Reducing transmission expansion by co-optimizing sizing of wind, solar, storage and grid connection capacity

TL;DR

This paper tackles the transmission expansion bottleneck facing deep decarbonization by introducing a GenX-based VRE-Storage extension that endogenizes interconnection sizing and enables co-location of wind/solar with storage behind a single interconnection. Through a 2030 WECC Western Interconnection case, and three scenarios (Fixed Interconnection, Optimized Interconnection, and Co-Located Storage) across multiple battery-cost trajectories, it shows substantial reductions in required interconnection capacity (up to $ ext{GW-km} $ declines of about $8$–$10 ext{ extpercent}$) and shifts in resource siting, with PV/inverter and wind/interconnection ratios converging to $ ext{roughly }1.5 ext{–}1.6 $ and $1.2 ext{–}1.3$, respectively. Co-located storage demonstrates higher value than standalone storage (roughly $22$–$25 ext{ extpercent}$ at low penetration rising to $46$–$56 ext{ extpercent}$ at high penetration) and promotes greater wind deployment by enabling transmission-cost reductions, though the coarse transmission representation likely overstates these gains. The results underscore the importance of modeling co-location and endogenized interconnection sizing to capture the full value of storage and to inform policymakers, investors, and planners, while also calling for improved network detail and computational efficiency in future macro-energy models.

Abstract

Expanding transmission capacity is likely a bottleneck that will restrict variable renewable energy (VRE) deployment required to achieve ambitious emission reduction goals. Interconnection and inter-zonal transmission buildout may be displaced by the optimal sizing of VRE to grid connection capacity and by the co-location of VRE and battery resources behind interconnection. However, neither of these capabilities is commonly captured in macro-energy system models. We develop two new functionalities to explore the substitutability of storage for transmission and the optimal capacity and siting decisions of renewable energy and battery resources through 2030 in the Western Interconnection of the United States. Our findings indicate that modeling optimized interconnection and storage co-location better captures the full value of energy storage and its ability to substitute for transmission. Optimizing interconnection capacity and co-location can reduce total grid connection and shorter-distance transmission capacity expansion on the order of 10% at storage penetration equivalent to 2.5-10% of peak system demand. The decline in interconnection capacity corresponds with greater ratios of VRE to grid connection capacity (an average of 1.5-1.6 megawatt (MW) PV:1 MW inverter capacity, 1.2-1.3 MW wind:1 MW interconnection). Co-locating storage with VREs also results in a 10-15% increase in wind capacity, as wind sites tend to require longer and more costly interconnection. Finally, co-located storage exhibits higher value than standalone storage in our model setup (22-25%). Given the coarse representation of transmission networks in our modeling, this outcome likely overstates the real-world importance of storage co-location with VREs. However, it highlights how siting storage in grid-constrained locations can maximize the value of storage and reduce transmission expansion.

Figures (24)

• Figure 1: GenX Co-Location and Optimized Interconnection Module Overview for Each Configurable Resource. This figure was adapted from nrel_pv_battery_2021.
• Figure 2: Fourteen-Region Model of the Western Interconnection. The region CA_N includes WEC_CALN and WEC_BANC in northern California. The region CA_S includes WECC_SCE and WEC_LADW in southern California.
• Figure 3: Box Plots of Wind and Solar PV Clusters' Average Ratio of VRE to Inverter/Grid Connection Built and Scatter Plots of Ratio of VRE to Inverter/Grid Connection Built vs. Interconnection Costs with 3.75 GW of System-Wide Battery Capacity for Optimized Interconnection Scenario. (a) Average Ratio of PV to Inverter Capacity (red dashed line represents the fixed assumed ratio of 1.3 MW of solar PV to 1 MW of inverter capacity), (b) Average Ratio of Wind to Grid Connection Capacity (red dashed line represents the fixed assumed ratio of 1 MW of wind to 1 MW of grid connection capacity), (c) Scatter Plot of the Ratio of Solar PV and Wind vs. Interconnection Costs ($/kW/yr) for the Low VRE-Cost Scenario with 3.75 GW of Forced System-Wide Battery Capacity, and (d) Scatter Plot of the Ratio of Solar PV and Wind vs. Interconnection Costs ($/kW/yr) for the Mid VRE-Cost Scenario with 3.75 GW of Forced System-Wide Battery Capacity.
• Figure 4: Interconnection Capacity and Inter-Zonal Transmission Buildout. (a) Interconnection Capacity in Low VRE-Cost Scenario, (b) Interconnection Capacity in Mid VRE-Cost Scenario, (c) Inter-Zonal Transmission Capacity in Low VRE-Cost Scenario, (d) Inter-Zonal Transmission Capacity in Mid VRE-Cost Scenario. Brackets indicate the percent decline of the optimized interconnection or co-located storage scenario relative to the fixed interconnection scenario.
• Figure 5: Zonal Solar, Wind, and Battery Capacity and Inter-Zonal Transmission Capacity Differences between the Optimized Interconnection and Fixed Interconnection Scenario. This scenario represents 3.75 GW of new battery forced into the system. The grey areas represent metropolitan statistical areas treated as demand centers.