Energy & Power
Tri-generation system promises greener power for off-grid homes
By Anthony Capkun
July 30, 2014 – A “tri-generation” system fuelled entirely by raw plant oils could have great potential for isolated homes and businesses operating outside grid systems say the people behind a small-scale combined cooling, heat and power system, which has been designed to provide “dependable electricity” without requiring grid connectivity.
Developed by a consortium led by Newcastle University (including researchers from University of Leeds, University of Ulster and three Chinese universities)—and funded by the Engineering and Physical Sciences Research Council (EPSRC) through the RCUK Energy Programme—the waste heat produced by the system is used for cooling and heating, thereby recovering the maximum amount of energy.
“The challenge,” explained professor Tony Roskilly of Newcastle, “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. Our solution was to incorporate advanced electrical storage into the system—both batteries and the latest supercapacitors—combined with innovative system control.”
Before designing the system, the team logged the minute-by-minute energy use in households. In a typical United Kingdom house, for example, heating demand is largely stable when hot water and space heating is required. In contrast, 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 consortium is a generator that runs constantly at high efficiency, coupled to the electrical storage system so that it can match sharp peaks in electrical demand when required.
A domestic-scale tri-generation system of this type would be rated between around 6kW and 9kW, equivalent to the amount of power needed were the following domestic appliances to be switched On simultaneously: lighting, TV, fridge/freezer, kettle, microwave, vacuum, washing machine and dishwasher.
Waste heat is captured and stored via hot water tanks for heating and hot water needs. Cooling for refrigeration or air-conditioning via an absorption chiller can also be run off the waste heat.
“Energy storage unlocks the key to the most efficient use of the tri-generation system,” said Roskilly.
To make the system even greener, the team has shown the system can be powered by biofuels.
“We wanted to avoid running the tri-generation 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…”
PHOTO: Tri-generation research laboratory at Newcastle University. Photo Mike Urwin, Newcastle University.