Global Issues

A solar mirror of whitening light

Imagine a beam of energy so powerful that it can melt iron or steel – or even titanium. Picture how it is formed to focus the heat from the sun – using a vast array of giant mirrors, high on a mountain range in Central Asia, with clear air and open skies above. And think of the temperatures it could reach, up to 3,000 degrees C, halfway to that of the sun’s surface.

This is what happens in Uzbekistan’s solar furnace, situated 50 miles east of the country’s capital Tashkent. It was built in the Soviet era as a source of heat to melt or test materials. It tested materials and equipment, and it was also used to develop advanced ceramic materials for high-tech industry. It was kept top secret, and indeed continued to be tightly guarded until 2009.

There are 62 great mirror systems – heliostats, spread out in eight terraces on a smooth mountain slope. They gather in the sun’s heat and focus it on a parabolic concentrator. A window in the centre of the concentrator dish enables the full force of the beam – around one full megawatt of power – to pour on an area just one metre in diameter.

Making ceramics

A ceramic is what you get if you take a non-metallic substance and fire it at a high temperature. Humans started doing this around 20,000 years ago with clay, turning it into pottery; another early ceramic was brick. The high-temperature firing turns the material into something hard – though often brittle – and resistant to heat or corrosion.

Today there is a demand for ceramics for a wide range of situations, and a continuing effort to develop new ones. In the clean and instantly adjustable heat, over 150 compositions of oxide material have been created, with metal ingredients ranging from aluminium to zirconium.

For the oil and gas industry, it can produce ceramic balls for coating with material to filter and clean gases; or ceramic pontoons to reduce oil evaporation in storage. For the electrical power industry, it can produce porcelain insulators and safety locks to withstand heavy currents. There are thread drivers for the textile industry and fireproof material for the chemical industry. There are infrared emitters used in the treatment of various diseases and the sterilisation of surgical and dental instruments. There are also abrasives for manufacturing.

Condensation

Research is carried on as well as production, with some of the investigations looking at the process of condensation, and at what happens when the rapidly-heated materials are cooled in the open environment, and how condensation streams develop.

Among the other research areas are the formation of ultra-dispersed particles under then impact of concentrated solar radiation.

Green hydrogen

The solar furnace can generate electricity by shining directly on to a photovoltaic unit, and the electricity produced can then be passed through water to produce hydrogen by electrolysis. This is the conventional way to make hydrogen, in a two-stage process.

But high-temperature heat from the furnace can also drive a series of chemical reactions that pull apart the hydrogen and oxygen atoms that are bonded together in water molecules. The chemicals are reused with each cycle of the process. It’s called thermolysis and it generates hydrogen directly from solar energy, in what is potentially a much more efficient energy conversion.

The sheer size and power of the equipment is also making it an attraction for an increasing number of tourists. With an average of 280 sunny days each year, the choice of location speaks for itself.

The power of the sun is described by Prof. Robert Walsh in Living with a Star on Saturday 3 September in the Phoenix Cinema, Kirkwall, at 11.30 am.

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