Since the Energy Bureau released a new policy on May 31, distributed PV only arranged about 10G subsidy scale, and before June 1, the national distributed PV installation scale has exceeded 10GW, so after June 2018, distributed PV may have no national subsidy. If there are no subsidies, projects with full access to the grid, projects with a small proportion of self-use, and areas with low electricity prices will see a significant drop in revenue and no investment value. Pure photovoltaic project investment income declined, so people will look to photovoltaic energy storage, hoping to make a breakthrough in this field and increase new income.
Photovoltaic energy storage is not the same as grid-connected power generation, to increase the battery, as well as battery charging and discharging devices, although the initial cost to increase 20-40%, but the scope of application to a much wider. According to different applications, solar photovoltaic energy storage power generation system is divided into four types: off-grid power generation system, and off-grid energy storage system, grid-connected energy storage system and multi-energy hybrid micro-grid system.
1 photovoltaic off-grid power generation system
Photovoltaic off-grid power generation system, which does not depend on the power grid and operates independently, is used in remote mountainous areas, powerless areas, islands, communication base stations and street lights and other applications. The system consists of photovoltaic array, solar controller, inverter, battery pack, load, etc. The photovoltaic array converts solar energy into electricity when there is light, and supplies power to the load through the solar controller and inverter, and charges the battery bank at the same time; when there is no light, the battery supplies power to the AC load through the inverter.
Off-grid photovoltaic power generation system is specially designed for use in areas without grid or in areas with frequent power outages, and is a rigid demand. The off-grid system does not depend on the grid, but relies on the "use while storage" or "storage before use" mode of operation, and does the "sending charcoal in snow" thing. For families in areas without a grid or frequent power outages, off-grid systems have a strong practicality, the current cost of off-grid photovoltaic kWh about 1.0-1.5 yuan, compared to grid-connected systems are much higher, but compared to the cost of fuel generators kWh 1.5-2.0 yuan, more economical and environmentally friendly.
2 and off-grid energy storage system
Grid-connected PV power generation system is widely used in applications such as frequent power outages, or PV self-generation can not be surplus to the grid, the price of electricity for self-consumption is much more expensive than the price of grid-connected electricity, the price of peak electricity is much more expensive than the price of valley electricity.
The system is composed of a photovoltaic array made of solar cell modules, a solar grid-connected machine, a battery pack and a load. The PV array converts solar energy into electricity when there is light, and supplies power to the load through the solar control inverter, and charges the battery bank at the same time; when there is no light, the battery supplies power to the solar control inverter, and then supplies power to the AC load.
Compared with the grid-connected power generation system, the off-grid system increases the charge and discharge controller and battery, which increases the system cost by about 30%, but the application range is wider. First, it can be set to the rated power output at the peak of the electricity price, reducing electricity expenses; second, it can be charged at the valley of the electricity price, and discharged at the peak, using the peak and valley price difference to make money; third, when the grid blackout, the PV system as a backup power to continue to work, the inverter can be switched to off-grid mode of work, PV and battery can be powered to the load through the inverter.
3 photovoltaic grid-connected energy storage system
Grid-connected energy storage photovoltaic power generation system, can store excess power generation, improve the proportion of self-generation and self-consumption, applied to the PV self-generation and self-consumption can not be surplus online, self-consumption electricity price than the price of grid electricity is much more expensive, wave-peak electricity price is much more expensive than wave-level electricity price and other applications. The system consists of PV square array composed of solar cell modules, solar controller, battery pack, grid-connected inverter, current detection device, load, etc. When the solar power is less than the load power, the system is powered by the solar energy and the grid together. When the solar power is greater than the load power, the solar energy is partly powered to the load and partly stored through the controller.
In some countries and regions, where a PV system was installed before and then PV subsidies were removed, a grid-connected energy storage system can be installed to allow PV power to be completely self-generated and self-used. The grid-connected energy storage machine can be compatible with inverters of various manufacturers, and the original system can be left unchanged. When the current sensor detects a current flowing to the grid, the grid-connected energy storage machine starts to work and stores the excess electricity in the battery, which can also turn on the electric water heater if the battery is also full. When the household load increases at night, the battery can be controlled to send power to the load through the inverter.
4 Micro-grid energy storage system
The micro-grid system consists of solar cell arrays, grid-connected inverters, PCS two-way converters, intelligent switching switches, battery banks, generators, loads, etc. The PV array converts solar energy into electricity when there is light, and supplies power to the load through the inverter and charges the battery pack through the PCS two-way converter; when there is no light, the battery supplies power to the load through the PCS two-way converter.
Microgrid can fully and effectively play the potential of distributed clean energy, reduce the unfavorable factors such as small capacity, unstable power generation and low reliability of independent power supply, ensure the safe operation of the grid, and is a useful supplement to the large grid. Microgrid can promote the upgrading of traditional industries and can play a huge role from the perspective of economic and environmental protection. Experts say that microgrid application is flexible, the scale can be from several kilowatts to tens of megawatts, large to factories, mines, hospitals and schools, small to a building can develop microgrid.
The main advantages of microgrid system compared with pure off-grid system
1、Wider application scope, off-grid system can only be used off-grid, while micro-grid system includes all applications of off-grid and grid-connected system, with multiple working modes
2, flexible system configuration, grid-connected inverters can be selected according to the actual situation of the customer, single or multiple free combination, string inverter or centralized inverter, and even different manufacturers of inverters can be selected. The power of grid-connected inverters and PCS converters can be equal or different.
3, high system efficiency, micro-grid system photovoltaic power generation through the grid-connected inverter, can be used directly to the load nearby, the actual efficiency of up to 96%, two-way converter mainly plays the role of voltage stabilization.
4, strong carrying capacity, micro-grid system grid-connected inverter and two-way converter can supply power to the load at the same time, when the light conditions are good, the carrying capacity can be increased a lot.
