Growers dig deep for energy

New research has examined the potential to harness solar energy stored in the top layer of the earth's surface to warm vegetable-growing greenhouses, says one of the nation's leading horticultural bodies.

AUSVEG spokesman Michael Bodnarcuk said the process was known as geothermal heat pumping (GHP) and worked by drawing heat from the ground with a long loop of water-filled pipes buried under a few metres of soil.

"The technology involved in geothermal heat pumping is very exciting and could revolutionise the way the industry cultivates vegetables, in a manner which is both effective and environmentally friendly," Mr Bodnarcuk said.

Mr Bodnarcuk said that as water flowed it was warmed by heat retained in the earth from solar energy. The pipes then run through the greenhouse, regulating the temperature inside.

"This allows greenhouses to stay at a constant temperature without the need to continually run conventional, and wasteful, heating systems," he said. "In Europe and the USA, heat pumping has been used for decades as a conventional heating method. The system essentially acts as a reverse refrigerator, with the main exception being that it harnesses only natural and clean energy from heat stored in the ground."

Initial results found that, as well as providing clean energy, GHP also maintained "excellent vegetable growth performance".

The project, led by Jeremy Badgery-Parker, was funded by HAL using the National Vegetable Levy, voluntary contributions from industry and matched funds from the Australian Government.

"Through the use of geothermal heat pumping, greenhouses have been successful in maintaining steady temperatures of 18C, an ideal temperature for stimulating vegetable growth. As well as maintaining this temperature, for every kilowatt of electricity input into GHP, 4kW of heat energy are supplied back to the greenhouse, which is a very efficient rate of return," Mr Bodnarcuk said. "As the price of conventional fuels is continually rising, it is especially important that the vegetable industry considers alternate energy sources."