IEEE Power & Energy Magazine - July/August 2021 - 68

connects to can follow the control target. Moreover, a
static var compensator is installed in each storage station
to help reduce the voltage fluctuation caused by the
rapid change of the storage active power output.
5) Reliability improvement: The storage station also
helps to improve the reliability of the power system,
especially the essential load of the local network.
Figure 4 shows the aggregated storage station business
model. It follows a build-lease transfer model: investors
built the storage station and leased it to the power grid
company. The power grid company pays a rental fee, which
is internalized as transmission charges in retail electricity
tariffs. The rental fee is set according to transmission
asset cost recovery schemes. Currently, a condition for the
business model's success is that the rental fee is acceptable
to the grid company. However, eventually, the rental fee
should be determined by a market mechanism.
Distributed Storage From Mobile
Communication Base Stations
Mobile communication base stations are normally installed with
backup batteries to enhance their reliability. While providing an
uninterruptable power supply, the batteries' unused capacity
can be regarded as distributed storage that could be deployed to
provide power system flexibility. Furthermore, with the development
of electric vehicles, the number of retired vehicle batteries
will grow in the next few years. After retirement, these
batteries could be reutilized as an uninterruptible power supply
for base stations. Although the capacity of the backup batteries
at a single base station is small, the total amount of storage
is considerable. The Chinese government reports that, in 2019,
1.74 million new base stations were constructed, expanding the
country's total to 8.41 million. Moreover, as 5G commercialization
begins, the number of base stations and a single base station's
battery capacity will simultaneously grow.
Before using base station backup batteries to provide
flexibility, suitable aggregation is needed. Since backup batteries
are fully distributed resources and each one is small,
directly dispatching them is unrealistic. Thus, they should
be aggregated into large-scale virtual storage for power system
applications. Such aggregation needs two key technologies,
described in the following:
1) Dispatching platform: The mobile communication base
station dispatching platform is the interface between the
distributed base station battery storage and the power
system operation center. It is connected to the BMS in
each base station. It communicates with base stations,
obtains their operation information, and aggregates
them as integrated storage. The aggregated storage
information is sent to the power system dispatching
center for operation applications, for example, demand
response and ancillary services. Simultaneously, the
dispatching platform receives real-time data from power
systems, makes decisions for each base station, and
sends orders to local BMSs. The dispatching platform
has the following basic functions: base station backup
battery management, distributed resource aggregation,
power system applications (e.g., peak shaving, demand
response, and frequency regulation), cost and payment
settlement, and so on.
Cloud Energy Storage
Dispatching Platform
Investor 1
Controllable Storage Station
Batteries
Bidirectional
ac/dc Converters
Yuan
Investor 1
Balance
Power Grid
BMS
Controllable Storage Station
Batteries
Bidirectional
ac/dc Converters
- Investment Cost
Yuan
Yuan + Rental Fee
Bidirectional Energy Flow
Single-Direction Energy Flow
Communication
Money
Yuan Transmission Charge
Load Side
figure 4. The aggregated storage station business model.
68
ieee power & energy magazine
july/august 2021
BMS
Investor N
Controllable Storage Station
Batteries
Bidirectional
ac/dc Converters
Yuan - Investment Cost
Investor N
Balance
Yuan
Yuan
+ Rental Fee
BMS
IEEE Power & Energy Magazine - July/August 2021

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