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INTEGRATING VARIABLE RENEWABLE INTO THE GRID: KEY ISSUES GREENING THE GRID

GRID INTEGRATION TERMINOLOGY Balancing area: the collection of generation, transmission, and loads within the metered boundaries of the responsible entity (i.e., the balancing authority) that maintains balance between supply and demand within this boundary.

Capacity value: the contribution of a plant to reliably meet demand, measured either in terms of physical capacity (kW, MW, or GW) or as a fraction of the power plant’s (%).

Flexibility: the ability of a power system to “Greening the Grid” aims to modernize the power system so that it can accommodate large- respond to changes in electricity demand scale integration of variable resources. Photo from iStockPhoto 17755781 and illustration from iStockPhoto 8294603. and supply.

Demand response: voluntary (and To foster sustainable, low-emission term, aspirational renewable energy targets compensated) load reduction used as a development, many countries are establishing establish a vision that can drive innovation system reliability resource. ambitious renewable energy targets for their in the policies and system operations that electricity supply. Because solar and wind support clean energy. Also critical are Grid integration of renewable energy: tend to be more variable and uncertain than “grid-aware” incentives (e.g., rewarding the practice of power system planning, conventional sources, meeting these targets wind and solar generators that incorporate interconnection, and operation that enables will involve changes to power system planning technologies that contribute to grid stability), efficient and cost-effective use of renewable and operations. Grid integration is the practice which both motivate investment in renewable energy while maintaining the stability and of developing efficient ways to deliver variable energy and mitigate negative impacts of reliability of electricity delivery. renewable energy (VRE) to the grid. Good integrating these resources to the grid. Grid integration study: an analysis of a set integration methods maximize the cost- of scenarios and sensitivities that seeks to effectiveness of incorporating VRE into the As planners consider scaling up VRE inform the stakeholders on the ability and power system while maintaining or increasing generation, the inherent variability of wind needs of a power system to accommodate system stability and reliability. and solar resources complicates evaluations of whether a system with significant VRE has significant VRE. When considering grid integration, adequate supply to meet long-term electricity Storage: technologies capable of storing policymakers, regulators, and system demand. A variety of approaches exist for electricity generated at one time and for use operators consider a variety of issues, which estimating the capacity value of VRE, as well at a later time. can be organized into four broad topics: as techniques that enable utilities and power system operators to use wind and solar to Variable renewable energy (VRE): • New renewable energy generation reliably meet electricity demand. technologies whose • New transmission source varies over time and Integrating distributed photovoltaic (PV) • Increased system flexibility cannot easily be stored. VRE sources include results in unique benefits and • Planning for a high RE future. solar, wind, ocean, and some challenges compared to the integration of generation technologies. utility-scale wind and solar power. Significant NEW RENEWABLE ENERGY localized growth in PV can raise concerns Variability: the changes in power demand GENERATION such as voltage violations and reverse power and/or the output of a generator due to Power system planners can secure and flow in low-voltage distribution systems. underlying fluctuations in resource or load. sustain investment in new VRE generation However, various studies have shown that Uncertainty: the inability to perfectly predict by aligning targets and incentives with positive impacts (e.g., reduced line losses electricity demand and/or generator output. grid integration considerations. Long- and avoided generation costs) can also result INTEGRATING VARIABLE RENEWABLE ENERGY INTO THE GRID: KEY ISSUES

from distributed PV. Updating interconnection storage are emerging as tools for increasing Grid integration studies illuminate the standards, procedures, and distribution flexibility at very high penetrations of VRE. obstacles and opportunities that wind and planning methodologies to better reflect the solar integration could pose to a power characteristics of distributed PV can help realize Options for procuring flexibility vary based system, helping to dispel grid integration these benefits and delay or even prevent the on the regulatory context. For vertically myths and misperceptions that inhibit large- need for grid reinforcement. integrated utilities, contractual or policy scale deployment. These studies also lay the mechanisms provide the primary basis for foundation for prioritizing and sequencing encouraging the uptake of flexibility measures. Related Fact Sheets grid integration investments. In contrast, partially or wholly restructured • Scaling Up Renewable Energy Generation: power markets motivate flexibility through Aligning Targets and Incentives with Grid Related Fact Sheets incentives and market design mechanisms, Integration Considerations • Grid Integration Studies: Data such as sub-hourly dispatch, ancillary services • Using Wind and Solar to Reliably Meet Requirements markets, and price-responsive demand. Electricity Demand • What are the Costs of Managing a System with Significant VRE? • Grid-Integrated Distrbuted Solar: Related Fact Sheets • Wind and Solar on the Power Grid: Myths Addressing Challenges for Operations and Misperceptions and Planning • Sources of Operational Flexibility • Methods for Procuring Power System Flexibility NEW TRANSMISSION • Balancing Area Coordination: Efficiently Written by J. Katz and J. Cochran, National Integrating Renewable Energy into the Grid Scaling up VRE generation requires grid Renewable Energy Laboratory. • The Role of Storage and Demand expansion and upgrades so that power Response systems can access high-quality solar and wind resources, which are often remote Greening the Grid provides technical from existing transmission networks. A PLANNING FOR A HIGH RE FUTURE assistance to planners, well-crafted combination of policies, rules, In any power system, planning activities regulators, and grid operators to overcome and procedures encourages investment in include assessing long-range demand and challenges associated with integrating large-scale transmission expansion. These evaluating options for expanding capacity variable renewable energy into the grid. measures not only improve the utilization of and transmission. With the introduction of VRE, but also potentially defer the need for significant VRE generation, power system network refurbishment. planning increasingly focuses on evaluating FOR MORE INFORMATION options for increasing flexibility across the Jennifer Leisch power system. USAID Office of Global Climate Change Related Fact Sheets Tel: +1-202-712-0760 • Grid Planning Methods for Expansion and Grid integration studies help establish the Email: [email protected] Upgrades flexibility requirements and build confidence among investors and operators that the Jaquelin Cochran National Renewable Energy Laboratory INCREASED SYSTEM FLEXIBILITY power system can be operated reliably at Tel: +1-303-275-3766 Accessing sources of operational flexibility increased VRE levels. A grid integration study Email: [email protected] becomes increasingly important in systems simulates the operation of the power system with significant grid-connected solar and under various scenarios, identifies potential Greening the Grid is supported by the U.S. wind energy. System operating procedures constraints to reliability, and evaluates the Government’s Enhancing Capacity for Low and market practices—especially the cost of actions to alleviate those constraints. Emission Development Strategies (EC-LEDS) program, which is managed by the U.S. Agency implementation of real-time forecasting, faster Robust grid integration studies are based on for International Development (USAID) and scheduling, and ancillary services—are often significant stakeholder input, along with a Department of State with support from the among the least-cost options for unlocking broad set of foundational data. U.S. Department of Energy, U.S. Environmental significant flexibility without significant Protection Agency, U.S. Department of Agriculture investments in new physical infrastructure. Although grid integration studies usually and U.S. Forest Service. Another important institutional flexibility option include production cost simulations to model is operational coordination between balancing unit commitment and economic dispatch, authority areas, which enables sharing of determining the system-wide costs of resources through reserve sharing, coordinated integrating solar and is much scheduling, and/or consolidated operation. more challenging. The full costs and value of VRE assets to the power system depend on Other sources of flexibility include flexible dynamic and complex interactions among greeningthegrid.org | ec-leds.org conventional generation and transmission these generators and a system’s loads, reserves, NREL/FS-6A20-63033 May 2015 networks. Additionally, and thermal generators, and transmission networks.