Biogas power made easy

Biogas power made easy

Stephan Heubeck, NIWA, with the biogas-powered generator. (Photo: Rupert Craggs, NIWA)

NIWA research is demonstrating how easy it is for farmers to generate electricity from biogas.

A simple DIY job

It took less than two hours to convert an off-the-shelf generator to run on biogas at Dexcel’s Scott Farm, near Hamilton in the Waikato. Equipment with a total load of 9–10 kW ran happily for over two hours on electricity from the generator. And, unlike petrol or diesel, there was almost no black soot or odour. The total cost of conversion, including labour, was under $500.

The biogas was collected using a small (25m2) experimental cover on the anaerobic pond of the dairy farm’s effluent treatment pond system. "The biogas contains 70–80% methane," says NIWA scientist Dr Rupert Craggs, "and after you recover the energy, you still have a nutrient rich effluent to spread on pasture."

Keeping costs down

"At the moment it looks like you need a herd size of about 1000 cows, but smaller farms would be economic if you are collecting waste from feed pads or wintering pads," says Rupert Craggs. "The two main costs are the generator (which many farmers own already) and the cover for your ponds. Much of our research has focused on improving the efficiency of anaerobic digestion in ponds to make them smaller and therefore less costly to cover. Our next step is to trial a low-cost cover on a full-scale pond designed to promote biogas production."

Technology uptake: key to climate change mitigation

Collecting biogas from wastewater is not novel. Most large domestic wastewater treatment plants do it, and there are existing farm-based technologies but these are not cost-effective. NIWA’s research attempts to bridge the gap between technology development and technology uptake; an essential step in tackling New Zealand’s relatively high agricultural emissions.

NIWA gratefully acknowledges the expertise of Entec Services, Auckland, in advising on generator conversion, and funding from the Foundation for Research, Science & Technology.

See this related project.