Grid and different phases of VRE Integration

The integration of Variable Renewable Energy (VRE) sources, such as wind and solar, into power grids is a crucial part of the global energy transition. As the share of these intermittent energy sources grows, the grid must evolve to handle new challenges in supply stability, flexibility, and overall system operations. As per IEA, the process of VRE integration follows six distinct Stages, each marked by increasing VRE penetration and the need for greater flexibility. These Stages and the approximate percentage of VRE in the power mix require regulatory actions for each stage and have been listed below.

Stage 1: Limited Impact on System Operations (VRE < 5%)

In the initial stages of integrating Variable Renewable Energy (VRE), its contribution to the total power generation mix is typically low, often below 5%. Consequently, the impact on the grid is minimal, and the operational dynamics remain largely unchanged as only a limited number of VRE plants are installed, the net load (demand minus VRE generation) closely aligning with actual demand and the power system operates similarly to how it did before VRE integration.

Regulatory Action: Encourage early investments in VRE projects by offering incentives such as feed-in tariffs, Net metering, Rooftop Solar, RE banking and renewable energy certificates (RECs). Set up basic VRE grid integration guidelines.

Stage 2: Increasing Ramping Requirements (VRE 5–15%)

As the share of Variable Renewable Energy (VRE) increases to approximately 5–15%, the discrepancies between load and net load become more pronounced. In this Stage, characterized by a VRE share ranging from 5–15%, noticeable variations between net load and actual load, and the need for more frequent and rapid adjustments in generator output, conventional power generators must ramp up and down more often to balance the fluctuations in VRE generation. Consequently, grid operators begin to implement advanced scheduling and forecasting tools while enhancing operational practices to effectively manage this growing variability.

Regulatory Action: Mandate the use of Scheduling and forecasting tools to predict VRE generation and demand more accurately. Introduce policies for flexible power generation to ensure conventional plants can ramp up and down more effectively. Begin drafting flexible grid operation standards and Develop market for ancillary services.

Stage 3: VRE affects System Operation (VRE 15–25%)

At this stage, the share of Variable Renewable Energy (VRE) rises to between 15% and 25%, significantly influencing the grid's operating patterns. During this Stage, characterized by a VRE share of 15–25%, net load becomes increasingly unpredictable, giving rise to the well-known "duck curve." This pattern is marked by a midday dip in demand due to high VRE output, followed by a sharp ramp-up in the evening as VRE generation declines. As a result, there is a growing need for flexibility measures that extend beyond conventional grid resources to effectively manage this variability and uncertainty.

 Regulatory Action: Enforce stricter forecasting requirements and grid code revisions to manage the variability introduced by the "duck curve." Introduce incentives for energy storage systems, demand response, and other flexibility resources, develop curtailment policy, incentivize GH2/EVs. Implement time-of-use tariffs to manage demand.

 Stage 4: VRE Dominates Power Generation during certain periods (VRE 25–50%)

At this stage, the share of Variable Renewable Energy (VRE) increases to between 25% and 50%, with periods during the day when VRE meets nearly all electricity demand. However, this substantial integration presents operational challenges, particularly in maintaining grid stability amid rapid shifts in supply and demand. Characterized by a VRE share of 25–50%, this Stage underscores the need for advanced operational solutions and regulatory reforms to effectively manage the system's response to these fluctuations and ensure reliable electricity supply.

Regulatory Action: Formulate policies to strengthen grid stability during periods of high VRE penetration. Require investment in advanced grid management systems and encourage the use of energy storage through favorable regulatory frameworks. Adjust market rules to allow faster dispatch of flexible resources.

 Stage 5: Surplus Energy and the Need for Storage (VRE 50–75%)

As the share of Variable Renewable Energy (VRE) rises to between 50% and 75%, the grid begins to experience periods when VRE output exceeds local demand. To prevent grid overload, this surplus energy must be either stored or exported. Characterized by a VRE share of 50–75%, this Stage highlights the critical need for energy storage systems, demand response mechanisms, and enhanced grid infrastructure to effectively manage excess energy and maintain stability. Additionally, implementing these solutions may require more costly measures to ensure grid stability, particularly when conventional generation levels are low.

Regulatory Action: Mandate the deployment of large-scale energy storage solutions and support the development of demand response programs. Introduce policies for surplus energy export or trade. Incentivize grid expansion and infrastructure upgrades to manage large VRE shares effectively, introduction of appropriate market products (CFDs, capacity market etc.) to address negative pricing scenarios, Open for Cross border trade of VRE.

Stage 6: Harmonizing Grid Operations for Long-Term Adaptability (VRE > 75%)

In the final Stage, the grid operates with a Variable Renewable Energy (VRE) share exceeding 75%, relying almost entirely on renewable energy for extended periods. During times of low VRE availability, such as periods of insufficient sunlight or wind, energy storage systems and dispatchable generation must compensate for the shortfall. Characterized by a VRE share greater than 75%, this Stage necessitates a close match between net load and generation profiles, alongside a reliance on long-duration energy storage and dispatchable generation to maintain balance. Furthermore, extensive cross-border electricity trade and advanced systems become essential for ensuring grid stability.

 Regulatory Action: Establish rules for long-duration storage systems and introduce regulations for cross-border energy trade. Create a market for ancillary services that can support grid balancing. Encourage the development of dispatchable renewable resources like hydro or biomass for reliability

The inevitability of smart grids can be aligned with the various stages of grid evolution outlined above. Here's a breakdown of which Stage corresponds to each of the factors mentioned previously:

Smart grids become inevitable particularly during Stage 3 (Grid Decentralization and Prosumers) and Stage 4 (Energy Storage and Electric Vehicles), as these developments necessitate advanced grid management capabilities. However, the transition to smart grids is supported by all Stages outlined, culminating in a comprehensive approach to modernizing the power system to meet current and future challenges.

Conclusion

The integration of VRE into the grid is a Staged process that brings new challenges at each stage as the share of renewables increases. Moving from minimal VRE impact in Stage 1 to grid matching in Stage 6 represents the evolving energy systems of the future. Each Stage requires careful planning, the deployment of advanced technologies, and regulatory frameworks to ensure the reliability and efficiency of the grid which must become smart ultimately. While states like Karnataka, Gujarat, Rajasthan, and Tamil Nadu have already reached stage 4, the country as a whole remains in stage 2. Consequently, we need to implement measures that are appropriate for stage 4.

( Disclosure- Concept and Graphs sourced from IEA)