IEEE Power & Energy Magazine - July/August 2021 - 72

Distributed Storage
From Heating Networks
In recent years, the coupling of electricity and heating systems
has become tighter. Heat networks can store large amounts,
making them an ideal way of providing flexibility to the
power system. In China, such a distributed storage ability has
been exploited for mitigating wind power curtailment. Heating
systems supplied by wind power are depicted in Figure 8.
The first project involving heating systems as virtual storage
to accommodate wind power was proposed by the National
Energy Administration of China in 2015. It was mainly
implemented in areas with rich wind power resources, such
as Inner Mongolia, Liaoning, Jilin, and Hebei. In those areas,
excess wind output during periods with electricity demand
valleys is allocated to heat generation via electric pumps and
boilers. The thermal energy produced from wind energy can
be directly consumed or stored in a heat network or heating
storage facility. At the same time, the heat generated from
wind power can provide more flexibility to combined heat
and power unit operation. The virtual storage scheme can
thus further deepen wind power integration.
Until now, many policies have been promulgated to
make this kind of project widely known. For example, in
Hebei, transmission and distribution prices in off-peak load
periods are set to be 30% of those in peak load periods to
enable heating operations supplied by wind power. Also,
subsidies and tax relief schemes are available to companies
that provide heat supplement services through wind power.
At present, many pilot projects for heating systems supplied
by wind power have been finished and successfully operated,
including large-scale demonstrations (more than
100 MW). According to an estimate in " Planning of Northern
Area Clean Energy Heat Supplying in Winter (2017-
21), " published by the National Energy Administration of
China, the use of clean energy for heat supplies in northern
China will reach 70% in 2021, with wind energy being the
prevalent source.
Wind Farm
Electric Boiler
The successful implementation of heating systems supplied
by wind power shows the great potential of using heat networks
to provide virtual energy storage services for power systems. A
primary heat pipeline of hot water (at an average temperature
of 90 ºC) with a diameter of 1 m and a length of 1,000 m has a
heating storage capacity of 9.16 MWh if its temperature can
be flexed by 10 ºC. For Beijing, with a 2,000-km heat network,
the equivalent energy storage capacity can reach 18 GWh.
Heating systems supplied by wind power are an effective way
to harness the energy storage capability of heat networks.
In the cloud-based virtual storage aggregation framework,
a heat network can be considered the energy storage component,
while combined heat and power units, electric boilers,
and electric heat pumps can be viewed as power conversion
components. The combination of these mechanisms will
make them act like an equivalent electricity storage system.
From the power system point of view, equivalent electricity
storage from multiple heating networks in different cities can
be aggregated to form a cloud-based energy storage system.
The network can be aggregated with batteries, compressed
air energy storage, and other energy storage systems. It can
act as an energy storage provider and can be used by power
grids and consumers, such as industrial parks.
However, successfully aggregating distributed heat storage
(to provide different flexibility services to the power system)
greatly depends on business models. The key is a fair
profit-sharing mechanism between the power and heating
sectors. This is because the heat network operator may not
have the incentive to use the pipeline heat storage capacity.
After all, its operation losses would increase when providing
energy storage services. Therefore, the additional profit
accrued on the power system side from using heat energy
storage services should be shared with heat network operators.
This money should not only cover the cost increment
incurred from providing energy storage services but give
enough incentive to the heat network operator to make it
willing to participate in the storage aggregation scheme.
Fortunately, the profit increment
from power system operation is
generally much higher than the
cost increment in heat network
operation. This suggests that
power and heating systems can
achieve win-win solutions based
on the cloud-based energy storage
framework.
Heating Network
Combined Heat
and Power Plant
Electric and Heat Users
Power Grid
figure 8. Distributed storage from heating systems.
72
ieee power & energy magazine
Discussions
Through the review of current
trials, we can conclude that the
key aspects of making the cloudbased
energy storage technology
and general business model work
in China are threefold, as summarized
in the following:
july/august 2021
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