Frontiers in multi-benefit value stacking for solar development on working lands


 Global solar power generation is predicted to expand significantly in the coming decades. Croplands and rangelands - commonly called working lands - will likely absorb a significant share of new utility-scale solar capacity due to land availability and proximity to existing load centers and transmission infrastructure. Beyond meeting energy needs, working lands already provide critical ecosystem services like food production, nature-based recreation, and biodiversity conservation. In the context of such competition for working lands, studies and real-world experiments have begun to investigate the co-location of solar with agriculture, habitat conservation, and water conservation, including through low-impact solar development. This has resulted in a patchwork of co-location approaches across multiple disciplines such as energy planning and policy, food systems science, and natural resources management. Prior work is also largely dominated by approaches to co-locate just one activity with solar development. However, beyond this patchwork lies a new frontier — an emerging need for broader and more deliberate consideration of multiple energy and non-energy activities on working lands. Therefore, in lieu of the current array of fragmented approaches and to facilitate a more systematic exploration of this new frontier, we offer a new Multi-Benefit Value Stacking (MBVS) framework to explore land use efficiencies from co-location of solar generation and non-energy uses on working lands, a clear conceptual definition of such opportunities and the scales at which they can be considered, a table of compiled examples, and key gaps for research and policy.


Introduction
Global solar photovoltaic (PV) capacity grew rapidly from 70 GW in 2011 to 942 GW in 2021, accounting for nearly 3.7% of electricity generation in 2021 [1]. It is predicted to expand significantly in the coming decades, propelled by falling costs, policy incentives, and climate change mitigation goals. Croplands and rangelands-commonly called working lands since they are actively managed for farming, ranching, and forestry-will likely absorb a significant share of new utility-scale solar capacity due to land availability and proximity to existing load centers and transmission infrastructure [2]. For instance, in the United States, to meet California's goal of 100% clean energy by 2045, 35%-50% of all solar capacity will likely be on working lands [3]. Beyond meeting future energy needs, working lands already provide critical ecosystem services like food production, nature-based recreation, and biodiversity conservation.
In the context of such competition for working lands, studies and real-world experiments have investigated the co-location of solar and agriculture through solar-centric, vegetation-centric, and co-optimized agrivoltaic systems [4][5][6][7][8] (see Mamun et al (2022) [9] for a review). Examples include beekeeping or growing shade-tolerant crops under solar panels. Beyond agriculture, there is nascent but growing research on co-locating solar generation with habitat conservation and water conservation [10], including through low-impact solar development [11].
While optimizing land use for multiple benefits is not a novel concept, prior work is largely dominated by approaches to co-locate just one activity with solar development. Some notable exceptions include co-locating pollinator habitat with both solar and agriculture [12] and co-locating solar and agriculture with horticulture and dairy-grazing [13]. This has resulted in a patchwork of co-location approaches across multiple disciplines such as energy planning and policy, food systems science, and natural resources management. However, beyond this patchwork lies a new frontier-an emerging need for broader and more deliberate consideration of multiple energy and non-energy activities on working lands.
To facilitate a more systematic exploration of this frontier, we offer a novel multi-benefit value stacking (MBVS) framework to explore land use efficiencies from co-location of solar generation and non-energy uses on working lands, a clear conceptual definition of such opportunities and the scales at which they can be considered, a table of compiled examples, and key gaps for future work in research and policy.

Definition
MBVS is the combination of energy and non-energy land uses on working lands to augment the total sum of benefits achieved through land management. The MBVS framework brings together the concept of value-stacking from the field of energy and the concept of multiple-benefit conservation [14] from the fields of natural resources management and food systems science (see figure 1).
Value-stacking is an established concept in the field of energy, where compatible energy applications such as solar generation and battery storage are co-located to increase profitability and provide multiple grid services. Multiple-benefit conservation is an emerging concept in natural resources management and food systems science, where land is  intentionally managed for ecological and societal cobenefits [14,15]. Currently, value-stacking does not consider agricultural and conservation co-location and multi-benefit conservation does not include energy co-location. In the context of increased solar deployment, mounting water constraints and growing conservation needs, this is an opportune time to employ the MBVS framework to systematically explore how energy and non-energy uses of working lands can be co-optimized from technical and policy standpoints. To clarify, we use the phrase 'energy uses' to mean energy production directly on the land such as through solar PV installations. Bioenergy crops grown on working lands are considered crop production for the purposes of this article, even though they are used to generate energy subsequently. Further, while we do not consider wind energy generation, exploring the compatibility of competing renewable energy technologies on working lands represents a useful future expansion of the MBVS framework.
MBVS can thus be of two types: (a) vertical stacking, where multiple land use activities are integrated (or layered) at the field level; and (b) horizontal stacking, where multiple land uses are optimized across an operation or region to maximize feasibility, efficiency, and profitability.

Scales of consideration
We identify three distinct but interlinked scales at which MBVS can be conceptualized for solar development (see figure 2): field (a crop field/livestock pasture or paddock), operational (an entire farm/ranch) and regional (an agricultural region containing many farms/ranches). Distinct decision-makers and policies operate at each scale. At the field level, a farmer or rancher can vertically stack a solar project with agricultural activities (e.g. livestock grazing, row cropping) or nature conservation (e.g. reduced soil erosion, native plant restoration, wildlife habitat). For instance, a farmer could combine agrivoltaics with battery storage, where a portion of the solar panels are dedicated to on-site fertilizer production. The revenue streams for the farmer would include crop sales, the sale of solar energy and ancillary grid services, and the sale of excess fertilizer to nearby farms. Additionally, through horizontal stacking, solar can be integrated into a farmer's income diversification strategy at the operational scale. For instance, the introduction of water use constraints (such as due to the Sustainable Groundwater Management Act in California) could result in fallowing of a portion of an existing farm. The landowner could then pursue low-impact solar development with pollinator habitat on the fallowed land with continued crop production on the remaining land. Together, the field and operational levels constitute landowner decisionmaking. At the regional scale, solar facility siting can be optimized for competing land use benefits (e.g. food production, nature conservation, and amenity values). All three scales are influenced by national and international policies, commitments to climate change mitigation, and clean energy goals.
Assessing solar development opportunities through the MBVS framework enables stakeholders to intentionally consider: (a) the extent to which a range of co-located energy and non-energy activities could be compatible rather than competing, shifting from single-purpose land use planning to more complex and layered multi-use landscapes, (b) how solar development can support the long-term viability of working lands at three distinct scales, and (c) the central role of farmers and ranchers at the field and operational levels in deciding the mix of uses on their private lands. This perspective can inform decisionmaking by landowners, solar developers, local governments, and policymakers balancing energy and non-energy land uses.  [20], although further research is needed. (e) Overall, prior work has repeatedly pointed to the relative nascence of our understanding of the co-benefits and disadvantages of solar generation stacked with existing uses on working lands [21]. With some exceptions, prior work has also focused on stacking PV systems with just one non-energy use, rather than the multiple uses often present in such landscapes.

Key gaps in research and policy
The identification of this new frontier highlights the need for various future directions of work on MBVS from both research and policy standpoints.

Research gaps
Drawing on table 1, we highlight several research gaps: (a) Evaluating feasibility of multi-benefit stacks at scale and by geography: First, as table 1 shows, agrivoltaics are a growing area of research but there is limited work on bundling nonagricultural land uses like conservation with solar development, perhaps because solar development is a high-impact activity. Some research has investigated nature conservation under solar arrays [8,40,41], such as conservation of Kit Fox habitat in California's San Joaquin Valley [20], but examples are limited. With the growing deployment of solar projects on working lands, there is thus a need to identify (a) conservation approaches that can be stacked with solar PV, and (b) conservation approaches that can be stacked with both agriculture and solar PV, either horizontally or vertically. Second, many 'stacked' solutions, even in agrivoltaics, are currently either demonstrative academic projects or small-scale applications on farms that can afford them. There is thus a need to evaluate existing and new stacked solutions to identify the most feasible, scalable, and financially viable multi-benefit value stacks by geography.
Third, as the last column in table 1 illustrates, vertical stacking at the field level is more commonly considered than horizontal stacking in terms of how landowners allocate their land at the operational level and how their decisions collectively impact regional land use. This relative paucity of horizontal stacking approaches could be due to the lack of an accepted conceptual framework, the complexity of accounting for multiple ecological and economic variables, and the recency of solar generation expansion on working lands. Nevertheless, it is a key gap that needs further research and analysis. (b) Bundling multi-benefit payments: Despite growing global interest in payments for ecosystem services (PES), few studies have explored the legal and technical possibilities for landowners to 'bundle' distinct PES with other multi-benefit stack components. In the US, for example, new funding opportunities to combine solar with ecosystem services are beginning to address this need [42], but similar efforts will be needed in other contexts.
(c) Centering landowner decision-making: Private landowners often decide whether to put solar arrays on their lands based on factors like profit and viewshed, and in the face of climate-related challenges around water constraints and habitat conservation. Prior work on siting solar capacity has often relied on geospatial optimization and stakeholder analysis to identify least-conflict lands [3] at the regional, state and national scales. The critical variable of landowner decision-making at the field and operational levels thus needs more attentionhow does a landowner decide the mix of land uses on their property, and what are the factors that drive their decisions? Such research can offer a more nuanced qualitative understanding of the key factors that influence decision-making in ways that complement quantitative spatial studies. (d) Accounting for climate-driven shifts in working lands: Extreme heat and water scarcity are already impacting working lands and can strongly influence landowner decision-making. For example, landowners may enter long-term land leases with solar developers when they anticipate land fallowing due to decreased water availability [43]. Research on how climate-driven shifts will impact working lands can assist local and state government agencies as they engage stakeholders from the energy, agriculture, and conservation communities. This process would ensure that multiple goals can be achieved: habitat conservation, renewable energy development, protection of prime farmland from conversion, and food security.

Policy gaps
From the policy perspective, we find several opportunities: (a) Integrated land use and energy planning: Prior work has repeatedly pointed to the need for increased cross-sector coordination across policymakers, the solar industry, and farmer groups and improved alignment of policy incentives across energy planning, land use planning, water security, and nature conservation [44]. For instance, improved coordination can facilitate the provision of adequate transmission capacity to support utility-scale solar generation. It can also help account for future water availability, land fallowing, and conservation of high-quality habitat in solar siting. (b) Simplify how farmers and ranchers can unlock multiple, value-stacked income streams: Many working lands are privately-owned, which means that land productivity is directly tied to the livelihoods and well-being of landowners. Access to value-stacked income streams via novel agricultural technology (AgTech) approaches, ecosystem service markets [45], and private sector sustainable sourcing initiatives could thus enable farmers and ranchers to increase and diversify their income. For example, rancher cooperatives could be created to streamline the establishment of solar leases by livestock operations, while maintaining grazing for improved soil health. This could unlock new income from carbon offsets. (c) Develop multi-purpose environmental policies, wherein national, state, regional and local policies work in tandem towards the optimal combination of energy and non-energy services. For example, government agricultural subsidies could provide financial and technical support for piloting and deploying integrated solar-cropping systems, reducing the financial burden and risk to small farmers and ranchers.

Data availability statement
All data that support the findings of this study are included within the article (and any supplementary files).