In recent years, due to the rise in raw material prices, the cost of photovoltaic systems has dropped slowly. To complete the transition from “optional” to “strong” energy storage, it requires both policy support and technological and product innovation to promote photovoltaic storage. With the development of the industry, how to configure energy storage? How to choose the plan? What are the value-added functions of energy storage? These need to be understood before calculation. Only after designing a good plan and adding energy storage can there be more benefits.

▲Guriwatt energy storage project case

01-How to configure energy storage?

Taking Jiangxi Province as an example, the province requires applicants to participate in the province’s new photovoltaic power generation competition in 2021, and can voluntarily choose the construction mode of photovoltaic power storage integration, and the energy storage standard should not be lower than 10% of the installed capacity of photovoltaic power plants. Capacity/1 hour. In principle, the energy storage power station will be built at the same time as the photovoltaic power station, and the solar-storage integration project that meets the construction conditions will be given preferential support in the competition selection score. If it is a 100MW photovoltaic power station, the energy storage should be equipped with 10MW/10MWh, that is, a 10MW energy storage converter and a 10MWh energy storage battery. At present, the price of the energy storage converter is about 0.3 yuan/W, and the price of the lithium battery is about 1.2 Yuan/Wh, the cost of the energy storage system increases by 15 million Yuan. If the construction cost of the photovoltaic system is 3.5 Yuan/W, the cost of the energy storage 10% capacity/1 hour increases by about 4%. The comprehensive cost of electricity for a 10MW photovoltaic power station is about 0.4~0.6 yuan/(kWh·time).

02-What kind of technical solution is adopted?

Currently, there are mainly AC-side coupling schemes and DC-side coupling schemes on the market for optical-storage fusion solutions.

The AC side coupling scheme means that photovoltaics and energy storage are connected on the AC side, and the energy storage system can be connected to the low-voltage side or centrally connected to the 10kV ~ 35kV busbar. The DC side coupling scheme means that the energy storage system is connected to the DC side. In this scheme, the photovoltaic inverter needs to reserve an energy storage interface, and the overprovision ratio can also be appropriately increased. When the light is particularly good, the power of the components is greater than the power of the inverter. A part of the energy storage can be separated from the DC side. The DC side energy storage efficiency is high, but it is not flexible enough. At present, most of the energy storage on the new energy side adopts the AC side coupling scheme.

03-What are the value-added functions of the energy storage system?

Large-scale solar-storage systems use fixed electricity prices to connect to the grid, and there is no peak-valley electricity price, so they cannot take advantage of peak-valley price differences. However, large-scale energy storage systems also have multiple value-added functions, which can provide peak shaving, black start, demand response, etc. for grid operation. A variety of services can effectively realize peak-shaving and valley-filling of the power grid, relieve peak power supply pressure, promote new energy consumption, and provide a new way for the safe and stable operation of the power grid.

Peak shaving: As an active energy storage device, the energy storage power station can output power to the grid during the peak load of the grid to share the power supply task of the regional power grid; Excess electricity is stored and functions like a pumped storage power station. For the electric energy storage facilities built in the wind power station, the priority is given to the use of the wind power station, and the rich capacity can participate in the auxiliary service market, and the electric energy storage facilities can be built on the power generation side, or participate in the auxiliary service market transactions as an independent entity; or on the user side The constructed electric energy storage facility can be regarded as a distributed power source and sold to the nearby electric power users, and as an independent market entity, it can perform deep peak regulation. There is a subsidy for peak shaving, and the compensation standard ranges from 200 yuan to 1000 yuan per MWh.

Black start: When the grid has short-term or long-term faults or is completely black due to faults, the energy storage power station enters the corresponding operating state. The energy storage power station has a small starting power and a high success rate of one-time startup. It can give priority to supplying power to important loads in the area, and The method of upward recovery is used to complete the black start of the power grid and speed up the recovery process; the participation of energy storage power stations in black start can effectively solve the problem of insufficient power supply for black start of local power grids, which is of great significance to the recovery of the power system after the collapse and reduce the loss of large power outages; and Compared with the traditional black start power supply, when the energy storage power station participates in the black start, the start-up speed is faster, more economical, more reliable, and has a very broad prospect.

Demand response: Energy storage power stations participate in grid demand response, which can stabilize grid load, improve power generation efficiency, reduce energy loss and protect the environment, thereby achieving a win-win situation for society, power grids, power plants and customers. This is the goal that demand response can achieve. It can alleviate problems such as backup shortages and transmission congestion, help reduce electricity price fluctuations, reduce market participation risks, and participants can obtain certain benefits.

04-Key Technology of Photovoltaic System

With the addition of energy storage, the PV-storage system technology will become more complex, and the charging and discharging time and power of the battery are very critical. It is necessary to ensure the safe and stable operation of the photovoltaic, energy storage and power grid, and to fully consider the economy. It is necessary to open up hardware and software and system-level barriers.

There are many devices in the optical-storage fusion system, and it is necessary to solve the problem of hardware and software interface compatibility between different devices. If the devices come from different manufacturers, the difficulty and cost of power station design, equipment procurement, operation, and maintenance will increase. Most importantly, different The communication interface schemes between devices are different, and the integrator needs to make compatible processing for different protocols and interfaces, which is relatively difficult, so try to use products from the same company during design.

The most critical thing for energy storage system integration is the safety management of the DC side, that is, the safety management of the battery system, which requires a very complete system protection design. Cells, modules, battery clusters, and battery system management, the four levels are interlocking. A good system protection design can know their operating status in real time, especially the temperature and voltage of the battery, which can be monitored and controlled from time to time. , if a fault occurs, it can realize step-by-step protection and fast linkage protection.

Compared with the traditional power station economical dispatch mode, when the photovoltaic storage power generation system is dispatched, it is necessary to fully consider the effective management of the internal batteries and converters of the energy storage power station, so as to improve the operation efficiency of the entire photovoltaic storage power station. safety and economy.