The composition and working principle of photovoltaic power generation system

The photovoltaic power generation system is mainly composed of photovoltaic modules, controllers, inverters, batteries and other accessories (grid-connected batteries are not required). According to whether it depends on the public grid, it is divided into off-grid and grid-connected two kinds, in which the off-grid system is independent operation and does not need to rely on the grid. The off-grid photovoltaic system is equipped with a storage battery, which can ensure the stability of the system power, and can supply load electricity when the photovoltaic system does not generate electricity at night or when the power generation is insufficient on rainy days.

No matter what form, the working principle is that the photovoltaic module converts light energy into direct current, which is converted into alternating current under the action of the inverter, and finally realizes the function of electricity and Internet access.

1. Photovoltaic modules

Photovoltaic modules are the core part of the entire power generation system, which is composed of photovoltaic module sheets or photovoltaic modules of different specifications cut by laser cutting machines or steel wire cutting machines. Because the current and voltage of a single photovoltaic cell are very small, it is necessary to obtain high voltage in series first, and then obtain high current in parallel, output through a diode (to prevent current input), and then package in a stainless steel, aluminum or other non-metal frame, install the glass above and the backplane on the back, fill in nitrogen, and seal. The photovoltaic modules are combined in series and parallel to form a photovoltaic module array, also known as a photovoltaic array.

Working principle: The sun shines on the semiconductor P-N junction, forming a new hole-electron pair, under the action of the P-N junction electric field, the hole flows from the p region to the n region, the electron flows from the n region to the p region, and the current is formed after the circuit is switched on. Its role is to convert solar energy into electricity, and sent to the battery for storage, or to promote the load work.

Component type:

① monocrystalline silicon: photoelectric conversion rate ≈18%, up to 24%, is the highest conversion rate of all photovoltaic modules, generally using tempered glass and waterproof resin packaging, durable, service life is generally up to 25 years.

② polysilicon: photoelectric conversion rate ≈14%, similar to the production process of monocrystalline silicon, the difference between polysilicon is that the photoelectric conversion rate is lower, the price is lower, the life is shorter, but the polysilicon material is simple to manufacture, save power consumption, low production cost, so it has been vigorously developed.

③ Amorphous silicon: photoelectric conversion rate ≈10%, and monocrystal silicon and polysilicon production method is completely different, is a thin-film solar cell, the process is greatly simplified, silicon material consumption is very little, lower power consumption, its main advantage is in low light conditions can also generate electricity.

2, controller (off-grid system use)

The photovoltaic controller is an automatic control device that can automatically prevent the battery from overcharging and overdischarging. Using high-speed CPU microprocessor and high-precision A/D analog-to-digital converter, it is a microcomputer data acquisition and monitoring control system, which can quickly and real-time collect the current working status of the photovoltaic system, obtain the working information of the PV station at any time, and accumulate the historical data of the PV station in detail. It provides an accurate and sufficient basis for evaluating the rationality of PV system design and testing the reliability of system component quality. It also has serial communication data transmission function, which can centrally manage and remotely control multiple PV system sub-stations.

3. Inverter

Inverter is a device that converts direct current generated by photovoltaic power generation into alternating current, photovoltaic inverter is one of the important system balances in the photovoltaic array system, and can be used with general AC power supply equipment. Solar inverters have special functions with photovoltaic arrays, such as maximum power point tracking and islanding protection.

Solar inverters can be divided into the following three categories:

① Independent inverter: Used in an independent system, the photovoltaic array charges the battery, and the inverter takes the DC voltage of the battery as the energy source. Many individual inverters also have integrated battery chargers that can charge the battery with AC power. Generally, such inverters do not come into contact with the power grid, and therefore do not require islanding protection functions.

② Grid-connected inverter: the output voltage of the inverter can be sent back to the commercial AC power supply, so the output chord wave needs to be the same as the phase, frequency and voltage of the power supply. The grid-connected inverter will have a safety design that automatically turns off the output if it is not connected to the power supply. If the grid power supply jumps, the grid-connected inverter has no power supply function.

(3) Standby battery inverter: a special inverter, by the battery as its power supply, with the battery charger to charge the battery, if there is too much power, will be recharged to the AC power end. This inverter can provide AC power to the specified load when the grid power supply is switched off, so it needs to have islanding protection function.

4, battery (not required for grid-connected system)

The battery is the device for storing electricity in the photovoltaic power generation system. At present, there are four kinds of lead-acid maintenance-free batteries, ordinary lead-acid batteries, colloidal batteries and alkaline nickel-cadmium batteries, and lead-acid maintenance-free batteries and colloidal batteries are widely used.

Working principle: During the day, the sun shines on the photovoltaic module, generates DC voltage, converts the light energy into electricity, and then transmits it to the controller, after the overcharge protection of the controller, the electricity from the photovoltaic module is transmitted to the battery for storage, for use when needed.