The use of Solar Photovoltaic (PV) Systems is expanding across the country. Safety can be a special challenge for emerging technology like these systems because fewer resources are available. Understanding the foundations of Solar PV systems will help you better understand the safety protocols unique to the equipment.
Read this full article and others like it HERE in the Summer 2022 issue of Electrical Safety in the Workplace Magazine.
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 comprising individually framed PV modules. These modules are electrically linked to generating 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 consumed.
There are two types of PV systems.
- In fixed-tilt / 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 on the ground. Fixed tilt panels utilize direct and diffused solar irradiance.
- Tracking/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.
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 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 the 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 a fault current of over 6000 amps for 2-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 the 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 govern Solar PV systems specifically.
- All conductors and overcurrent protection devices in a PV installation are required to transfer at least 125% of a PV systems source’s short circuit current or fault current.
- 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 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 the 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 conversion 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 increase in the industrial market.
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Dave Hernandez, PE, CEM, GBE, CESCP is a distinguished Professional Engineer licensed in 52 US jurisdictions and serves as the Chief Executive Ofﬁcer at Electrical Power & Safety Co. (https://epsco. co), a world leader in electrical safety. He has overseen over 20,000 electrical projects, sits on various industry committees, and has published several white papers.