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Fig 3: Communication structure with BEMI
© ISET, Kassel

Fig 4: Market participants in the BEMI pool
© ISET, Kassel
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DINAR research project

In the concept developed as part of the DINAR project, the energy consumers and operators of decentralised plants become market participants who can supply or accept electrical energy in accordance with their current requirements (Fig 2). What were previously pure energy traders now offer additional energy services. The energy service company (ESCO) conducts a bi-directional energy trade between its customers and overriding energy markets such as the EEX electricity exchange, therefore acting as both energy supplier and consumer. Additional opportunities for marketing decentrally generated electricity include selling balancing energy or participating in the balancing energy market.

The ESCO supplies its customers with key information about variable consumption and feed-in tariffs, which are generated, for example, from the EEX’s current spot market price. These tariffs are issued via a central control centre to decentralised decision-making units, the Bi-directional Energy Management Interfaces (BEMIs). These respond by automatically connecting/disconnecting loads or decentralised energy systems and therefore minimise the electricity costs for the customer. Because the customer response to variable tariffs within the supply area can be relatively precisely forecasted, for ESCOs this procedure represents a reliable and – for the customer – transparent and flexible instrument for influencing the load and generation process.

instrument can be used, for example, to avoid having to restrict the electricity fed in from wind turbines or photovoltaic systems when these sources exceed the current load. If the ESCO were to artificially lower the consumption tariff, the ‘electronic energy manager’ in the affected grid section would respond by connecting loads. In future that could also include plug-in hybrid vehicles.

Bi-directional Energy Management Interface (BEMI)

For largely automated, decentralised energy management, the customers need corresponding hard and software to automatically connect and disconnect electrical loads and generators. For this purpose the researchers have developed a Bi-directional Energy Management Interface (BEMI), which, as a decentralised computer, replaces the conventional meter cupboard as part of the house connection (Fig 3). It receives key information from the central control centre, in particular the price profile for the following day. Based on this, the optimum utilisation schedule for all connected devices is calculated. These include loads such as cooling devices, hot water boilers, air conditioning systems, washing machines, dryers and, if available, power generators such as CHP plants. In future, systems with battery banks, charging equipment for electric vehicles and fuel cell heating devices could also play an important role.

A meter interface records the used and generated electricity and transmits this data to the central control centre. Recording load and generation data at 15 minute intervals makes it possible to calculate and pay for the optimised use of devices in respect to time also in the liberalised electricity market. Some devices, such as refrigerators whose internal temperature is monitored by the BEMI, can be controlled without the customer noticing. With other devices, such as washing machines, the customer must be informed of the planned use so that they have the opportunity to amend the schedule calculated by the BEMI. That is achieved with a standard handheld computer with WLAN, which the consumer uses to request information and modify the schedules and parameters.

The Web interface provided by the BEMI can also be used for remote accessing via the Internet. Consumption and generation data for the billing are transferred to a central server and presented there. The same applies to measurement values for the voltage, frequency and impedance for the grid monitoring, which are provided by the BEMI’s measurement and control interface (MSI).

Implementation and test operation

The BEMI was realised as a laboratory experiment as part of the DINAR project. For demonstration and verification purposes, two test households were assembled in the ISET’s DeMoTec laboratory (Fig. 1). These have various types of cooling devices and tumble-dryers, which are managed by the BEMIs. Two different kinds of CHP plants are operated in the test households to simulate heat requirement profiles. In order to separate the heat requirement and electricity generation time-wise, the plants are connected via storage facilities to the heat sink. The BEMIs also optimise the use of CHP plants with regard to the content of the heat storage tanks.

This system was continuously tested by the DeMoTec laboratory from July to October 2007, whereby the variable tariffs were transmitted from the EEX for one of the households and from the regional supplier, the Städtische Werke Kassel AG, for the other household. The management system enabled savings to be made, for example around 8% of the overall net costs for a cooling device per annum.

Applications

Potential applications for the BEMI system also include active energy management, which can be used, for example, to integrate fluctuating generation. In a simulated scenario, the load management was used with 6400 BEMIs for washing machines and refrigerators in order to balance out a feed-in deficit from photovoltaics and wind energy. Centralised medium and peak-load power plants are currently used for this purpose. With the BEMI management system, the necessary output from these power plants would reduce by around 30%.

Remote meter reading and grid condition monitoring also make it possible to incorporate smart metering functions and distribution network services. These functions help the distribution network operators run the grid and integrate distributed generators. They include monitoring the supply situation, improving the voltage quality and monitoring grid bottlenecks. To make this possible, a large number of the Bi-directional Energy Management Interfaces (BEMIs) must be bundled together by an overriding component. This ‘Pool-BEMI’ forms the technical interface between the ESCO and the distribution network control centres and is currently being developed.

The principle of decentralised decision-making is also used for the superordinate management. This means that the Pool-BEMI also does not directly decide on the use of decentralised generators and loads. It is intended, however, to extend the mechanism of variable tariffs used in the DINAR project so that the BEMI can supply the Pool-BEMI with information on available resources, for example potential generation sources, and thus play a more active role. The Pool-BEMI activates these resources with the help of price signals that are supplied to the BEMI as key information.

In addition, it is also connected to the distribution network operator and provides a technical interface for the distribution network services. The BEMI technology also enables decentralised energy systems such as photovoltaic systems and small wind turbines to be incorporated into the system as active units.

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Project coordination
ISET, Uni Kassel