Grid-connected solar power systems convert solar energy into electrical energy directly to the grid via a grid-connected inverter, without the need for battery storage. Grid-connected solar power represents the future direction of solar power development and is one of the most attractive energy utilization technologies of the 21st century. Compared to off-grid solar power systems, grid-connected systems have the following advantages:
1. It uses clean and renewable natural energy, solar power, to generate electricity without consuming non-renewable and limited carbon-containing fossil energy. It produces no greenhouse gases or pollutants during use, is in harmony with the ecological environment, and is in line with the strategy of sustainable economic and social development.
2. The generated electricity is fed into the power grid, which serves as an energy storage device, eliminating the need for batteries. This reduces the construction investment by 25%–45% compared to independent solar photovoltaic systems, thereby significantly lowering power generation costs. Eliminating batteries also improves the system's mean time between failures (MTBF) and reduces secondary pollution from batteries.
3. Photovoltaic cell modules are perfectly integrated with buildings, generating electricity and serving as building and decorative materials. This allows for the full utilization of material resources and enables them to perform multiple functions. It not only helps reduce construction costs but also enhances the technological content of buildings, increasing their market appeal.
4. Distributed construction allows for decentralized power generation and supply, with flexible access to and from the power grid. This not only enhances the power system's ability to withstand war and disasters but also improves the load balance of the power system and reduces line losses.
5. It can play a peak-shaving role. Grid-connected solar photovoltaic systems are a hot topic and key area of development in the field of photovoltaic applications in developed countries around the world. It is the mainstream development trend of solar photovoltaic power generation worldwide, with a huge market and broad prospects.
The principle and composition of grid-connected power generation systems:
Solar photovoltaic (PV) power generation relies on solar cell modules and utilizes the electronic properties of semiconductor materials. When sunlight shines on a semiconductor PN junction, a strong built-in electrostatic field is generated in the PN junction's barrier region. This causes non-equilibrium electrons and holes generated in the barrier region, or those generated outside the barrier region but diffused into it, to move in opposite directions under the influence of the built-in electrostatic field, leaving the barrier region. This results in an increase in the P-region potential and a decrease in the N-region potential, thereby generating voltage and current in the external circuit, converting light energy into electrical energy. Solar PV power generation systems can be broadly classified into two categories: grid-connected systems, which connect to the public power grid through a standard interface, resembling a small power plant; and stand-alone systems, which form their own closed-loop circuit. Grid-connected systems convert received solar radiation energy into high-voltage direct current (DC) through photovoltaic arrays. This DC is then inverted by an inverter and outputs a sinusoidal alternating current (AC) that is in phase and frequency with the grid voltage. The photovoltaic array of the stand-alone power generation system first converts the received solar radiation energy directly into electrical energy to supply the load, and stores the excess energy in the form of chemical energy in the battery after passing through the charging controller.
Composition of grid-connected power generation system
1. Solar cell modules:
A single solar cell can only generate about 0.5 volts, far below the voltage required for practical applications. To meet the needs of real-world applications, solar cells need to be connected into modules. A solar cell module contains a certain number of solar cells connected by wires. For example, a module may have 36 solar cells, meaning that a solar module can generate approximately 17 volts.
Solar cells connected by wires and sealed together form a physical unit called a solar cell module. These modules offer a degree of resistance to corrosion, wind, hail, and rain, and are widely used in various fields and systems. When an application requires higher voltage and current than a single module can meet, multiple modules can be assembled into a solar cell array to achieve the necessary voltage and current.
2. Inverter:
Inverters are devices that convert direct current (DC) to alternating current (AC). Since solar cells generate DC power, while typical loads are AC loads, inverters are indispensable. Inverters can be classified by their 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 grid-connected solar power systems to feed the generated electricity into the power grid. Inverters can also be classified by their output waveform into square wave inverters and sine wave inverters.
