Visions for the energy transition
Past president of CIGRE, Editor-in-Chief for CIGRE Science and Engineering (CSE) Journal
According to S&P Global [1] “Energy transition refers to the global energy sector’s shift from fossil-based systems of energy production and consumption — including oil, natural gas and coal — to renewable energy sources like wind and solar, as well as lithium-ion batteries”. Although this is rather simplistic the impact of renewables is present at all voltages in the network from low voltage (LV) to ultra-high voltage (UHV). In addition, the location of the renewable generation is variable and difficult to predict. It is also not always located at the load. The introduction of electric vehicles on a large scale introduces mobile resources with the location of the battery and load being uncertain.
At the advent of the renewable generation in the 1990’s the initial thoughts were that the development of the grid especially at the transmission voltage level, would not be necessary as each load would merely be supplied by its own renewable source of generation. This proved totally incorrect, and the opposite materialised with renewable generation being in remote areas where the presence of high solar radiation or wind was evident. The necessity of overhead lines increased as did the need for cables connecting offshore wind farms to the grid. In addition, the installation of solar panels on houses as well as storage has created power flow in the LV grid that was not present previously.
The other well-known issue is that inverter-based resources (IBR) provide energy but not the ancillary services required for stable grid operation. This has required innovative solutions by grid operators as well as developments of power electronics such as grid forming inverters to resolve the issue. In this respect, hydropower generation may play a fundamental role in terms of regulating system voltage and frequency, under the concept of large batteries.
Although the initial installation of renewable generation was subsidised, the expectation is that the momentum of installation of renewables is likely to continue and perhaps increase as the funding and requirements from industry for “clean” energy grows.
The advent of green hydrogen will somewhat change the landscape with renewables being used to produce hydrogen which is in turn used for transport, electricity generation and other chemical formulation. This concept, of renewables being used to produce other materials which is used for various applications, can be expanded, and allows for a truly non fossil fuel world. Other gases can be used instead of hydrogen in some applications such as liquid air or nitrogen which is used to drive a synchronous generator.
Digitalization advances are and will also become a fundamental instrument on the true implementation of the Energy Transition improvements.
With this background I would like to share my vision of the future grid.
The location of large-scale renewables is likely to remain in remote areas away from the load centres. This will require long transmission lines linking to hubs which will enable connection from the renewable generation sites to the load centres. The concept of a global grid has been studied by CIGRE and published in Technical Brochure 775 (TB775). This indicates that the technology is feasible. This links remote renewable sites to load centres in other areas or continents.
The Transmission network will also be required to connect the grid scale inverter-based resources (IBR) to the existing grids. The transmission line design will therefore range from low impedance ultra-high voltage lines to shorter thermally limited lines utilising high temperature and high temperature low sag conductors. These technologies together with real time monitoring linked with flexible AC transmission system (FACTS) devices will likely enable maximum power transfer catering for unknown generation capacity and future power transfer requirements.
The use of high-voltage DC (HVDC), merging of AC and DC systems and the expansion of the HVDC grid is likely to be used to optimise the operation and power flow within the grid. As the grid expands due to remote location of IBR, the national boundaries are likely to become blurred with power being exported from Africa to Europe, Asia etc.
The management of IBR on large grid operations will require large amounts of storage. Where pumped storage resources and locations become exhausted, large-scale storage will become necessary. This can be realised via battery technology reliant on inverters for grid connection or gas technologies such as liquid air or hydrogen which can drive synchronous generators thereby providing necessary inertia and fault level for frequency and voltage support.
The electrification drive or use of electrical energy to replace fossil fuels is likely to continue at pace. This includes transport, industrial processes, household applications, heating, cooling, etc. Storage used for these devices will enable excess energy to be used for charging during high IBR energy production and enable ancillary services to be provided when required using customer generation. This is likely to be available at all voltage levels.
The merging of distribution and transmission grid issues is likely to expand with inertia, fault level support, frequency support and advanced protection and operation methods being applicable down to the LV level. This will require smart devices linking and monitoring the internet of things for optimal grid design and operation. The end use customer is likely to continue to expand their role as an integral component of the future grid operation. Markets will need to ensure the correct investment and enticement of ancillary services is encouraged.
CIGRE has been proactive in the understanding of technology direction and has developed a future grid vision over the past 10 years. This has guided the Technical Committee in selecting topics for study and development. The future work has been identified and is summarised here:
- The issue of cyber security is paramount as devices become more and more internet connected. The information technology/operational technology (IT/OT) environments may become more blurred with clear strategies being required on security, architecture, and operations.
- The integration of power electronics at all voltage levels is an issue to be understood especially as the installation of these devices at the medium voltage (MV) and LV level may not comply to all the required technical standards.
- The challenge of intermittent IBR on operations will continue to be an issue until the advent of large storage and extensive storage at MV and LV levels can provide the required ancillary services.
- Protection of networks (including LV) with active components and varying fault levels will need innovative solutions.
- Planning of the network will require innovative solutions with load and generation being stochastic. The integration of HVDC grids and AC networks as well as the use of DC on MV and LV systems within AC systems will also require new ideas.
- The design of tools for analysis and modelling of the various components will need to be continually enhanced. This will also need to include power electronic devices at the MV and LV level in addition to the models used at the HV and UHV levels.
- The engagement with the end user is likely to become more critical as they are an integral part of the grid energy and ancillary service supply chain.
It is likely that expansion of IBR is likely to continue and accelerate. The use of the energy in producing gas (air or hydrogen) for use in transport and industry will enable the evolution of energy being entirely sourced from renewable sources. The development of power electronic devices enabling inertia support with storage will enable increased penetration of IBR in existing networks.
The energy transition is an exciting prospect that challenges the existing paradigms and allows for development of existing innovations never thought possible. It is indeed an exciting time for engineers in all spheres. Organisations such as CIGRE is critical in resolving these issues enabling experts from around the globe to solve common problems.
Thumbnail credit: Photo by Bruno Figueiredo on Unsplash
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