Micro-machining technologies could allow solar panels to wear contact lenses, enhancing their electrical efficiency.

Researchers in China say the Fresnel lens – a cheap alternative to conventional lenses – could be used to focus the light going into solar panels, considerably increasing their efficiency.

Fresnel lenses were invented by French engineer and scientist Augustin-Jean Fresnel. They are essentially two-dimensional equivalents of conventional optical lenses, but they have ridges in concentric rings that focus the light to a point behind the lens, without the precision machining required for a perfectly curved lens.

The lenses have never taken off in photography because the concentric rings mean that some light is not focused at the gaps between the ridges.

The Fresnel design has key advantages though, as it is cheaper and easier to produce, and can be used to significantly reduce the depth of the lens compared to a standard convex lens.

In the area of solar panels, researchers have attempted to use bulky and cumbersome parabolic reflectors to boost efficiency.

Now a team from the State Key Laboratory of Precision Measuring Technology & Instruments, at Tianjin University, in China, is developing a technology that allows them to craft an array of microscopic cones, rather than concentric ridges, to achieve the same effect.

The cones focus incident light to a point at a more precise depth on the photoactive layer in the panel.

Initial tests with a precision-machined Fresnel solar collector showed that researchers could obtain a peak power four times that possible with a standard panel at low resistance.

The difference in power falls off quickly as the device's resistance rises, which happens as it gets hotter under sunlight and as a by-product of its generating electricity. However, the difference is enough to boost electrical output enough to offset the additional cost of the Fresnel collector, so that the overall cost of solar panels can be reduced.

Use as simple addition to older, less efficient solar panels, Fresnel’s idea might also make them viable for applications where modern devices of higher efficiency are not commercially viable.

The results of recent tests are accessible here.