Solar Power Systems: What Electrical Workers Need to Know to Stay Safe

If you've spent any time in traditional electrical work, you know how to read a system. You understand the hazards and how to approach them.

But when it comes to solar power, it's a whole different ballgame.

These systems present unique hazards that workers and safety managers can't afford to overlook. Let’s walk through how they work, what makes them unique, and how to make sure your team is prepared to work on them safely.

How a Photovoltaic (PV) System Works

The difference between solar power, using photovoltaic (PV) systems, and traditional electrical systems lies in how they generate and deliver power.

Traditional electrical generation systems start with a fuel. Burning that fuel (or splitting an atom, in the case of nuclear facilities) creates heat. That heat creates steam; the steam turns a turbine, which generates alternating current (AC) electricity.

At a nuclear plant, for example, a generator might produce 22,000 volts of AC. That voltage is stepped up by a transformer to as much as 350,000 volts for long-distance transmission, then stepped back down at substations to the 120/240 volts AC used in homes and businesses.

In a PV system, that fuel is replaced by the sun’s energy. Semiconductor material inside a photovoltaic cell absorbs photons from sunlight, which creates voltage and current.

Think of each cell as a very small battery that produces about five-tenths of a volt. Since individual cells don’t produce much on their own, we have to connect them together.

PV System Configurations

There are two basic ways to connect electrical sources: series and parallel.

In a series configuration, you connect the positive end of one source to the negative end of the next. Voltages are additive. Connect two 1.5-volt batteries in series, and you get 3 volts. Add a third, and you get 4.5 volts. Current stays constant.

In a parallel configuration, you connect positive to positive and negative to negative, just like jump-starting a car. Voltage stays constant, but current doubles.

PV systems combine both configurations. A group of cells connected in series forms a module. Mount several modules on a steel frame, and you have a panel. Wire a series of panels together, and you have a string.

As you add modules in series, the voltage climbs. Connect enough of them, and you can reach up to 1500 volts DC.

Those strings are then brought together in a combiner box, where they're connected in parallel. Voltage stays at 1500 volts, but now the current (the combined output of all those strings) is much greater.

From there, that high-voltage DC power goes to an inverter, which converts it to alternating current. A transformer steps up the voltage for transmission, and the rest of the process looks much like a traditional electrical grid.

Safety Hazards in PV Systems

The configuration and function of PV systems present unique safety challenges. Here are the most important considerations:

1. The power can't just be “turned off”

In a traditional facility, you can de-energize equipment. But a PV system produces electricity as long as the light is hitting the panels. Even moonlight can generate power.

That means there are parts of these systems where achieving an electrically safe work condition (locked out, tagged out, and verified as de-energized) can be very difficult or simply not possible.

2. Back feeds and parallel circuits

Because the strings are connected in parallel, electricity can flow through the system in multiple directions. A solid lockout/tagout program has to account for all of those sources. You can't assume that disconnecting one source has isolated the equipment.

3. High DC voltages and super strings

1500 volts is the maximum rated voltage for the wiring and connectors in most systems. A “super string” is created when too many modules are connected in series, resulting in voltages exceeding 1500 volts. Exceeding that voltage rating is dangerous and can cause insulation failure, arcing, and equipment damage. This is an engineering and commissioning issue, not just a maintenance one, but it’s important to look out for and to keep in check with good administrative controls.

Keep in mind, at a PV system’s maximum 1500 volts DC, the restricted approach boundary defined by NFPA 70E is 1 foot, 5 inches. Equipment that's had an arc flash study performed will have the restricted approach boundary printed right on the label. Workers within a restricted approach boundary must wear rubber insulating gloves.

4. The environment

PV equipment lives outside, so it’s vulnerable to UV exposure, hail, dust storms, lightning, and wind. Mother Nature takes its toll over time. Wind movement causes wiring to rub against steel panel frames, wearing down insulation. Moisture and debris create poor connections inside combiner boxes. These conditions increase the risk of arc flash events over time if equipment is not regularly inspected and maintained.

Plus, the worksite environment presents its own hazards: the risk of falls during rooftop installations is significant.

Arc Flash Risks in Solar Systems

Since PV systems produce direct current rather than alternating current, arc flash hazards are different from those of typical electrical systems.

Put simply, sustained DC arc flashes are less likely to self-extinguish than AC arc flashes. For example, single-phase AC current naturally crosses zero 60 times per second, which tends to interrupt an arc.

That also creates greater uncertainty in hazard calculations. Incident energy analysis for DC systems requires an engineer with specific expertise in DC modeling, not just standard AC arc flash experience. It is important to note that DC arc flash equations are still being "dialed in" by the industry. Unlike traditional AC systems, the physics of a DC arc in a high-voltage PV environment is an evolving field of research. Because the standards are continuously updated as new testing data emerges, it is vital to partner with an engineering firm that stays at the forefront of these developments.

But like with all other electrical equipment and systems, the only way to determine arc flash hazard is through an arc flash study.

Read more about arc flash hazards and labeling

While system design is critical, the reliability of safety features depends entirely on proper maintenance. Environmental factors like moisture, debris, and thermal cycling can degrade insulation and loosen connections over time, significantly increasing the risk of a fire or arc flash.

Furthermore, the accuracy of any arc flash study assumes that protective devices will operate exactly as intended; if a breaker or fuse is poorly maintained and fails to clear a fault promptly, the resulting incident energy can far exceed the levels indicated on safety labels, rendering standard PPE inadequate.

Built-In Safety Features and Their Limits

PV systems come with several safety design features, particularly finger-safe design. Standard connectors and combiner boxes are intentionally too small for a worker to accidentally insert a finger and be shocked.

MC4 Connectors

MC4 connectors are the standard connectors used throughout the industry to link solar modules together. Since the conductors aren't accessible at the connection point, workers connecting modules in series generally don't need to put on rubber insulating gloves.

But, and this is a big but, MC4 connectors should never be disconnected under load. If current is flowing (so, any time the sun is shining), taking those connectors apart can create an arc that burns hands. The label on the connector says it plainly and should be taken seriously.

Finger-Safe Equipment in Combiner Boxes

Inside a combiner box, fuse blocks and bus connections may be covered or designed to be finger-safe. But that does not mean the box is safe to reach into without full protection. On the output side, where conductors run to the inverter, guarding is often limited or absent. Those conductors may be exposed and energized at up to 1,500 volts DC.

Any time a worker places their hands inside a combiner box for voltage verification, live-dead-live testing, troubleshooting, or diagnostic work, rubber-insulated gloves rated for the circuit voltage are a minimum requirement. Depending on the shock and arc-flash risk assessment, additional arc-flash PPE may also be necessary.

Signs of a Prepared Team

A prepared team can do more than perform the technical tasks. They understand how PV systems work and how to approach them. All workers should:

• Understand how PV systems generate and store voltage

• Identify restricted approach boundaries

• Know what PPE, including rubber insulating gloves, is required

• Follow all proper procedures for electrically safe work conditions, including the live-dead-live test

• Accurately apply your written lockout/tagout program to the specific installation architecture

• Read an arc flash label

If your team cannot consistently or reliably do all of these things, it's a great idea to close the training gap before the next maintenance cycle.

Solar systems are genuinely unique. If you're responsible for teams working on or near PV systems, the question to ask isn't just whether they're technically capable. It's whether they've been trained to identify the hazards and protect themselves from them.

Interested in our solar energy safety solutions or solar-specific electrical safety training for your team? Contact Guidant Power to learn more about our dedicated PV safety training program.