Distribution Grid Energy Flexibility: The Ebalance-Plus Technologies Developed for the University of Calabria Demo Site ^†

Abstract

The integration of renewable energy sources is one of the principal issues of the electric power system. The ebalance-plus project to achieve this goal will implement and test a management energy platform and new business models. Such solutions will be tested in four demo sites located in Spain, Denmark, France, and Italy. The Italian demo site is considered in this paper. After the first part, in which the configuration of the Italian demo site is described, the technological solutions implemented to provide energy flexibility are listed.

1. Introduction

With the high penetration of renewable generation and distributed energy resources, the distribution grid is facing new operational challenges due to their intermittent characteristics and increased grid utilization. Local flexibility markets can provide opportunities for transmission and distribution system operators to cope with these challenges [1]. Indeed, the integration of renewable energy sources is becoming one of the principal issues of the electric power system. In this context, energy flexibility has been introduced as one of the most significant concepts in energy systems and accordingly, it has captured attention [2,3,4].

In this context, various frameworks have been defined to ease the energy flexibility and in particular, the associated market. Indeed, in [5], a new bidding and pricing mechanism for local markets taking into account the external energy and flexibility markets has been introduced. In [1], a review of the energy flexibility market is presented, starting from local flexibility to the DSO-TSO coordination to provide energy flexibility.

The ebalance-plus project aims to exploit the flexibility of distributed energy resources (DERs) and end-users using different market mechanisms in the power system. It is a research and innovation project action at the European level with the participation of 15 organizations from 10 different countries.

To achieve this goal, the ebalance-plus project will implement and test a communication and management energy platform (energy balancing platform) and new business and management models. The technical, economic, and social aspects are also considered.

The energy balancing platform is based on a hierarchical architecture composed of management units (MU) located in some grid domains (building level, DER level, secondary substations, and primary substations). The implemented energy balancing platform, algorithms, and MU solutions will be tested in four demo sites located in Spain, Denmark, France, and Italy.

The demo site in Italy will be implemented at the University of Calabria Campus (defined as UNC demo) and will involve some office buildings with the related photovoltaic plants installed on the rooftop of the same building and two student’s residences. At the same time, the MV/LV substations that supply the office buildings are considered. All the end users represent an integrating part of the same demo.

The Italian demo site integrates electric storage with communication interfaces and algorithms to support the balancing and reliability services, heat pumps to address power-to-heat, and smart-grid architecture to improve network capacity and avoid potential congestion risks.

It will be an opportunity to test several technologies with the goal to increase the energy flexibility of the distribution grid, increase distribution grid reliability, and design and test new ancillary models to promote new energy flexibility markets. These objectives allow unlocking the energy flexibility market in distribution grids to support end-users, distributed energy resources managers, and energy operators.

In the first part of the paper, the need of energy flexibility and the possible way to provide it are described, then, the structure of the UNC demo site and how the flexibility services can be carried out are presented.

2. Energy Flexibility: How to Provide It

There are various initiatives that intervene regarding the rules for participation in the markets and the methods of managing physical dispatching in real time to provide energy flexibility. Among the various proposals, there is that of introducing the possibility of participation in the markets of both production units and consumption units.

There will be new subjects responsible for the management of the various markets, although the TSO and the DSO maintain their role. The new subject, named aggregator, should represent the interface between the TSO and the end-users, communicating the profiles and providing services to the grid.

For this scope in Italy, mixed enabled virtual units (UVAM) have been introduced. They represent the experimentation of new resources and new dispatching services provided by the aggregation of individual end-users. They are characterized by the presence of production units, storage systems, and consumption units. Currently in Italy, the UVAMs are enabled to provide services such as congestion resolution, balancing, tertiary reserve, but the intention of Terna (the Italian TSO) and of the ARERA (Authority of Energy and Environment) is to experiment with the participation of UVAMs in other types of services, such as secondary regulation, and to gradually involve consumers in the tertiary one [6,7].

There are different ways to provide energy flexibility. It can be implemented both at the load level and at the generation level. Generally, it is preferred to avoid the variation of the electric load profile, therefore, of the end-user behavior, for which it is preferred to operate at the generation level or to use Energy Storage Systems (ESSs). In fact, the use of ESSs allows one to modify both the load and generation profile seen from the grid without acting directly on these profiles.

A well-known way in the literature to modify the load profile concerns the Demand Response, which requires active end-user interaction, or in any case, requires schedulable and interruptible loads. These loads can be remotely controlled according to different logics to pursue different objectives. It is possible to operate by reducing the maximum power absorbed by the grid, reducing power peaks, moving the electrical load in the hours in which there is higher production, or in any case, a surplus of power, or with other strategies.

If ESSs are not used, controllable loads are required, which can be scheduled over time. Considering the household environment, these loads can be smart devices, which allow them to change their work cycle, to be interrupted and resumed later. Among the various domestic loads, those that can generally be scheduled are appliances such as the washing machine, dishwasher, and heat pumps.

This also requires the collaboration of the end-user, who is willing to provide flexibility services, to program the different loads, making them schedulable throughout the day.

Flexibility services can be requested in different ways, but generally, they must be programmed, i.e., the day before the next one, both the load profile and the availability to vary the same profile must be known. This is necessary for the purposes of requiring flexibility.

The structure of the demonstrator has been implemented to be able to implement and observe what has been described and theoretically defined.

3. UNC Demo Site Configuration

The UNC campus includes a variety of buildings (laboratories and classrooms, administrative offices, a library, and student residence) that represent both electric and thermal passive loads. The campus is mainly supplied by an MV substation with a ring distribution grid in MV (the contracted power is of 8 MW) that feeds 28 medium/low voltage secondary substations. Currently, several renewable energy generation plants are operating, and some buildings and generation plants have been equipped with monitoring and control systems. The campus can be thought of as an aggregation of consumers, prosumersm, and producers.

It starts from the “Megacentrale”, which consists in the primary MV/MV substation, with the transformers, the medium and low voltage sections to supply all the UNC campus buildings, the office, and residential buildings, by a ring MV line. Among the office buildings, four buildings are included, considering those equipped with photovoltaic plants installed on the rooftop, named “Cubo 18B”, “Cubo 44B”, “Cubo 41B”, and “Cubo 30B”. The considered office buildings consist of buildings of different floors where students, professors, researchers, staff, and facility managers are present. For these buildings, a new lighting led system has been installed equipped with a lighting regulation system. Two of them will be selected to test smart storage at the building level. Among the residential buildings for students, the Monaci residential centre was chosen. It was equipped with a PV system. Five apartments were selected, applying a social criterion, that will be equipped with IoT devices to make them controllable and smart loads. Then, a building named “Chiodo2” was chosen, where a hybrid AC/DC microgrid has been deployed. It consists of three nanogrids installed and connected to a common DC bus operating as a unique hybrid AC/DC microgrid. This microgrid integrates two PV plants, one Stirling-engine mCHP, a lithium battery energy storage, several electric loads, and some controllable loads. Moreover, one heat pump with thermal storage was installed.

The Megacentrale and the secondary (MV/LV) substations, which supply the selected office buildings, are also involved in the UNC demo.

4. How to Provide Flexibility Services in the UNC Demo Site

The UNC demo site objectives are:

• Increasing the energy flexibility of buildings’ energy loads and their self-generation systems (e.g., RES plants and CHP);
• Testing smart-grid automation and control technologies to unlock the available flexibility provided and increase the resilience of the electric distribution grid.

The main objectives of the devices/upgrades that would be deployed are:

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Improve the control, automation, and communication (with the DSO/Aggregators) of primary substations;

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Improve the control, automation, and communication of secondary substations;

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Enable and improve the management of flexibility resources (m-CHP unit, PV plants, and electric and thermal storage);

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Test a demand response program and evaluate the responsiveness of the end-users using IoT devices and small smart storage units;

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Integrate the energy management system and flexible resources in the project platform;

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Increase office building flexibility using smart storage systems.

As part of the UNC demo, given the different involved structures, it will be possible to offer various flexibility services, depending also on the different use cases in which the UNC demo is involved.

Several ebalance-plus technological solutions will be tested: a customer management unit (CMU), distributed energy resources management units (DERMU), a low-voltage grid management unit (LVGMU), and a medium-voltage grid management unit (MVGMU). CMU and DERMU send the building’s and DER’s status, respectively, to the LVGMU, which is monitored by the energy ebalance-plus platform. Then, the energy ebalance-plus platform through the LVGMU collects and calculates the available flexibility by specific prediction models that are implemented. On the other hand, the MVGMU provides optimum voltage and reactive power regulation at the MV level and facilitates flexibility. In addition, smart-grid solutions are provided to increase the grid observability and allow the DSO to make better decisions on energy flexibility as an important value for grid resilience.

5. Conclusions

In the first part of the paper, a discussion about energy flexibility was reported, and the solution to provide such flexibility was described. Then, after a section in which a short description concerning the design of the UNC demo site was reported, the ebalance-plus technological solutions to be deployed in the UNC demo to activate the energy flexibility service was indicated.