Combined heat and power (CHP) generation systems are well established in municipal and industrial settings, but one day it is hoped that homes could have their own domestic electrical energy storage system, providing heating, power, refrigeration and air conditioning.
The universities of Leeds, Newcastle and Ulster are collaborating with Shanghai Jiao Tong and Guangxi universities and the Beijing Institute of Engineering Thermophysics in China to develop a biofuel micro-trigeneration system, which will include a cryogenic-based energy storage system.
‘The whole system has a generator which will produce electricity for domestic use. It will also generate waste heat, which will be used to provide heating, hot water, and to heat or convert the cryogen in the energy storage system,’ said Leeds University’s Prof Yulong Ding.
The system will take in surplus electricity during off-peak hours and use this to help produce a cryogen from a gaseous input, such as air. By producing the cryogen, the system is therefore storing energy. During peak demand, the system expands the cryogen (waste heat from the generator heats the cryogen) to convert it into a liquid and release the stored energy, generating electricity in the process.
When the cryogen is expanded, the system will also release very cold gas that can be subsequently used for purposes such as adsorption refrigeration. An adsorption refrigeration cycle does not use any mechanical energy, only energy from heat; that is, it absorbs the waste heat to produce energy for refrigeration.
‘That very cold gas will be used for refrigeration and in summer, also for air conditioning. In winter the refrigeration system will also generate heat, which will be combined with waste heat released by the generators [to provide heating and hot water]’ said Ding. ‘So the whole system really can work in summer and winter.’
There is no combustion process involved in the cryogenic energy storage technique, as there is in compressed air energy storage systems. This, claim the researchers, adds to the environmental benefits of the proposed system. Furthermore, they hope to use biofuels to power the system’s generator.
‘The system will certainly help with combating CO2 emissions because it can use biofuels or renewable energy, and possibly we will have a very low temperature system and we can sequester CO2 for other uses or for deep-sea storage,’ said Ding.
At the research stage, the engineers will use biofuels such as vegetable oil in a piston-based (rather than turbine-based) diesel engine generator. But Ding emphasised that the system will not be wholly dependent on biofuels.
‘In my view, there probably won’t be sufficient supplies of biofuels, so you can use other renewable fuels, such as solar or wind power,’ he said.
Ding added that the new system would also be useful to address one of the main problems of using renewable but intermittent sources of energy, such as solar and wind power, by storing the energy and releasing it when required.
The researchers hope to have a prototype system built by 2011. It will be aimed primarily for use in the home, but it may be scaled up for use in industrial-based environments.
The £1.4m project will be supported by the UK’s New and Renewable Energy Centre (NAREC) and two Chinese companies — steel business Angang Group and cryogenic machinery manufacturer Sichuan Air Separation Plant.
An international team plans to develop a biofuel micro-trigeneration system, which will include a cryogenic-based energy storage system.