Renewable energy – is it a ‘mission impossible’?
Innovations spark a light on the widespread use of various types of renewable energy in Hong Kong
With studies showing that more than half the electricity used in Hong Kong is currently generated by burning coal – while wind and solar energy account for less than 2 per cent of local consumption – concerns about global warming and environmental crises are reaching new heights.
What are the barriers to the widespread use of renewable energy in Hong Kong, as well as other parts of the world?
“Despite the adequate sources of wind and solar energy in Hong Kong, the low power identity of renewable energy makes it rather expensive,” says Tianshou Zhao, chair professor of mechanical and aerospace engineering at Hong Kong University of Science and Technology (HKUST) and director of the HKUST Energy Institute.
“At the same time, the intermittent nature of renewables presents an imperative need to develop large-scale electrical energy storage systems for integrating them to enable a stable and sustainable supply of energy, even on less windy and sunny days,” Zhao says. “Actually, the introduction of more than 20 per cent intermittent energy from renewable sources without the required storage could destabilise the grid, with looming threats of voltage increases and frequency fluctuations.”
Zhao, an internationally renowned expert in energy engineering, explains that the development of renewable energy in Hong Kong is still at an early stage. The primary task is to identify a pragmatic, convenient and cost-effective way to store renewable energy.
The HKUST Energy Institute aims to become a global leader in cutting-edge research, development and education in sustainable energy generation, storage, distribution and utilisation through multidisciplinary methodologies. It fully supports Zhao and his research group of 90 professionals in conducting studies into renewable energy technologies.
Believing that a genuine breakthrough in energy technologies requires an interdisciplinary approach, Zhao has been working on three innovative concepts in energy storage – fuel cells, flow batteries and lithium-air batteries – by bringing together the sciences of electrochemical technologies and thermo-fluids.
Converting the chemical energy from a fuel into electricity through a chemical reaction of hydrogen and oxygen without burning, the fuel cell is a clean, efficient and scalable type of renewable and an effective enabling energy for mobile phones, computers, cars, submarines, home electricity, military batteries and hospitals, as well as power plants with grid.
The real miracle is that it can boost the power density from around 30-50 mW/cm2 to about 200 mW/cm2, representing a four- to-sixfold improvement. This means it can store more power in a smaller-sized container, offering a more cost-effective, space-efficient energy storage solution. For example, a 5-cc fuel cell keeps a mini trolley running for 10 hours.
Nevertheless, Zhao stresses that there is still room for improvement in terms of the lifespan of a battery. “According to Bill Gates, all the batteries on earth can store only 10 minutes of the world’s electricity needs,” he points out.
In the search for an alternative with a longer lifetime, higher scalability and better cost-effectiveness, Zhao and his research group also focus on flow batteries. This is basically a rechargeable flow cell in which an electrolyte containing one or more dissolved electroactive elements flows through an electrochemical cell that reversibly converts chemical energy directly into electricity.
The third type of energy storage solution Zhao has been studying is the lithium-air battery, an all-solid-state, metal-air battery chemistry that uses oxidation of lithium at the anode and reduction of oxygen at the cathode to introduce a current flow. Its major appeal is its extremely high specific energy, a measure of the amount of energy a battery can store for a given weight. However, efforts are still being made to overcome snags such as low practical capacity, poor cycling performance and low round trip efficiency.
Fuel cells, flow and lithium-air batteries are all key storage devices, each with their own unique features for the use of renewables. But how soon will they be ready for wide application in Hong Kong in the pursuit of a sustainable future?
According to Zhao, fuel cells are already available on a small scale, while flow batteries may probably be ready for general use in a few years’ time. On the other hand, there are still several issues to tackle concerning the lithium-air battery.
Concerning the issue that the development of renewables in Hong Kong is lagging behind other parts of the world, Zhao emphasises that renewable energy is more expensive than traditional sources, and therefore requires more innovations to reduce costs. Research into renewable energy storage technology is clearly a key element in terms of the success of renewable energy development in Hong Kong.
“It is estimated that renewables can potentially provide 19.6 billion kWh per year to meet 43 per cent of the total demand for electricity in Hong Kong, but there is still a long road to travel if we want to catch up with the global pace in adopting renewable energy,” says Zhao, who hopes that the SAR government can produce a long-term vision on clean energy and provide investment to support the development of renewable energy technologies while formulating polices to raise public awareness about the benefits of renewables.
In order to ensure clean air and a stable climate for our children and grandchildren, we must make responsible decisions about our energy sources. Perhaps this is the principle that keeps “recharging” Zhao and his group in carrying out their research to overcome existing obstacles to renewable energy storage.
In September, Zhao was selected as a Highly Cited Researcher 2014 and 2015 by multinational mass media and information firm Thomson Reuters. This is the second consecutive year he has made the list, which includes some of the world’s most influential scientific minds.
In an important message to all researchers, as well as the new generation of scientists, Zhao says: “If you enjoy your research, you will be able to make one breakthrough after another.”