I. Scenario Definition
With the rapid popularity of electric vehicles, the demand for charging facilities is growing. However, different charging scenarios have different needs for charging facilities. Therefore, when planning charging facilities, we need to consider different scenarios and needs.
First, we need to determine the charging scenarios. Different scenarios such as city, highway and park have different needs. In the city scenario, private cars are dominant, so plug-and-play slow chargers can meet the demand and protect the battery. In high-speed scenarios, long-distance vehicles are predominant, and a large number of fast-charging piles are needed to meet time-critical demands. According to the whitepaper, more than 70 per cent of users believe that charging queues in high-speed service areas are too long, and close to 50 per cent of customers feel that the power is too low and more fast-charging piles are needed.
However, the scenarios are not very clearly delineated, and sometimes it is necessary to consider the overlay of demand in multiple scenarios, so we need to take into account the actual load situation for capacity and power allocation.
2. System introduction
A common optical storage and charging system generally contains four main parts, which are platform service system, charging system, power distribution system and security system. Among them, the platform service system is the core of the whole system, including system monitoring, data acquisition, remote control and other functions. Through the platform service system, real-time monitoring and management of the optical storage and charging system can be realised to ensure the normal operation of the system and enhance the efficiency of charging service.
The charging system is the main equipment of the optical storage and charging system, including inverter, PV module, battery, charging pile and so on. PV panels are the core component of the optical storage and charging system. The power distribution system mainly includes transformers, switchgear, cables and other equipment. Through the power distribution system, it can achieve reasonable distribution and regulation of the power generated by the optical storage and charging system. Security system mainly includes video monitoring, alarm system and so on. Through the security system, real-time monitoring and management of charging equipment can be carried out, and possible security risks can be found and solved in time.
Strategy Development
3.1 Spontaneous Self-use Mode
The main objective of this model is to utilise as much power as possible from PV generation and prioritise the charging of EVs. As an example, in the car park of a shopping mall, a large number of EVs enter in the evening, when the PV generation is already weak. Therefore, a certain amount of power needs to be stored during peak PV generation and used during the evening peak. In addition, the access of a large number of EVs can lead to load shocks, which need to be buffered and regulated using energy storage devices. Batteries can be prioritised to charge EVs when PV is plentiful, and excess power can be stored in batteries to meet early morning or night-time power demands. At the same time, the photovoltaic storage and charging system also needs to consider the access capacity of the PV, the battery charging and discharging power and the relationship between the PV power generation and the EV power consumption, in order to formulate the most optimal strategic planning.
3.2 Responding to time-sharing tariff model
Different regions adopt different electricity charging prices in different time periods to encourage the power consumption side to try to maintain the balance of power consumption. For electric vehicle charging piles, the price of charging rises during peak hours, when the optical storage and charging system can store the energy when the PV energy overflows and use it during the peak hours of charging. The construction of this photovoltaic storage charging system needs to consider the peak-valley price difference and peak electricity consumption, for example, the peak price 1.14, the valley price 0.31, the peak-valley price difference reaches more than 80 cents, and at the same time, this peak price is at the peak of EV charging, so that there can be a greater return. Unlike self-generation and self-consumption, time-sharing tariffs are price responsive.
3.3 Standby mode
The demand for power backup consists of three main categories. The first is rigid demand, which requires the use of energy storage for capacity expansion to reduce the strain on transformers due to limited transformer capacity and high power supply costs. The second is emergency demand, for example, when power is limited in summer, power backup can support the demand for electric vehicle charging, while the optical storage and charging system is also a microgrid, which can also support important equipment in off-grid mode. The third category is purely off-grid scenarios, where more battery capacity needs to be configured to ensure that power demand is met at different times.
3.4 Demand Management and Dynamic Capacity Expansion
Demand refers to the fact that the grid company will detect at regular intervals whether the power purchased by the plant exceeds the reported demand value, and if it exceeds it, it will charge an extra fee. At this time, the energy storage system can detect the power of the grid point, once a large number of charging pile access, buy power is fast exceeding the demand, the energy storage will discharge, to avoid the extra charge. Dynamic capacity increase, on the other hand, means that when the plant's buying power exceeds the transformer's capacity, the battery discharges the stored reserve power to cut the peak power, thus reducing the cost of transformer capacity increase. This scenario is more common when EV charging piles are connected in large numbers. The construction of this type of power station needs to consider the system power to meet the use of charging piles. It is also necessary to set up a response mode that can automatically discharge the battery when the purchased power exceeds a set value. In addition, the design of EMS software, such as setting up rotating charging pile charging and reducing the charging power can also reduce the amount of instantaneous power bought from the grid.
Core Functions
4.1 Switching on and off grid
Under normal circumstances, the load will draw power from the grid, but when the grid is suddenly disconnected, the system automatically switches to battery power and quickly disconnects from the distribution grid, thus ensuring that no islands will be formed and no hazards will be caused to grid maintenance personnel.
4.2 Battery Reservation
By setting the DOD of the battery, i.e. the depth of discharge of the battery, when the battery power is lower than this DOD, it can only be charged and cannot be discharged, thus realising power reservation. In this way, the energy storage system is able to respond to the peak power consumption of the charging pile in a timely manner, and at the same time meet the needs of time-sharing tariffs, demand management, dynamic capacity expansion and other scenarios.
4.3 Three-phase unbalanced output
Since some high-power charging piles are single-phase and the power grid is three-phase, one of the phases may have higher relative charging power, and some local power grids require three-phase balancing. Therefore, the energy storage system needs to have the function of three-phase unbalanced output or unbalanced charging to meet the needs of different loads.
4.4 Load Monitoring
The energy storage system also needs to have functions such as load monitoring in order to carry out real-time monitoring and data analysis of power consumption and revenue, and there are many functions that can be developed in this part, such as power consumption revenue, carbon revenue and so on. In addition, the following functions are also common in special scenarios, some of the optical storage charging station required functions.
Business Prospects
Multiple application scenarios mean multiple business models. When the future of optical storage charging becomes optical storage charging and discharging, it will be able to enter the power trading market, realise power auxiliary services, and even obtain carbon trading. In addition, optical storage charging can also be combined with emerging technologies. For example, the use of AI technology for data analysis, to achieve intelligent prediction of photovoltaic power generation, enterprise load, electricity prices and other factors, and optimise the scheduling system energy. This is when the strategy is not limited to simple self-generation or time-sharing tariffs, but a more complex and economical mode of operation. Another example is DC microgrid, optical storage direct flexible is also a hot topic at this stage, but due to the relative lag in standards, DC loads are also not defined on a large scale, so there is no wide range of applications, but in the future, this is also a strong correlation with the optical storage charging field.