Power to the people

Wentworth shire in rural Victoria may become the site of one of Australia's most ambitious engineering projects. A private company plans to build a 1 km high solar tower surrounded by a 5 km wide greenhouse to generate electricity to power up to 200000 homes. If it proceeds, the large-scale venture will be a commercial version of a 200 m tall, 50 kW prototype built near Manzanares, south-eastern Spain, in 1982. It ran with minimal maintenance for 7 years, delivering power night and day to the local grid.

The principles of solar tower technology are simple. Hot air is generated from solar energy in a glass or polycarbonate greenhouse surrounding the tower. Within the tower, temperatures fall by 1°C per 100 m of altitude, so the air at the top of a 1 km-tall tower will be about 10°C cooler than at the base. Heated air entering the tower from the surrounding greenhouse increases the temperature differential, so the hot air rises by convection, just like the updraught in a chimney. The rising air spins wind turbines mounted in the tower to generate electricity. At night, heat stored in solar cells during the day is released to continue heating air and powering the turbines. Although the capital cost of building a solar tower is high, the final product is non-polluting and very cheap to run and maintain.