Most solar energy devices work better when they face the Sun. Computer-based solar tracking systems have therefore been developed to allow devices to accurately follow the Sun's trajectory in the sky or to keep them at an angle which maximizes output in various conditions, for instance, when there is cloud cover. Replace electronics and motors by mechanical hardware and you have passive, electricity-independent solar tracking, which relies on, for example, the thermal expansion of materials. Now, M. Natarajan and T. Srinivas from the Vellore Institute of Technology, India, report a weight-based tracker for solar thermal collectors, providing a compact design that minimizes tracking errors.
The system uses two variable tracking weights and a spring to control the motion of the collector; flow valves allow water to flow in or out of the weights, inducing rotation of the collector around its axis. For a collector 1.5 m long and 0.75 m high, the tracking load is up to 50 kg. The water can be re-used on a daily basis, and the flow valves are adjusted seasonally to match the Sun's apparent speed. While passive solar tracking systems are generally less precise and adaptable to fickle weather than active closed-loop trackers, the collector design used by the researchers does not require fine tracking. Such systems are useful in isolated settings and high insolation areas, and the researchers' design is also simple and low maintenance, offering additional resilience.