Agrivoltaics

Introduction

Fig. 1: Sheep under solar panels, an example of grazing agrivoltaics. (Source: Wikimedia Commons)

Commercially, electrical power from solar energy is collected through solar farms, which are large plots of land that are covered in rows of photovoltaic cells; the electricity from these photovoltaic cells is fed into the grid and used by consumers. However, a major challenge in the process of commercializing solar energy is the amount of land required to feasibly and economically produce industrial-scale energy - unlike many oil, natural gas, and coal power plants, a solar farm needs between 5 and 10 acres per megawatt; as such, a 20 MW solar farm could occupy up to 200 acres. [1] Furthermore, many contemporary solar installation practices are harmful for the ground environment of the solar farm - grading the land, removing excess vegetation, and adding gravel to stabilize the photovoltaic cells can all render the land unusable for wildlife. [1]

To address these concerns and make better use of the ground underneath the solar panels, increased attention has been given to systems that co-locate photovoltaic cells and agricultural cropland for dual use electricity-food production. [2] These "agrivoltaic" systems have shown promise in preliminary trials and are being actively investigated as a future direction for commercial solar farms.

Implementation and Cost

Agrivoltaic systems can be arranged in a number of different configurations, all of which involve placing a standard photovoltaic installation paradigm - such as fixed position, stilt-mounted, or 1-axis tracker solar cells - on the same piece of land as either grazing, pollinator, or crop farmland. [3] For grazing configurations, agrivoltaics is limited to livestock that have a low chance of harming the photovoltaic cells, such as chicken or sheep. An example of grazing agrivoltaics is shown in Fig. 1.

The National Renewable Energy Laboratory conducted a technical cost analysis of each of the possible agrivoltaic combinations to produce a solar farm rated at 500 kW. [3] The data for the study was collected from eight American states. Based on the results (shown in Table 1), the NREL determined that agrivoltaic systems would have a cost premium of between $0.07/W_DC to $0.80/W_DC. Relative to the baseline cost of a non-agrivoltaic fixed position solar farm of $1.53/W_DC, this represents a percentage increase of between 5% and 52% per W_DC. [3]

In addition to these theoretical cost analyses, there have been some preliminary trials that attempt determine the profit of agrivoltaic systems when implemented at commercial scale. Perhaps the most notable of these trials was the APV-RESOLA project conducted by the Fraunhofer Institute for Solar Energy Systems. [4] The project, which began in 2016 at the Heggelbach agrivoltaic farm in the German state of Baden-Württemberg, used stilt-mounted solar cells in combination with four plants - potato, winter wheat, celeriac, and clover grass to investigate the feasibility of a crop farmland agrivoltaic configuration. To quantify the relative productivity of single-use land to the dual-use agrivoltaic system, the researchers computed the land equivalent ratio (LER) for each plant-solar cell combination during 2017 and 2018. The LER is defined as the ratio between the land area required for a single-use system to achieve the productivity of a dual-use system; a value greater than 1 means increased productivity of the agrivoltaic system relative to the single-use configuration. [4] The researchers found that the LER was between 1.56 and 1.87 for all configurations, depending on the year and plant grown; in particular, the relatively hot and dry year of 2018 had larger land equivalent ratios. [4] The full results of the APV-RESOLA project are shown in Table 2.

Conclusion

Agrivoltaic systems are still undergoing active research and development; however, there have been several committed efforts from academic, industrial, and government organizations to advance the technology. For example, both Italy and China have commercial agrivoltaic projects currently deployed. [5] Hopefully, more work in this field will contribute to a more sustainable future.

© Nikesh Mishra. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.

References

[1] J. Macknick, B. Beatty, and G. Hill, "Overview of Oportunities for Co-Location of Solar Energy Technologies and Vegetation," U.S. National Renewable EnergyLaboratory, NREL/TP-6A20-60240, December 2013.

[2] J. Macknick et al., "The 5 Cs of Agrivoltaic Success Factors in the United States: Lessons From the InSPIRE Research Study," U.S. National Renewable EnergyLaboratory, NREL/TP-6A20-83566, August 2022.

[3] K. Horowitz et al., "Capital Costs for Dual-Use Photovoltaic Installations: 2020 Benchmark for Ground-Mounted PV Systems with Pollinator-Friendly Vegetation, Grazing, and Crops." U.S. National Renewable Energy Laboratory, NREL/TP-6A20-77811, December 2020.

[4] M. Trommsdorff et al., "Combining Food and Energy Production: Design of an Agrivoltaic System Applied in Arable and Vegetable Farming in Germany," Renew. Sustain. Energy Rev. 140, 110694 (2021).

[5] M. A. Al Mamun et al., "A Review of Research on Agrivoltaic Systems," Renew. Sustain. Energy Rev. 161, 112351 (2022).