Solar concentrator makes use of telescope mirrors

The University of Arizona’s tracker prototype supports two curved, highly reflective glass mirrors, each measuring 10ft by 10ft.

‘Most mirrors used in solar power plants are used for thermal generation by focusing light onto a long pipe used to heat water into steam,’ team lead Prof Roger Angel said. ‘This requires the mirrors to be shaped like a cylinder. What we have learned here at the Mirror Lab is how to bend the glass to high accuracy so as to focus to a point or a line.’

The US Department of Energy recently granted $1.5m (£964,000) to Angel’s research group to extend the mirror-making process to the so-called thermal method for making solar electricity. The mirror-making process will be optimised for cost-efficient mass production. The group has already patented its method for making dish-shaped glass mirrors.

The mirrors focus sunlight onto a 5in glass ball and from there to a small array of 36 highly efficient photovoltaic (PV) cells, developed originally to power spacecraft. They convert a broader range of the solar spectrum into electricity than regular cells.

The ball lens is coated to maximise transparency for the incoming rays. Angel said that an undergraduate student working in the lab, Ivan McCrea, discovered a new way of coating the lens for very high transmission.

Another student, Blake Coughenour, a graduate student in the UA’s College of Optical Sciences, is working on the optics to more efficiently couple the dish-collected sunlight to the cells.

‘Because we are focusing highly concentrated sunlight onto the cells, we had to design an effective cooling system for the cells,’ Coughenour said. ‘Otherwise, they would melt within seconds.’

A unit of fans and radiators is attached to the solar cell array, keeping them about 36^oF above ambient air temperature.

‘The tracker is fully automated,’ Coughenour said. ‘The system wakes itself up in the morning and turns to the East. It knows where the sun will rise even while it’s still below the horizon. It tracks the sun’s path during the day all the way to sunset, then parks itself for the night.’

In recent test runs, the prototype module generated 2.5kw of electricity, enough to meet the power demands of two average US households.