Dual-use solar: What it is and how it can help ease tensions between clean energy deployment and land use
Achieving global decarbonization requires the rapid and widespread deployment of clean energy infrastructure, a diverse suite of technologies, and innovative solutions.
Solar power is a key asset in the transition to clean, carbon-free electricity with the potential to account for nearly half the United States’ electricity generation by 2050. The estimated land required to host these solar projects, however, is equal to 0.5% of all U.S. land. While this may not seem like much, finding suitable space that does not infringe upon protected lands, habitats, and waterways and that has support from local communities can be challenging. Solar is increasingly difficult to site, with growing community opposition driven by concerns including encroachment on prime agricultural land, aesthetic changes to local environments, and ecosystem impacts. Solutions that address these concerns and maximize land-use efficiency will be valuable, particularly when traditional solar development is not suitable to the local context.
Dual-use solar, meaning the co-location of solar with another land use, is one such budding solution. It has the potential to provide added environmental, social, and economic benefits while mitigating community concerns of traditional solar development. Despite limited implementation, the prospect of dual-use solar is touted in industry and academic discourse as a win-win innovation that maximizes the potential benefits and reduces the challenges of siting conventional utility-scale solar.
There are three different examples of dual-use solar, each with their own unique opportunities, challenges, and best-use cases.
1. Agrivoltaics
Agrivoltaics involves co-locating some form of agricultural activity with solar arrays, either by mounting panels above or directly interspersing them with crop production or livestock grazing.1 While some definitions of agrivoltaics include non-agricultural activities with ecosystem benefits, like growing pollinator habitat, we categorize these activities separately as ecosystem services-based solar. As explained below, ecosystem service configurations for dual-use solar differ significantly in system requirements and maintenance compared to solar co-located with crop and livestock agricultural activities.
Existing research on agrivoltaics highlights numerous potential synergies between agricultural activities and solar panels. In co-location with crops, solar panels offer shade that alleviates heat stress, optimizes light conditions, and reduces water evaporation from the soil, which can increase crop yields, reduce water use for irrigation, and extend growing seasons, especially in drylands or drought-prone areas. In the context of livestock co-location, panels serve as sources of shade and shelter, effectively reducing heat stress on the animals. Livestock grazing beneath the panels can also reduce the need for mowing and increase nutrient cycling, which in turn enhances soil health.
While research suggests that agrivoltaics can offer multiple benefits, the technology is still in its early implementation. The complexity of agrivoltaic sites creates significant technical barriers to deploying utility-scale projects, requiring wider spacing between panel rows and higher panel height than traditional panels and modifications for irrigation, wind stress, livestock, and worker safety – none of which are currently the industry norms. For example, panels may need to be made adjustable to allow farm workers to tend to crops and to allow access for farm equipment and machinery. As a result, current installations are limited to small-scale, experimental projects that face significant site design challenges, high-cost requirements, and added risk for developers, especially when compared with conventional ground-mounted solar.
Shade-tolerating crops such as leafy greens and root vegetables are most suitable for co-location, but suitability is highly dependent on the local context and site design. For co-location with grazing animals, sheep have proven to be the most compatible livestock, yet the U.S. sheep industry is not well positioned for sheep grazing to be quickly scaled. The industry currently accounts for only 1% of nationwide livestock industry earnings. Deploying sheep-grazed solar sites at scale would require training a new generation of herders, expanding associated industry supports, and growing the size of existing flocks.
In summary, agrivoltaic solar projects are suitable for smaller scale solar, a limited set of crop types, specialized livestock, and specific climatic conditions. Without significant design and cost breakthroughs for utility-scale projects, agrivoltaics deployment will likely be limited to niche circumstances and may be most useful where conventional utility-scale solar development is not practical or possible. Although agrivoltaics may not be scalable, the added benefit opportunities provided by this kind of creative solution demonstrate the potential to maximize the positive impact of clean energy projects.
2. Ecosystem services-based solar
Ecosystem services-based solar, sometimes referred to as “ecovoltaics,” is the co-location of solar with vegetation not intended for agricultural production. These configurations can create a range of environmental, social, and economic benefits while mitigating the local impacts of solar development. Planting native or other specialized vegetative cover can provide ecosystem services of soil restoration, carbon sequestration, water management, dust mitigation, erosion control, pollinator habitat, and habitat for other bird or wildlife species. Local permitting processes may already require practices that mitigate environmental impacts. However, more targeted actions could not only mitigate potential impacts but also provide added environmental benefits. Like other dual-use systems, there are additional upfront costs and modifications required compared to traditional solar, but alterations are often less significant than for agrivoltaics and can be worked into existing solar developments. Further, the operations and maintenance costs for solar systems with native or perennial groundcover have been found to be significantly less than turfgrass or conventional groundcover alternatives.
To date, ecosystem services-based solar is also the most widely deployed form of dual-use in the United States. A study of existing solar sites in the Midwest found that planting native grassland habitat on these sites has the potential of a three times increase in pollinator supply, a 65% increase in carbon storage potential, and increases in water retention compared to the prior agricultural land uses. The researchers projected these impacts to the anticipated solar buildout in the region by 2035, which accounts for 5% of the U.S. Department of Energy’s anticipated need for the nation, and found that native grassland vegetation strategies could conserve over 9000 tons of annual sediment loss from erosion and retain 40 million cubic meters of water runoff annually. Existing supportive programs in states like Minnesota have promoted voluntary uptake of such practices, signaling that developers find the provision of ecosystem services useful and complementary to solar deployment.
Ecosystem services-based dual-use solar offers an opportunity to further explore how sustainable land management practices could be more effective in increasing utility-scale solar deployment while providing significant co-benefits for communities and ecosystems.
3. Floatovoltaics
Floatovoltaics, also known as floating solar, refers to the installation of solar systems on water bodies such as lakes, ponds, reservoirs, canals, or other artificial water bodies. In these systems, the same panels used for traditional ground-mounted systems can either be mounted above or float on top of bodies of water. Mounted systems use structures that support and hold the solar panels above the water’s surface. Floating systems mount panels on buoyant structures that are held in place using anchors or mooring lines tied to shore. Floatovoltaics best apply to bodies of water that are otherwise unsuitable for other uses, such as irrigation canals, water reservoirs, or retention ponds.
Floatovoltaics offer several advantages. The presence of water beneath the solar panels can cool the panels, leading to greater efficiencies in electricity production than traditional solar systems. Likewise, the shading effect of the panels can reduce the rate of water loss due to evaporation, an advantage particularly beneficial for drought-prone regions. By utilizing existing bodies of water, these systems can also increase land use efficiency and could help alleviate competition for land. Floatovoltaics can be easier to construct and decommission compared to traditional solar sites as they do not require as many permanent modifications to the landscape. However, additional research is still needed to assess the impact of solar panels on water quality, aquatic life, and birds.
To date, deployment is very limited in the United States. Like agrivoltaics, floatovoltaics are most suitable as a tailored energy solution where a specific opportunity arises. A 2018 NREL study identified bodies of water in the U.S. that would be suitable for deploying floatovoltaics. They found that covering 27% of identified areas with floating panels could produce 10% of the nation’s current electricity generation, a sizable technical potential but still a niche application in practice compared to the scale of utility-scale solar needed to achieve decarbonization objectives.
Floatovoltaic solar systems are best suited for bodies of water that are otherwise inaccessible to other uses and as such, are functionally limited in the scale of implementation. Nonetheless, these configurations demonstrate the value of a clean energy deployment approaches that maximize land-use efficiency.
Dual-use solar potential
Deploying a range of technologies and innovative solutions is crucial in the transition to a carbon-free energy future. The potential to co-locate solar with other land uses to provide additional social, economic, and environmental benefits is a major departure from traditional energy development, which has historically been in tension with other types of land use. While dual-use solar should not be considered a silver-bullet solution to the barriers of deploying utility-scale solar, it can prove a complementary development to utility-scale efforts while providing opportunities to integrate greater local benefits into solar system design. Implementing dual-use solar at any scale will require supportive policy and land use regulations, developer interest, community support, and a robust understanding of how it can be applied in a local context.
This is the first of a three-part blog series on dual use-solar’s potential within the broader context of utility-scale solar. Later blog posts in this series provide additional context on the policy landscape and the potential feasibility of dual-use solar within California’s San Joaquin Valley.
1 Terms like “agri-solar,” “agri-PV,” or “solar-sharing” refer to the same concept as agrivoltaics.
