Smarter grids for reliable electricity transport
An EU-funded project has developed a probabilistic approach to providing a reliable and affordable electricity supply to European consumers. It uses innovative methods to address the challenges of an increasingly interconnected, flexible and renewables-dominated system.
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Electricity power systems are becoming more complex, while increasing amounts of energy are being generated from weather-dependent renewable sources. This raises the uncertainty of electricity generation, making managing power system reliability increasingly important. Historically, this has been done using a methodology called the N-1 rule. The EU-funded GARPUR project has developed a new approach, based on assessments of probability and risk.
Seven transmission system operators (TSOs) in different countries, 12 research and technological development providers and an expert in innovation management collaborated on the four-year project.
According to project coordinator Oddbjørn Gjerde of SINTEF Energy Research in Norway: Until now, the so-called N-1 rule which basically means that the system must be able to function even if one part, such as a power plant or transmission line, fails has governed European electricity transmission system reliability. A weakness in this approach is that probabilities of failure and the consequences for society are not considered, while it seeks to achieve equal reliability of supply everywhere in the system.
Therefore, the N-1 rule is not suited to recent changes in the European power system, such as the growth of intermittent electricity generation (solar and wind), demand-side management, and energy storage. Also, achieving equal reliability across the entire system can become disproportionately expensive.
Predicting possible power interruptions
The GARPUR consortium developed an innovative way of managing the reliability of the power system. This maintains high levels of reliability in the European electricity transmission grid while maximising social benefits and cost savings.
There are two main elements of the GARPUR methodology that are novel, explains Gjerde. First, it considers both the probability and the consequence (i.e. the risk) of something going wrong and, secondly, it takes into account the socio-economic impact of that failure.
The risk-based methodology deploys mathematical models to predict the location, duration and number of power supply interruptions. Algorithms translate these into potential costs to consumers, while a quantification platform compares the outcomes of alternative reliability management approaches. With this information, TSOs can improve their operational decisions and investments. The key is finding the optimal balance between the cost of providing a reliable electricity supply and the cost of power interruptions.
With the GARPUR methodology, the risk (probability x consequence) is known, so different alternatives can be compared and the most beneficial selected, says Gjerde.
Switch to risk-based reliability management
TSOs involved in the project tested the reliability management alternatives with very promising results. French Electricity Transmission Network RTE concluded that the new approach should lead to similar reliability as the N-1 rule at lower cost, and Landsnet (Iceland) showed how it can be used for real-time risk assessment. Elia (Belgium) demonstrated how the new approach can solve major reliability issues, while Statnett (Norway) used it in a system expansion study where power reliability was maintained with savings of about 25 %, mainly by lowering investment costs.
A test case was also carried out by SINTEF, which illustrated how a probabilistic approach and flexible transmission limits may allow for higher socio-economic surplus.
The new approach was designed to seamlessly fit into existing TSO processes, so that it can be progressively implemented. Furthermore, the project consortium produced an implementation roadmap for the deployment of its technical and regulatory solutions.
The GARPUR TSOs are now implementing or planning to implement at least parts of the new methodology, and other TSOs are expected to follow, Gjerde says.