John Spears and SDG were the sustainable development consultants to the 2008 Beijing Olympics and consulted on the design of the Olympic Village, including two Zero Energy Buildings within it. The Zero Energy School reflects the past and the future of China. The thick compressed earth wall that wraps around the north side of the building represents the Great Wall of China. The glass structure on the south side represents the future and also incorporates solar PV panels. Those panels produce the power for the building and solar water heating panels provide hot water, in addition to acting as a greenhouse for growing plants and providing natural heating of the building. The thick earth wall on the north absorbs the heat from the greenhouse and helps heat the building at night. Shades help control the light and heat in the summer and vents open to ventilate the building. Natural cooling is provided by earth tubes buried in the ground that cool the ventilation air for the building with the natural coolness of the earth. Rainwater is collected from the roof to provide drinking water for the occupants. Dry, waterless composting toilets process waste into organic fertilizer for use in the plantings in the building. The building is designed like a living machine. It uses only natural energy sources and processes and requires no central power, water, or sanitation system.