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Managing energy

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Energy Global,

Ratimir Brester, Product Owner, and Vivian Bullinger, Product Marketing Management, Solar-Log GmbH, Germany, explore energy management systems for increased grid stability as more sectors electrify.

In the course of the energy transition, the global demand for electricity is increasing. The electrification of sectors, especially within heating and mobility, are two factors that play a decisive role in this. In order to meet the rising energy demand, the supply of electricity – ideally from renewable sources – must be expanded and the ap-propriate grid infrastructure must be in place. This poses some challenges for all parties involved, energy producers and grid operators, which are solved with feed-in management and so-called energy management systems, among other things.

New requirements to ensure grid stability

The electricity grid used to be a one-way street of a few central large power plants whose energy flowed to many consumers. Today, consumers have become so-called ‘prosumers‘ (producers and consumers) who both purchase and feed in electricity. The increase in generation plants has made the core task of grid operators – maintain-ing grid stability – more complex. In order for the interaction between the decentralised ‘prosumers’ to function smoothly and grid stability to be maintained, feed-in management is needed. This places controllability requirements on each ‘prosumer‘.

Simple feed-in management – limited feed-in (x-%)

The regulations or requirements of feed-in management differ in their complexity. As a rule, this means that the larger the plant, the more complex the requirements that the plant must fulfil. These requirements are implemented with the help of energy management systems, such as the Solar-Log energy manager.

A simple feed-in management system with a fixed power allocation, e.g. 70% of the installed power, means that the system automatically regulates itself to x-% of the system power. This measure ensures that in the event of an energy surplus, an excess of electricity does not flow into the grid and cause an energy overload. This can be implemented in very different ways, from direct x-% specification via control devices of the grid operator to independent regulation to x-% at the grid connection point, taking into account production and local consumption. The latter has the charm that it covers the local demand for energy as best as possible with locally produced energy and thus relieves the grid not only in terms of feed-in, but also in terms of consumption.

A central function of the energy management system is therefore to limit the x % feed-in to the grid. In many countries, fixed or dynamic power limits are now prescribed. This limit can be flexibly set for different threshold values. In this way, different requirements (70% regulation, 50% or 60% regulation with storage promotion, 0% regulation in Spain, etc.) can be served.

In practice, a bidirectional measuring device is usually installed for this purpose, which records the energy flows at the grid connection point and transmits this information to the energy management software (EMS). In practise, a controller responsible for the EMS evaluates this information and regulates the energy flow from a power source, for example the local photovoltaic (PV) system.

However, it can also happen that the grid operator sends a control specification via its controllers and regulates the system to this value. Depending on the size of the system and the installation location, the specifications can vary greatly, as the grids have grown historically.

Interconnection control – PV power plants

The larger the PV plant, the more complex the implementation of feed-in controls becomes. Especially in PV power plants where many inverters come together, the demands on the EMS increase.

In order to reliably implement feed-in management for plants of such sizes, several energy management devices are linked together via an Ethernet network. Through this networking, the control signals of the grid operators can be exchanged among each other. With Solar-Log, such complex architectures can be realised via the interconnection control principle. Here, the signals from the grid operator are received at the master EMS and distributed to the connected inverters via the slave EMS. For this system architecture, the Solar-Log System allows the master to be coupled with up to nine slaves in the network. By networking the EMS, complex requirements (several plant sections and feed-in points and many different inverter manufacturers) can be implemented.

By using the interconnection control license, it is also possible to divide the system for direct marketing. By using slave units, the system is divided into areas. A separate direct marketer can then be selected for each area. Any reduction commands from the direct marketers are prioritised with the commands from the energy suppliers and documented accordingly. This makes it possible to implement a wide variety of scenarios and react to the respective needs on site.

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