New Guidelines for Safety in Agri-PV Installations
The recently released AgriSolar Best Practices Guidelines by Solar Power Europe officially recommends module-level power electronics for Agri-PV safety and supports other recent such documents that have been recently released, such as the Installation Guidelines for Agri-PV in Japan. This, of course, is not news to us at SolarEdge where module-level power electronics (MLPE) is at the core of our PV system architecture and a key enabler for our advanced multilayer safety features. Agri-PV (also called Agrivoltaics), for the uninitiated, is the dual use of land for agricultural and solar energy production Solar installations can be placed on trackers to ensure complete control of the amount of sun reaching the plants and maximum benefit to both solar and crop production.
“… it is recommended to apply Module Level Power Electronics in Agri-PV systems to reduce risk of electric shocks and fires”
Solar Power Europe (SPE), Best Practices Guidelines for Agrivoltaics
Below, you can find a review of safety suggestions offered by the SPE Best Practices Guidelines, as well as “Agrivoltaics in India, Challenges and Opportunities”, as well as additional safety recommendations in a guideline document prepared by Japan’s New Energy and Industrial Technology Development Organization (NEDO).
Why is “Safety” critically important in Agri-PV?
Safety is of course important in every PV installation. Maintenance staff, installers, and first responders must be able to work safely on a property. Similarly, the people and property populating both commercial and residential sites, require protection. In an Agri-PV installation, however, the situation is compounded by the combination of two ventures sharing one piece of land. Many ground-mount PV installations are gated to ensure that no outside individuals enter the site and interact with equipment or cabling. However, in agrivoltaic sites, farmers work in close proximity to the PV products using large machinery and irrigation, making gating impossible and increasing the potential risk of electrical shock. In some installations, animals share their grazing lands with PV panels, possibly leading to cable damage. This is significant, as the deterioration of cabling can result in fire risk.
As a nascent industry, ensuring safety in Agri-PV is even more important. As the Best Practices Guidelines explains: “… incidents of fire and electric shocks could be detrimental to the growth and public acceptance of Agri-PV, especially in the early stages of the market, when dedicated binding standards and regulations are yet to be published or enforced.” Before regulation is enacted, the industry must self-regulate so it can grow effectively. This is also emphasized by the recently published “Agrivoltaics in India, Challenges and Opportunities” document. One of the seven key findings in the document determines that: “on the agricultural side, farmers’ safety concerns due to the proximity to high voltage cabling, as well as constraints on the mobility of farm equipment, are the main challenges.”
What can impact safety in Agri-PV?
As in any electrical plant, electrical shock and fire are the two main safety risks in PV installations. As explained above given the dual-usage of land in Agri-PV sites, there is an increased risk of fire and electrical shock.
Electric shock can occur when an individual (or animal) touches a high-voltage element.
While the risk of fire is minimal in a PV plant, it can be caused by the creation of an electric arc. This can occur if there is a small gap in a connection, or when an electric current jumps between two wires, for example when the insulation is frayed or damaged. As mentioned, an Agri-PV site provides more opportunities for damage to the equipment, therefore leaving it open to additional safety challenges.
Why is MLPE considered superior for safety?
1 – Visibility and control
In conventional PV installations, solar modules are attached to each other in a string and interact with the inverter through that string. In such installations, there is no visibility of each module’s performance and it’s not possible to automatically identify the location of a fault if one occurs. This can waste valuable time when troubleshooting a safety issue and require costly on-site visits With MLPE, O&M staff are appraised of the exact location of any fault or issue, ensuring quick resolution, often remotely.
The ability to monitor and manage each individual module provides important control of the entire system, which means that the system can be shut off when needed.
With an agrivoltaic installation, the aim is to have as little intrusion as possible by maintenance staff, so as not to interact with the crops or interfere with farm operation. Because of the module-level visibility provided in MLPE systems, when intervention is necessary, the location is pinpointed and limits onsite maintenance visits.
2 – Arc fault detection
The ability to determine the exact fault location and address it directly is critical in maintaining system safety. With MLPE, it is possible to determine the location of an arc and mitigate it. Japan’s New Energy and Industrial Technology Development Organization (NEDO) explains the value of MLPE in Agri-PV installations very well:
“...even if the electric circuit is opened in these locations [solar plants based on string inverters, nb], the solar cells will continue to generate power as long as the solar cells are exposed to sunlight. Voltage continues to be applied to the array side. Also, if a ground fault or short circuit accident occurs, a closed electrical circuit may form, and current may continue to flow. Therefore, even if you open the electric circuit in the connection box or stop the inverter, risk of electrical shock or fire remains. In order to prevent electric shock, it is necessary to reduce the voltage to, for example, 60 V or less. Methods for this include shielding the solar cells from light and using MLPE (Module Level Power Electronics) in which equipment is attached to each solar cell module.”
SolarEdge improves on basic MLPE system safety
We often say that safety is part of the SolarEdge DNA. When SolarEdge split the functionality of the inverter with the invention of the Power Optimizer, the key motivator was to make sure each module performs at its maximum potential But another equally important goal was increased system safety. Essentially, SolarEdge designs for safety, taking optimal advantage of MLPE with these features:
SafeDC™ and Rapid Shutdown
SafeDC™, integrated into every SolarEdge system, automatically brings the system to a touch-safe voltage level whenever the inverter is shut down. Why is this important? In conventional solar systems, shutting the inverter down with a safety switch or other device leaves high voltage on the modules and in the cabling as long as the sun is shining. In a SolarEdge system with SafeDC™, each panel is quickly reduced to 1V during grid failures or AC power shutdown, removing the risk of electric shock to maintenance workers, farmers or first responders. The feature also prevents secondary events. For example, if cabling has lost some insulation and an arc develops, SafeDC™ will operate automatically and prevent the arc from becoming a safety hazard. This is the only feature on the market that can handle such events.
Sense Connect
Sense Connect is one of the most significant safety features in the SolarEdge safety suite, embedded in S-Series Power Optimizers. They are designed to prevent arcs from forming. Before an arc can develop, the temperature in the connector will increase. Sense Connect is able to detect that change of temperature and alert the inverter to shut off. Coupled with the SolarEdge Monitoring Platform that indicates the location of the fault, this early warning system helps keep agrivoltaic installations safe.
Temperature sensing in SolarEdge inverters enables monitoring the AC and DC side interface installation as well as aids in detecting bad connections before they turn into an arc. When abnormal temperatures are detected, the system will even shut down the inverter.
Temperature sensing in inverter and Smart Reconnect Mechanism
SolarEdge inverters are also equipped with temperature sensing to help identify a hazard and prevent it from escalating. Temperature sensing in SolarEdge inverters enables monitoring the AC and DC side interface installation as well as aids in detecting bad connections before they turn into an arc. When abnormal temperatures are detected, the system will even shut down the inverter. The smart reconnect mechanism can get the inverter up and working when safe, for minimal system downtime.
A zucchini grows underneath solar panels embedded with SolarEdge Power Optimizers. MLPE technology such as these offer enhanced safety in Agri-PV installations.
Other important Agri-PV best practices for safety
In addition to critical site protection as described above, several other practices should be adopted to keep Agri-PV safe.
Signage
Sometimes low tech is critical. Installing signs around the site can help maintain awareness of the installation and remind farmers and other site visitors to pay attention to their environment in order to protect themselves, the installation and crops.
Cable placement
Cables can be buried deep in the ground in order to keep them safe from roaming animals or machinery (and to keep the animals and machinery safe from them). Of course, plant roots and irrigation needs must be taken into consideration when determining placement. According to an Indian study, cabling for most of their pilot projects was installed overhead to avoid interaction with it. They concluded that it’s important to ensure that the overhead cables remain taut.
Module height
Placing modules at specific a height over the crops is important for ensuring plant crop health but also to keep the machinery safe.
What’s the next step?
When safety issues are addressed in the planning stages of an Agri-PV installation, the addition of solar energy production to an agricultural site can be an excellent opportunity for farmers to extract more value and profit from their land.
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