BYD strides forward with a high voltage battery storage system

Storage systems are complex and can be evaluated against more than just one criterion. Sometimes, particularly strong properties in two different areas can actually technically cancel each other out. In this case, all that counts is the compromise, which can be optimal for every application in a different way. For that reason, we always begin with the following disclaimer: The jurors judge individual innovations, but cannot choose the best overall storage system.

BYD has now launched a battery storage system that advances progress in three categories: modularity, charging and discharging capacity, and efficiency. With regard to efficiency, the company also creates transparency, and has submitted its technology to pv magazine’s storage system comparison. The judges therefore decided to select BYD for the pv magazine award in the category of top innovation.

To increase efficiency, BYD has given the new battery a high output voltage. There are real and fake high voltage batteries of this type. The fake ones use a transformer or a step-up converter to produce the high voltage. This in itself brings little or no increase in efficiency. The BYD system is one of the real ones: The company connects the batteries in series, so that the output voltage increases with each module. The variant with a storage capacity of 10 kWh delivers more than 400 V. The high voltage of the BYD battery makes it possible to dispense with the transformer in the battery inverter. This in theory increases efficiency. And measurements show that the concept also works in practice, although with a system performance index of 89.0%, the gap between it and the previously tested low voltage systems is not huge. A discussion about this shows the parameters and applications that determine whether high voltage will be able to deliver its full potential in the future.

Apart from the Chinese manufacturer, only Sony currently has a “real” high voltage battery on the market. One reason for this could be that the insulation requirements increase, and manufacturers therefore refrain from using high voltage systems.

A major step in the new BYD product is its charging and discharging performance. The battery can be fully charged or discharged within an hour. ­Technicians say it has a C-rate of one. The battery with a capacity of 10 kWh can therefore be operated with a capacity of 10 kW. For five minutes, it can even deliver twice that output. In the home sector, C-rates of only a quarter to three quarters are common.

High C-rates can be relevant when peak loads occur in off-grid systems where the network is not available as a safety feature. This is also the case in business models in which peak loads are capped in commercial operations, where the battery is supposed to generate additional income through the marketing of primary control power, or where it serves as an emergency power supply. In a private home, it is conceivable that the battery could be used to quickly charge an electric car with the stored solar power. However, all of these applications require the proper power electronics. Currently, BYD batteries can be used with the SMA Sunny Boy Storage, which is designed for low power home applications. BYD is working to form partnerships with other manufacturers for other applications. Soon BYD and the inverter manufacturer Kostal will release a solution.

What catches the eye in a first look at the system is its modular design. The batteries are stacked on the floor. A plug system connects them and no wiring is required. But the details go even further. Since each module has its own battery management system, modules of differing ages can also be combined with each other, even though the capacity of the new modules used in the series configuration could be slightly reduced. This facilitates replacement and expansion after a few years. Since a module has a capacity of just 1.28 kWh, the capacity can be finely graduated to suit the application. Several towers can be connected in parallel to provide a total of up to 57 kWh. As a result, the system is also suitable for applications in commercial companies.