Ma Yajun is a farmer in China's Shaanxi province, from the village of Qiqiao. Back in 2007 he developed and installed a simple solar water heating system onto his roof, made from a grid of 66 modified glass water bottles , all connected to one another and attached to his sloping roof. Each morning Yajun fills the bottles with water from a hose simply by filling the first one, and allowing the water to run through them all until there is enough for all his family to have a shower later that day. Because the surface area is so great compared to if he had filled the water into a tank, it takes a lot les sun to heat the water to a reasonable temperature.
During the day, the sun heats the water in the bottles. When at the end of the day, any member of his family wishes to have hot shower, he releases a valve which allowS the now sun-warmed water to run from the roof into the shower to which it is connected.
Already several other members of the village have asked him to install such water heating systems on their roofs.