By Alexandre Oudalov, Manager of the Power Systems of the Future, Hitachi ABB Power Grids
Delivering renewable energy to where it is needed
Governments around the world are facing a monumental challenge: a massive increase in renewable power production capacity will be needed to meet legally binding climate targets –how to deliver this huge wave of primarily variable electricity to where it is needed in a timely, efficient and reliable way?
The answer lies within the world’s power networks.
Advances in electricity transmission technology will allow us to connect the highest quality renewable energy sources with end consumers – from desert solar to Arctic winds, and powerful rivers to faraway oceans.
Connecting from west to east shifts peak demand and solar production times, while linking north and south will enable us to balance the varying electricity demand profiles of hot and cold or dark and light seasons.
Expanding the capacity of existing interconnections and adding new connections to link isolated electric power systems and remote renewables to deliver a broad range of social, environmental and economic values.
So how will this ‘bridging’ be possible?
Two or more power systems can be interconnected and operate synchronously – at the same frequency, using HVAC (high-voltage alternating current) transmission lines or asynchronously, keeping their own frequencies, using HVDC (high-voltage direct current) converter stations and lines.
The advantage of synchronously interconnected power systems is that they can remain stable while integrating gigawatt-size power plants. Scaling up and pooling generating units results in lower generation cost. Sharing reserves within a synchronous area reduces the system operating cost
HVAC transmission lines are typically a preferred choice for shorter distances of a few hundred kilometers and when interconnecting power grids with compatible frequencies. Longer HVAC transmission distances are possible; however, they require special reactive power compensation which makes it more costly.
Enlarging the size of synchronously interconnected system increases complexity, vulnerability and cost. That is where DC technology comes into the spotlight and helps to overcome the fundamental limits of utilizing AC technology for:
- long-range power transmission via overhead lines;
- short- and mid-range subsea connections between countries, islands and offshore energy sources; and
- connection of regions with incompatible frequencies.
Maximizing the power of interconnection
HVDC transmission technology has been used for decades for efficient bulk electricity delivery over long distances and the interconnection of asynchronous grids running at different frequencies via back-to-back stations or subsea cables. It has benefited millions of consumers around the globe.
Technological innovation in valves and processors for control systems has unlocked almost unlimited possibilities for managing electricity networks with a high share of renewable sources, with lower inertia and greater feed-in variations than ever before.
The true power of HVDC interconnectors is demonstrated when providing various dynamic grid support services to enhance system stability and resilience.
In addition, fully controllable and flexible HVDC interconnectors can effectively limit short circuit currents and help to restore power supply following system-wide blackouts.
One great example of an effective combination of power trading in the expansive region of southern Africa and the stabilization of weak AC power networks is the Caprivi Link interconnector, which joins Namibia and Zambia’s electricity grids. The 950-kilometer overhead line ensures reliable power transfer capability between the eastern and western regions of the Southern African Power Pool and Voltage Source Converter-based HVDC technology helps to stabilize these weak networks and prevent blackouts under critical contingencies.
Connecting the dots
The carbon-neutral energy system requires us to connect all the dots, including:
- local and remote clean energy sources;
- diurnal and seasonal energy storage;
- more electrified mobility and heating loads; and
- sites where excess renewable electricity can be converted to clean fuels in applications where direct electrification is impossible or economically not feasible.
A high level of interconnection will enable society to exchange and use clean energy at the highest levels of efficiency, resilience and reliability.
It is crucial that the foundations – specifically, the short-, medium- and long-distance interconnections – needed to accelerate us towards a carbon-neutral energy system, are laid down now. The technology is proven, but trust is also needed to build these cross-border links. Now is the time for deeper collaboration with and across regulators and policymakers. The combination of technology and trust will enable countries to reach their carbon-neutral goals.
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