The flexibility of this power generation system lies in the fact that when the sunlight is strong, the photovoltaic power generation system can supply power to the AC load while sending the excess power into the grid; and when the sunlight is insufficient, that is, when the solar cell array cannot provide enough power to the load, it can draw power from the grid to supply power to the load.
I. Structure of Grid-Connected Photovoltaic Power Generation System
A solar photovoltaic power generation system connected to the public power grid is called a grid-connected photovoltaic power generation system. The system structure includes components such as solar cell arrays, DC/DC converters, DC/AC inverters, AC loads, and transformers.
Grid-connected photovoltaic (PV) power generation systems can convert the direct current (DC) output from solar cell arrays into alternating current (AC) with the same amplitude, frequency, and phase as the grid voltage, enabling connection to the grid and the transmission of electrical energy to it. The flexibility of this system lies in its ability to supply excess power to the grid while simultaneously supplying AC loads during periods of strong sunlight; conversely, when sunlight is insufficient and the solar cell array cannot provide enough power to the loads, it can draw power from the grid to supply power to the loads.
In the past, due to the high cost of solar cells, photovoltaic power generation was mostly used in dedicated, stand-alone systems, such as demonstration projects in aerospace, border islands, or remote areas. With the emergence of new photovoltaic materials, the continuous decline in product prices, the continuous improvement in conversion efficiency, the introduction of advanced power electronic devices and microprocessors, and the application of advanced control strategies, the research and large-scale promotion of photovoltaic grid-connected technology have become increasingly possible. Photovoltaic utilization is gradually developing towards urban grid-connected photovoltaic power stations, building-integrated photovoltaic systems in residential communities, and small-power residential grid-connected photovoltaic systems.
II. Forms of Grid-Connected Photovoltaic Power Generation Systems
The initial form of integrating photovoltaics with buildings was to install a general solar cell array on the roof or balcony of a building and equip it with a battery for independent power supply, or to connect it in parallel with the public power grid through an inverter controller and transformer output, so that the power grid and the photovoltaic array jointly supply power to the building.
A further form of integrating photovoltaics with buildings involves embedding photovoltaic modules into building materials, using specialized materials and processes to incorporate these modules into components such as roofs, exterior walls, and windows. In this way, the photovoltaic modules can be used directly as building materials while simultaneously generating electricity, further reducing power generation costs.
When photovoltaic power generation systems are integrated with buildings, they are typically connected to the grid. Compared to stand-alone photovoltaic power generation systems, these systems have the following five major advantages:
1. On rainy days or at night, the power grid supplies power to the load. This eliminates the need for energy storage devices in the system, reducing system costs, avoiding the hassle of maintaining and replacing batteries, and increasing the reliability of power supply.
2. The electrical energy generated during periods of sunshine can be used to power the loads inside the building, and any surplus can be fed back to the power grid;
3. In grid-connected photovoltaic power generation systems, there is no limitation on the state of charge of the batteries, and electrical energy can be stored and drawn from the grid at any time;
4. When designing the tilt angle of the solar cell array, the angle corresponding to the maximum solar radiation received throughout the year can be selected to maximize the power generation capacity of the solar cell array;
5. The solar radiation intensity is high in summer, and the solar cell array generates relatively more electricity. Summer is also the peak period for electricity consumption, with high utilization rates and large power consumption of cooling equipment such as air conditioners. This can play a role in peak shaving for the power grid.
