The planning of energy supply systems is getting more and more complex and involves increasing amounts of data. In the past, these data have been stored on the computer in simple text files, which were accessible via text editors. At present, powerful database management systems (DBMS) provide mature tools for handling data. However, these instruments are not yet widely used in the energy sector Therefore, sample solutions for two standard problems of energy planning are presented, namely, the management of time series and of technology data. In addition, the database structure of the energy-optimization model ecco is discussed in detail.