The objective of this trial was to evaluate the cost effectiveness of a simple means of providing supplementary solar energy for bulk barns. A group of sixteen gas fired barns was used, arranged in two rows of eight under a continuous common roof that includes the space between the rows. The barns are built of hollow cement blocks with common walls and hold twelve standard boxes each. The roof comprises 50 mm of insulation between two layers of corrugated iron and is painted dark red. There are two openings in the ridge centre line through which the fresh ventilation air is ducted down to the barns. The total roof area is 600 m².A light steel framework supports a sheet of 500 gauge transparent polyethylene above the roof; the gap varies from 150 mm at the eaves to 300 mm at the ridge centre line. Air is drawn in under the plastic at the eaves and passes up the slope of the roof into the vents.In the first year (1998) the system was only observed, but in 1999 continuous instrumentation was installed. This showed that despite some degradation and damage to the plastic the system provided 28% of the total seasonal heat requirement; a proportion of this derives from the recovery of heat lost through the barn structure. The saving in gas paid for the cost of the plastic sheet in nine days.