Southern Africa faces an unprecedented challenge: deploying low-carbon electricity at a massive scale to meet economic growth, electrification, and climate goals. The potential land use and freshwater impacts of this energy infrastructure build-out are poorly understood. Large hydropower, while often promoted as cost-effective and low-carbon, has historically underestimated negative social and environmental impacts. Wind, solar, and battery technologies offer promising alternatives, but also present their own challenges. Siting conflicts can lead to delays and cost overruns. Careful planning that considers competing conservation and societal land uses is crucial for rapid and low-impact renewable energy development. Much of the literature on sustainable hydropower focuses on minimizing, rather than avoiding, impacts. Existing studies often co-optimize hydropower generation with socio-environmental criteria, but fail to assess the cost-effectiveness of substituting higher-impact hydropower projects with alternatives like wind and solar. These studies often overlook the dispatchable nature of hydropower and rarely assess individual projects' temporal generation patterns. Although some research examines the cost-competitiveness of specific hydropower plants, it typically doesn't screen projects based on socio-environmental criteria. The variability and uncertainty of wind and solar generation necessitate large battery storage or flexible generation sources like hydropower or natural gas, complicating planning. Large-scale wind and solar projects also face land use conflicts. Failure to consider social and environmental siting criteria can lead to cost underestimation and project failure. Southern Africa, with its high electricity demand, hydropower dependence, and significant biodiversity, epitomizes these conflicts. This study aims to determine how excluding the most environmentally and socially damaging projects impacts optimal electricity pathways and system costs in Southern Africa.

The existing literature highlights the tension between the need for large-scale renewable energy deployment in Africa and the potential for significant environmental and social impacts. While studies have examined the sustainable development of hydropower, many focus on mitigation rather than avoidance of negative consequences. These studies often optimize hydropower portfolios alongside socio-environmental factors but don’t explore the cost-effectiveness of replacing high-impact hydropower projects with other generation sources like wind and solar. The dispatchable nature of hydropower versus the variability of wind and solar is often overlooked, as is the need for a power system-level approach that considers individual project impacts. Previous work has begun to address this by exploring the potential for wind and solar to replace hydropower but often uses a simplistic, annual generation-based substitution approach, neglecting the temporal variability of hydropower generation. While some research analyzes the cost-competitiveness of specific hydropower plants in Africa, few incorporate socio-environmental screening to identify and potentially avoid projects with high negative impacts. The literature also underscores the land use requirements and siting conflicts associated with large-scale wind and solar projects, highlighting the need for comprehensive planning that incorporates environmental and social considerations to ensure project feasibility and prevent cost overruns.

The analysis comprised four stages: (1) renewable resource characterization, (2) environmental and social screening of candidate resources, (3) capacity expansion modeling, and (4) scenario comparison. Wind and solar resource potential was quantified using technical, physical, economic, and socio-environmental criteria. Hydropower analysis used project-specific design specifications for 34 major planned projects. Seven scenarios were developed to represent varying levels of socio-environmental constraints: (1) Base (all projects included), (2) Legal (excluding strictly legally protected areas), (3) Social (excluding areas important for livelihoods and high-displacement hydropower), (4) Environmental (excluding other protected areas and hydropower on large free-flowing rivers), (5) Environmental and Landscape (adding forested areas exclusions), (6) All Exclusions (combining previous exclusions), and (7) All Exclusions No New Hydropower (a hydropower moratorium). Wind and solar resource mapping adapted the MapRE framework, integrating resource assessment and multi-criteria analysis at 500m resolution, then aggregating to larger project areas. Hourly capacity factor time series were developed using weather data, and costs were estimated based on distance to infrastructure. Hydropower characterization used a spatially distributed hydrological water management model (VIC-Res) to simulate energy availability. Reservoir footprints were modeled using project locations, dam heights, and a DEM to estimate inundation areas and impacts on protected areas, populations, and croplands. For each scenario, suitable projects were inputted into GridPath-SAPP, an open-source capacity expansion model, to determine cost-optimal electricity generation portfolios. The model is a mixed integer program that considers each hydropower plant individually, not as a fleet. The model optimized the investment in generation and transmission infrastructure from 2020-2040, accounting for hourly demand, generation capacities, and various costs and constraints, including a primary reserve margin. Scenarios were compared based on capacity requirements, costs, emissions, and socio-environmental impacts, both with and without a carbon emissions target (50% reduction of 2020 emissions by 2040).

Socio-environmental protections significantly altered resource potential and optimal electricity portfolios. In the 'All Exclusions' scenario, solar potential decreased substantially (to 17% of the base case), while wind potential decreased less dramatically (to 72%). Planned hydropower capacity reduced to 58% of the base case. Without socio-environmental exclusions, 176 GW of new generation capacity was needed by 2040, with wind and solar accounting for half. Increasing protections required more solar, battery, and gas, and less hydropower; a hydropower moratorium led to significant increases in wind, solar, battery, and gas. A low-carbon target dramatically altered the results, requiring 50 GW of additional capacity (compared to the base scenario without a carbon target), mostly wind, solar, and hydropower. With combined low-carbon and socio-environmental targets, capacity increased but hydropower decreased significantly. The model showed that only a fraction of proposed hydropower projects are cost-competitive, even without socio-environmental constraints (around 18 GW out of 41 GW). Applying constraints further reduced the selected hydropower capacity to 10-12 GW (25% of planned capacity). The geographic distribution of selected hydropower projects varied across scenarios, with more projects in the Zambezi and Kwanza river basins in less constrained scenarios. Applying protections resulted in modest increases in system costs (0.4-2.3% for no-carbon target scenarios and 3-6% when including a carbon target), avoiding significant land and freshwater impacts. The ‘Base’ scenario, without protections, risked inundating 400 sq km of legally protected areas, 1500 sq km of conservation areas, and displacing over 150,000 people; these impacts were substantially reduced by applying protective measures, reducing displaced populations to under 20,000. This study demonstrates that avoiding the most damaging impacts of renewable energy development is possible with modest cost increases.

This study demonstrates the feasibility of avoiding the most significant social and environmental impacts of wind, solar, and hydropower development in Southern Africa while simultaneously meeting ambitious low-carbon electricity targets. The results highlight the substantial potential for low-impact wind and solar development and the disproportionate environmental and social costs associated with a large fraction of proposed hydropower projects. The relatively modest cost premiums associated with incorporating socio-environmental protections into the energy planning process suggest that the cost of inaction—in terms of environmental degradation, social displacement, and project delays—likely outweighs the additional costs of implementing more sustainable energy development pathways. The model results underscore the importance of integrating comprehensive environmental and social impact assessments into energy system planning from the outset. It is critical to consider not only the technical and economic aspects but also the long-term societal and ecological consequences of energy infrastructure investments. Although cost increases were modest in this study, other costs such as cost overruns due to conflict may be significant and were not considered in this study. International support is crucial to help Southern Africa adopt sustainable low-carbon pathways.

This research shows that a low-carbon electricity system in Southern Africa can be achieved while significantly mitigating social and environmental impacts. While achieving both a low-carbon target and stringent socio-environmental protections resulted in increased costs (3-6%), these premiums were relatively modest compared to the potential costs of large-scale, high-impact hydropower development. The study emphasizes the importance of incorporating socio-environmental criteria into energy planning and highlights the substantial potential of wind and solar energy. Future work should focus on further refining impact assessments, incorporating additional environmental and social criteria, and exploring the implications of different policy mechanisms for incentivizing more sustainable energy pathways.

This study’s conclusions rely on available data and model assumptions. While efforts were made to incorporate comprehensive data sets for environmental and social screening, data availability varied across countries, potentially influencing the precision of impact assessments. The model’s assumptions about demand elasticity, technology cost trajectories, and international transmission capacity could also impact results. Additional environmental impacts of dams not directly quantified here (e.g., GHG emissions from inundation, fish diversity impacts) should be considered in future studies to provide a more comprehensive assessment.