There must be a balance between the energy supplied and the energy consumed for proper function of the electricity distribution system. At the same time, thanks to environmental measures, more and more renewable energy sources (RES) are being integrated into the grid – photovoltaic and wind power plants can have large weather-related fluctuations in energy supply. These fluctuations place greater demands on the management of the balance in the distribution network and therefore the current approach in the Czech Republic to this issue is outdated. It needs to be modernized.

The current way of regulating the electricity network

Electricity in the distribution network is regulated based on specific values of operating parameters – voltage and frequency. When these parameters are changed in the network, it causes an imbalance between the supply and consumption of electricity. When such an imbalance exists, we have to regulate consumption or supply in a timely manner. There are several ways to do this:

Reducing or increasing the electricity supply

We address the problem of imbalance in the distribution network on the supply side. If more appliances start to consume electricity at the same time, we supply more electricity to the grid. On the converse case, we supply less electricity when there is less consumption. In theory, this idea is simple, but in practice it has some drawbacks. The main disadvantage is the inertial effect of major sources of electricity such as coal and nuclear power plants. The regulation of their power takes minutes and is in the order of units of percentages, but we need a response in seconds to maintain a reliable supply of electricity. Typically, it may not even be a case of increased consumption, but a failure of the supply of renewable energy source due to weather changes (e.g. photovoltaics or wind power). This method of regulation is therefore more suitable for hydroelectric power plants, which can react within seconds but account for less than 3% of the total energy produced in the Czech Republic.

Electricity storage

Electricity can currently be stored in the grid, for example, by means of pumped storage hydropower stations with an efficiency of 50-85 %, electrochemical cells in the form of various batteries and accumulators with an efficiency of 75-95 %, compressed air with an efficiency of 27-70 % or gas production such as hydrogen or methane with an efficiency of around 50%. However, the lower efficiency and high costs associated with the acquisition and maintenance of these storage systems do not favour their mass deployment.

System services

System services are the current answer to the immediate regulation of the balance in the distribution network. They are a combination of energy resources and energy storage. They take care of the continuous supply of energy according to specified voltage and frequency parameters. They influence the distribution network by means of rapid supply and withdrawal. Electricity that is fed to the grid comes from battery storage, diesel generators or pumped storage plants. At the same time, system services regulate the proportion of reactive power in the distribution network by connecting inductive or capacitive loads. However, this responsive component of distribution is very costly and not always completely environmentally friendly.

 

These measures imply that the current quality management of the distribution network, while functional, is economically challenging. Moreover, the financial impact will increase over time due to the inclusion of a larger share of intermittent renewable sources, which require a larger amount of backup energy in the functional distribution network.

Another disadvantage of the current situation is the location of energy sources far away from the consumption site. Therefore the distribution network is not resilient to interruptions in the transmission lines. In addition, locating power sources at the consumption site results in lower losses in the grid itself. Ideally, so-called microgrids are formed – groups of sources and consumption sites of electricity that are able to operate in connected mode to the distribution grid (on grid) or disconnected (off grid) also known as island mode operation. A microgrid often involves a single property owner, where energy consumption can be covered by its own resources and communication between energy production and consumption takes place within a single software solution. However, connecting multiple microgrids and the main grid requires advanced control mechanisms.

 

Picture 1. Central control of individual microgrids for interconnection of energy supply and consumption
Picture 1. Central control of individual microgrids for interconnection of energy supply and consumption

Smart grid as a solution

Smart grids use sensors and communication between the energy source and the energy consumer. The grid can supply exactly as much energy as is consumed at any given time. This results in higher efficiency and reliability of electricity supply. Ideally, the network can operate without system support services. The smart grid allows the connection of elements with significant fluctuations in supply or consumption, such as photovoltaic panels, wind farms or electric vehicle chargers. At the consumer level, the smart grid allows cost optimisation and switching on appliances when electricity is cheapest on the grid. Smart grids are also the vision of the EU, described in Directive 2019/944.

AXIOM in the smart grid

The principle of the smart grid is a system platform, integrating all measuring and control systems that are available, regardless of manufacturer or communication protocol. The AXIOM platform integrates all measured variables, based on which it can decide how to control the smart grid system. In addition, it enables compliance with the ISO 50 001 standard for energy management. With a simple user interface, two-factor authentication and the ability to assign different rights to each user to view or control smart grid elements AXIOM can be used by both the electricity supplier/distributor and the customer in the form of a company or individual.

Picture 2 AXIOM offers a quick overview of the efficiency of renewable energy sources
Picture 2. AXIOM offers a quick overview of the efficiency of renewable energy sources

Thanks to the interconnectedness of the smart grid system, AXIOM can give command for full charging of connected electric vehicles when the photovoltaic (PV) panels or wind turbines are fully operational. On the other hand, it will decide to diminish or completely shut down charging if other, more critical systems connected to the smart grid require power at that moment. Such digital interconnection of renewable energy sources with consumption can work not only for photovoltaic farms or large wind turbine farms but also for small sources such as PV panels on the roofs of houses or apartment buildings. In the context of a smart grid, there is no need for so-called peak shaving, which is the limitation of energy supply to only a contracted value. In reality, this means that when the PV plant is well lit, individual PV segments are deliberately disconnected to produce less energy so that the plants are not fined for supplying too much energy to the grid. The smart grid can use this overproduction of energy for local controlled consumption or battery storage. Connection to CHMI makes possible for the platform to predict in advance from weather forecasts which renewable sources will be or not available in the future.

AXIOM not only for Smart Grid

AXIOM is not only an energy management tool, but as an integration platform it can incorporate all systems that enable communication. It is a multifunctional platform for automating and controlling technologies within buildings, industrial facilities, machines or entire cities, districts and regions.

 

Tomáš Sedlář Smart Solution Consultant