Impact of Siting Ordinances on Land Availability for Wind and Solar Development

The work investigates how local siting ordinances—particularly setbacks and related restrictions—affect the land area and technical potential available for wind and solar development in the United States. As siting ordinances have become increasingly common and diverse, understanding their impacts is critical for realistic resource assessments and power-sector planning. The study compiles a machine-readable database of ordinances and quantifies their effects through spatial modeling and scenario analysis, highlighting the scale of potential reductions in developable land and capacity, and the importance of representing these constraints in models.

Data collection and database: Ordinances were collected for wind (2018 and 2022) and solar (2022) and compiled into a machine-readable database with fields for state, city/town (where county zoning absent), county, feature type (e.g., road, structure, height), value type (e.g., meters, tip-height multiplier, dBA), value, citation, and comments for clarification or unit translation. Ordinance coverage and types: By 2022, 1,800+ wind ordinances (≈300 in 2018) and 800+ solar ordinances were cataloged. Types include structure, road, property line, transmission, water, and railroad setbacks; sound limits; height limits; moratoria/bans; density limits; lot size; shadow flicker; total installation size; coverage limits; and maximum project size. Setback distributions: For wind (multiplier by tip height), 50th/90th percentiles across counties are: road/transmission/rail 1.1/2.0; property line 1.1/3.0; structure 2.0/4.0; water 1.2/10.6. For PV (fixed meters), 50th/90th percentiles: road/transmission/rail 30/76 m; property line 15/46 m; structure 61/152 m; water 30/76 m. Spatial modeling framework: A national renewable energy supply modeling framework was used, with an 11.5-km grid covering the contiguous U.S. and approximately 87,000 wind sites, applying detailed exclusion analyses around roads, structures, streams, and other spatial constraints. Technologies modeled include land-based wind, offshore wind, rooftop PV, utility-scale PV, concentrating solar power, and geothermal. Structures data included Microsoft Building Footprints. Spatial siting considerations incorporated airspace (e.g., airports, DoD lands, radar and line-of-sight, NEXRAD, military routes), environmental (e.g., habitats, wetlands, protected areas, slope/elevation), and social/regulatory factors (e.g., wells, pipelines ROW, bans, height limits, setbacks, shadow flicker, sound limits, existing infrastructure). Scenarios: Four scenarios quantify impacts on technical potential: - No Setbacks (Baseline): Excludes legally/administratively protected and unsuitable areas only. - Surveyed Setbacks: Baseline + existing setback ordinances where collected. - 50th Percentile Setbacks: Surveyed + extrapolation of 50th percentile setbacks to areas without ordinances. - 90th Percentile Setbacks: Surveyed + extrapolation of 90th percentile setbacks. Outputs and analyses: For each scenario, available capacity (TW) and land area (million km²) were computed for wind and solar. County-level area impacts were mapped. Additional analyses evaluated the distribution of resource availability by gen-tie distance to transmission and the capacity factors of remaining resources (all capacity vs. top 1 TW) under each scenario.

- Ordinances catalog: 1,800+ wind ordinances (≈300 in 2018) and 800+ solar ordinances (2022). - Extrapolated setbacks can substantially reduce resources: up to 87% reduction for wind and 38% for solar, depending on setback size. - Land and capacity impacts (technical potential): • Solar: No setbacks 147 TW (4.6M km², 100%); Surveyed 144 TW (4.5M km², 98%); 50th percentile 121 TW (3.8M km², 82%); 90th percentile 91 TW (2.8M km², 62%). • Wind: No setbacks 14 TW (4.7M km², 100%); Surveyed 12 TW (4.0M km², 87%); 50th percentile 4 TW (1.2M km², 26%); 90th percentile 2 TW (0.6M km², 13%). - Setback distributions observed across counties: Wind tip-height multipliers (50th/90th percentiles): road/transmission/rail 1.1/2.0; property line 1.1/3.0; structure 2.0/4.0; water 1.2/10.6. PV fixed setbacks (m) (50th/90th): road/transmission/rail 30/76; property line 15/46; structure 61/152; water 30/76. - Ordinance types recorded (counts, 2022 examples): wind structure setbacks (378), road setbacks (355), property line setbacks (359), sound restrictions (224), transmission setbacks (183), height limits (91); solar structure setbacks (136), road setbacks (142), property line setbacks (234), height limits (190). - Spatial variability matters: counties with denser infrastructure and structures can experience larger area reductions under the same setback rules. - Gen-tie proximity: the largest decreases in available resource occur closest to existing transmission infrastructure when binned by gen-tie distance. - Modeling implication: Accurately capturing setback ordinances is important for resource assessments and power-system modeling.

The findings demonstrate that local siting ordinances materially constrain the technical potential for wind and solar, directly addressing the question of how setbacks and related rules impact land availability. The reductions are notably larger for wind than for solar when applying representative (50th/90th percentile) setbacks, indicating wind development is more sensitive to typical setback distances. Spatial context—including density of roads, structures, and environmental constraints—drives heterogeneous impacts across counties. Incorporating observed and extrapolated setbacks shifts both the quantity and spatial distribution of developable resource and affects the quality of remaining sites, as reflected in capacity factor summaries. These results underscore the need to represent siting ordinances in supply-curve modeling, transmission planning (via gen-tie analyses), and decarbonization studies to avoid overestimating renewable potential and misallocating investment and policy focus.

This work assembles a national, machine-readable database of wind and solar siting ordinances and applies a detailed spatial modeling framework to quantify their effects on land availability and technical potential under multiple scenarios. Key contributions include documenting the prevalence and diversity of setbacks, summarizing typical setback magnitudes, and demonstrating that realistic siting constraints can reduce wind and solar technical potential substantially, with larger relative impacts on wind. Future research and development directions include expanding coverage to additional ordinance types that are difficult to model, improving scalable methods (e.g., surrogate modeling) for complex constraints such as sound, and developing semi-automated tools (e.g., LLMs) for continuous, efficient ordinance identification and extraction as local rules evolve.

- Not all ordinance types are readily modeled; the analysis focuses on setbacks and a subset of commonly represented constraints. - Ordinance collection is labor-intensive and subject to change; databases require frequent updates to remain current. - Extrapolation using 50th and 90th percentile setbacks introduces uncertainty where local ordinances are absent. - Results reflect technical potential under specified spatial exclusion layers and may vary with alternative data sources or parameter choices.