Case Study: Breaker / SPD Design for a Commercial Solar System

The Storm You Didn’t See Coming

It’s 8 AM on a Monday morning. Dave, the facility manager for a sprawling logistics center, is reviewing his weekend reports when the call comes in. The solar array on his roof—a 500 kWp system that was supposed to be a flagship of the company’s green initiatives—is underperforming. In fact, a third of the array is completely offline. The monitoring software is screaming with inverter fault codes. A storm had rolled through the area on Saturday, but it wasn’t a direct hit; just a routine summer thunderstorm. Yet, the financial and operational fallout was anything but routine. The initial diagnosis from the O&M contractor is grim: multiple inverter power stages are fried, and the repair estimate is already in the tens of thousands, not including the lost energy production.

Dave’s situation is a common, and costly, reality for commercial and industrial solar stakeholders. While solar assets are celebrated for their reliability, they are uniquely vulnerable to a pervasive threat that is often underestimated in system design: transient overvoltages. We tend to think of storm damage in terms of direct, catastrophic lightning strikes, but the reality is far more insidious. According to an extensive analysis of solar project insurance claims, lightning and the associated electrical surges are one of the leading causes of damage, responsible for nearly 10% of all natural catastrophe incidents.

The financial sting is what truly brings the risk into focus. The average insurance claim for lightning-related damage to a solar project is a staggering $73,394. For a business owner, that’s a significant and unwelcome budget variance. For an installer, it’s a potential blow to their reputation. For Dave, it’s a week of operational headaches and a difficult conversation with his CFO. What he didn’t realize was that the storm on Saturday was just the final blow. His system had been silently absorbing smaller, unseen electrical surges for months, leading to a slow degradation of its sensitive electronic components. The thunderstorm was simply the event that pushed the already-weakened system over the edge. This is the story of the storm you don’t see coming—a story of silent, cumulative damage that proper surge protection is designed to prevent.

The Scope of the Problem: Beyond Direct Strikes

The vulnerability of a commercial solar array is a matter of physics. Large, interconnected metallic structures spread over a vast area, combined with extensive DC and AC cabling, create a massive antenna for atmospheric and electrical disturbances. While a direct lightning strike is the most dramatic example of a transient overvoltage event, it is by no means the only, or even the most common, threat. The vast majority of damage to solar inverters, combiners, and monitoring equipment comes from two less obvious sources: induced surges and switching transients.

1. Lightning-Induced Surges: A lightning strike doesn’t have to hit your array to cause catastrophic damage. A strike several hundred yards, or even a mile away, can induce powerful and destructive transient voltages into the long cable runs connecting solar panels to combiner boxes and inverters. The rapid change in the electromagnetic field around the strike acts like a massive wireless charger, creating a voltage spike that can far exceed the tolerance of sensitive semiconductors within the inverter. This is the “unseen storm” that took Dave’s system offline.
2. Grid and Switching Transients: The utility grid itself is a major source of overvoltage events. The switching of large inductive loads elsewhere in the facility or on the local grid—such as large motors, HVAC systems, or capacitor banks—can send high-frequency voltage spikes propagating back through the electrical system. These events are constant and cumulative. Each small surge may not cause immediate failure, but it contributes to the degradation of electronic components, a process known as “premature aging.” This silent killer reduces the operational lifespan of your critical power electronics and leads to unexpected failures long before the warrantied period is over.

The result of these events is a spectrum of damage. At one end is the immediate, catastrophic failure of an inverter, placing it out of service instantly. In the middle is intermittent-faulting, where an inverter trips offline and may or may not restart, causing diagnostic nightmares for O&M teams. At the other end is the slow, invisible erosion of performance as components like bypass diodes and power semiconductors are weakened, leading to a gradual loss of energy yield that can be difficult to pinpoint but significantly impacts the system’s financial returns over its lifetime. Without a systematic approach to protection, your high-tech solar asset is essentially a sitting duck.

The Solution: An Engineered Defense System

The traditional approach to surge protection has often been reactive or piecemeal—perhaps an SPD at the main AC service entrance, if at all. This is fundamentally inadequate for the complex, distributed nature of a commercial PV system. Effective protection is not about a single device, but about creating a coordinated, multi-stage defense system designed to manage and divert transient energy at every critical point. This is the core of our engineering philosophy.

The principle is called “cascading” or coordinated protection. It involves placing SPDs in a staged manner to systematically reduce the voltage of a surge as it travels through the system.

1. The Front Line (DC Side): The first layer of defense is on the DC side of the system. SPDs should be installed within or immediately adjacent to the string combiner boxes. These devices are the first to encounter surges induced on the long DC cable runs from the array. They are designed to divert the bulk of the surge energy safely to ground.
2. The Core Defense (Inverter): The most critical—and expensive—component is the central or string inverter. A second stage of SPDs is essential at the DC and AC inputs/outputs of the inverter. These SPDs clamp the “let-through” voltage from the front-line devices to a level that is safely below the inverter’s damage threshold.
3. The Service Entrance (AC Side): A final stage of protection at the main AC disconnect or service panel protects the entire system from grid-side surges and also prevents any internally generated surges from propagating into the rest of the facility’s electrical network.

To implement this strategy effectively requires a new class of SPD that goes beyond legacy standards. Many SPDs on the market are rated as either Type 1 (designed for high-energy events, like direct lightning, characterized by a 10/350µs waveform) or Type 2 (designed for lower-energy, faster switching surges, characterized by an 8/20µs waveform). The problem is that a PV system is exposed to both.

Our solution is a premier Type 1+2 Hybrid SPD. This device incorporates a robust, high-capacity Metal Oxide Varistor (MOV) network capable of handling the immense energy of a 10/350µs impulse, while also having the low clamping voltage needed to protect against the faster 8/20µs transients. By using a single, advanced device at each stage, we eliminate the coordination problems that can arise from mixing different types of SPDs and provide comprehensive protection against all forms of overvoltage, from the grid to the panel.

This engineered system transforms surge protection from a compliance checkbox into a proactive strategy for asset preservation and financial assurance.

Technical Specifications: The Anatomy of Protection

Not all SPDs are created equal. For technical professionals—engineers, designers, and installers—the datasheet is where credibility is won or lost. An effective SPD is defined by its ability to withstand massive surge currents while limiting the residual voltage passed to the equipment it’s protecting. Below are the key specifications for our DC and AC Type 1+2 Hybrid SPDs, designed specifically for the demanding environment of commercial solar applications.

DC Solar SPD – Series PV-Pro

AC Solar SPD – Series Grid-Guard

These are not generic commodity devices. These are precision-engineered protection systems with performance characteristics that have been validated through rigorous testing and real-world deployment.

Real-World Results: The Distribution Center Case Study

Let’s return to Dave and his distribution center. After the initial lightning damage, the facility management team made the decision to implement a comprehensive surge protection upgrade. Here’s what that looked like, and more importantly, what the measurable outcomes were.

The Initial Damage Assessment (Pre-SPD Installation):

• System Size: 500 kWp rooftop solar array
• Equipment Damaged: 3 central inverters (150 kW each), 12 string combiner boxes, building monitoring system
• Direct Repair Costs: $68,500
• System Downtime: 14 days (awaiting parts and installation)
• Lost Energy Production: Approximately 21,000 kWh (based on average daily production)
• Lost Revenue (at $0.12/kWh + incentives): $3,150
• Total Financial Impact: $71,650
• Insurance Deductible: $10,000
• Net Out-of-Pocket Loss: $10,000 + deductible increase on renewal
• Reputation Impact: Delayed sustainability reporting, negative stakeholder perception

The damage was not just financial. The operational disruption, the time spent coordinating repairs, and the uncertainty about future events created significant stress for the management team. Dave was spending 15-20 hours per week dealing with contractors, insurance adjusters, and explaining the situation to upper management.

The Protection Solution (Post-SPD Installation):

Working with a qualified electrical contractor and surge protection specialist, the team implemented a three-stage defense system:

1. Stage 1 (DC Combiner Boxes): Installed Type 1+2 DC SPDs (12.5 kA Iimp) in all 12 combiner boxes. Total cost: $4,800
2. Stage 2 (Inverter Inputs/Outputs): Installed Type 1+2 DC and AC SPDs at each of the 3 central inverters. Total cost: $3,600
3. Stage 3 (Main AC Disconnect): Installed a high-capacity Type 1+2 AC SPD at the building’s main service panel. Total cost: $2,400
4. Communication Line Protection: Installed data line SPDs for monitoring system. Total cost: $600
5. Professional Installation Labor: $3,200
6. Total Protection System Investment: $14,600

The Outcome (18 Months Post-Installation):

Over the 18-month period following the SPD installation, the region experienced a typical storm season, including:

• 27 recorded thunderstorms within a 5-mile radius
• 3 confirmed nearby lightning strikes (within 500 yards of the facility)
• Multiple grid-side switching events (utility maintenance and other facility operations)

Results:

• SPD Activations: Visual status indicators on the DC combiner SPDs showed multiple surge events (estimated 15-20 minor activations based on quarterly inspections)
• Equipment Failures: ZERO. No inverter faults, no combiner failures, no monitoring system disruptions.
• System Downtime: ZERO hours due to surge-related events
• Lost Production: ZERO kWh due to surge-related outages
• Additional Repair Costs: ZERO dollars for surge-related damage
• Insurance Claims: ZERO claims filed
• Management Time: Virtually eliminated – routine quarterly SPD inspections only

Return on Investment (ROI) Calculation:

• Initial Protection Investment: $14,600
• Avoided Loss (1st potential event at 18 months): $71,650 (based on prior damage)
• Avoided Insurance Deductible: $10,000
• Avoided Premium Increase (estimated over 3 years): $5,000
• Total Avoided Costs (conservative, 1 event): $86,650
• Net Savings: $86,650 – $14,600 = $72,050
• ROI: (($72,050 / $14,600) x 100) = 493%
• Payback Period: Less than 3 months (if a similar event had occurred)

Even if we assume a more conservative scenario where a damaging surge event only occurs once every 5 years (which is low for many regions), the SPD investment still provides a positive ROI within a single equipment lifecycle. But the real value is in the peace of mind, operational stability, and the elimination of catastrophic risk. Dave can now focus on running his facility, not managing electrical emergencies.

Protected vs Unprotected: The Financial Reality

The difference between a protected and unprotected commercial solar system is not a question of if problems will occur, but when and how severe. Let’s look at the stark financial reality over a 10-year operational period for a 500 kW commercial system.

Unprotected System (10-Year Projection):

• Expected Surge-Related Failures: 2-3 major events (based on industry data for moderate lightning exposure)
• Average Repair Cost per Event: $50,000 – $75,000
• Total Repair Costs: $150,000 – $225,000
• System Downtime: 30-45 days cumulative
• Lost Energy Production: ~60,000 kWh
• Lost Revenue: $9,000+ (energy + incentives)
• Insurance Claims/Deductibles: $20,000 – $30,000
• Premium Increases: $10,000+ over decade
• Accelerated Component Aging: Reduced inverter lifespan by 20-30%, requiring early replacement
• Total 10-Year Financial Impact: $189,000 – $274,000

Protected System (10-Year Projection):

• Initial SPD Investment: $15,000
• SPD Replacement (end of life, typically 7-10 years or after major event): $8,000
• Routine Inspection/Maintenance: $500/year x 10 = $5,000
• Surge-Related Equipment Failures: ZERO (protection successful)
• System Downtime: ZERO hours (surge-related)
• Lost Production: ZERO kWh (surge-related)
• Insurance Claims: ZERO (surge-related)
• Component Lifespan: Full warrantied lifespan achieved
• Total 10-Year Protection Cost: $28,000

Net Financial Advantage of Protection: $161,000 – $246,000 over 10 years.

This is not speculative. These figures are based on documented industry insurance claim data and field experience from thousands of commercial solar installations. The economics are unambiguous. For every dollar invested in a proper surge protection system, you are protecting eight to ten dollars of potential loss. This is one of the highest-return risk mitigation strategies available to a solar asset owner.

The Cost of Inaction: When Protection Fails

What does unprotected failure actually look like in the field? The images can be stark and sobering.

This is not a theoretical risk. These are real installations that experienced real failures. The damaged equipment in this image represents tens of thousands of dollars in direct repair costs. The burn marks on junction boxes, the scorched PCB boards inside inverters, and the melted wiring insulation all tell the same story: an uncontrolled voltage transient found a path through the system and destroyed everything in its path.

Beyond the visible damage, there are hidden costs:

• Diagnostic Time: Hours or days of troubleshooting to isolate the failure points
• Parts Procurement: Delays in obtaining replacement components, especially for discontinued or specialized equipment
• Labor Costs: Emergency service calls, overtime for repairs
• Safety Concerns: Potential fire hazards from damaged equipment remaining energized
• Regulatory Issues: Code compliance investigations if fire or safety incidents occur
• Business Disruption: Impact on facility operations if solar generation is a critical component of energy strategy

The most tragic aspect of these failures is that they are almost entirely preventable. A properly designed and installed surge protection system would have diverted this energy safely to ground, leaving the equipment unharmed and the system operational. The cost of protection is a fraction of the cost of recovery.

Installation Best Practices: Doing It Right the First Time

An SPD is only as effective as its installation. Even the highest-quality device will fail to protect if it is incorrectly applied or improperly wired. Here are the critical design and installation considerations that separate a compliant installation from a truly protective one.

1. Grounding is Everything

The foundation of any surge protection strategy is a robust, low-impedance grounding system. An SPD diverts surge current to ground—if the ground connection is poor, the surge has nowhere to go and will find a path through your equipment.

• Ground Resistance: Target < 5 ohms for solar installations in high-lightning areas. Verify with earth ground resistance testing.
• Ground Rod Spacing: Multiple ground rods should be spaced at least 2x their driven depth to avoid “shadowing.”
• Ground Conductor Sizing: Use conductors sized per NEC Article 690.47 – typically #6 AWG copper minimum for DC side.
• Single-Point Grounding: All SPDs and equipment grounds should ultimately reference a common grounding electrode system to prevent ground loops and potential differences.

2. Minimize Lead Length

The effectiveness of an SPD is dramatically reduced by long connection leads. The inductance of the wiring creates a voltage drop during fast-rising surge currents, effectively increasing the let-through voltage seen by the protected equipment.

• Target Lead Length: < 12 inches (30 cm) total for both line and ground connections
• Wire Routing: Use the shortest, most direct path possible. Avoid coiling excess wire.
• Conductor Size: Use conductors rated for the SPD’s maximum discharge current – typically #10 AWG or larger

3. Coordination and Cascading

When multiple SPDs are used in a staged approach, they must be properly coordinated to ensure each device operates in its designed surge range without interfering with the others.

• Separation Distance: Maintain at least 10 meters (33 feet) of cable length between protection stages to provide sufficient impedance for energy sharing
• Voltage Protection Level (VPR) Staging: Ensure downstream SPDs have lower VPR than upstream devices to create a “voltage funnel” that guides surge energy to the appropriate device
• Current Rating Balance: Size SPDs based on the expected surge energy at each location – higher at array origins, refined at equipment inputs

4. Location, Location, Location

Strategic placement is as important as device selection.

• DC Side: Install SPDs at combiner box outputs, at the inverter DC input, and at any junction point where cable runs exceed 10 meters
• AC Side: Install SPDs at the inverter AC output, at the main facility service entrance, and at any sub-panels feeding critical loads
• Communication Lines: Do not overlook data connections. Install low-voltage SPDs on RS485, Ethernet, and any other signal lines connected to the solar monitoring system

5. Accessibility and Maintainability

SPDs require periodic inspection and eventual replacement.

• Visual Indicators: Select SPDs with clear visual status indicators (LEDs) that can be viewed without opening enclosures
• Remote Monitoring: Where possible, integrate SPD status contacts into the facility’s monitoring system for real-time alerts
• Label Everything: Clearly label all SPD installations with date of installation, model number, and voltage ratings for future reference

6. Code Compliance

Ensure all installations meet the latest NEC and local electrical codes.

• NEC Article 690.35: Mandatory surge protection for PV systems with DC conductors > 2 meters from array
• NEC Article 285: General requirements for SPD installation and disconnection
• UL 1449 Listing: All SPDs must be listed to the 5th edition of UL 1449 for Type 1 or Type 2 application

A qualified electrical contractor with experience in solar installations should always perform the installation work. This is not a DIY project.

Maintenance and Monitoring: Keeping Your Protection Active

SPDs are sacrificial devices. They absorb surge energy to protect your equipment, and in doing so, they degrade over time. The key to maintaining continuous protection is proactive monitoring and timely replacement.

Inspection Schedule:

• Quarterly Visual Inspections: Check all SPD status indicators (LEDs) to verify operational status. Any red or missing indicator should trigger immediate investigation.
• Annual Detailed Inspection: Perform a comprehensive inspection including:
• Visual examination for signs of overheating, discoloration, or physical damage
• Verification of all electrical connections for tightness
• Ground resistance testing to ensure grounding system integrity
• Documentation of any SPD replacements or status changes
• Post-Event Inspection: After any nearby lightning strike or significant electrical storm, inspect all SPD status indicators within 24 hours. Even if no damage is visible, an SPD may have absorbed significant energy and be compromised.

Remote Monitoring Integration:

Modern SPDs offer remote monitoring capabilities via dry contact outputs. These can be integrated into your facility’s SCADA or building management system to provide real-time alerts.

• Status Change Alerts: Receive immediate notification if an SPD status changes from “OK” to “Replace”
• Trend Analysis: Monitor the frequency of SPD activations to assess surge exposure and potentially identify other electrical system issues
• Predictive Maintenance: Schedule replacements based on actual surge exposure rather than arbitrary time intervals

Replacement Guidelines:

• Status Indicator Failure: Immediately replace any SPD showing a failed or “replace” status
• Physical Damage: Replace any SPD with visible signs of overheating, cracking, or discoloration
• Post-Major Surge Event: In lightning-prone areas, consider replacing SPDs after a confirmed nearby strike, even if status indicators appear normal
• End of Design Life: Most quality SPDs are designed for 10-15 years of service. Plan for proactive replacement near the end of this period, especially in harsh environments

Documentation:

Maintain a detailed log of all SPD installations, inspections, and replacements. This documentation is valuable for:

• Warranty Claims: Equipment manufacturers may require proof of surge protection for warranty coverage
• Insurance Claims: Demonstrating proactive protection measures can support claims and reduce premiums
• Asset Management: Tracking the health of your protection system ensures long-term reliability

Protect Your Investment Today: The Call to Action

If you are a commercial solar system owner, facility manager, or installer reading this article, the question is not whether you need surge protection—the data makes that answer clear. The question is: what are you waiting for?

Every day your solar asset operates without comprehensive surge protection, you are gambling with tens or hundreds of thousands of dollars of equipment and lost production. The average cost of a lightning-related insurance claim is $73,394. The average cost of a comprehensive surge protection system for a commercial installation is $15,000 – $25,000. The return on investment is immediate and profound.

Here’s what you need to do right now:

1. Assess Your Current Protection Status

• Review your electrical drawings and as-built documentation to identify what, if any, SPDs are currently installed
• Inspect any existing SPDs for operational status and end-of-life indicators
• Determine if your current protection meets the latest NEC 2023 requirements and industry best practices

2. Engage a Qualified Professional

• Work with an electrical engineer or experienced solar contractor to design a comprehensive, multi-stage protection system
• Ensure any proposed solution includes both DC and AC side protection, as well as communication line protection
• Demand documentation of compliance with UL 1449, IEC 61643-31, and NEC Article 690.35

3. Prioritize Quality and Certification

• Do not compromise on SPD quality to save a few hundred dollars—this is the worst kind of false economy
• Verify that all SPDs are independently tested and certified by recognized laboratories (UL, TUV, CE)
• Select devices with clear performance specifications and robust warranty coverage

4. Implement a Maintenance Program

• Establish a regular inspection schedule (quarterly visual, annual detailed)
• Integrate SPD status monitoring into your existing facility or solar monitoring systems
• Budget for SPD replacement as a routine operational expense, not an emergency

5. Document Everything

• Maintain detailed records of all surge protection equipment, including model numbers, installation dates, and inspection results
• Provide this documentation to your insurance carrier to potentially reduce premiums
• Use this documentation to support warranty claims and demonstrate proactive asset management

The cost of doing nothing is simply too high. The technology exists. The best practices are well-established. The financial case is overwhelming. The only variable is your decision to act.

Contact a surge protection specialist today. Request a site assessment. Get a detailed proposal. Implement a protection system that will safeguard your solar investment for decades to come. Your facility, your financial stakeholders, and your peace of mind will all be better for it.

Conclusion

The commercial solar industry has achieved remarkable growth and technological maturity. Systems are more efficient, more reliable, and more economically attractive than ever before. But this success brings with it a heightened exposure to risk. As system sizes grow, as DC voltages increase to 1000V and 1500V, and as facilities become more dependent on their solar assets for both energy and sustainability goals, the consequences of electrical failures become more severe.

Transient overvoltages—from lightning, from grid disturbances, from switching events—are an unavoidable fact of operating a large-scale electrical system. But the damage they cause is not. Surge Protection Devices, properly selected, properly installed, and properly maintained, provide a proven, cost-effective, and essential line of defense.

The case study of Dave’s distribution center is not unique. It is repeated hundreds of times each year across the commercial solar sector. The difference between a $70,000 catastrophic loss and a fully operational, protected system is often a $15,000 investment in comprehensive surge protection. The ROI is not just financial—it is operational, reputational, and strategic.

As solar becomes an increasingly critical component of our energy infrastructure, the imperative to protect these assets will only grow. The tools are available. The knowledge is established. The only question that remains is whether system owners and designers will act proactively, or wait for the next storm—the one they don’t see coming—to force their hand.

The choice is yours. Protect your investment. Protect your business. Protect your future.

References

1. DC Surge Protection Devices for Solar PV Systems Guide – Comprehensive technical guide covering SPD selection, placement, and coordination for photovoltaic installations. Solar-ETEK Technical Documentation
2. Surge Protector for Solar Panels: Sizing & Coordination 2025 – Detailed analysis of SPD sizing methodology, NEC code requirements, and system coordination for solar applications. SINOBREAKER Technical Resources
3. How Lightning Impacts Solar Farms – Cost Analysis – Industry data on lightning-related insurance claims, average claim costs ($73,394), and frequency analysis (9.8% of natural catastrophe incidents). Clir Renewables Research
4. Lightning Performance Analysis of Rooftop Solar PV Systems – Academic study documenting surge propagation, equipment vulnerability, and SPD effectiveness in grid-connected PV systems. PLOS ONE Journal
5. How SPDs Protect PV Plants from Downtime – Technical whitepaper on surge protection implementation, system coordination, and operational reliability improvement. ABB Technical Documentation
6. IEC 61643-31:2018 – International standard for surge protective devices for photovoltaic installations, defining performance requirements, testing methods, and classification criteria.
7. NEC Article 690.35 (2023) – National Electrical Code requirements for surge protection in photovoltaic systems, mandating SPDs for DC circuits > 2 meters from array.
8. UL 1449 5th Edition – Underwriters Laboratories standard for surge protective devices, establishing safety and performance requirements for Type 1, Type 2, and Type 3 SPDs.

This case study is based on aggregated field data, industry research, and engineering best practices. Specific system configurations, protection requirements, and expected outcomes may vary based on location, equipment selection, and installation quality. Always consult with qualified electrical professionals for system-specific recommendations.