Author: Yipianlvye

The “rechargeable, interchangeable, and upgradable” way of energy supplementation has never just been a slogan for NIO. For a long time, many people have equated NIO’s energy supplementation method with battery swap. However, NIO has made great achievements in charging technology as well.

Now let’s talk about NIO’s charging technology and the interaction between battery swapping and the power grid.

Types of Charging Piles

Integrated Pile Cabinets

Have you noticed that the NIO 20 kW small DC fast charger is much larger in size compared to the 7 kW AC home charger?

This is because the 20 kW small DC fast charger has a charging machine cabinet that integrates charging pile, so the size is much larger than that of a home charger that only has a current switch and communication.

The upper limit of the charging power is determined by the power module configured inside the charging machine cabinet.

Taking Tritium’s charging cabinet as an example, each charging power module is 25 kW, and the capacity of the pile cabinet can accommodate up to 3 sets, so the power represented is 75 kW.

As the charging current for a fast charging pile is large, the cable temperature will rise, and the charging current will decrease accordingly, thus reducing the charging speed. There are two solutions to this problem:

• Increase the cable area and enhance the current carrying capacity (make it thicker)

• Use better cooling technology to cool down the cable more quickly (liquid cooling)

Tritium’s liquid cooling interface can make the charging cable thinner and more user-friendly for car owners, but the cost is higher.

The power grid commonly uses a 60 kW charging pile, with a single module being 15 kW, and four modules are used.

As there is no liquid cooling, the pile depends solely on air cooling. When the fan rotates at full speed, it makes a lot of noise, and the heat dissipation efficiency is low, leading to a high failure rate.

The advantage of the integrated pile cabinet is that the charging machine cabinet is smaller in size and easy to move. It can work as long as the electricity capacity is sufficient.

The disadvantage is that the charging power limit is not high, limited by the power module and heat dissipation. Moreover, the shape of the cabinet must compromise with the charging power, and is usually designed to be long and wide like a large refrigerator, making it easier to install and transport.

Separation of Cabinet and Pile

As the name suggests, the charging machine cabinet and charging pile are set separately.

The high voltage electricity is input into the charging machine cabinet through the boxed transformer substation (sub-box). According to the charging gun requirements, the charging power is configured, and the charging pile status can be monitored in the cloud, making maintenance easier.

The charging machine cabinet can determine how much charging power and how many power modules should be configured based on the site’s electricity capacity and area, and the distance between the charging machine cabinet and the charging pile can be flexibly changed.Advantages of High-power Charging:

The charging power can be very high, as the high-power modules are placed inside the cabinet, which can be located far away from the charging pile, vehicles, and people. The cabinet is not restricted and can be freely expanded, thus achieving high-power charging.

Since the charging pile is not limited by the charging cabinet, the shape of the charging pile can be varied, and large refrigerator-shaped charging piles are not necessary. Each car manufacturer with its own energy replenishment system has its unique design, making charging piles easily recognizable.

Disadvantages and Solutions:

The main disadvantage of using high-power charging modules is that separate cabinets are required, which occupy a larger area. High-power supercharging mostly uses the cabinet and pile separation structure. When using multiple high-power charging modules placed in the same cabinet, the volume can be so large that it will not be suitable for the combined cabinet and pile structure due to heat dissipation requirements, and may even be as large as a freight container.

Solar Energy Storage Charging

The structure is basically the same as the cabinet and pile separation structure, but with an additional storage cabinet. If conditions permit, solar panels and V2G charging piles can be added. Solar energy storage charging is a new trend in the charging industry.

Due to the large impact on the power grid during high-power output and also the waste of reserve capacity with many idle capacitors, high-power charging systems require a power storage cabinet to reduce the impact on the power grid.

Currently, there are several schemes for the solar energy storage charging:

Storage Charging

High-power charging piles generally require a storage cabinet to reduce the impact on the power grid. For example, Electrify America has a charging station with a 350 kW supercharging module and a Tesla 350-degree, 210 kW power storage system.

Since the electricity price in the United States is market-driven, the price difference between peak and off-peak electricity prices is very large. As a result, the storage system stores electricity when prices are low and outputs it at high prices, which can minimize the impact on the power grid and alleviate demand surges. Furthermore, in addition to the regular electricity charge, the United States also employs demand charges. Even if two clients consume the same amount of electricity, they may receive different electricity bills due to differences in electricity consumption.

What are the demand charges?

Electricity companies impose a punitive electricity charge by taking the highest peak value of electricity consumption in one day (usually 15 minutes).

For regular electricity charges, the electricity consumed is charged according to the number of kilowatt-hours (kWh) multiplied by the electricity price; for peak and off-peak usage, the electricity consumption is only multiplied by different electricity prices.The demand charge is the maximum power usage per unit time multiplied by the demand charge (kW x demand charge). Moreover, the demand charge has a punitive nature, which is tens or even hundreds of times higher than the normal electricity price. Sometimes, the demand charge can account for more than half of the electricity bill.

In other words, American power companies hope that their customers have a smooth power demand curve and do not have sudden and extreme peak periods because the more extreme the peak, the more outrageous the electricity bill.

Charging stations are the most disliked peak users by power companies, especially high-power charging stations, which are heavily penalized by the demand charge.

Therefore, American charging service companies have a strong motivation to set up energy storage, after all, the numbers on the electricity bill cannot be underestimated. If the site conditions permit, photovoltaics can be additionally installed, which is the second form – solar energy storage and charging.

Solar Energy Storage and Charging

Tesla is the most famous in this field.

In 2019, the V3 supercharger was built in Las Vegas, with a lot of publicity claiming that photovoltaics and energy storage can provide a continuous supply of power to the charging station, reducing the reliance on the power grid.

The ideal is full and the reality is skinny.

Most of the solar energy storage and charging stations currently use parking sheds to install photovoltaics, and the area that can be laid out is limited.

Affected by the area of land, local sunshine conditions, and the number of charging piles installed, photovoltaic power generation accounts for only 5% to 10% of the total charging electricity, and it is still far from getting rid of reliance on the power grid.

Like Tesla’s first solar energy storage and charging station in Shanghai, the promotion says “the integrated solar energy storage and charging solution, the “magic” of the natural energy cycle, lighting up Shanghai again.”

Looking at the results, the photovoltaic coverage is about 200 square meters, and with Shanghai’s conditions, it can generate about 130 kWh of electricity per day.

This station has two groups of V3 cabinets, six supercharging piles, one destination charging pile, but 130 kWh of electricity is not enough for six supercharging piles to charge for an hour.

The energy storage capacity is even smaller, with only four Powerwalls. One Powerwall can store 13.5 kWh of electricity, and all four can only store 54 kWh, which is not enough to fully charge a Model 3/Y.

It can be seen that this station is mainly for publicity purposes, and the proportion of photovoltaics or energy storage in charging is very small.

Therefore, for solar energy storage and charging stations with small photovoltaic coverage, photovoltaics only play an auxiliary role in charging, and the greater significance lies in demonstrating the concept of green energy.

This is also why Tesla has been advocating “solar energy storage and charging” for a long time, but it has rarely been implemented.

However, in the context of “promoting solar energy in the whole county,” the significance is completely different.

With the introduction of the policy of promoting solar energy in the whole county, China’s distributed photovoltaics has ushered in a new round of development boom.However, there are many types of roofs in the building industry, which have scattered resources and varying individual scales. Moreover, the limited capacity of the power grid may cause adverse effects such as changes in the direction of the tide, overvoltage, and misoperation of relay protection. Therefore, it is hoped that photovoltaic power generation can be consumed locally, which is achieved through the “photovoltaic energy storage and charging” solution.

The photovoltaic power generated by nearby roofs and carports are gathered together, and cloud-based energy management system (EMS) is used to achieve “self-use and surplus electricity storage”. This solution realizes the balance between energy production and consumption, relieves the pressure of distribution network capacity, saves expansion costs, and improves the reliability and economy of customer-side power supply, thereby constructing an intelligent microgrid.

By making the electric vehicles become helpers for local photovoltaic power consumption, rather than a new burden on the power grid, it achieves a better solution.

However, this requires a lot of communication and coordination work with various departments, and it is not an easy task.

V2G + Photovoltaic Energy Storage and Charging

Going further, the electric vehicle is not only a load, but also a member of energy storage that can both charge and discharge. This is the ultimate ideal.

SAIC RisingAuto has cooperated with Tezign to establish a demonstration station equipped with:

• a 40 kWp photovoltaic carport

• 210 kWh energy storage

• 9 DC charging and discharging piles with a total power of 150 kW, and 1 charging pile with a power of 45 kW

The energy storage here uses the retired batteries of electric vehicles, which is a part of the battery’s hierarchical utilization. After the fire at the Dahongmen Energy Storage Station in Beijing in 2021, the new version of “Various Requirements for Preventing Power Accidents” issued by the National Energy Administration has clearly stated that “large and medium-sized electrochemical energy storage power stations should not use ternary lithium batteries or sodium sulfur batteries, and should not use retired power batteries for hierarchical utilization.”

Many people thought that using retired batteries for storage is no longer possible.

However, this is still possible, but not for large-scale use. The use of batteries with a capacity of MWh is definitely not allowed, and for hundreds of kWh, retired power batteries with high consistency and traceability must be carefully selected. At this station, the power batteries are directly removed from the package without separation.

To protect the power batteries, the power of the V2G charging piles is not very high. The charging and discharging power of this station is 16.6 kW, and most V2G charging piles have a power similar to this, between 15 kW and 17 kW.

In addition to flat parking lots, there is another V2G + photovoltaic energy storage and charging solution for vertical parking lots used by the State Grid.

At the Jiangbei Geek Space in Nanjing, the station is equipped with:

• a 200 kWp photovoltaic roof

• 3 MWh energy storage

• 243 fast charging piles and 147 slow charging piles, with a total power of 12,000 kW

This is a composite parking lot with two underground floors and eight above-ground floors. In the service experience area on the first floor, electric vehicle enterprises can display vehicle models and there are also dining areas that provide food and beverage services.

This requires a large capital investment, and State Grid has only done a few pilot projects.

The biggest obstacle to the development of V2G is car owners’ anxiety about battery degradation.

As the most expensive component of an electric vehicle, many car owners are very afraid of battery degradation. As long as the battery is charged and discharged, there will be loss, and the degree of loss varies depending on the different battery systems.

V2G needs to charge and discharge in order to achieve peak shaving and valley filling. To shave peaks, discharge is required, and to fill valleys, charging is required. In any case, it will accelerate the aging of the battery.

Compared with the loss of the battery, the electricity fee charged by V2G is negligible. To convince car owners not to worry about battery degradation, the cycle life of batteries is already very long, and any claims to the contrary are simply wishful thinking.

Light Charging and Battery Swapping

Use the energy storage properties inherent in battery swapping stations to replace energy stored by solar charging.

NIO is the fastest in this field.

In patent CN215663038U, the combination of photovoltaics and battery swapping stations has been demonstrated.

As mentioned before, the power generated by the photovoltaics in the carport is not sufficient, and at most serves as an auxiliary charging function. This point is also proven in the patent.

There are three ways to use photovoltaic power generation here:

Shared power supply of the grid and photovoltaic charging stations

NIO is very clear that photovoltaics alone are not enough to support the charging demand of charging stations, and power from the grid is still needed, which indirectly proves that the amount of power generated by the photovoltaics in the carport is not much.

Photovoltaic power supply for battery swapping station (residual power storage)

Just like a general energy storage station can store the electrical energy generated by photovoltaics, a battery swapping station can also store the electrical energy generated by photovoltaics when no one is charging.

Photovoltaic grid connection (residual power grid connection)

When neither the charging station nor the battery swapping station needs excess energy, the photovoltaic power generation is incorporated into the grid to achieve power supply revenue from the power system.

The difference from general energy storage is that battery swapping stations usually do not discharge from the battery swapping station to the grid. The main reason is that when there is a peak period of power demand, there is usually also a peak period of battery swapping demand, and the battery swapping station cannot simultaneously meet both demands. The priority must be to take care of the needs of car owners.Shen Fei mentioned in the 2022 NIO Power Day: “Noon may be the time for everyone to rest and have lunch, many users go to swap batteries, and that is often when electricity prices are the highest.

We will predict in advance how many users will come to swap batteries in that hour, fill up the batteries when the price of electricity is not too expensive, try to avoid charging during the most expensive time, and not delay the next time point when users come to swap batteries.”

He also mentioned that NIO is currently testing bidirectional battery swap stations, which discharge electricity to the grid, and can interact with the power grid at second-level and minute-level speeds.

Isn’t this conflicting with what was mentioned above that “Battery swap stations usually do not discharge electricity from the station to the grid“?

Shen Fei talked about frequency regulation, which only requires a second-level and minute-level response.

Peak shaving balances power consumption by changing the amount of electricity used, while frequency regulation stabilizes the power frequency when it deviates from 50Hz in the power system.

Frequency regulation needs to cooperate with the grid’s automatic generation control (AGC). It adjusts the power generation power in real-time based on the instruction issued by the power dispatching agency according to the adjustment rate to meet the power system’s frequency requirements.

The performance indicator of frequency regulation is the weighted average of the response speed, adjustment rate, and response accuracy. This indicator is the basis for the compensation of the frequency regulation dispatch, which will directly affect the benefits.

Compared with thermal power, lithium-ion battery storage can be quickly responded, accurately regulated, and well-suited for frequency regulation auxiliary services.

Therefore, NIO’s battery swap station enters into frequency regulation, not peak shaving.

This article is a translation by ChatGPT of a Chinese report from 42HOW. If you have any questions about it, please email bd@42how.com.