Solar PV systems offer a number of benefits, ranging from financial savings to environmental advantages and energy independence. As these benefits are driving the installation of PV systems around the world, the industry has gained a better knowledge of the needs for PV system safety.
In general, PV systems are safe, reliable, and do not inherently pose a danger to people or property. However, it is important to remember that during the daylight, PV panels and cables are energised with high DC voltages. Without taking the proper precautions, these high DC voltages can present electrocution risks to installers, maintenance personnel, and firefighters.
With this in mind, safety is an important consideration during installation, maintenance, and in the event of a fire.
During the installation process, installers connect PV modules that typically have an output voltage of 30-60V. While the voltage from a single panel can be safe, connecting several of these modules serially in a string creates a high voltage, which can be dangerous to installers during system installation.
Once modules are connected in a string, the voltage can reach up to 1500V DC. After connecting the strings to an inverter, the PV system will operate at these high voltages. Shutting down the main circuit breaker will shut down a traditional string inverter, but it will not shut down the DC voltage which will remain high in the daylight. This means that while performing standard installation or operations and maintenance (O&M) functions, such as DC and AC electrical testing or IV curve testing, maintenance personnel can be exposed to these high voltages.
Another scenario in which safety is a concern is in the unlikely event of a fire. Not many fires have been reported so far that have involved PV systems, and in most of the reported ones, the PV system was not the cause of the fire.
When approaching a fire scene with a PV system, firefighters are aware that the system is energised with high voltage DC as long as the panels are illuminated, and as such they take measures to mitigate any risk. While firefighters commonly cut off the electric grid supply as a precaution before gaining close access to extinguishing the fire and spraying water to douse the flames, additional measures may be necessary.
Due to increased safety awareness in combination with evolving PV markets and proliferation of solar energy, more stringent safety regulations are being called for by fire authorities, insurance companies, and utility companies around the world. Experts in the fields of electrical safety, PV, fire safety, and insurance are working together to develop PV safety codes.
Safety measures elsewhere
For instance, Germany, a market leader in PV safety requirements, implemented the VDE 2100-712 for safety in cases of firefighting or maintenance for protection against electrocution. The guide provides recommendations for the planning and construction of PV systems on buildings to prevent dangerous touch voltages in case of failure of the protective measure “double or reinforced insulation” (e.g. in the case of fire).
In Austria, the regulations are even stricter. According to the country’s OVE R11-1: 2013 code, a disconnection close to the source – the module – is required, depending on the situation.
The US has also implemented strict safety requirements, such as NEC 2014 and NEC 2017 Rapid Shutdown, which requires DC voltage in circuits running more than a certain distance from the array (10 feet for NEC 2014, 1 foot for NEC 2017) to the inverter has to be lower than 30VDC within 30 seconds of rapid shutdown initiation. In addition, NEC 2017 also requires that the voltage on the conductors within the array be lower than 80VDC within 30 seconds. This is intended to create a safe zone on rooftop installations where first responders can access the rooftop and create vent holes that help release trapped gasses. This is a necessary step in firefighting and can help reduce the damage to buildings caused by fires.
While it can be difficult and expensive to address these increasing safety standards with traditional string inverters, because they cannot reduce DC voltage even if they are turned off, module-level power electronics, such as power optimisers, act as an effective solution. While the main function of power optimisers is to increase energy output from PV systems by constantly tracking the maximum power point (MPPT) at the module level, they also provide enhanced safety.
From the planning stage, PV systems can be designed to reduce certain risks that may cause fires. For instance, in SolarEdge systems, an earth fault will create an insulation fault reaction that is designed to lead to system shutdown. Not only is the inverter disconnected, but the power optimisers are designed to shut down and enter safety mode, reducing the string current to 0 Amps. In case of a second fault, the SolarEdge system is designed to minimise the chance of reverse current to flow, which subsequently reduces fire risks.
As more users adopt solar as a source for their energy needs, the industry remains focused on improving the safety of these systems. To date, the industry has addressed these concerns by developing increasingly stricter safety standards and relying upon cost-effective, innovative technology. We believe that technological innovations will help set higher standards, such as arc detection.
As technology continues to advance, it is important to understand local safety standards, address the needs of the system owner, and explore available products on the market when planning PV sites, in order to provide maximum safety.