Frequently Asked Questions
Source: Farmer's Guide to Going Solar
Silicon-based PV cells are the most widespread solar photovoltaic technology used. Research shows that "leaching of trace metals from modules is unlikely to present a significant risk due to the sealed nature of the installed cells."
Some solar modules use cadmium telluride (CdTe). Cadmium compounds are toxic, but studies show that such compounds cannot be emitted from CdTe modules during normal operation or even during fires. Industrial incineration temperatures, which are much higher than grassfires, are required to release the compounds from the modules.
There have been relatively few studies on microclimate effects under solar modules, but the research shows there is little to no average impact. Air temperatures tend to be cooler under the panels during the day and warmer under the panels at night. One study found that air temperature, humidity, and crop temperature under modules was similar to conditions of full sun. This study found that soil temperatures at night under the modules was less than that of soil temperatures in full sun all day. There have been no studies linking solar development with pest problems, but studies have shown how native plants can thrive underneath solar installations.
Solar modules will actually cool crops and vegetation underneath during the day, and keep them warmer at night. Studies have shown these temperature differences cancel out and that mean daily crop temperatures were similar under modules compared to full sun crops and there was no impact on crop growth rates. Modules can provide farmers the ability to grow shade resistant crops and to diversify crop selection, while also extending growing seasons and reducing water requirements. One study found that shading from solar modules produced lettuce crop weight equal to or greater than lettuce grown in full sun.
A security fence can keep out larger animals. Fencing can be built to accommodate smaller animals such as kit foxes. Areas beneath the modules can be reseeded to provide habitat and forage to pollinators, birds, and other small species.
Sheep are commonly are being used for grazing for vegetation control at solar facilities in the United States and Europe as sheep do not climb on or harm the modules. Raising the PV modules in height is not necessary to accommodate grazing as vegetation is accessible beneath the modules at standard heights. Cattle grazing is generally not compatible with PV facilities due to the risk of damage to modules. Sheep grazing to control vegetation growth can benefit local shepherds, solar operators, and the land due to a reduction in mowing, herbicide, and other vegetation management needs.
Solar modules create an opportunity for avian interactions. PV modules are generally less reflective than windows and are installed at numerous airports. Nonetheless, avian injuries and mortalities may occur through collisions with power lines, vehicles, fencing, and solar equipment and structures such as modules. There are some concerns that birds might misconstrue solar installations for bodies of water and attempt to land on them, but this has not been proven. A 2017 comprehensive survey of all solar and bird interactions in the UK determined that “bird collision risk from solar panels is very low. There is likely to be more of a collision risk to birds presented by infrastructure associated with solar PV developments, such as overhead power lines.”
Solar modules require the use of other electrical equipment, such as inverters and connection boxes, which emit some noise. The frequency of most inverters is 50-60 Hz, which is within the range audible to humans and well below the higher frequencies used to repel animals. Sound is generally not audible at the edge of the fenced boundary, but if audible, the sound is similar in volume to background noises and dissipates to inaudible 50 – 150 ft from the edge of the boundary.
Yes, solar installations can support native vegetation and pollinator habitat species. Low-height plants can thrive underneath solar panels, avoiding the need for mowing while also avoiding shading panels. Two states (MN and MD) have developed pollinator-friendly solar certifications to promote planting of pollinator habitat underneath utility-scale solar projects. Pollinator habitat can benefit local farms and can also host beekeeping operations.
There has not been any documented evidence of solar modules increasing food prices. Solar projects planted with pollinator habitat can actually help increase local agricultural yields through increased pollination and other beneficial insect services. Two states (MN and MD) have actually developed pollinator-friendly solar certifications to promote planting of pollinator habitat that can benefit local farms.
In addition, solar can provide several benefits to farmers that may offset capital costs of installing solar:
- Solar can be installed with zero upfront capital cost through leasing.
- Solar can be installed on marginal agriculture lands and provide a different source of revenue for the farm. This different revenue stream can offset operating expenses of the farm and provide economic resiliency in poor growing years.
- Solar does not need to be installed on current or projected growing areas.
- Co-location of solar and crops installations can be designed to optimize for both electricity and food production.
- Shade from the solar modules can allow for planting high value, shade resistant, and hand-harvested crops that may not normally be available in markets (i.e. lettuces in desert areas, etc.).
Herbicide is currently sprayed around some solar modules to prevent weed growth. Agrochemicals should not be an issue. Care should be taken to not spray modules themselves, but if it occurs the modules can be washed off with water.
Yes, solar can power irrigation equipment. Solar can offset power required for pumping and provide power to remote irrigation systems, requiring no grid connection. Solar irrigation pumps are currently in use in Africa, South America, and India.
Depending on the current land use of the lessee, solar may or may not be allowed on the site. If current operations are suitable to solar or land exists that is not be used, solar may be suitable.
Solar systems can be installed on marginal or salt degraded land or at the margins of fields where no farming occurs. If there is a desire to grow crops underneath and in between solar modules, smaller tractors or hand management are options. There is no one-size-fits-all solar design and developers should account for land and farming needs in the design process.
You should not burn crops underneath or around solar installations; this could lead to electrical fires and damaged equipment. However, solar can still be installed at the farming site where no burning needs to occur. This need should be communicated to the solar developer upfront during the site selection process.
Solar can be installed in flood plains, but all electrical equipment will have to be installed above the projected level of flooding. Raising equipment could increase the cost of installation and may negatively impact the economics. Also, the cost of insurance will be higher for PV systems in a flooding area. An area that will not be flooded may be better suited for PV installation.
Various levels of power generation loss due to soiling should be incorporated into PV system generation estimates. NREL’s PV Watts soiling calculator uses an average soiling loss of 2%, but these losses are highly dependent on local weather and soiling conditions. Having vegetation underneath and around solar panels can reduce the levels of dust and soiling on panels.
Land can be reverted back to farmland at the end of the operational life for solar installations. A life of a solar installation is roughly 20-25 years and can provide a natural rest for the land, increasing the value of the agricultural land. Planting legumes underneath the solar installation can increase nitrogen levels. Giving soil rest can also increase the useful life, maintain soil quality, and contribute to the biodiversity of agricultural land.
There are different benefits of co-locating solar and crop production for solar energy developers and farmers.
Benefits to solar developers include:
- Reduced installation costs – use previously tilled agricultural may prevent the need for expensive grading to flatten land to a usable level.
- Reduced upfront risk – geotechnical risks can increase the cost of solar installation due to increased testing needs. Previously tilled agricultural land was identified as the “least risk option” during a series of surveys with solar installers.
- Reduced legal risk – by using previously disturbed land, solar installers can reduce the risk of up front litigation during the environmental review process.
- Potential increase PV performance – vegetation under modules can contribute to lower soil temperatures and increase solar performance.
Benefits to farmers include:
- Reduced electricity costs
- Diversification of revenue stream:
- Increased ability to install high-value, shade resistant crops for new markets
- Marketing opportunity to sustainability-mindful audience
- Ability to maintain crop production during sliar generation
- Allow for nutrient and land recharge of degraded lands.
Raising the height of PV modules can increase the cost of the solar installation. Due to the increased wind loading on higher structures, the length of steel foundational posts underground would likely need to increase to accommodate the additional structural loading.