Tapping more solar

Tiny pillars with dimensions on scale of billionths of a metre could spell cheaper and more efficient solar cells, according to researchers at Lawrence Berkeley National Laboratory and the University of California at Berkeley.

Unlike conventional solar cells, nanoscale pillars offer a much larger surface area for collecting light. They are more sensitive to light and hence more efficient at converting collected light to electricity.

A new and more controlled method of producing large-scale arrays of highly-ordered nanoscale pillars of cadmium sulphide on aluminium, with a thin coating layer of cadmium telluride, holds promise. The pillar array showed an efficiency of 6%. Higher performance and simpler fabrication is possible say the team of researchers who believe nanopillar arrays are a new path to versatile solar modules.

Cool Energy, a startup based in Boulder, CO, is developing a system that could help make solar energy competitive even in relatively dark and cold climates.

The company's system combines a conventional solar water heater with a new Stirling-engine-based generator that it is developing. In cool months, the solar heater provides hot water and space heating while in warmer months, excess heat is used to drive the Stirling engine and generate electricity.

The system is designed to provide almost all of a house's heating needs. But the generator, which will produce only 1.5 kilowatts of power, is designed to work with power from the grid, although the power is enough to run a refrigerator and a few lights in the event of a power failure.

The company's key innovation is the Stirling engine, which is designed to work at temperatures much lower than ordinary Stirling engines. In these engines, a piston is driven by heating up one side of the engine while keeping the opposite side cool. Ordinarily, the engines require temperatures of above 500 °C, but Cool Energy's engine is designed to run at the 200 degrees that solar water heaters provide.

Stirling engine's efficiency is limited by the difference in temperature between the cool and hot side. Typically, reaching the necessary high temperatures using sunlight requires mirrors and lenses for concentrating the light and tracking systems for keeping the concentrators pointed at the sun.

To make a practical Stirling engine that runs at low temperatures and doesn't require concentrators, the engineers addressed the heat leak problem by using materials that do not conduct heat. Like plastics and ceramics.

The third prototype is expected to raise efficiencies and also cut costs.

Any reason why this won’t work?