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Fig. 2: Overall system for decentrally organised energy management
© ISET, Kassel
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Energy management – centralised or decentralised?

How can decentralised power generators and loads be optimally integrated into the low-voltage grid in future? Is it better to coordinate them centrally or does decentralised energy management offer more advantages? These competing approaches are currently being examined in various research projects, whereby the focus is not on technical solutions but on whether and how the systems will be able to be integrated in the liberalised single EU market. In particular, the features of the market, such as discrimination-free grid access and the separation of grid operation and generation, must remain.

Centralised energy management

With a centralised energy management system, the bundling of various power generators in combination with storage facilities and loads creates, in an ideal situation, a ‘virtual power plant’. This has the same features as a large-scale power plant (see BINE Projektinfo brochure 2/2002): it can be centrally controlled on the basis of schedules and provides system services. It can also participate in electricity markets by bundling its capacities.

These advantages of centralised management also bring with them two disadvantages: the central control point represents a ‘single point of failure’, which means that it has to be securely designed with appropriate redundancy built in. In addition there is considerable communication expenditure in terms of issuing schedules and monitoring the plants online, with the complexity of the centralised optimisation growing exponentially with the number of generators and loads. Therefore in technical terms it is only sensible to implement centralised management for a small number of generators and loads, but not for hundreds or thousands of generators in the low-voltage grid.

In addition to these technical difficulties, legal problems arise in the liberalised energy market if, for example, loads and generators involve different owners. There are also no individual market participants who have access to both the grid and the power plant data in order to optimise the generation mix and grid management.

Decentralised energy management

Decentrally organised control of power plants and loads is more robust than centralised management, less complex and has fewer communication requirements – features which are particularly important in view of the large number of generators and loads. The decisions are made by decentralised energy management systems that can optimise the electricity generation and connect and disconnect loads. In order that these optimisation decisions optimise the entire system, they are controlled using key information such as feed-in and reference tariffs.

In the DINAR project, the researchers investigated the organisational and technical prerequisites required to optimise the behaviour of energy generators and loads through variable tariffs and automatic device management.

Projektinfo 02/2008:
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ISET, Uni Kassel