Will system integration of renewables be a major challenge by 2023?

Analysis from Renewables 2018

System integration of renewables is already a major challenge, and has been for some time. But it is a problem that can be successfully remedied in a cost-effective manner.

Several countries have experienced decelerating variable renewable energy (VRE) deployment due to system integration concerns or periods of high curtailment, even during the early days of VRE expansion. Ireland, for example, put a moratorium on new wind developments following major concerns about the “security and stability of the power system” in 2003, when wind technology contributed 2% of annual generation. Challenges were subsequently analysed in a systematic manner, and a strategy for resolving them was designed and implemented. As of 2017, Ireland had 25% wind power in its generation mix and is moving towards 39% by 2023 while maintaining reliability and without significant additional costs. Similarly, curtailment levels of the Electricity Reliability Council of Texas (ERCOT) peaked around 20% in 2009 due to wind power capacity increasing more quickly than required grid infrastructure. Since then, the grid has been built out and curtailment has fallen to a healthy level (below 2%).

Wind and solar PV are technically different from conventional forms of electricity generation. Their maximum instantaneous output depends on how much wind and sunlight are available at any given moment, which makes their output variable and only partially predictable. VRE can be deployed at very different scales – from large offshore parks to small home systems. Plant location is constrained, however, because sites with favourable wind and solar resources may not be where the electricity is needed. In addition, their technical response characteristics, especially during grid disturbances, are determined by control software settings rather than by inherent technical design.

These properties – variability, partial predictability, and location constraints – can make it difficult for power systems to accommodate higher amounts of VRE. What is needed to manage system integration is power system flexibility, which encompasses all system components that facilitate the reliable and cost-effective management of variability and uncertainty in both supply and demand. Maintaining a reliable supply of electricity requires that supply and demand be balanced continuously across all timescales, from sub-seconds to years – it is thus useful to consider flexibility along these timescales.

Previous IEA analysis has identified different phases of VRE integration. They are characterised not only by a specific penetration level, but by the main integration issues and challenges, covering technical, regulatory, market and institutional aspects. It is important to note that a variety of system-specific factors influence how much an increase in VRE will affect overall system flexibility.

  • Phase 1: The first set of VRE plants are deployed, but they are basically insignificant at the system level; effects are very localised, for example at plants’ grid connection points.
  • Phase 2: Changes between load and net load become noticeable, but the existing system is flexible enough to achieve system integration.
  • Phase 3: Greater swings in the supply-demand balance prompt the need for a systematic increase in power system flexibility beyond what can be relatively easily supplied by existing assets and operational practices.
  • Phase 4: VRE output provides the majority of electricity demand in certain periods, requiring both operational and regulatory modifications. Operational changes involve power system stability, determining the way the power system responds following supply or demand disruptions, and regulatory changes may include new rules for VRE to provide system services.

Moving smoothly from one phase to the next requires that measures become increasingly interrelated and complex. Ultimately, a systematic transformation of the electricity system, and the wider energy system overall, is required.

System integration phases, transition challenges and flexibility measures

Further VRE deployment beyond Phase 4 to Phases 5 and 6 is possible, but requires the electrification of other end-use sectors, seasonal storage and the use of synthetic fuels such as hydrogen. Most countries are presently at Phase 1 or 2 but are striving towards higher phases.

Selected countries by integration phase and share of VRE, 2017


Today, China – the world’s largest wind and solar market – is facing a number of substantial integration challenges. However, curtailment levels have been declining and several measures have been instituted to further alleviate challenges. It is expected that a number of other countries will also face system integration challenges in the next six years, which will likely lead to some instances of temporarily slowed deployment and periods of elevated curtailment.

That said, projections have become more dependent on countries successfully addressing system integration challenges for two main reasons. First, in 2017 the majority of VRE generation occurred in countries with shares of 5-10% annually. In this range, system integration challenges are relatively modest and can be handled through several straightforward options. Once shares exceed 10%, however, a more systematic approach to system integration is required. Second, VRE expansion has become more reliant on solar PV technology, and at higher shares of VRE, integration challenges tend to occur sooner for technologies with lower capacity factors. Hence, the shift from wind to solar capacity additions makes system integration measures even more necessary.

Share of variable renewables in global electricity mix, 2017-2023


Shares of VRE in many countries are forecast to be much greater in 2023 than in 2017. They are expected to rise from 5‑10% to predominantly 10-20% annually by 2023, and countries with annual VRE generation of 20‑40% will also increase significantly. The number of countries with 10-20% VRE generation is expected to double between 2017 and 2023 (from 15 to 30 countries), and those with a 20-40% share are also expected to double.