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Small-scale trigeneration system offers hope for refrigeration in developing world

Newcastle University researchers believe system which runs on raw plant oils will offer potential for off-grid buildings in the UK as well as improving cold chain prospects in countries with intermittent power supply

Newcastle University researchers have developed a small-scale trigeneration system fuelled by raw plant oils which they believe could have great potential for off grid homes and businesses and for the developing world.

The consortium led by Newcastle University and funded by the Engineering and Physical Sciences Research Council (EPSRC)has developed the system for off-grid businesses, particularly farms, and for applications in the developing world. The team has incorporated advanced electrical storage into the system to make it more efficient and more able to accommodate fluctuating demand for electricity.

In a follow-up study funded by EPSRC, the Department for International Development and DECC, Prof. Roskilly’s team 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.

They 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.

A domestic-scale tri-generation system of this type would be rated between around 6 kW and 9 kW electricity (equivalent to the amount of power needed if the following domestic appliances are switched on at the same time: lights, TV, fridge freezer, kettle, microwave, vacuum cleaner, washing machine, and dishwasher).

The consortium also included researchers from the Leeds, Ulster, and three Chinese universities.

Energy storage is based on water heat storage and a hybrid battery and super-capacitor electricity storage system. Also research on a cryogenic energy storage system has been patented by Leeds University.

Project leader Professor Tony Roskilly of Newcastle University said: “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. Our solution was to incorporate advanced electrical storage into the system, both batteries and the latest super-capacitors, combined with innovative system control.”

They believe that the unit addresses the challenge of small-scale CHP, where turning on an appliance such as a pump or a kettle can increase the electrical load several fold in a matter of seconds, and where attempts to match the competing demands of electricity and heating or cooling can seriously undermine the units’ efficiency.

Before designing the system, the team logged the minute-by-minute energy use in households, knowing that previous studies had lost important detail by averaging demand over longer timescales. In a typical UK house, for example, they noted, heating demand is largely stable when hot water and space heating is required. In contrast, electricity consumption can ‘bobble around’ 100W or so most of the day, but reach peaks of 7 kW or more within seconds, and for just a minute or two.

The solution developed by the Newcastle-led consortium is a generator that runs constantly at high efficiency, coupled to the electrical storage system so that it can easily match sharp peaks in electrical demand when required.

Waste heat is captured and stored via hot water tanks for heating and hot water needs. Cooling for refrigeration or air conditioning is provided via an absorption chiller running off the waste heat.

Professor Roskilly said: “Energy storage unlocks the key to the most efficient use of the trigeneration system.”

To make the system even greener, and more appropriate for the developing world, the team has also shown the system can be powered by biofuels.

Professor Roskilly said: “We wanted to avoid running the trigeneration system using biodiesel or other highly-processed fuels from raw materials, so instead, we developed a system for using the oils obtained from pressing crop seeds.”

He said: “Crops like jatropha and croton 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.”

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