Overview of Grid Integration Issues
To foster sustainable, low-emission development, many countries are establishing ambitious renewable energy targets for their electricity supply. Because solar and wind tend to be more variable and uncertain than conventional sources, meeting these targets will involve changes to power system planning and operations. Grid integration is the practice of developing efficient ways to deliver variable renewable energy (RE) to the grid. Robust integration methods maximize the cost-effectiveness of incorporating variable RE into the power system while maintaining or increasing system stability and reliability.
Grid integration spans a variety of issues, including:
- New RE generation
- New transmission
- Increased system flexibility
- Planning for a high RE future
1. New Renewable Energy Generation
Power system planners can secure and sustain investment in new variable RE generation by aligning targets and incentives with grid integration considerations. Long-term, aspirational renewable energy targets establish a vision that can drive innovation in the policies and system operations that support clean energy. Also critical are “grid-aware” incentives (e.g., rewarding wind and solar generators that incorporate technologies that contribute to grid stability), which both motivate investment in renewable energy and mitigate negative impacts of integrating these resources to the grid.
As planners consider scaling up variable RE generation, the inherent variability of wind and solar resources complicates evaluations of whether a system with significant variable RE has adequate supply to meet long-term electricity demand. A variety of approaches exist for estimating the capacity value of variable RE, as well as techniques that enable utilities and power system operators to use wind and solar to reliably meet electricity demand.
Integrating distributed photovoltaic (PV) solar power results in unique benefits and challenges compared to the integration of utility-scale wind and solar power. Significant localized growth in PV can raise concerns such as voltage violations and reverse power flow in low-voltage distribution systems. However, various studies have shown that positive impacts (e.g., reduced line losses and avoided generation costs) can also result from distributed PV. Updating interconnection standards, procedures, and distribution planning methodologies to better reflect the characteristics of distributed PV can help realize these benefits and delay or even prevent the need for grid reinforcement.
2. New Transmission
Scaling up variable RE generation requires grid expansion and upgrades so that power systems can access high-quality solar and wind resources, which are often remote from existing transmission networks. A well-crafted combination of policies, rules, and procedures (designed, for example, through an "RE Zones" approach) encourages investment in large-scale transmission expansion. These measures not only improve the utilization of variable RE, but also potentially defer the need for network refurbishment.
3. Increased System Flexibility
Accessing sources of operational flexibility becomes increasingly important in systems with significant grid-connected solar and wind energy. System operating procedures and market practices—especially the implementation of forecasting, faster scheduling, ancillary services, and grid codes and power purchase agreements—are often among the least-cost options for unlocking significant flexibility without significant investments in new physical infrastructure. Another important institutional flexibility option is operational coordination between balancing authority areas, which enables sharing of resources through reserve sharing, coordinated scheduling, and/or consolidated operation.
Other sources of flexibility include flexible conventional generation and transmission networks. Additionally, demand response and storage are emerging as tools for increasing flexibility at very high penetrations of variable RE.
Options for procuring flexibility vary based on the regulatory context. For vertically integrated utilities, contractual or policy mechanisms provide the primary basis for encouraging the uptake of flexibility measures. In contrast, partially- or wholly-restructured power markets motivate flexibility through incentives and market design mechanisms, such as sub-hourly dispatch, ancillary services markets, and price-responsive demand.
4. Planning for a High RE Future
In any power system, planning activities include assessing long-range demand and evaluating options for expanding capacity and transmission. With the introduction of significant variable RE generation, power systems planning increasingly focuses on evaluating options for increasing flexibility across the power system.
Grid integration studies help establish the flexibility requirements and build confidence among investors and operators that the power system can be operated reliably at increased variable RE levels. A grid integration study simulates the operation of the power system under various scenarios, identifies potential constraints to reliability, and evaluates the cost of actions to alleviate those constraints. Robust grid integration studies are based on significant stakeholder input, along with a broad set of foundational data.
Although grid integration studies usually include production cost simulations to model unit commitment and economic dispatch, determining the system-wide costs of integrating solar and wind power is much more challenging. The full costs and value of variable RE assets to the power system depend on dynamic and complex interactions among these generators and a system’s loads, reserves, thermal generators, and transmission networks.
Grid integration studies illuminate the obstacles and opportunities that wind and solar integration could pose to a power system, helping to dispel grid integration myths and misperceptions that inhibit large-scale deployment. These studies also lay the foundation for prioritizing and sequencing grid integration investments.