Contributed by Tony Morton, global technical head for power systems at engineering and technical consultancy, Vysus Group
Developers, operators, and regulators must work together to maximize connections in a renewables-rich environment. Electricity grids, and the renewable energy and battery storage projects that connect to those networks, are evolving so that they can meet net-zero demands while simultaneously maintaining and delivering power supplies in a safe, secure and reliable manner.
Infrastructure designed to concentrate synchronous fossil fuel generation within a few large centers has, as a consequence, given way to more flexible next-generation networks in which stability is more likely to be provided by what are called grid forming technologies – both old (synchronous condensers) and new (grid-forming electronics), and more widely spread across the network.
The latter can help to address compliance and stability impacts in a mixed system. These issues add to the technical challenges known to be posed by variability and weather issues ranging from day-to-day and from season to season, and which engineers and power systems are working to solve even as the climate around them changes.
And crucially for developers of renewable energy projects including wind and solar, help in understanding and responding to these stability issues is the type of project support that is increasingly being required by regulators, utilities, and grid operators.
The pace of renewables growth has surpassed even the wildest expectations in the last 20 years, and demand for ever-more volumes of green electricity shows few signs of slowing in the decades ahead. For networks, that will increase the need for a smarter approach to connections, along with more demands on generators to provide grid support services.
Electricity grid networks 2.0
The grid system required to maximize the role of renewable energy goes well beyond simply building new wires to those places where it is windy or sunny, to those areas where the waves crash or the tides rip.
Connections from this new class of generator systems to either existing or newbuild grids, and the shift from mainly synchronous plant to the asynchronous or electronic generators found in many renewables projects, dictate a very different set of demands.
These include abstract services that might at one time have been taken for granted: system strength, inertia, frequency stability, frequency response, and fault ride-through, among others – an entire set of grid network properties that traditionally were underpinned by mechanical principles.
The current generation portfolio, by contrast, relies increasingly on electronic systems and is more appliance than machine. It is within this shift where grid forming technologies, rather than grid following kit, comes into play.
And it is why leading-edge modeling is so important. Mapping any facility’s impact on the existing grid, as well as how the network will perform taking into account all the other generation around it – solar, wind, batteries, etc – can help to identify constraints, as well as routes to resolution, at the earliest stage.
Grid forming technologies are particularly important in areas with high levels of renewable penetration.
One technology that is becoming better understood as it currently stands is the ‘virtual synchronous machine’ – an electronic inverter that is controlled to behave, from the point of view of the external network, in the same way as a synchronous machine (subject to limitations). This includes the use of a ‘virtual equation of motion’ within the control system to mimic the way inertia in a real machine causes its grid voltage to change in certain predictable ways during major disturbances on the power system.
The requirement for such technology is only increased when growth in renewable energy sources is focused in areas with weak grids, where they are part of relatively isolated and geographically spread-out grid networks – i.e. with few interconnections – and across any combination of those.
Particularly impacted markets include Australia, Ireland, and parts of Canada and the United States, but it is a challenge coming to all grid networks as the renewables revolution continues.
Much of the low-hanging fruit, in terms of relatively straightforward connections to the grid and regardless of the specific market, has already been picked.
Constraints and restrictions are more commonplace and, in systems where grid forming is required, system operators and/or regulators will often provide an incentive for the services supplied alongside the electricity produced.
How and whether particular developers and particular projects can tap into that revenue requires a very steep level of expertise, something Vysus Group knows well from first-hand experience.
And while the cost can sometimes be equally steep, the benefits – particularly over the lifetime of a generation asset, and when compared with other available alternatives – far outweigh the upfront and operational spending required.
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Solving the Murray puzzle
The West Murray Zone in south-eastern Australia is illustrative of the type of problems that can be encountered. The area presented operators with a stability challenge under certain conditions driven largely by asynchronous generation with ‘weak grid’ issues, including wind and solar plants.
The projects in question were located across the boundaries of two network operators and had complied with the rules as defined when originally connected. And the stability problem itself was the result of the interrelation of all elements, rather than any single source.
Solutions to the issues identified were devised and implemented in a collaborative fashion, with individual projects, the network operator, and regulators cooperating to identify and then address the challenges presented. Importantly, the resolution of these issues was found to lie not with costly additional equipment, but instead with careful tuning of existing control systems in consultation with OEMs and with system integration experts.
The guidance provided by specialist and experienced advisors including our team at Vysus Group was key to establishing the forward path, with a proactive approach adopted from day one in order to test and validate proposed models. Constraints adopted as short-term measures to address stability issues have since been eased.
West Murray highlighted a number of key lessons for power systems facing similar challenges.
These include the requirement to determine the needs and limitations of any given network and to ensure that connecting projects deploy the technologies necessary to meet specific requirements, from the OEMs upwards.
Furthermore, all parties – manufacturers, developers, utilities, system operators, and regulators – need to work together towards a common goal. Flexibility, transparency, and pragmatism were key to addressing the issues in the West Murray Zone.
A key insight from this process is that a holistic approach to control system tuning across multiple installations delivers superior results compared with the naïve attempt to apply one-size-fits-all standards at the level of individual installations. In some cases, performance issues were resolved through deliberate departures from over-rigid performance standards at particular sites. Engineering insight can reveal where adherence to tightly prescribed standards is actually doing more harm than good.
This expert advice, deployed at the earliest stage, was also crucial to both defining and then meeting the challenges presented.
Success in a net-zero world
Grid connections and system security issues like those encountered in West Murray pose a great challenge to the ongoing roll-out of renewable energy projects and, ultimately, the achievement of worldwide net-zero goals. But it’s a challenge that can be met with expert support, building on experience to date with smart system integration.
Newbuild variable generation carries implicit complications whenever it joins a dynamic system, and must increasingly ensure that it can proceed towards operation without disruption and to the satisfaction of regulators and system operators.
Grid-forming technologies are an increasingly important tool in achieving the needs of developers in these regions, and the increasingly important renewables projects they are working to build, to the satisfaction and high demands of the wider energy system.
About the author:
Tony Morton is the global technical head for power systems at Vysus Group. The power team at Vysus Group, a standalone engineering and technical consultancy offering specialist services that support the energy transition and renewables projects, is uniquely positioned to enable this new generation of connection technologies.
Vysus Group, with a team of experts based around Asia Pacific and North America, has a track record of supporting more than 10GW of development over nearly two decades, particularly in areas of high penetration and weak networks, where the constraints are at their most acute.
Source: Renewable Energy