![](images/Logos/PV%20Magazine.jpg)
July 6, 2023
By
MICHAEL SCHOECK
Grassland agrivoltaics show minimal difference in
forage yield to traditional growth
A Colorado State University study found that
despite a 38% reduction in light availability, a C3 semi-arid
grassland only reduced aboveground productivity and photosynthesis by
6%, pointing to the feasibility of grassland agrivoltaics.
![](images/images_07_07_2023/Jacksgarden-1200x509.jpg)
Agrivoltaic installation at Jack's Solar Garden
in Longmont, Colorado. Jack's Garden
Agrivoltaic systems, where solar
photovoltaic arrays are co-located with crop or forage production, can
alleviate the tension between expanding solar development and loss of
agricultural land. However, the ecological ramifications of these
arrays are not yet well known.
Agrivoltaics bring notable benefits, including creating microclimates
for crops, shade to grazing animals, improved forage quality, and
increasing farmer income and income stability. While the installation
of traditional solar arrays tends to increase soil compaction, reduce
soil carbon and nutrient content, and reduce water retention, care can
be taken during the installation phase to minimize the impacts on soil
and vegetation. Agrivoltaic solar arrays may be better able to
maintain crucial ecosystem services such as carbon storage, water
retention, and habitat quality.
A new report by Colorado State University used field measurements and
a plant hydraulic model to quantify carbon-water cycling in a
semi-arid perennial grassland growing beneath a single-axis tracking
solar array in the Rocky Mountain State.
Although the solar array reduces light availability by 38% during the
day, photosynthesis and above ground primary productivity were reduced
by only 6–7% while evapotranspiration or the evaporation of water from
soil into the atmosphere decreased by just 1.3%.
These minimal changes in carbon-water cycling occurred largely because
the sample plants’ photosynthetic traits underneath the panels changed
to take advantage of the dynamic shading environment.
The test results indicate that agrivoltaic systems can serve as a
scalable way to expand solar energy production while maintaining
ecosystem function in managed grasslands, especially in climates where
water is scarce compared to sunlight.
Agrivoltaic systems are promising in water-limited regions such as the
Western U.S. due to their capacity to moderate thermal environments
and reduce plant water-use and soil evaporation. Semi-arid and arid
grasslands are a favorable location for such arrays given their short-statured
vegetation and relatively flat topography, the CSU report found.
The U.S. is home to close to 40 million acres of grassland for hay
production and non-alfalfa forage. It has been estimated that close to
10 million acres of high-density photovoltaic systems are needed to
achieve statewide decarbonization goals by 2050. Thus, the report
notes that managed grasslands have the potential to house an
increasing amount of collocated agrivoltaic systems at a meaningful
scale while concurrently increasing land-use efficiency.
However, the CSU report affirms certain unknowns still exist about the
long-term impacts of agrivoltaic systems, including the degree to
which reductions in light availability will limit plant
photosynthesis, and thus forage production.
Water retention in grassland agrivoltaics could also translate into
enhanced ecosystem resistance to weather extremes such as droughts or
heat waves.
Overall, many uncertainties remain regarding the highly dynamic
microclimate within agrivoltaics, the physiological responses of
plants to microclimate variability, and how solar arrays impact carbon
and water cycling at decade-level time scale.
Jack’s Solar Garden
In the U.S., where the CSU study was undertaken at the first widely
studied agrivoltaic project, Jack’s Solar Garden, a 1.2 MW, 3.5-acre
solar field in Longmount, Colo., with new crops grown underneath since
2020, studies have been undertaken for just the last few years.
Widespread adoption of agrivoltaics in managed grasslands will depend,
in part, on the degree to which ecosystem function within the array
can be maintained despite reductions in light availability.
At Jack’s Solar Garden, the CSU study used plant hydraulics and soil
hydrology to simulate grassland growth and hourly carbon-water fluxes
over a 23-year time period forecast. Using single-axis tracking
panels, common smooth brome pasture grass grows underneath and between
the solar panels in 17 foot spaced rows.
The CSU model was measured with plant traits and driven by a
combination of measured and reanalysis-derived weather data. The study
group partitioned the agrivoltaic system into four locations:
Areas underneath the eastern and western edges of the solar field
receive additional precipitation from panel runoff, and experience
full sunlight in the morning and afternoon, respectively.
Locations between the panel rows experience a microclimate similar to
a non-agrivoltaic grassland (with the exception of minor morning and
afternoon shade).
Locations directly under the solar panels are mostly shaded and
receive reduced direct precipitation inputs. The CSU group compared
these within-array locations to a control plot located 32 feet away
that had similar vegetation composition and management history but not
influenced by solar panels.
The impact of agrivoltaics on grassland function will likely differ
across climates and species. While reductions in productivity are
commonly observed in more moderate moisture ecosystems, drier regions
may experience increases in plant growth under solar arrays due to
more acute water limitation in those environments, the study found.
The CSU study was undertaken using C3 type grass, a cool season grass
type found in cooler temperature environments and less sunlight
requirements, with high moisture retention and high frost withstand.
Future studies by the group will focus on C4 grassland plots, which
are warmer environment, high light factor grass with lower moisture
requirements.
The report was led by Steven A. Kannenberg of West Virginia
University, with participation by Matthew Sturchio and Alan K. Knapp
of Colorado State University, and Martin Venturas of Universidad
Politécnica de Madrid.
Green Play Ammonia™, Yielder® NFuel Energy.
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