Protecting a Solar Farm From Lightning

Solar farms are just big fields covered with conductive material. They’re almost asking for a lightning strike, which can damage or destroy solar panels, inverters and other critical equipment. So it’s no surprise that lightning activity and surge-related over-voltage abnormalities are identified as leading causes of solar project downtime. Lightning can be destructive even when it’s not a direct hit. Indirect lightning events generate an electromagnetic force that induces overvoltage and transients on AC and DC power conductors and data lines. The good news is solar owners and developers can protect their investment from the fallout of lightning strikes.

Step 1: Protect the Grounding System

Comprehensive soil resistivity measurement is the first step in designing a solar grounding system. Soil resistivity is a measure of how much soil resists the flow of electricity. A proper test will use the Wenner four-point method, which corresponds to IEEE Std. 81. The Wenner test uses four probes spaced at equal distances to measure how much electricity is conducted between them through the soil. The distance between the test probes results in soil resistivity data at the equivalent depth. It is considered to be the most reliable soil resistivity test.

After obtaining a thorough understanding of how soil conducts electricity and obtaining multilayer soil resistivity test results, specialized grounding software can help model the best grounding system for an array. By using a computer model, designers can complete a comprehensive fault analysis. Safety step and touch voltage evaluation can also be performed for the entire project, including solar panels, inverter and transformer stations and the perimeter fence layout.

Step 2: Surge Protection

In addition to proper grounding and bonding, it is crucial to install both AC and DC surge protection devices at key points throughout a solar site to protect panel module circuits, inverter stations and critical control circuits at the combining switchgear box. It is recommended that a comprehensive network of quality SPDs be installed throughout the solar farm’s AC and DC power distribution to protect critical circuits against hardware damage and from operational disruptions resulting from lightning and non-lightning related transients.

Although lightning-generated transients are by far the most intense surge events, surges originating elsewhere can be at high voltage levels as well. For example, lightning-induced surges initiated by direct lightning strikes can produce momentary voltages up to 75 kV at their point of impact. Indirectly coupled surge impulses originating from nearby lightning activity, on the other hand, generate voltage bursts up to 25 kV.

Step 3: Lightning Protection System

The National Fire Protection Association (NFPA 780) and International Electro-Technical Commission (IEC-62305) standards suggest solar developers take stock of lightning risk to establish a baseline for lightning protection systems. In other words, it’s the developer or owner’s responsibility to conduct a cost-benefit analysis and decide what type of lightning protection should be added to an array.

Regardless of risk, it’s unfortunately true that external lightning protection system design and installation is not a common practice for solar farms, large or small. However, lightning protection of solar arrays by traditional Franklin rod systems is still subject to concerns regarding effectiveness, shadow effects, installation cost and appearance.

As an alternative to the traditional Franklin rod system, early streamer emitter (ESE) type lightning air terminals can protect a solar farm.

Want to learn more tips and tricks for your solar system, or are you interested in learning more about solar in general? Check out the HahaSmart blog to see new information updated on a daily basis!

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