Business as usual isn’t an option.
It is accepted far and wide that climate change is a genuine threat and that our emissions of ‘greenhouse gases’ is a significant contributor to climate change.
We need to find ways to reduce our emissions of greenhouse gases from electricity generation, heating and transport. University of Southampton is amongst many that are undertaking research to address these issues.
These research pages provide you with some background detail behind the latest research projects at University of Southampton that are related to transmitting electricity more efficiently.
Global demand for electricity will continue to increase in the coming decades. The U.S. Energy Information Administration’s United States International Energy Outlook 2016 (IEO2016) reference case, states that global generation of electricity will increase progressively from 2.2x1013 kWh in 2012 to 3.7x1013 kWh in 2040, making it the world’s fastest-growing form of end-use energy consumption[1] .
Although fossil fuels will continue to be major part of electricity generation, both developing and developed economies are making significant investments in renewable generation[2] . For example, in 2015, India set a target of 175 GW of renewable generation by 2022[3] . In Europe, the 2030 climate and energy framework set a 27% target share for renewable energy by 2030, with a view to reducing greenhouse gas emission by 40%, relative to 1990 levels[4].
Renewable electricity generation sources such as hydro, wind and solar have been used for many decades - these technologies are well proven although improvements continue to be made. However the infrastructure needed to transmit very large amounts of electricity from far distant and inhospitable locations to major cities and industry isn’t well established. Therefore plans include renewable sources of electricity generation on a large scale will have a major impact on electricity transmission systems.
The European Network of Transmission System Operators’ Ten Year Network Development Plan[5] forecasts around 150 billion euros of investments to upgrade the grid infrastructure so that we can exploit extra renewable generation. For example in Germany, the Südlink project will require the construction of 700 km of 500 kV underground high-voltage direct current transmission infrastructure from the north coast to customers in the centre and south of the country, in order to use electricity generated from offshore wind. High voltage subsea cables have been used sucessfully for a long time but land-based transmission grids such as the Südlink in Germany pose many challenges, including finding an economically viable way of insulating the cables.
High voltage, high power electricity transmission cables are usualyly manufactured using a central high voltage copper conductor which is insulated from the ground by a polymeric (plastic) insulation which, at present, is generally based upon polyethylene. The cost of copper on the London Metal Exchange on 27th July 2018 was 6250 USD/ton; in contrast, the recent cost of polyethylene has been around 1300 USD/ton[6] . When electricity flows through a cable, the copper conductor heats up, in the same way that the heating element in a kettle does, and this limits the amount of power that can be transmitted. One way around this, is to increase the voltage, so that the current that flows for a given amount of power is reduced. However, this then requires that the thickness of the electrical insulation around the conductor is also increased, which then reduces the ability of the cable to cool itself by conducting heat away from the conductor, through the plastic insulation.
A simple solution would be to increase the size of the conductor but, because of the cost of copper, this is economically unattractive. Perhaps there is a natural limit to the amount of electrical power that can be transmitted economically through a cable if it’s manufactured using polyethylene insulation materials.
The POLYMAT, NanocompEIM and CableSure research projects, funded by the UK Engineering and Physical Sciences Research Council and Innovate UK, try to understand whether there is a limit to the amount of electricity that can be transmitted, economically, and then to design better insulation materials so that more electrical power might be transmitted from remote sources of renewable generation to consumers more economically.
The aims of the research were to understand the factors that limit the ability of today’s materials to cope with the conditions that they will experience in the new high voltage, direct current electricity transmission systems. From this work we will be able to develop better transmission systems. The problems can be divided into materials issues, electrical issues and thermal issues.
The team focussed on modifying well-known insulation materials using ideas based upon nanotechnology. Nanoparticles are very small, less than 1/1000 of the diameter of a human hair in size. They are produced naturally in many different processes (e.g. burning a candle, volcanic eruptions) and are now used in applications ranging from sun screen to car tyres, because their small size gives them unique characteristics. In our projects, we set out to introduce nano-particles into different polymers in various controlled ways, in order to improve the behaviour of the composite material. We hoped to tailor the behaviour of the new system to fit the latest and future technological applications.
An ideal insulation material would be able to withstand the applied voltage without conducting any electricity but, in reality, this doesn’t happen. All materials conduct electricity to some degree and while we understand conduction in metals and semiconductors well, for example, we still do not understand how currents flow through insulators like polymers. The team aimed to improve understanding of this area. Prof Nick Quirke at Imperial College, London led this part of the project. He used advance computing techniques to study the behaviour of electrons in simulated computer analogues of real materials. Prof Alun Vaughan at the University of Southampton led the experimental theme of the work which involved manufacturing the new materials.
Insulation material should not conduct electricity, however increasing the ability of electrical insulation to dissipate heat will make the device more reliable. In a cable this means it can carry more electrical power for a given size of conductor. As copper is expensive this is, economically, very attractive. The CableSure project aimed to disperse nanosheets of the material boron nitride (thermally conducting but electrically insulating) within polymers. The aim was to increase the overall thermal conductivity while reducing electrical conduction. Since boron nitride is very expensive, to make this economically viable, it was essential that the boron nitride could be dispersed very efficiently. This required the boron nitride to be carefully modified. This work was led by Prof Gary Stevens of Gnosys Global, an SME based in Guildford, together with Dr Thomas Andritsch of the University of Southampton.
[1] International Energy Outlook 2016, Chapter 5. Electricity, https://www.eia.gov/outlooks/ieo/electricity.php, viewed 2/8/17
[2] U.S. Energy Information Administration, ‘International Energy Outlook 2016’ (U.S. Department of Energy, 2016), pp. 81-83
[3] India Infoline News Service, 2015: Megawatts to Gigawatts in Renewable Energy production’, http://www.indiainfoline.com/article/news-top-story/2015-megawatts-to-gi..., accessed 4 June 2017
[4] European Commission 2030 Climate and Energy Framework’, https://ec.europa.eu/clima/policies/strategies/2030_en, accessed 4 June 2017
[5] European Network of Transmission System Operators, Ten Year Network Development Plan http://tyndp.entsoe.eu/, viewed 2/8/17
[6] S&P Global Platts Petrochemical Index (PGPI), https://www.platts.com.es/news-feature/2014/petrochemicals/pgpi/ldpe, viewed 27/7/18