Success Story: EnBW Energie Baden-Württemberg AG

Development of an application for the implementation of the Renewable Energy Sources Act (EEG)

Company portrait

EnBW Transportnetze AG – Neutral authority within the electricity market
EnBW Energie Baden-Württemberg AG, headquartered in Karlsruhe, is the third largest German energy company with around five million customers. EnBW’s core activities focus on the business areas of electricity, gas and energy and environmental services.
EnBW Transportnetze AG operates the transmission network as one of EnBW’s core companies. In cooperation with other national and European transmission system operators, EnBW Transportnetze AG creates the basis for competition in Germany and Europe by making its extra-high voltage network available to all market participants on transparent and non-discriminatory conditions for the transport of electricity.
Within the EnBW control area of Baden-Württemberg and Vorarlberg, EnBW Transportnetze AG is responsible for the constant balance between electricity consumption and electricity generation. The control zone is managed in one of the most modern main control centres in Europe at the Wendlingen site. Here the grid is monitored around the clock with the aid of powerful process computer systems. In addition to network management, the network industry establishes the principles for the commercial use of the 380/220 kV transport network (extra-high voltage network) on the basis of the applicable national and international regulations. In addition, comprehensive tasks arise from the Renewable Energy Sources Act (EEG) and the Act on the Maintenance, Modernisation and Expansion of Combined Heat and Power Generation (KWK-Gmod).

Background: The EEG

The Act on the Priority of Renewable Energies (Renewable Energy Sources Act – EEG) has been in force since April 2000 and was amended in August 2004. The statutory objective of the EEG is to significantly increase the contribution of renewable energies (hydropower, wind power, biomass, solar radiation energy, etc.) to the electricity supply. To achieve this goal, the EEG regulates the following points in particular:

  • The priority connection of renewable energy installations to the general electricity supply networks.
  • The priority purchase, transmission and remuneration of the electricity generated by these plants by the respective grid operators.
  • The nationwide equalisation of the purchased and remunerated electricity.
  • The level of compensation for the electricity taken up with priority. The remuneration depends on the energy source, the type and location of the installation and the date of commissioning.

Figure 1
The tasks of EnBW Transportnetze AG in implementing the EEG

EnBW Transportnetze AG has a key role in implementing these legal regulations (Figure 1). As the transmission system operator responsible for the control system, EnBW Transportnetze AG is obliged to give priority to the purchase and payment of the energy volume received and paid for by the various network operators within the EnBW control area. The avoided network use fees, which are to be determined according to good practice, are to be deducted from the remuneration. Within the framework of the nationwide equalisation scheme, EnBW Transportnetze AG, together with the other transmission system operators responsible for the rules, is responsible for balancing and settling the energy volume consumed and the remuneration payments made for it among themselves. The electricity that subsequently remains in the network of EnBW Transportnetze AG is sold proportionally to all electricity supply companies that supply electricity to final consumers in the EnBW control area (suppliers). These electricity supply companies are obliged by law to receive and pay for the electricity.

The task

After the EEG came into force in April 2000, the tasks that this created for EnBW Transportnetze AG were quickly and successfully solved with the help of an MS Access application and MS Excel. However, the steadily growing share of renewable energies in the power supply, the associated increase in data volume, legal changes and the associated adjustments to organisational processes made it increasingly difficult and, in the long term, impossible to implement the tasks with the existing tools. The development of a new, comprehensive and future-proof application based on modern and reliable technology was preferable to adapting the existing solution under the given conditions. The requirements for the new application for the implementation of the EEG were thoroughly analysed and described in detail in a detailed specification sheet. The analysis was to take particular account of the new requirements in connection with the planned EEG amendment. Adjustments to the specification sheet were therefore necessary until immediately before the amendment came into force in August 2004.

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Within the scope of a Europe-wide tender, PTA GmbH was commissioned in September 2004 with the development of the new application on the basis of the present specifications. The new requirements in connection with the EEG amendment made it necessary to provide certain functionalities already in October 2004. Further modules had to be provided step by step in November, December and January. The modular structure and the need for the step-by-step implementation of the individual modules, some of which are very extensive, in a short sequence made the highest demands on project organisation, quality management and release management. However, through the close and trusting cooperation between the employees of EnBW Transportnetze AG and PTA GmbH and the targeted reinforcement of the PTA project team, a smooth and timely introduction of all modules could be guaranteed.

The solution

Due to the technical know-how available at PTA GmbH and the existing detailed specification sheet, only a few detailed questions remained to be clarified with regard to the technical requirements. During the technology selection and the technical design of the application, PTA GmbH worked out and implemented a concept in coordination with EnBW, which is closely oriented to the development guidelines of EnBW and fully takes into account the specific technical requirements. In concrete terms this means a distributed application (multi-layer architecture) using J2EE technology (Figure 2). The client is realised as a “rich client” based on Java Swing. It thus offers a wide range of possibilities that are controlled by the presentation layer directly on the client. The JDesktop framework developed by PTA GmbH is used to ensure processing according to the ModelView Controller pattern (MVC). The business logic is completely mapped on the application server. Session Beans control the process. The communication with the database is realised via JDBC and is controlled by the persistence layer on the application server. The SAP Web Application Server 6.40 is used as the application server and Oracle 9i is used as the database management system. The client is installed on a Citrix Metaframe Server.

Figure 2
Multilayer architecture and J2EE technology

Figure 3 
From “fat client” to “rich client

In order to ensure the smooth introduction of the modules within the tight schedule chain prescribed by law, it was initially decided not to physically separate the described logical layers (presentation, business logic and persistence). In the first implementation step, all 3 layers were installed on the client, which thus became a “fat client”. This meant that it was initially possible to do without the application server. Communication with the database was carried out directly between the client and the database server, whereby the client was also installed on a Citrix Metaframe server.
After the complete implementation of all modules, the complete application was then transferred to the desired architecture without risk in the second implementation step without the deadline pressure imposed by the legal regulations (Figure 3). The presentation layer could remain unchanged on the client. Only the interfaces to the application server (business delegate classes) had to be adapted. The persistence layer and the business logic were completely transferred to the application server. Session beans were implemented to control the processes on the server and specific data access objects (DAOs) were set up for data access. No changes were made to the user interface and the scope of functions as a result of this 2nd implementation step, so that ongoing operations were not affected at any time.


“The application realised by PTA GmbH represents a significant support for us in the daily operative implementation of the EEG with our market partners. There are several aspects to be emphasised in the cooperation with PTA GmbH that have distinguished PTA GmbH and its employees:


  • Sound expertise, which was successively expanded during the cooperation to include specific energy industry know-how.
  • High flexibility to meet the ambitious milestone plan, both in terms of staff deployment and the successive programming of the individual modules.
  • Intensive support during the entire course of the project, which was made possible above all by the physical proximity of the PTA office and proved to be optimal for this project due to the complexity of the subject and the changes in the scope of services resulting from legal and association-related changes during the project.
  • Convincing philosophy in the cooperation with the customer: cooperation that is as long-term as possible, which is translated into reality with the consistent transfer of know-how to the personnel required for application support and maintenance after the project is completed and with more extensive on-site support.”

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