Environmental Science Division (EVS)a Division of Argonne National Laboratory

New EVS report evaluates emerging issues for utility-scale solar energy development and describes approaches to address those issues through compensatory mitigation, monitoring, and adaptive management

December 22, 2016

The solar energy industry in the United States has seen dramatic growth in the past decade and this growth is expected to continue. The important benefits of utility-scale solar power facilities (that is, facilities that feed power into the transmission grid) include decreased greenhouse gas emissions and decreased emissions of toxic air pollutants. However, like other large-scale power sources, solar energy generation impacts the environment and society. Solar energy generation has significant land requirements which could result in barriers to continued rapid solar development. Other key impact issues include landscape-level ecological impacts (e.g., bird fatalities) and visual impacts (including glare). A new report by EVS scientists, entitled Understanding Emerging Impacts and Requirements Related to Utility-Scale Solar Development, discusses these issues and innovative approaches being considered to address these and other impacts through strategies such as onsite and compensatory mitigation, long-term monitoring, and adaptive management.

Impacts to land use can be mitigated through the use of distributed (rooftop) solar as well as other strategies, such as co-location with other productive land uses like agriculture and other energy production systems. Previously disturbed or degraded lands and formerly contaminated sites also could provide a significant portion of the land required for utility-scale solar installations, although additional assessment of the suitability and economic feasibility of specific sites would be needed.

One of the emerging issues discussed in the report is the incidence of bird fatalities associated with solar facilities. Observed bird fatalities are related to collisions with solar panels or other facility structures. Additionally, it has been observed that bird fatalities occur when birds fly through areas of concentrated sunlight near solar power tower facilities, which use mirrors to focus sunlight onto collector towers and heat liquid to run the turbines that generate power. Mitigation measures to limit bird fatalities include better siting of projects to avoid sensitive bird habitats and nesting locations, and other measures to reduce the potential attraction of birds to solar facilities (e.g., deterring birds from evaporation ponds). Agency and industry working groups are currently gathering information and designing research on what attracts birds to solar facilities, the numbers of bird fatalities occurring, and the effectiveness of additional monitoring and mitigation measures.

Another emerging issue examined in the report is the potential for large visual impacts from utility-scale solar facilities due to their large size, reflective surfaces, geometry of their solar arrays, and lighting at night. Recently, both the DOE and the Bureau of Land Management (BLM) have published guidance on visual impact mitigation methods for solar facilities. Considerable progress has also been made by the BLM in developing and applying an improved methodology to assess visual impacts at a landscape-scale, and applying compensatory mitigation and long-term monitoring protocols.

Approaches that address the impacts of utility-scale solar development, such as those described above, include compensatory mitigation, long-term monitoring, and adaptive management. Compensatory mitigation involves actions or projects undertaken to offset (or "compensate") for some of the adverse impacts of solar projects. In some cases compensatory mitigation can address regional conservation issues and public concerns, and allow the successful completion of proposed projects.

Long-term monitoring strategies can help in understanding cumulative, landscape-level impacts. An important use for monitoring data is to detect changes in resource conditions in relation to "management thresholds." Management thresholds identify pre-specified levels of change in measured indicators (e.g., a percentage change in vegetation cover) that trigger the need for action. Exceeding management thresholds indicates the need to adopt new or revised mitigation measures, other project requirements, and/or related management actions, especially if the monitoring data suggest that existing mitigation measures are not adequate. This approach, known as adaptive management, helps project managers evaluate whether management actions are achieving specific, clearly defined outcomes. The report recommends that monitoring partnerships between federal, state, and local agencies be established whenever possible, to pool monitoring funds and to reduce the costs of long-term monitoring.

Although the strategies discussed in this report are still being evaluated in terms of feasibility, effectiveness, and cost, they provide promising new approaches for evaluating impacts and offer several options for resolving emerging concerns. In the case of siting solar facilities on previously used lands, the report details how some key impact issues may be avoided entirely. The report also explains how landscape-scale compensatory mitigation strategies can provide a better understanding of the nature and magnitude of impacts prior to solar development, to determine which impacts require further mitigation in a regional context and how to mitigate those impacts effectively. Finally, the report describes the use of appropriately designed, long-term monitoring and adaptive management programs to maximize mitigation effectiveness. Implementation of these strategies as appropriate in planning new solar facilities should go a long way towards addressing concerns associated with continuing solar development.