IEEE Electrification - September 2021 - 76

power system is undergoing a transition to IESs with a
high penetration of renewable energies.
In the next five years, the State Grid Corporation of
China (SGCC) plans to invest more than US$70 billion
annually to promote the upgrading of the power system to
the Energy Internet. Besides power companies, the Chinese
government also devoted a significant amount of
funding to IESs during the last five years. The State Development
and Reform Commission of China issued the
Development Guidance for the " Internet+ " Smart Energy
(Energy Internet), which aims to initially build the energy
Internet industry by 2025. In 2016, the Ministry of Science
and Technology funded a five-year project called Fundamental
Theory of Planning, Operation, and Trading of the
Energy Internet, which covers all rounds of the Energy
Internet, including design, operation, and business models.
From 2015-2019, the National Natural Science Foundation
of China (NSFC) has supported more than 100
projects in the fields of the Energy Internet or integrated
energy. The total funding level is more than 70 million
CNY (about US$11 million). Figure 1 illustrates the word
cloud of these project titles. These projects cover a wide
range of topics in the modeling, planning, operation, control,
and marketing of integrated systems.
Multi-energy microgrids (MEMGs) are special IESs that
offer a cluster of small multi-energy sources, energy storage
systems, and loads. They may be either grid connected
or islanded, and they have clearly defined boundaries,
such as in industrial parks or islands. When several
MEMGs are connected, they can exchange energy with
each other. This motivates many business models. China
has also issued many policies to support energy trading in
IESs. The design and operation problems under these
business models should be thoroughly investigated.
This article introduces some business models, planning,
and operational methods for MEMGs. We take the
IES in the Hongdou industrial park as an example to illustrate
how energy trading is carried out, and we introduce
the energy management platform designed for this IES.
We also discuss some opportunities and challenges.
Business Models
One MEMG is a representative prosumer. When MEMGs
are networked, they can trade energy with the main grid
or exchange power with each other. The latter exchange is
known as transactive energy. It is more complicated than
traditional trading with the energy market from a local
perspective because each MEMG has to cope with multiple
agents, especially when various kinds of energy resources
are involved. Here, we introduce three possible market
schemes that are promising in MEMGs: the MEMG-to-grid
market, MEMG-to-user market, and peer-to-peer (P2P)
market. Figure 2 illustrates the structures of these markets,
showing how they differ from each other.
MEMG-to-Grid Market
This scheme requires the MEMG to be connected to the
main grid, and a bidirectional energy flow is allowed. This
is the most commonly used mode in China. The SGCC
supports the development of MEMGs, which will buy its
surplus energy. MEMGs can also buy energy from the grid
if a power shortage exists. China also sets the price of
power purchases from MEMGs. The prices for different
kinds of energies are also different. For PV panels, the
price is 0.35 CNY/kWh, 0.4 CNY/kWh, and 0.49 CNY/kWh
in three different regions. Meanwhile, there are also subsidies
for PV users: 0.05 CNY/kWh for commercial PV power
stations and 0.08 CNY/kWh for distributed PVs. For
onshore wind power, the price varies from 0.29 CNY/kWh
to 0.47 CNY/kWh. For offshore wind power, the price is
0.75 CNY/kWh. This market model is simple and provides
substantial support for MEMGs. The price and subsidy policy
also accelerates the development of multi-energy systems.
In this market mode, the grid serves as an infinite
bus that can balance the power mismatch in an MEMG.
This also gives much flexibility to the design and operation
of an MEMG. The owner of the MEMG does not need
to consider the problem of energy curtailment.
MEMG-to-User Market
This scheme applies to MEMGs with both grid-connection
and islanded modes. In the grid-connection mode, users
have two options: buying power from the MEMG or the grid,
which leads to a more complex pricing mechanism. The
owner of an MEMG needs to bid a proper price to maximize
its own profit. In the islanded mode, the capacity planning
of an MEMG is the most important task; it ensures the economic
efficiency and reliability of the system. The capacity
planning is mainly determined by the load demand. A large
capacity may lead to energy curtailment, which reduces
economic efficiency. However, a small capacity results in a
power shortage, which does harm to the reliability.
Figure 1. A word cloud for the Energy Internet and integrated energy
supported by the NSFC.
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IEEE Electrification Magazine / SEPTEMBER 2021
P2P Market
This scheme also applies to both grid-connection and
islanded modes. P2P networks exist widely in the field of
computer science for resource sharing, where computers
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