Christiaan Huygens College is the first CO2-neutral, plus energy school in the Netherlands. Thanks in part to the Energy Roof used in its construction, the school building designed by RAU generates more energy than the school needs for its own use. This surplus energy will be used in the adjoining sport hall and nearby apartments by Trudo housing corporation. The energy costs saved by all three buildings together amount to 130,000 euros a year.The new building of the Christiaan Huygens College uses a compact construction in order to limit the surface area of the façade, thus reducing excess heat in summer and heat loss in winter as much as possible. “As a result, the Energy Roof is able to work to its fullest capacity,” says Thomas Rau. At the same time, well-insulated windows allow natural daylight to flood the building without causing overheating.The Energy Roof was developed by SolarTech International in cooperation with Volantis and Eindhoven University of Technology. It is a thermal system based on solar power, which uses an evacuated tube collector with a heat exchanger which is invisibly incorporated into the insulating layer of the roof construction. The tube collector is covered in synthetic roofing material with an integrated layer of photovoltaic cells that generate electricity. During peak hours, the system produces more energy than the school, the sport hall and the adjoining homes need. That surplus is stored in an underground water bell storage system. In the winter, this energy can be brought back up to heat the buildings.As Thomas Rau explains, “Simply using high-tech tools is not enough. The client and the architect need to direct an intense collaborative process, in which consultants, engineers and suppliers and all the expertise they contribute are closely involved in the development from the very first sketch.”