Tecsol has been active in the research and development of telemonitoring for thermal solarsystems over the last 15 years. Performance monitoring was considered to be an essentialpart of the guaranteed solar performance concept that the company proposed in order ensurethat collective solar systems were both technically and economically viable.During this technical development period, the telemonitoring tools were greatly improved andsimplified. First of all the solar system management functions were linked to data collection, makingit possible to detect failures in the working order, and this led to the notion of preventivemaintenance by means of warning signal emissions. The next major step was the use of the e-mailprotocol for data transmission and finally, the Internet for world wide display. Each step in themonitoring process has been tested, simplified and approved, making it possible to propose apermanent monitoring tool at a low cost.