VNSR generation: a renewable energy on the horizon

The power system as a control process


Renewable energy on the horizon: a Cigré JWG helps operators prepare for increasing VNSR penetration

The past few years have seen a considerable increase in the integration of Renewable Energy Sources (RES) on electricity power systems worldwide. RES integration is set to grow in the coming decades, and experts expect most of the increase to be from Variable Non-Synchronous Renewable (VNSR) generation.

Cigré Joint Working Group (JWG) C1/C2/C6.18 has been keeping an eye on VNSR generation, which is set to alter the fundamental behaviour of power systems and introduce new challenges to the energy sector. In this changing context, the Cigré JWG assessed the readiness of power systems to cope with renewable penetration. Here we take a look at their methods, survey results and recommendations.

Survey design based on a novel concept

To conduct its research, the JWG issued a qualitative and quantitative survey to 50 Cigré members throughout the world. The working group received 30 completed surveys from 19 countries across Europe, North America, Oceania and Asia.

The survey was based on a novel concept that views a power system as a control process.

The power system as a control process

The power system as a control process

The system’s challenge is to manage the control process ‘outputs’ (voltage, frequency, thermal line loadings and plant limits) with changing ‘inputs’ (plant portfolio changes, increased variability and non-synchronous generation). This ‘control process’ approach provided a systematic structure to examine different issues at varying levels of renewable penetration. Based on this framework, the survey was divided into quantitative and qualitative sections:

  • The quantitative section asked for power system information (system size, forecast growth levels, etc.).
  • The qualitative sectiondelved into the specifics of the power system and the impact on operating it with increasing amounts of renewable penetration.


A look at the findings

The JWG analysed the survey results to assess the impact of non-synchronous renewable generation on the electricity power system, broadly structured around the inputs, control capabilities and control strategy variables as set out above. Here are the principal findings:


Most of the assessed power systems are aiming for high-level VNSR penetration over the next decade. With these changing inputs, it will be important to ensure the right long-term commercial signals for a complementary generation portfolio mix.

Control capabilities

Forecast accuracy is considered a key requirement for all VNSR penetration levels. The research shows that additional grid infrastructure will be required for medium- and high-level VNSR. Survey results also clearly point to the increasing role of ancillary services in the secure operation of future power systems worldwide.

Control strategies

With higher levels of VNSR, both new and existing conventional plants will need to increase their dispatch and ramping capabilities. As the level of VNSR increases, there will likely be a need for new operational strategies adapted for high VNSR. Several transmission system operators are examining potential strategies at present.

Market developments

A power system’s flexibility and operational security must align with market structures. And the need for flexibility and performance will grow as VNSR becomes increasingly integrated. As a result, it is important that any market reform ensures that generators have adequate incentives to provide system performance.

Recommendations for power system operators

After discussing these findings, the JWG came up with several recommendations to manage this transition to increasing VNSR penetration:

  • Develop a broad understanding of policy objectivesthat will materially impact the power system’s operation (such as increasing levels of renewable energy, the introduction of electric vehicles, etc.).
  • Conduct more technical studiesto examine the impact of VNSR penetration on power systems.
  • Adhere to and enforceGrid Code provisions.
  • Plan for greater system performance(which may include system flexibility through demand-side management, energy storage, and smart grid initiatives) as increasing levels of VNSR will fundamentally change the characteristics of power systems around the world. 
  • Ensure that the right technical requirements are incentivisedthrough the energy market, and that these incentives are consistent with power system operations.


Interested in learning more?Read the full technical brochure N° 527: ‘Coping with limits for very high penetrations of renewable energy’.

A special thanks to the Cigré members that participated in the Joint Working Group for this study!

Jonathan O’Sullivan (Convener 2009-2012, Ireland), Konstantin Staschus (Convener 2008-2009, Germany), Frank Groome (Secretary), David Jacobson (Canada), Marian Piekutowski (Australia), Hannele Holttinen (Finland), J. Charles Smith (USA), Daniel Brooks (USA), Michael Power (Ireland), Cristobal Castro Gonzalez (Spain – Canary Islands), Bernd Weise (Germany), Michael Negnevitsky (Australia), Bruno Cova (Italy), Biljana Stojkovska (United Kingdom), Paul Ravelli (Australia), Jérôme Duval (France), Gerd Kjolle (Norway), Dieter Quadflieg (Germany), Qianjin Liu (China), Ruperez Jesus (Spain – Canary Islands), Martin Kleimaier (Germany)