Electrical Hazards in Solar Photovoltaic (PV) Systems
By: Dave Hernandez, Contributor
The use of Solar Photovoltaic Systems is expanding across the country. Safety can be a special challenge for emerging technology like these systems because there are fewer resources available. Understanding the foundations of Solar PV systems will help you better understand the safety protocols that are unique to the equipment.
Solar PV systems generate direct current (DC) power from sunlight. This energy is then commonly inverted to alternating current (AC) to supply loads or is interconnected to electrical grids. The process of transforming DC to AC power is performed through inverters. The energy created can also be transferred to battery packs for storage.
Solar PV systems consist of arrays that are comprised of individually framed PV modules. These modules are electrically linked to generate the voltage and current needed to supply the electrical load.
PV systems can be engineered as standalone or grid connected services. Standalone systems are not connected to an electrical grid, and typically utilize battery storage banks to reserve the energy until needed. Standalone systems operate on DC power. Grid connected services are interconnected with an electrical grid, and supply energy produced from the solar panels to the grid. Owners of grid connected services benefit from metering cost reduction because these services produce power on generation metering with a net subtraction for the amount of power that is consumed.
There are two types of PV systems. In fixed tilt or flat plate systems, PV modules are installed at a fixed angle and orientation, and panels remain in the position they were installed in. They can be installed on rooftops, poles, or the ground. Fixed tilt panels utilize direct and diffused solar irradiance. Tracking or concentrator systems are engineered to track the sun as it moves across the sky, to optimize positioning for maximum solar irradiance. Tracking systems require external cooling components because they are in constant direct sunlight and a significant amount of energy is exchanged.
Code governing Solar PV systems can be found in the National Electrical Code (NEC) article 690. The main electrical section contains details for Solar PV system installation. Also, IEEE Standards 928 and 929 provide engineering recommendations for ground mounted PV systems.
Understanding the Potential Risks
PV modules, panels, and equipment can generate significant current and voltage and cause serious injuries. Operating voltages can surpass 600 volts DC, and currents at a sub field level can produce hundreds of amps.
Live parts like exposed conductors, panel connections, busses, and inverter switch gear can cause electrical shocks and burns if they come into contact with skin. Even small amounts of current can be transferred through sweaty hands (a common condition with solar equipment that is located outside). Current higher than 20 mA can flow into the body and pose a severe risk.
The higher the voltage, the greater the chance that current will flow through the victim’s body.
High-voltage shock over 440 volts can completely burn away the protective layer of outer skin. Body resistance and lethal currents can cause momentary death. Involuntary muscle contraction in the chest, throat, and diaphragm can cause respiratory failure. Current that passes through the heart can cause ventricular fibrillation, one of the primary causes of death related to electrical shock.
The best possible method to avoid electrical shock is to follow procedures for establishing an electrically safe work condition (ESWC) as outlined by NFPA 70E standards.
Solar PV systems with battery banks can be a potential arc flash hazard due to the stored energy in the batteries. Shorting terminals from a common 12 V battery bank can generate fault current of over 6000 amps for two-second durations. That energy release can cause serious burns or death if it comes into contact with skin or a person. Exploding battery banks could release lead-acid and cause acid burns on skin or blindness if it comes in contact with the eyes.
As part of the charging process, these systems release flammable hydrogen gas that can be hazardous, so battery banks should be kept in a well-ventilated area. Any flames or devices like controls with relays or switching elements that could create a spark should be kept at a safe distance.
Arc flash hazards may exist in inverter switchgear. This equipment can carry thousands of amps of available fault current because it connects and combines all solar equipment utilized in the DC to AC inversion process.
There are many unique codes designed to specifically govern Solar PV systems.
All conductors and over current protection devices in a PV installation are required to transfer at least 125% of short circuit current or fault current of a PV systems source.
Equipment grounding conductors for Solar PV inverters must be large enough to handle the highest current that could flow through the circuit.
Disconnect switches must be accessible and clearly marked with arc flash hazard information. This can be specific information developed from an arc flash study, or the tables method as outlined in the NFPA 70E.
Solar modules or panels should be wired so they can be removed without interrupting the grounding conductor of another source circuit. This is a safety mechanism that mitigates the need to de-energize when changing out parts.
If fuses are utilized, it’s mandatory that power can be disconnected from both ends of either a line or load side of the fuses.
Lightning, ground faults and line surges can produce high voltages even in low voltage installations due to the wiring and DC to AC inversion rates of Solar PV systems. Since they are built in exterior settings, most will experience lightning or storm conditions at some point.
All exposed metal parts should be grounded and bonded to ensure safety in exterior installations.
As Solar PV systems become more popular, it’s important to stay current with safety protocols.
Solar provides the best ROI when it comes to renewable energy. Residential and commercial buildings have readily adopted solar technology. It won’t be long until Solar PV systems proliferate in the industrial market. ESW
Dave Hernandez, PE, CEM, GBE, CESCP is a distinguished Professional Engineer licensed in 52 U.S. jurisdictions and serves as the Chief Executive Officer at Electrical Power & Safety Co (https://epsco.co), a world leader in electrical safety. He has held responsible charge of over 20,000 electrical projects, sits on various industry committees, and has authored several publications.
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