The trigeneration research laboratory at Newcastle University [Cedit: Mike Urwin]

Green 'trigeneration' system for off-grid homes

An innovative ‘trigeneration’ system fuelled entirely by raw plant oils could offer greener power for off-grid homes, farms and businesses.

The small-scale combined heat, power and cooling system has been designed by a consortium led by Newcastle University to provide reliable electricity, heating and refrigeration without the need for a mains connection.

Waste heat produced by the power generation system is used for cooling and heating while advanced electrical storage incorporated into the system that boosts efficiency and makes it more able to cope with the daily fluctuating demand for electricity.

“The challenge was to design a system that could simultaneously satisfy the more predictable needs for heating and hot water, as well as the wildly varying demand for electricity in a small dwelling,” said Professor Tony Roskilly, of Newcastle University,

“Our solution was to incorporate advanced electrical storage into the system, both batteries and the latest supercapacitors, combined with innovative system control.”

While Combined Heat and Power units that produce electricity from a generator and heat from the cooling system and exhausts have been used by large businesses for many years, on small premises turning on an appliance such as a pump or a kettle can increase the electrical load several fold in a matter of seconds making it hard to match the competing demands of electricity and heat.

Previous studies into domestic power often looked at average demand over long timescales, but by logging minute-by-minute energy use in households the team found that while in a typical UK house heating demand is largely stable, electricity consumption can hover around a 100W or so most of the day, but reach peaks of 7kW or more in a matter of seconds, and for just a minute or two.

The solution developed by the Newcastle-led consortium, which was funded by the Engineering and Physical Sciences Research Council (EPSRC) through the RCUK Energy Programme, is a generator that runs constantly at high efficiency, coupled to the electrical storage system so that it can meet sharp peaks in electrical demand.

Waste heat is captured and stored via hot water tanks for heating and hot water needs, while cooling for refrigeration or air conditioning via an absorption chiller can also be run off the waste heat.

The consortium, which also included researchers from University of Leeds, University of Ulster, and three Chinese universities, wanted the system to be both green and suitable for applications in the developing world, so they also demonstrated that the system can be powered by biofuels.

“We wanted to avoid running the trigeneration system using biodiesel or other highly-processed fuels from raw materials,” said Roskilly. “So instead, we developed a system for using the oils obtained from pressing crop seeds, like those from jatropha and croton.

“These crops can grow in harsh environments and on poor-quality land and so could be well-suited to providing fuel in developing countries, as cultivating them would not adversely affect food production. The potential demand for this technology in such countries is very large.”

In a follow-up study funded by the EPSRC, the Department for International Development and the Department of Energy and Climate Change, Roskilly is exploring how the trigeneration system can be used on small farms in the developing world to refrigerate and process food crops, to reduce post-harvest losses.

The Newcastle team are currently examining the long-term performance of the system running on ‘raw’ plant oils and are in discussion with manufacturers with a view to commercialising the design.   

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