areas, you should consider choosing a module with a larger number of batteries in series. This type of module has a higher open circuit voltage, so in actual use, even if the open circuit voltage drops due to an increase in temperature, the solar cell module can still work near the optimal operating point of the module.
In actual work, we must also pay attention to prevent the “hot spot” effect of the solar cell array. The square array may be partially blocked. When the series components are partially blocked, the current flow capacity of the blocked components will decrease, which will consume the power emitted by the unblocked components, resulting in heat generation. In order to prevent the occurrence of the “hot spot” effect, a bypass diode must be connected in parallel next to each series component. When the component is blocked, the current can pass through the bypass diode, so that the blocked component does not constitute a load.
The battery is the energy storage device in the photovoltaic power generation system. Its function is to store the surplus electric energy emitted by the square array when there is light, and it can be used by the load at night or on cloudy and rainy days. Especially in the independent photovoltaic power generation system, it is necessary to configure the battery. . The battery is the most expensive component in the photovoltaic system except the solar battery, and it is also the most maintenance component. Its performance directly affects the reliability and cost of the photovoltaic power generation system. It is necessary to configure the controller to the battery during use. The charge/discharge of the battery is controlled to extend the service life of the battery as much as possible. The basic requirements of photovoltaic power generation systems for batteries are low self-discharge rate, long service life, strong deep discharge capability, high charging efficiency, low or maintenance-free, wide operating temperature range, and low price. At present, the commonly used batteries in independent photovoltaic power generation systems include lead-acid batteries and silicone batteries, and more expensive nickel-cadmium batteries are also available for higher requirements.