Hopes are high of developing free energy by utilising heat given off by composting green waste, writes Dick Ahlstrom.
Something for nothing is nice if you can get it, but particularly when it comes to a supply of energy. Researchers at Galway Mayo Institute of Technology hope to achieve this attractive financial equation by capturing unused energy given off by decomposing organic material.
Brendan Allen is a research scientist and project manager in the research section at GMIT. He and his group recently received €225,000 from the Department of Agriculture and Food to develop methods for maximising heat output from green compost and from slurry and trapping this for space heating.
"We are using compost and trying to optimise that heat at a farm-based level and at a municipal level," Allen explains. "We are coming up with technology to maximise that heat and use it in horticultural tunnels."
The large plastic and frame greenhouse tunnels are in regular use by farmers across the state. They are typically heated using electricity or gas, but are expensive to operate.
"The tunnels lose heat at a phenomenal rate. They are too expensive to heat during the winter," says Allen. Yet they only have to be kept at between 17 and 23 degrees to be useful and a heat supply taken for free from the composting process could provide the answer.
Two master's degree students are studying the composting process, how much heat is being produced and how it might be recovered. Green plant waste is being tested, with the students using standard wheelie bins to find the best mix of green materials to boost heat production. "We are also going to look at aerobic digestion of slurry," adds Allen.
He knows significant heat is given off during composting, having once measured the centre of a green compost heap at 60 degrees.
"It can get that hot in the centre. There is a lot of heat there but it is being lost to the air. If you get the composting vessel right and the ingredients right we could use that heat for some useful purpose like heating a horticultural tunnel."
The ingredient mix could be important, he believes. The students will assess how critical the green plant mix is and what might be added to boost heat output.
He assumes that some form of heat exchanger based on piped circulating water will allow the heat at the centre of the compost to be taken out and put to productive use. "We are trying to get the maximum heat without damaging the compost making process."
The result will be usable compost to improve soil and productivity, but also an extended growing season when using difficult to heat tunnels.
The initial designs for this two- year research project will be used to set up a pilot system based on composting that can provide a low level of heating in a tunnel. Allen isn't limiting himself to this application however.
"We want to see how far we can take this," he suggests. Towns and cities produce large volumes of green waste from trees, grass and hedging. Large scale composting plants might be able to produce enough heat to partially warm an entire building.
This represents a saving even if the building gains 50 per cent of its heat from composting. "If you could tap into that heat it will save on fossil fuel costs," says Allen.
The students got going on the research last month. "By the summer we will know a lot about the composting process and how to maintain heat levels." He believes that they will have a working system to test by next winter, when the cost of heating a tunnel using gas or electric becomes too high.
The research is also supported by Galway County Council and by Cáit Curran, a local organic horticulturist. Most of the composting and prototype work will take place at the Mountbellew Agricultural College, a partner college with GMIT. Any laboratory work will be conducted in GMIT's Dublin Road campus.