IEEE Power & Energy Magazine - July/August 2021 - 69

Batteries' unused capacity can be regarded as
distributed storage that could be deployed to
provide power system flexibility.
2) Dispatchable capacity evaluation of backup batteries:
Per the previous description, backup batteries should
provide an uninterruptible power supply to base stations
so that when disruptions occur, communication devices
can be supplied. The capacity of the batteries needs to be
divided into two parts. Capacity is needed for uninterruptible
power supply service, and the remaining amount
is dispatchable. Thus, before aggregating distributed resources,
it is necessary to evaluate such dispatchable capacity.
For 4G and earlier communication technologies,
the power load is relatively stable. So, the traditional solution
is to directly determine each base station's backup
duration requirements according to its location. For
example, according to the operational standards of
China Tower, base stations in a city should have at least
a 3-h backup duration. Those in suburbs should have at
least a 5-h duration, and those in the countryside should
have at least 7 h.
However, for 5G, the communication device power
load is traffic sensitive. The backup battery capacity
would usually have a much longer duration since it
needs to meet the most critical requirements. The flexibility
of the backup batteries cannot be fully exploited.
To precisely evaluate the dispatchable capacity of
5G base station backup batteries, new methods should
incorporate 5G communication devices' operation
characteristics along with the reliability of the power
supply. By dynamically evaluating the backup capacity
needed for reliability, the dispatchable capacity
of 5G base station backup batteries can be fully integrated
into a cloud storage operation.
In China, pilot projects have been launched to aggregate
distributed base station backup batteries as cloud storage.
Technical implementation and business models are being
demonstrated. In a China Southern Power Grid project, 56
base stations in the Baiyun district of Guangzhou have been
aggregated as cloud storage. The BMS is updated so that it
can actively discharge to meet part of the base station load.
Moreover, the switching power supply devices in eight base
stations have been replaced by bidirectional ac/dc converters
to enable energy to flow from the power system. In the
future, retired batteries could be installed at the base stations
to enhance capacity. A dispatching platform has been
established and communicates with each base station via the
public network. A summary of this project's concept is in
Figure 5, while Figure 6 illustrates the main components.
This project is a win-win for China Tower and China
Southern. China Tower provides the batteries and floor
Cloud Energy Storage
Dispatching Platform
Bidirectional Energy Flow
Single-Direction Energy Flow
Communication
Power Grid
Switching Power
Supply Devices
Communication
Devices
Base Station
BMS
Switching Power
Supply Devices
Batteries
Communication
Devices
BMS
...
Batteries
Base Station
figure 5. The conceptual framework for distributed base station battery cloud storage.
july/august 2021
ieee power & energy magazine
69
Communication
Devices
Base Station
Batteries
Bidirectional
ac/dc Converters
* Peak-Shaving Management
* Power Grid Interaction
* Battery State-of-Charge/State-of-Health
Monitoring
* Payment Settlement
BMS
IEEE Power & Energy Magazine - July/August 2021

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