Besides gathering data for later evaluation continuous monitoring is very useful. Errors are detected by self-analysis of the systems (plausibility checks of current measuring data, analysis of energy flow). Solar irradiance data measured by the system itself or data from the Internet are used for energy gain calculations. If there is a difference between calculated and real energy gains of the solar thermal system an error must have occurred: The Internet connection is used to send emails or SMS (short message service) for maintenance. Especially for solar thermal systems continuous monitoring is very important. Without monitoring system failures are imperceptible to the user because energy not gained by the solar thermal system is provided by conventional after-heating.

Conclusions

In future a great deal of homes will be equipped with computer and multimedia networks. Coming along with home networking more embedded systems with Internet connectivity will be used for controlling purposes. Bulk production will make the hardware affordable. Communication fees will be irrelevant. Remote administration and software updates of controller software via Internet will help to increase the efficiency of solar thermal systems. Breakdown durations of the systems will be minimized by self-analysis and automatic error message generation (email or SMS). With online visualisation and WAP-interface system control and error search is made very easy. Measuring data accessible via Internet enables external analysis of system performance to improve control algorithms. With more powerful controller hardware model based control algorithms will be feasible. They will help to increase energy efficiency.

Acknowledgement

We thank Projekttrager Julich (PTJ) and the Bundesministerium fur Wirtschaft und Arbeit (BMWA) for supporting this research work and RESOL (www. resol. de) for carrying out the embedded system.