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IEA (2024), Integrating Solar and Wind, IEA, Paris https://www.iea.org/reports/integrating-solar-and-wind, Licence: CC BY 4.0
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Infographic: Six phases of Variable Renewables Integration
The IEA’s phases of VRE integration framework outlines six phases of increasing solar PV and wind impacts on the power system. Each phase presents new challenges requiring targeted measures to enable the secure and cost-effective uptake of VRE. Phases 1 to 3, considered low phases of VRE integration, experience relatively low impacts, with most challenges addressable through straightforward modifications to existing assets or operational improvements. Phases 4 to 6 are considered high phases and mark increasing influence of VRE in shaping system operations, requiring a fundamental transformation of the power system.
Phase 1
VRE has no significant impact at the system level
The first set of VRE plants are deployed, but their impact is largely insignificant at the system level and the typical operating parameters of the system remain unchanged. Any effects are very localised, for example at the grid connection point of plants.
Load versus net load
The difference between load and net load is minimal
Phase 2
VRE has a minor to moderate impact on the system
As more VRE plants are added, changes between load and net load become more noticeable with a minor to moderate impact on the system such as faster and more frequent ramping of generators. Upgrades to operating practices such as integrating forecasting into dispatch and making better use of existing system resources are usually sufficient to achieve system integration.
Load versus net load
The difference between load and net load is noticeable
Phase 3
VRE determines the operation pattern of the power system
VRE determines the operation pattern of the power system and increases the uncertainty and variability of net load. Greater swings in the supply-demand balance prompt the need for a systematic increase in flexible operation of the power system that often goes beyond what can be readily supplied by existing assets and operational practice.
Load versus net load
The "duck" curve starts emerging, suggesting that more pronounced and longer ramps are required
Phase 4
VRE meets almost all demand at times
VRE output is sufficient to meet a large majority of electricity during certain periods, which may impact power system stability. A key operational challenge is related to the way the power system responds to maintain stability immediately following disruptions in supply or demand, which may involve advanced operational solutions and changes in regulatory approaches.
Percentage of hours covered by VRE
During a few hours of the year, almost all demand is covered by VRE
Phase 5
Significant volumes of surplus VRE across the year
Rising shares of VRE mean that without additional measures VRE availability will exceed demand during many hours and be in overall surplus for periods of a day or more. Achieving such shares under decarbonisation goals in an economic and secure manner requires increased measures to support VRE utilisation, such as large deployment of demand response, energy storage and grids, and more extensive solutions to ensure stability at low levels of conventional supply.
Percentage of hours covered by VRE
VRE generation can be higher than 100% of the local demand: surplus energy must be managed
Phase 6
Secure electricity supply almost exclusively from VRE
Phase 6 applies to regions looking to meet extremely high shares of annual electricity demand with VRE. The main challenges in this phase include operating a system largely dependent on converter-connected resources and meeting demand during extended periods of low wind and sun availability. Addressing flexibility needs can involve long-duration energy storage or extensive electricity trade with other regions.
Electricity generation and load profiles
Prolonged periods of low VRE availability need to be compensated for by storage and dispatchable generation
