I. Grid-connected photovoltaic power generation system
A grid-connected photovoltaic (PV) system consists of PV modules, a grid-connected PV inverter, PV meters, loads, bidirectional meters, a grid-connected cabinet, and the power grid. The PV modules generate direct current (DC) from sunlight, which is then converted into alternating current (AC) by the inverter to supply the loads and feed into the grid. There are two main grid connection modes for grid-connected PV systems: one is "self-consumption with surplus power fed to the grid," and the other is "full grid connection."
Generally, distributed photovoltaic power generation systems mainly adopt the "self-consumption and surplus power to the grid" model. The electricity generated by the solar cells is given priority to the load. When the load does not use up all the electricity, the excess electricity is sent to the grid. When the power supplied to the load is insufficient, the grid and the photovoltaic system can supply power to the load at the same time.
II. Off-grid photovoltaic power generation system
Off-grid photovoltaic (PV) power generation systems operate independently of the power grid and are typically used in remote mountainous areas, areas without electricity, islands, communication base stations, and streetlights. A typical system consists of PV modules, a solar controller, an inverter, batteries, and loads. When there is sunlight, the off-grid system converts solar energy into electrical energy, which is then used to power the loads and charge the batteries via a solar-controlled inverter. When there is no sunlight, the batteries supply AC power to the loads via the inverter.
It is highly practical for areas without power grids or areas that frequently experience power outages.
III. On-grid and off-grid photovoltaic energy storage systems
Off-grid photovoltaic power generation systems are widely used in places where there are frequent power outages, or where photovoltaic power generation is for self-consumption and surplus power cannot be fed into the grid, where the self-consumption electricity price is much higher than the grid-connected electricity price, or where peak electricity prices are much higher than off-peak electricity prices.
The system consists of photovoltaic modules, a solar grid-connected inverter, batteries, and loads. When there is sunlight, the photovoltaic array converts solar energy into electrical energy, which is then used to power the loads and charge the batteries via the solar-controlled inverter. When there is no sunlight, the batteries power the solar-controlled inverter, which in turn powers the AC loads.
Compared to grid-connected power generation systems, this system adds a charge and discharge controller and a battery. When the grid experiences a power outage, the photovoltaic system can continue to operate, and the inverter can switch to off-grid mode to supply power to the load.
IV. Grid-connected energy storage photovoltaic power generation system
Grid-connected photovoltaic power generation systems can store excess electricity, increasing the self-consumption rate. The system consists of photovoltaic modules, a solar controller, batteries, a grid-connected inverter, a current detection device, and loads. When solar power is less than the load power, the system is powered by both solar energy and the grid. When solar power exceeds the load power, part of the solar energy powers the load, and the remaining unused electricity is stored by the controller.
V. Microgrid System
A microgrid is a novel grid structure, a distribution network consisting of distributed power sources, loads, energy storage systems, and control devices. It can convert dispersed energy sources into electricity locally and then supply it to local loads. A microgrid is an autonomous system capable of self-control, protection, and management; it can operate either connected to the external power grid or in isolation.
Microgrids effectively combine various types of distributed power sources to achieve energy complementarity and improve energy utilization. They can fully promote the large-scale integration of distributed power sources and renewable energy, and achieve highly reliable supply of multiple energy forms to loads. They are an effective way to realize active distribution networks and represent a transition from traditional power grids to smart grids.
