Reducing Post-Harvest Losses Through the Use of Innovative Solar-Powered Refrigeration Systems 

Written for the AgriSolar Clearinghouse by Ridge to Reefs staff Emma Verlinden, Paul Sturm, and Phal Mantha

In 2017, the devastation following Hurricane Maria was catastrophic for countless coastal communities. The archipelago of Puerto Rico experienced mass power loss and severe food-supply shortages, leaving many rural communities without power for extended periods of time (in some cases for as long as 6 to 12 months). Agricultural lands became unusable, with crop fields devastated by high winds, extreme rainfall, and incessant flooding. Following the catastrophe, the only seed producer in the archipelago lost nearly their entire supply due to a lack of refrigeration caused by the extended power outage. Meanwhile, shelves were empty at stores due to nearly 90% of Puerto Rico’s food being imported and food spoiling during the power outage.

In response to this challenge, Ridge to Reefs designed a Mobile Solar Walk-In Refrigeration System to help farms reduce post-harvest losses and bring high-quality produce and refrigerated farm goods to market. Additionally, Ridge to Reefs led and assisted in the construction of numerous stationary iterations of this design at various locations throughout Puerto Rico. The mobile system design is constructed around a 6’x14’ single-axle enclosed trailer, with six (280-watt) photovoltaic panels mounted on the rooftop. CoolBot technology is paired with a 10,000 BTU window air-conditioning unit, 2,000-watt Pure Sine Wave inverter, 210 amp-hours of batteries, and a charge controller to maintain temperatures between 40and 55°F per the farmers’ needs. The panels atop the trailer provide 1.68kW of power with ample battery storage, reducing the risk of crop loss in the event of a major power outage. The trailer is fully insulated (to above R-20) throughout the walls, roof, and floor, allowing for heat resistance in even tropical climates. In all, approximately 275 cubic feet of storage is available inside the unit to allow farmers to efficiently store and transport their agricultural goods. Because the power systems are grid-tied in Puerto Rico, and with such high risk of natural disaster occurrences, Ridge to Reefs designed this highly agile system to be grid-independent, using commercial, off-the-shelf technologies as dictated by community need.

Design diagram of the solar-powered refrigerated trailer system.
Aerial view diagram of the solar-powered refrigerated trailer system.

The construction and deployment of a mobile refrigeration system presents a viable solution for producers to more efficiently transport and store their goods throughout tropical regions, especially those that are susceptible to natural disasters. The entire system was constructed for approximately $10,000 USD, but potential grant and funding opportunities for farmers seeking to transition to solar operations could allow technology of this sort to become more available. Additionally, this option may allow island communities to cultivate greater market portions of locally sourced foods by increasing the sales reach of small-scale agricultural operations. Many producers do not have access to refrigerated shipping methods, and having on-site cold storage and transport for their goods can prove very economically stimulating.

Costs of electricity in island regions such as Puerto Rico and Hawai’i are on average four times higher than in mainland communities, which can prove detrimental to the capabilities of local farms in these regions. By providing farmers with the capacity to store and distribute their produce independently, they are able to reinvest the saved costs and increased profits into their own operations and increase overall productivity. In this way, the solar-powered refrigeration systems also promote local circular economies.

Completed construction of the mobile solar-powered refrigeration prototype that was donated by Ridge to Reefs. 

The deployment of the mobile solar cold-storage system also taught our team and partners numerous valuable lessons. First, in mountainous regions, maneuvering a towed trailer system can be less than ideal and a task not every driver is comfortable with. It may be worth exploring integrating this sort of system into a “Sprinter” van or similar large van. Furthermore, the utilization of lithium iron phosphate or even lithium ion battery banks may offer significant advantages and may prove to be feasible improvements. With our system, an increase in battery bank capacity would have significantly improved standalone time and a battery bank capacity of closer to 300 or 350 amp-hours would have provided three to four days of standalone time. Additionally, with improvements in solar panel technology, many higher-output panels are available with the same dimensions. For example, 330-watt panels could be used for the next generation, allowing for higher power output. The Ridge to Reefs Team plans on first upgrading the existing mobile trailer with these improvements and is also seeking opportunities to construct and deploy similar systems in the future. 

The implications of solar integration into agricultural operations are vastly important, especially considering the global call for an increase in the utilization of renewable energy sources. While this system is a small-scale mobile refrigeration unit, Ridge to Reefs has also constructed numerous other stationary solar refrigeration systems throughout Puerto Rico to ensure the security of crops for farmers during times of distress. Systems such as these could create opportunities for producers in other tropical regions such as Hawai’i by allowing them to reduce crop wastage, reach new markets, recirculate money in their community, and address concerns  related to sustainability, food security, and developing local economies.

Photos courtesy of Ridge to Reefs

Case Study: Cozy Cove Farm

By Anna Richmond-Mueller, NCAT Energy Analyst

Just outside of Gurley, Alabama, a herd of grazing llamas and alpacas find refuge from the sun underneath a solar array. Tony and Cozette O’Neil, owners of Cozy Cove Farm, have been raising the animals since 1995, shearing their fleece to make yarn and felt. Today, the O’Neils are also proud renewable energy producers for their community, thanks to the 50-kW solar system that has been generating electricity since February 2013.

A retired NASA engineer, Tony has believed in the power of solar technology since his work on the solar-powered space station Skylab in the 1970s. In 2012, with an electric bill sometimes reaching $500 a month, he learned that he could generate and sell renewable energy to the Tennessee Valley Authority (TVA). The cost of solar equipment was decreasing around this time as well, making it the ideal time to install solar on their 54-acre farm. Working with Outpost Solar, the O’Neils planned a photovoltaic system consisting of 208 fixed-tilt panels in a 100-by-100-foot area, tucked away on a corner of their pastureland next to the Flint River. Because the array was built on a floodplain, the panels had to be elevated to seven feet above ground level. The unexpected change to the design had an upside: shade for more than 100 llamas and alpacas that call Cozy Cove Farm home.

The O’Neils took advantage of several incentives to build their solar array, which totaled $160,000 upon completion. The majority of the cost was covered by a 30% federal tax credit and a 25% USDA REAP grant. Smaller grants from state and local programs brought the out-of-pocket cost to just under $48,000. Alabama Farm Credit provided the O’Neils with a loan for the remaining amount, which they were able to pay back completely in October of 2017. In just under five years, the array paid for itself thanks to a 10-year contract with the TVA that paid them 22 cents per kWh of electricity generated.

Today, 10 years after the solar system’s completion, the O’Neils continue to benefit from its installation. Service and repair costs have been low, with only one panel needing replacement from damage in the first year. At the end of their initial contract, the O’Neils signed a subsequent contract for an additional 10 years that allows the TVA to purchase the electricity they produce at the same rate their utility charges them for their energy consumption. “This provides us with approximately $3,500 a year after all of our farm energy needs are paid for,” says Tony. He also encourages other farmers considering installing solar on their property to think long-term. “Electricity cost is only going to increase in the future, and the cost of solar panels and inverters are at an all-time low at present.” While many agrisolar projects are still in the first few years of operation, Cozy Cove Farm stands as a shining example for how agrivoltaic installations can benefit their owners for over a decade.

Photo credit: Scott Sklar, George Washington University

Case Study: Mustang Two Solar Facility

Indart sheep between rows of solar panels.

By Anna Richmond-Mueller, NCAT Energy Analyst

Just outside of Stratford, California, hundreds of sheep spend their days grazing between rows of solar panels at the Mustang Two solar park. The site, owned by Idemitsu Renewables, sits on 1,160 acres and produces enough clean energy to power over 50,000 homes. The 150-megawatt facility was constructed in 2020, with the sheep taking up residence shortly after. Courtesy of Indart Solar Sheep Grazing, the herd helps maintain the vegetation growing around the solar panels while also working to improve the biodiversity of the plants on site.

Indart Solar Sheep Grazing owner Ryan Indart had grazed several sites prior to adding Mustang Two to the list, building positive relationships within the solar community along the way. When a friend at SOLV Energy, the operators of the site, informed him that the conditional use permit required grazing, Ryan jumped at the opportunity. Mustang Two was the first site Ryan had to compete for, but he successfully won the bid to be the grazier on site. In 2021, he unloaded his sheep onto what was, at the time, the largest site in his portfolio.

Two years later, the Indart sheep continue to do their part in maintaining a safe, well-managed solar site. Despite not being the easiest location to graze, Ryan and his sheep have received great feedback from both SOLV and Idemitsu. The facility has a dense foxtail barley population, and the sheep can be selective about when they choose to eat the plant. Although the foxtail may not be ideal, grazing has many environmental benefits when done under the watchful eye of a knowledgeable rancher. Over time, Ryan’s sheep will help diversify the plant life and improve the soil quality at Mustang Two, as well.

Photo by NCAT

Case Study: Slate Solar PV Park

Indart sheep grazing around solar panels.

By Anna Richmond-Mueller, NCAT Energy Analyst

Located in Kings County, the Slate Solar PV Park produces power for hundreds of thousands of California citizens, while simultaneously providing food and shade for its resident sheep herd. The 390-megawatt site, owned by MN8 Solar and operated by Canadian Solar, rests on 2,120 acres and consists of almost 951,000 bifacial solar panels. Rather than relying solely on mowing, the operators count on Ryan Indart and his company Indart Solar Sheep Grazing to provide anywhere from 1,150 to 2,000 sheep to keep most of the site’s vegetation under control.

Ryan credits his solid relationships with his clients for the opportunity to graze at the site. The Slate facility is adjacent to another PV park, known as Mustang 2, where Ryan’s sheep were already grazing during Slate’s construction phase. He reached out to his contacts at Mustang 2 to see if anyone had connections at Canadian Solar and was given the number of the asset manager for Slate. One phone call and a positive reputation amongst the solar operators in his area later, Ryan signed a three-year contract to graze his sheep as part of Slate’s vegetation management plan.

Today, Ryan says he believes both Canadian Solar and MN8 Solar are happy with the partnership. Grazing animals can help lower the operations and management costs at a solar site, which is a high priority for the businesses involved. Although Slate does mow some sections of the facility as needed, the Indart sheep significantly reduce the area that needs mowing, all while finding respite from the hot California sun underneath the panels.

Photo by NCAT

Case Study: Indart Solar Sheep Grazing

Indart sheep between rows of solar panels.

By Anna Richmond-Mueller, NCAT Energy Analyst

As the average age of the American farmer continues to rise, the question of how to transition an agricultural operation to the next generation is a concern for current farmers. Can agrisolar offer a solution to help keep multi-generational farms and ranching operations profitable and in family hands? For Ryan Indart and his family in Clovis, California, solar grazing has given them the opportunity to not only keep their sheep operation up and running, but also to expand the business to include multiple partners and grazing sites across state lines.

The Indarts have been ranching and farming in California for generations. Ryan’s grandfather first introduced the family to ranching when he purchased 1,000 sheep in 1937, later selling the wool to the U.S. government to clothe American soldiers in World War II. His parents bought the operation in 1970 and ran the business for nearly 40 years before it was his turn to carry on the family legacy. However, his parents didn’t simply hand over the operation, and Ryan worked tirelessly to reach his goal of taking over the business.

Although he had moved away from his family land after college, Ryan always loved the sheep and wanted to return to raising them eventually. He knew he needed to earn enough money to either purchase his family’s operation or start one of his own. After earning his MBA from Notre Dame in 2002, he worked in commercial real estate for several years before he and his wife Beatriz moved back to Frenso County and purchased all aspects of the family business, from equipment to the sheep themselves.

The early years were far from stress-free, however. Like many farming families in America today, the Indarts struggled to turn a profit year after year. In addition to raising sheep for wool and lamb, they did tractor work and dry farmed a variety of crops, but none of their hard work reliably produced a consistent profit. Rising wages and the increased cost of living in California led them to seriously consider moving out of the area Ryan’s family has called home for generations. Thankfully, a single phone call set the family on a new course and opened the door for the creation of Indart Solar Sheep Grazing.

In 2018, Ryan received a call from a solar developer with a 1,600-acre solar facility in western Fresno County. Large solar systems were just beginning to pepper the Central California landscape, and the developer was looking for a local sheep grazier to help manage vegetation at the site. They reached out to the California Wool Growers Association, where Ryan was serving as President, and were directed to the Indarts’ operation. When the developer offered to compensate the family for their grazing services, Ryan thought “This could be a gamechanger.” He signed his first solar grazing contract just a few short months later and spent the rest of 2018 and 2019 expanding Indart Solar Sheep Grazing.

Comparison of land grazed (right) versus not grazed by Indart sheep at the Slate Solar Facility in Kings County, California.

Today, Indart Solar Sheep Grazing includes multiple grazing partners that share the Indarts’ high degree of professionalism, and Ryan takes a lot of pride in setting a value standard for the solar grazing industry. “We run an organized business. Whenever there’s a problem we’re always there to help solve it,” he says. Including partnerships, Indart Solar Sheep Grazing has over 10,000 sheep grazing over 15,000 acres from northern California to Arizona. 

Ryan is a wealth of knowledge but has one particular piece of advice for established farmers considering venturing into solar grazing: get comfortable with being uncomfortable. After his first contract in 2018, he regularly cold called solar companies whose facilities he saw in the area, offering them his services as an experienced grazier. “You’ve got to be willing to challenge your fears. Try something new. Make a phone call,” he says. “The worst thing that can happen is they say no.” He emphasizes that farmers must be willing to try new things and adapt to the current state of agriculture in the United States. “That’s what’s made us successful.”

Ryan Indart discussing solar grazing during the Central California Follow the Sun Tour with the AgriSolar Clearinghouse.

For new farmers trying to break into the agricultural industry, Ryan believes the barriers of entry to solar grazing are fewer than those encountered in traditional farming scenarios. Land access is a common hurdle for first generation farmers, but solar grazing provides immediate access to acres of land, often with quality forage for grazing animals. Contracts with site owners also mean farmers are making money throughout the year, rather than just during lambing season. “You have instant access to revenue,” Ryan says.

Looking to the future, the Indarts plan to continue expanding their business. With just over 3,500 sheep in their personal flock, the family’s goal is to reach about 5,000 animals total. Ryan says they may be more strategic about what clients they take on as well, and subcontract with other sheep graziers who share their business values as they reach the limit of where they can graze themselves. “It’s a huge blessing to be able to stay in business in California,” Ryan says. “But I couldn’t do this without a support system.”

When speaking about his company’s success, Ryan credits his family and team members that have been with him for years. Many of the team members are originally from Peru, and employment with the Indarts’ business has provided them with the opportunity to send their children to school or buy a home for their family. “I’m very grateful I can provide jobs for these guys, and help them better their lives,” Ryan says. “That’s what makes me happy.”

Finally, Ryan states that it’s wonderful to be a part of the renewable energy movement but emphasizes that “We’ve been doing this for generations.” With proper grazing techniques, graziers have helped improve plant diversity and soil health for years before solar grazing entered the scene. Ryan says he’s proud to continue what his grandfather started, and thankful for the chance to create jobs and opportunities for his employees that have become a part of his family.

All photos by NCAT.

Case Study: James River Grazing

Sheep grazing at the Mechanicsville site.

By Anna Richmond-Mueller, NCAT Energy Analyst

Located near Richmond, Virginia, the Mechanicsville solar park is one of the state’s first utility-scale solar sites. Covering over 220 acres, the 28-megawatt, single-axis tracking site provides a source of clean power to thousands of homes in the state. More than just a solar site, though, the location is also the home base for hundreds of sheep under the care of Eric Bronson and Sam Perkins at James River Grazing. 

James River Grazing started in 2016 when founder Eric Bronson noticed the solar industry beginning to take off in Virginia. A Virginia native, Bronson attended college at Montana State University and worked for several years on large, range-based livestock operations before returning to his home state. He knew he wanted to stay involved in agriculture, but without already owning land, he realized the upfront costs were prohibitive. Compared to raising cattle or growing crops, the lower initial investment needed to successfully farm sheep gave Bronson the chance to farm in a traditional production environment before the company received its first solar grazing contract in 2019.  

For solar sites without grazing plans, mowing must be brought in for vegetation management, a difficult task for many solar developers in recent years due to labor shortages. “The grazing came along at the perfect time,” Bronson says. He explains that the Mechanicsville site was being mowed about once a month, but with the integration of livestock, it was reduced to a “clean up” mow in the fall and smaller mows in early spring. Even then, “they’re not mowing one hundred percent of the site,” Bronson explains. Only about a quarter of the site is mowed at these times, significantly lowering the time and labor cost required to control the vegetation. 

Sheep grazing under the solar panels.

Operating on the Mechanicsville site didn’t come without its challenges, however. The site hosts between 100 and 300 ewes at a time, depending on the time of year and vegetation growth. While smaller operations will move flocks on and off location seasonally, James River Grazing operates on the site year-round. Not having facilities on-site and the expansive costs to move the sheep off-site is an added layer of difficulty that comes with grazing sheep on utility-scale sites. “Everything has to be portable,” Bronson points out. Nonetheless, James River Grazing’s efforts have been so successful that SunEnergy1, the solar developer for the site, hired Bronson as Director of Livestock for the entire company and has implemented solar grazing on a number of other sites, as well. 

With a total of six grazing sites and around 1,500 sheep, Bronson says James River Grazing is looking to continue its success by creating additional partnerships with developers across the region. While being one of the first to embrace solar grazing comes with some advantages, it also means that learning involved a significant amount of trial and error. “That was one of the biggest roadblocks,” Bronson says, referring to the lack of available resources to help guide them in the early days. Their knowledge and experience also put them in an ideal place to help solar developers create construction plans with solar grazing in mind, making it much easier for grazers to care for the sheep on site. James River Grazing is still working out the details for exactly how they plan on moving into the consulting space, but their track record of success will undoubtedly make them a valuable resource for solar developers and new grazers alike.  

All photos courtesy of James River Grazing.

Case Study: Solar Oysters LLC

Solar panels powering the Solar Oyster Production System (SOPS) platform.

By Anna Richmond-Mueller, NCAT Energy Analyst

From filtering water to creating habitats for other marine species, oysters are a vital component of the Chesapeake Bay’s ecosystem. On land, they are the center of a rich cultural heritage as one of the region’s most valuable fisheries. Generations of families have made a living harvesting the bivalves, whose reefs were once so large that they posed navigational hazards for ships traversing the Bay. However, decades of pollution, disease, and overharvesting have devastated the oyster population. Modern restoration efforts and harvesting regulations offer a glimmer of hope for the bivalve, and Solar Oysters is making a big impact with its revolutionary oyster-production platform powered by solar.

Prior to the establishment of Solar Oysters, the idea to create a floating solar array came to Mark Rice, President of the Baltimore-based engineering firm Maritime Applied Physics Corporation (MAPC), while he was working on a project on the Chesapeake Bay. A local power plant utilized Chesapeake Bay water to cool the plant, and there was a growing interest in mitigating thermal discharge into the Bay. Rice and his team decided the best course of action was to remove incident solar energy from the water to offset the thermal effluent. They knew solar panels would generate valuable electrical energy while also helping to keep water temperatures down and began designing floating solar platforms to tackle the problem. As they were planning the floating arrays, they realized a source of ballast was needed to weigh down the systems and found an opportunity to help improve oyster aquaculture in the Bay simultaneously. Led by Steve Pattison, the environmental strategy firm EcoLogix Group collaborated with MAPC to provide valuable insight about stakeholder engagement, local aquaculture, siting, and environmental permitting. The two companies formalized their relationship in 2019 with the launch of Solar Oysters LLC. By October 2021, Solar Oysters had raised enough money through private funding to construct the first Solar Oyster Production System (SOPS) prototype—a floating high-density oyster-production system automated through solar energy—in Baltimore Harbor.

Graphic design of the SOPS prototype.

Measuring 40’ by 25’, the platform has 12 375-watt solar panels attached to the roof capable of generating 36 kWh, alongside four on-board batteries with a 14.4 kWh storage capacity. The solar array powers a system of five vertically rotating ladders on timers, each consisting of 23 rungs capable of holding up to five oyster baskets per rung. This provides a maximum capacity of 575 baskets. As the ladders rotate, the oysters are exposed to different water quality parameters, including temperature, salinity, and dissolved oxygen, resulting in uniformity among all ladder basket positions. At the top of the rotation, the baskets are completely out of the water and exposed to sunlight before resubmerging as the next rung peaks. A manual spray wash system is mounted onboard and pulls water directly from the Bay, allowing those tending the platform to clean the baskets and oysters as needed.

SOPS ladder system
Platform manager Emily Caffrey with an oyster basket from the ladder system.

Compared to traditional oyster farming methods, the SOPS platform brings a technological advancement to an industry that has not changed considerably in decades. On farms where the oysters are grown at surface level in floating cages, workers must manually flip each cage over to prevent biofouling. Biofouling refers to the accumulation of organisms such as algae, barnacles, or mussels on the oyster shells and equipment, thus impeding the growth of the oyster population. SOPS greatly reduces the manual labor needed to keep the oysters healthy, thanks to the rotating ladders and spray system. Moreover, the system’s vertical design drastically increases the number of oysters produced per acre. While a traditional float farm may produce between 250,000 and 400,000 oysters per acre, SOPS can produce up to 250,000 oysters on one 0.02 acre-sized barge. This small footprint is an advantage in securing permits or leases compared to a traditional farm that often requires permitting several acres.

Solar Oysters’ first growing season was in partnership with the Chesapeake Bay Foundation as a participant in the Baltimore Harbor oyster gardening program. A grant from the Abell Foundation afforded Solar Oysters the opportunity to onboard spat-on-shell oysters in the fall of 2021. After the 2022 growing season, about 40,000 oysters were transplanted to the Chesapeake Bay Foundation’s sanctuary reef at Fort Carroll, where they significantly helped to advance the Foundation’s oyster-restoration efforts. That same day, Solar Oysters accepted an additional 490,000 spat-on-shell oysters for the upcoming 2023 growing season. Concurrently, seed oysters were being grown to evaluate the effectiveness of the SOPS technology for the oyster consumption market, onboarded at the same time as the first spat-on-shell cohort. After 12 months of growth, the seed oysters measured between 2.5 and 3 inches in length, a size that could take 18 to 24 months to reach using traditional growing methods.

Seed oysters.
Spat-on-shell oysters.

Solar Oysters’ goal is to develop, manufacture, and sell the SOPS technology to organizations focused on oyster restoration or growing oysters for market. In 2023, they plan to continue research on the SOPS platform as they narrow down the best practices for growing oysters on the prototype. Other improvements to the system will include installing a semi-automated spray wash system that replaces the current manual one onboard. The 2023 season will also see Solar Oysters continue to contribute to restoration efforts in the Chesapeake Bay. With such an encouraging first growing season of both spat-on-shell and seed oysters, the technology has the potential to address environmental concerns while also modernizing oyster aquaculture for growers in the Chesapeake Bay and beyond.

All photos courtesy of Solar Oysters LLC.

Case Study: Sunzaun Vertical Solar System

By Anna Richmond-Mueller, NCAT Energy Analyst

Sunstall, a California-based solar installer, is helping farmers harvest the sun twice with their new vertical solar system, known as Sunzaun. The Sunzaun vertical solar system was originally engineered by a company in Germany. After seeing successful installations of the product in Europe, Sunstall decided to bring the design to the United States. The market for agrivoltaic installations in America is growing, but one of the biggest barriers is tied to land use. Concern about installing solar on valuable agricultural land is common, and often increases as the solar system’s footprint increases. Traditional solar installations use a racking system to secure solar modules, which are then tilted to the appropriate angle on a horizontal axis. These tilted systems require a larger amount of land compared to vertical systems. Sunzaun is installed in a portrait orientation between two piles with no racking system involved. The minimalistic design uses holes in the module frames for a simple attachment to the piles without the need for a heavy racking system, while the bifacial modules themselves allow both sides of the panel to produce energy.

Sunzaun’s portrait orientation allows adjustments to be made more quickly during later stages of a project. In systems designed with a landscape orientation, the rails used to mount panels onto the racking system are cut to fit the expected panel size. Should the size of the panel change after all other components have been finalized, the project may be delayed significantly while the rails are reengineered to fit the updated panel size. Thanks to Sunzaun’s unique design, it is easy to adapt to a change in panel size by simply adjusting the distance between each pile. It is even possible to adjust the height of the panels from the ground if needed.

Completed in 2022, the first Sunzaun installation in the United States is located on a vineyard in Somerset, California. Although the vineyard owner already has rooftop solar on the property, an interest in new solar developments and agrivoltaics led to a new system within the rows of grapevines. Composed of 43 450-watt modules connected to a microinverter and two batteries, the Sunzaun system sits on a hillside between rows of grapevines. Only one row of vines needed to be removed to make room for the system, and harvesting equipment is still able to work in the field directly next to the Sunzaun. While it is too early to say for certain what additional benefits the Sunzaun may provide beyond on-site power generation, the benefit of preserving grapevines alone is a significant win for the winery.

As the United States continues to take steps to combat climate change, innovative solar system designs are more important than ever. The Sunzaun’s streamlined design reduces the time it takes to get agrivoltaic projects off the ground. When you factor in the ability to save valuable crops and viable land with a vertical system, the minimalistic approach that Sunzaun offers farmers becomes even more appealing. A successful growing season at the Somerset vineyard will hopefully reveal even more benefits to installing this promising product and encourage others to consider the value of a vertical solar installation as well.

All photos courtesy of Sunstall Inc.

Case Study: Soliculture Research Greenhouse

By Anna Richmond-Mueller, NCAT Energy Analyst

When it comes to conversations surrounding energy and water use in the modern world, the agricultural industry’s consumption of both is often at the forefront. As the world’s population continues to grow, humanity is tasked with the challenge of finding ways to meet both food and energy demands across the globe. “I really believe that greenhouse growing is the epitome of sustainable agriculture,” says Soliculture cofounder and CEO Dr. Glenn Alers. Whether it is the ability to greatly increase crop yields when compared to traditional open field growing, or the potential for increased water-use efficiency in combination with hydroponics, greenhouses could play a key role in addressing these concerns. Solar greenhouses also could also play a role in mitigating future energy crises. 

Soliculture began in 2012 as a startup in the Physics Department at the University of California Santa Cruz. Dr. Alers and his cofounder were conducting research on luminescent solar concentrator panels when he realized the technology’s agricultural potential. Luminescent solar panels utilize a luminescent dye that selectively absorbs a portion of the solar spectrum and readmits light at a different wavelength. The dye used in Soliculture panels absorbs the green portion of sunlight with low photosynthesis efficiency and converts it to red light with much higher photosynthesis efficiency. The panels enhance the light quality inside a greenhouse by optimizing the light spectrum for improved plant growth. Moreover, the panels contain bifacial cells that collect the light reflected from the crops planted below them. The red luminescent dye also enhances the power output of embedded cells by 15 to 32%, compared to a conventional panel. 

Installed Soliculture luminescent solar panels.

In 2019, Soliculture began a research project on Whiskey Hill Farms in Watsonville, California, aimed at developing these solar panels for use on hybrid high-tunnel greenhouses. As an active organic farm already growing produce in both field and greenhouse settings, Whiskey Hill Farms served as an ideal host for the project. The Soliculture research greenhouse was constructed from the ground up with help from a local high tunnel installer, measuring 120’ long and 25’ wide upon completion. Additional bracing was added to the roof structure, forming a “queen style” truss to support the weight of the panels. One half of the high tunnel was covered by a semi-clear plastic film that served as the control for the upcoming crop growth study, and the other was covered by Soliculture solar panels. These panels were specially designed for high tunnel greenhouses and had a cell coverage of 42%.  

Interior of research greenhouse with panels installed.

The project hit a temporary snag when waterproofing the panel racking system proved to be more of a challenge than expected. At first, horizontal mounting bars were attached to the tubing of the greenhouse’s roof frame and foam weather stripping was installed between the panels to create a watertight seal. Water was still able to leak through at the corners and where the mounting bolts connected the panels to the roof. Knowing the potential for these leaks to cause erosion and negatively impact crop growth, the Soliculture team returned to their laboratory and created a modified racking system specifically for high tunnel application. This new system used mounting brackets that attached to the bottom of the frame and utilized a rubber “T” gasket inserted between the panels to create a seal. Finally, the plastic film portion of the roof was attached to the panels using an aluminum channel screwed into the panel frame and “wiggle wire” to hold the plastic film in position. With a waterproof roof in place, the crop trail was ready to commence.  

The following crops were selected for planting following the completion of the high tunnel in mid-November: strawberries, red romaine lettuce, red butter head lettuce, cilantro, mustard greens, and turmeric. To ensure the trial’s results would translate to commercial production, the research team used common commercial growing methods throughout the duration of the trial. These methods included drip irrigation with untreated well water, sand filtration, and liquid organic fertigation. By the end of the trial, the majority of the crops grown under Soliculture panels matured close to two weeks ahead of those grown under the clear film portion of the high tunnel. The fresh weight for the under-panel crops was superior as well, with red butter head lettuce seeing the greatest benefit at 145% higher weight. Mustard greens weighed in at 95% higher, cilantro at 35%, romaine lettuce at 32%, and turmeric at 25%. The strawberry fruit showed no statistically significant difference in fresh weight, but the single 5’ by 120’ planted bed yielded more than 350 pounds of fruit by the end of July.  

Crops grown under Soliculture panels.
Crops grown under plastic film.

On top of the very successful crop trial, the power generated by the greenhouse panels was used by Whiskey Hill Farms to power their day-to-day operations. A total of 58 Soliculture panels provided the farm with a 6kW system, which was connected to an inverter. The AC power was then fed back into the farm’s power system, a testament to how greenhouse solar can benefit the farm beyond improving plant growth.  

The field of agrivoltaics is constantly evolving, with numerous researchers and farmers searching for the ideal nexus between the agricultural industry and energy production. Soliculture’s contributions to agrivoltaics is important for farmers who have reservations about growing food underneath and around solar panels. “We haven’t seen any negative effect on plant growth,” Dr. Alers says, referring to the Whiskey Hill Farms project and several other successful Soliculture installations across the United States and Canada. Greenhouse production has always had the potential to help alleviate the water crisis and increase the amount of food grown per acre, but Soliculture’s technology is giving it a bright future in energy production, as well. 

All photos courtesy of Soliculture 

Case Study: Mauntel’s Solar Sheep

Written By: Alex Delworth, Clean Energy Policy Associate; Center for Rural Affairs

Just off the campus of Maharishi University in Fairfield Iowa, sits a 1.1-megawatt (MW) solar farm. Beneath the panels, a flock of sheep and their newborn lambs are grazing, while beginning rancher Emily Mauntel and her Australian Shepherd Ziggy stand back and admire their work.

Solar farms pose a considerable opportunity for multipurpose agricultural uses in rural spaces. Iowa has seen a rapid increase in solar project development the past two years. According to the Solar Energy Industries Association, the industry is expected to add another 1,304 MW—a 250% increase over current installed capacity—during the next five years. Depending on the type of technology installed, this could mean between 6,520 and 13,040 acres of land will be used for solar production. With proper local siting, these projects will be required to plant and maintain native vegetation underneath the panels. This increase in open pasture presents a unique opportunity to combine traditional land uses with renewable energy development, such as pollinator habitats or open grazing for livestock. An opportunity Emily has already begun benefiting from.

Originally from Michigan, Emily relocated to Fairfield to attend Maharishi International University. While completing a three-month internship at a goat farm in Oregon as part of the university’s Regenerative Organic Agriculture certificate program, her interest in livestock grew. After the internship, she remained in Oregon for another year, working for various livestock operations and gaining experience in the industry. In late 2021, she moved back to Fairfield to work on the university’s vegetable farm and help her peers in their respective livestock businesses.

Emily Mauntel holding a solar-grazing lamb. Photo: Emily Mauntel

One day she and a friend were driving past a large solar array in Minnesota and noticed how the infrastructure was perfect for sheep grazing. They knew about the array in Fairfield, which is owned by the university and operated by Ideal Energy, a local solar company. She contacted the solar company to pitch the idea first and gained their approval before approaching the university. Both parties were ecstatic because the university had been looking for somebody to graze livestock and Ideal Energy saw an opportunity to avoid spending about $5,000 for annual landscaping, according to the company. Emily said the two parties came to an agreement that she would graze the array, which provided her an opportunity to access pasture in exchange for landscaping the solar farm. With this agreement, Emily benefited by not having lease payments for the time her sheep were on the farm, saving her approximately $360 per month according to Iowa State University’s land lease estimates, or about $2,520 for 2022.

Sheep grazing under solar array. Photo: Emily Mauntel

Once Emily had approval, she and her friend went into business together and purchased a 30-head herd of sheep from an auction in Texas. In May 2022, 29 ewes and one ram were dropped off on the six-acre, 1.1-MW solar farm. Before purchasing the herd, she surveyed the land and determined that, given the amount of growth on the site, she would be able to graze five sheep per acre. That is two more than usual because of how lush the plant life was on the property. The site was planted with a mix of flowering prairie species, including clover, fescue, broad-leaf plantain, and others, which served as a good food source. The sheep were allowed to roam freely throughout the solar array, something Emily said worked well. Overall, she believes rotational grazing would have been more efficient but would have required a larger investment due to the cost of a moveable fence.

Emily with her herd. Photo: Emily Mauntel

What makes this story especially interesting is that the agribusiness model directly addresses two major issues beginning farmers face—access to land and infrastructure. A 2017 survey by the National Young Farmers Coalition found that land access was the number one issue their respondents faced. Young farmers, according to the survey, are also the most inclined to rent, which makes finding land with the right infrastructure more difficult.

The Fairfield solar site’s infrastructure made the land even more attractive to Emily. She said it had sufficient fencing to hold her sheep and keep out predators. Due to the required native vegetation management, it also had plenty of food for the sheep, which means she never had to supplement food for them, except a mineral feed mix for nutrition. A water source to fill up the livestock troughs and an access road straight up to the gate also proved beneficial. Considering all of these factors, Emily was able to cut a lot of costs throughout the process.

Newly energized by the experience she has gained through solar grazers and managing her own livestock, Emily is now looking to return to the West to continue ranching. She and her business partner plan to sell their herd. Emily hopes to see the solar grazing model continue on the site, saying it has been a perfect opportunity for her to gain experience in the industry, and she believes it will be a great opportunity for the next person, as well.