IEEE Power & Energy Magazine - March/April 2021 - 47

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doubling of electricity demand from 35 to
70 TWh by that year.
As a result, the Danish power system of the
future is expected to be characterized by large
shares of intermittent renewable sources and
increased energy demand. These developments
lead to significant challenges. The gradual
phaseout of conventional power plants results
in lower rotational inertia and more volatile
frequency dynamics. Additionally, renewable
generation is less predictable compared to the
energy produced by conventional power plants,
leading to an increase in the system's balancing needs. Since these power plants have traditionally offered the bulk of power system flexibility and the required ancillary services, new
sources of flexibility are needed.
Demand-side management and the flexibility
of distributed energy resources (DERs), such as
EVs, stationary batteries, and heat pumps, can
be used to maintain the current high level of
security of supply, even in a power system that
is dominated by volatile renewable production.
Recent technological advances and cost reductions in information and communication infrastructure, sensors, and power electronics have
made DER control more economic and reliable. Commercial entities, called aggregators,
manage and control large numbers of DERs or
larger flexible loads to create new streams of
revenue by participating in the energy markets. DER characteristics make them suitable for providing a variety of power
system services and participating in various energy markets,
such as the day-ahead, intraday, balancing, and ancillary
services markets.
The Danish project EcoGrid 2.0 demonstrated how
demand-side flexibility can be used concurrently on different system levels by managing 800 flexible consumers who
offered services on both distribution and transmission levels. However, the distributed nature and the large number of
these resources compared to the traditional, highly centralized structure of power systems pose several new challenges
in power system operation.
While these new sources of flexibility can benefit the
system and increase the security of supply, their mass integration requires careful consideration of many issues. One

is the need for coordination between the transmission and
distribution systems. Another is the heterogeneity of the
technical characteristics of these new resources that can
result in various barriers in their integration in power system operation. Moreover, various reports and projects have
shown that the financial benefit to DER owners from offering flexibility to the power system is not sufficient for their
engagement. This means that motives that are not purely
financial must be found to convince owners to make their
flexibility accessible and/or use it for the benefit of the power
system. To overcome this, coordinated efforts to raise consumer awareness and engagement are required. The emergence of energy communities, the use of automation, reward
systems, user-friendly application programming interfaces,
and mobile applications along with governmental information campaigns can contribute to engaging asset owners in
utilizing their flexibility.
To enhance the security of supply, DERs and demandside management must provide power system services
within the reliability, accuracy, quality, and response time
criteria set by the system operator. Therefore, the aggregators of those resources, which act as an interface to the system and are responsible for service delivery, must ensure that
flexible resources meet those requirements. As presented
in the following section, a considerable research effort in
Denmark has focused on investigating control strategies,
monitoring techniques, communication issues, and aggregation and optimization models. As a result of those efforts,
many technical issues related to DER controllability have
been resolved, and the capability of DERs to offer power
system services has been demonstrated. However, the lack
of standardization in terms of prequalification, monitoring,
and validation for small and diverse resources is hindering
their potential.
An often overlooked aspect is that the functionalities of
the aggregators and not the individual resources should also
be prequalified, especially under extreme scenarios, i.e.,
information technology/communication failures, particularly warm or cold weather conditions, and so on. It is often
the case that the same types of flexible units participate in
power markets of different and, in many cases, neighboring
countries under different terms. This negatively affects the
business opportunities of aggregators who manage international portfolios and decreases the efficiency of the utilization of flexible resources on a regional or European level. To
this end, there are many efforts toward standardization in

By Jacob Østergaard, Charalampos Ziras,
Henrik W. Bindner, Jalal Kazempour,
Mattia Marinelli, Peter Markussen,
Signe Horn Rosted, and Jørgen S. Christensen
march/april 2021

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IEEE Power & Energy Magazine - March/April 2021

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