Solar photovoltaic modules and their supporting facilities are typically installed outdoors, making them vulnerable to lightning and surge threats. Are you worried that a microsecond-long surge could destroy your inverter worth tens of thousands of dollars, causing weeks of power generation loss? For EPC contractors and power plant owners, DC surge protection devices (DC SPDs) are not only a compliance requirement but also a core safeguard for protecting equipment, reducing risks, and maximizing return on investment (ROI).
What is a DC SPD?
DC SPD Definition: A DC Surge Protective Device (DC SPD) is a specialized electrical protection device used in direct current circuits to guard against transient overvoltage (such as lightning strikes, operational surges, etc.). When instantaneous high voltage occurs in the circuit (e.g., induced by lightning or surge caused by switch operations), it quickly conducts and discharges most of the surge current to the ground, thereby clamping the voltage within a range that equipment can withstand and preventing damage to photovoltaic modules, inverters, combiner boxes, and other components.
The working principle of DC SPD in solar energy systems
The working principle of DC SPD
Normal state:During normal system operation, the MOV (Metal Oxide Varistor) operates in a high-impedance state, directly connected in parallel between the line conductor and the ground conductor. It is essentially transparent to the circuit, causing almost no additional voltage drop or power loss under rated operating voltage, and does not affect normal line conduction or load operation.
Surge trigger:When transient overvoltage occurs on the line due to reasons such as lightning-induced surges, switch operations, or grid disturbances, and the voltage exceeds the continuous operating voltage (Uc) of the SPD, the MOV will rapidly switch from a high-resistance state to a low-resistance state within an extremely short time (usually in nanoseconds to microseconds). This effectively creates a low-impedance discharge path when overvoltage appears.
The surge current is quickly directed into the grounding system through this low-impedance path while suppressing the voltage rise on the line below the protection level (Up) of the SPD.
As a result, downstream equipment (such as inverters, controllers, monitoring units, etc.) experiences voltages limited within their safe tolerance range—well below their insulation withstand value—effectively preventing insulation breakdowns, component damage, or functional failures.
Surge ended: Once the transient overvoltage disappears and the line voltage returns to the normal operating voltage range of the SPD, the MOV will automatically revert to a high-impedance state, effectively “disconnecting” the discharge path. The system then resumes normal operation mode.
Since this entire process is completely contactless electronic action without requiring mechanical switches or manual intervention, the SPD can continuously operate online after single or multiple surge events. Replacement of modules is only necessary when long-term aging or severe overload causes internal disconnectors to activate, thereby achieving an operational characteristic of “one-time installation, long-term protection, automatic reset.”
Key installation locations of the solar power system SPD
Solar power systems typically require SPD installation in three locations to establish graded and coordinated protection. Through multi-level defense, a “layered interception and step-by-step discharge” protection strategy is implemented, effectively reducing the overall damage caused by lightning strikes and operational surges to the system.
Between the photovoltaic panel and the DC combiner box (Type 1+2 DC SPD)
At the DC output end of the component array and between the DC combiner box, a DC SPD with Type 1+2 functionality is typically installed. This position serves as the front-line defense where lightning-induced surges first arrive, primarily handling high-voltage impact energy generated by direct lightning strikes or nearby induced lightning on long cables.
Type 1+2 SPDs have a high surge current capacity, quickly directing large surge currents into the grounding system while limiting voltage to a lower protection level. This effectively reduces the impact of surges on photovoltaic module strings, DC terminals, and internal terminals of combiner boxes, preventing premature aging or damage to bypass diodes or connectors in modules due to overvoltage breakdown.
DC combiner box to inverter input (Type 2 DC SPD)
Between the DC output terminal of the DC combiner box and the DC input terminal of the inverter, a Type 2 DC SPD is usually added to form secondary protection. This level mainly addresses residual surges that are not completely eliminated by the previous protection stage, as well as operational overvoltages caused by internal system switching operations (such as DC circuit breaker opening/closing or reverse freewheeling).
The residual voltage of a Type 2 SPD is relatively lower, providing more precise protection. It can further clamp residual surge voltage within a range tolerable for the inverter’s DC side, thereby protecting critical components such as the inverter’s IGBT, DC capacitors, busbars, and control boards. This reduces inverter failures, downtime, and maintenance costs caused by surges.
Inverter AC output to distribution board (Type 2 AC SPD)
Between the inverter’s AC output and the AC distribution board, a Type 2 AC SPD is generally configured to protect equipment on the AC side. This level primarily guards against lightning strikes or operational surges from the grid side that may reverse into the photovoltaic system, such as overvoltages originating from transformers, high-voltage switch stations, or distribution lines.
By installing an SPD on the AC side, surge energy entering the system can be discharged before reaching the distribution panel, load circuits, and grid monitoring devices. This prevents damage to circuit breakers, contactors, electricity meters, monitoring equipment, etc., caused by overvoltage and enhances the safety and stability of the entire grid-connected system.
The significance of graded and coordinated protection
By configuring different types and levels of SPDs at the DC front end, DC intermediate stage, and AC output end, the solar system achieves a coordinated protection structure with primary discharge of large energy and refined secondary protection.
This multi-level protection not only effectively disperses the stress on individual SPDs but also significantly reduces overall system failure rates in projects with frequent lightning strikes, long transmission lines, or complex environments. It extends the lifespan of critical equipment, enhances long-term stability in power generation yields, and improves investment security for projects.
Types of DC SPD in photovoltaic systems
Type 1+2 DC surge protector
Type 1+2 DC surge protector integrates Type I and 2 protection functions, capable of handling high-energy impacts caused by direct lightning strikes as well as induced surges and operational overvoltages, meeting the combined testing requirements of IEC 61643-31 Class I + Class II.
This type of SPD is suitable for installation at the DC combiner box entry point in photovoltaic arrays, making it an optimal solution for areas with frequent thunderstorms or large outdoor ground-mounted power stations. Its internal structure typically combines discharge gaps and MOVs, providing both high-energy impact current (2mp, 10/350 µs waveform) resistance and precise clamping protection against induced surges.
Type 2 DC Surge Protector
Type 2 DC surge protectors comply with IEC 61643-31 Class II test requirements and are specifically designed to protect against overvoltages caused by induced surges and switching operations. They are typically installed at the DC input of inverters and are the most widely used protective devices on the DC side of photovoltaic systems.
Internally, they use MOV (metal oxide varistors) as core components, with a nominal discharge current (In) tested under an 8/20 µs waveform. These devices feature fast response speeds and high clamping accuracy, effectively protecting inverters from surge damage.
Economic Benefits of DC SPD In Solar Systems
Installing a DC surge protector is not just about meeting regulatory requirements; it is also a long-term investment that makes financial sense.
Reduce downtime losses
For photovoltaic power plants, the cost of downtime often far exceeds the damage cost of the equipment itself. A single lightning surge or switching overvoltage event can trigger protective shutdowns in inverters at best, or directly burn out core components worth tens of thousands of dollars at worst.
Take a 500 kW string inverter as an example: the replacement cost is approximately $30,000 to $50,000. However, if this occurs during the summer peak generation period, with a downtime of 4–6 weeks required for waiting on spare parts and completing replacements, the cumulative loss in generation revenue is often several times the value of the equipment.
DC SPDs clamp and discharge surges before they reach the inverter, turning this risk from a probabilistic event into a controllable variable. This ensures stable output even during thunderstorm seasons and fundamentally protects power plant revenues from being disrupted by weather events.
Extend equipment service life
The damage caused by lightning surges is often apparent, but even more challenging to detect and equally far-reaching in impact is the chronic damage from cumulative overvoltage on equipment. Each minor surge that goes unchecked leaves subtle traces on the gate oxide layer of inverter IGBTs, the junction area of module bypass diodes, and the insulation layer of DC cables.
Such damage is almost imperceptible during the early stages of system operation but accelerates device parameter drift and insulation degradation over time, eventually leading to concentrated failures such as premature inverter breakdowns, accelerated module output attenuation, and cable insulation breakdown—often occurring right after the warranty period ends.
An effective surge protection system safely diverts each surge event’s energy into the grounding system, blocking this path of cumulative damage. This helps inverters and modules operate stably until their designed service life, avoiding high unplanned capital expenditures for premature replacements.
Clear investment returns
From the perspective of procurement costs, the unit price of an industrial-grade DC SPD that complies with IEC 61643-31 standards typically accounts for only 1%–3% of the price of the inverter it protects.
For example, in a 10 MW ground-mounted power plant, the total cost of a complete DC-side SPD configuration usually does not exceed 0.5% of the project’s total CAPEX, yet it can continuously intercept every potential destructive surge event over a 25-year operational cycle. This proportion means that as long as the SPD successfully prevents one inverter damage incident during its lifecycle, all procurement and installation costs can be fully recovered, and subsequent protection becomes purely risk hedging benefits.
For EPC contractors managing multiple projects simultaneously, standardizing SPD configurations into project delivery specifications not only systematically reduces cross-project O&M costs but also helps win owners’ trust during bidding by projecting lower lifecycle O&M costs—creating differentiated competitive advantages.
When insurance companies include compliant SPD configurations as prerequisites for claims settlement, this investment’s implicit value becomes even more significant—not just safeguarding equipment but also providing legal and compliance foundations to ensure smooth insurance claims processing after extreme weather incidents.
| Metric | Without DC SPD | With DC SPD |
| Inverter Failure Risk | High | Significantly Reduced |
| Unplanned Downtime Frequency | Frequent | Greatly Reduced |
| Equipment Replacement Cycle | Shortened | Meets Design Life |
| Lifecycle O&M Cost | High | Controlled & Predictable |
Selection of Solar DC SPD
Step 1: Select the type based on the project situation
| Project Characteristics | Recommended Type |
| High lightning risk areas, large-scale ground-mounted plants, long distance between combiner box and inverter | Type 1+2 DC SPD |
| Rooftop distributed systems, urban projects, supplementary protection at inverter side | Type 2 DC SPD |
Type 1+2 DC SPD meets both Class I and Class II protection requirements, installed at the entrance of the DC combiner box, providing full-link protection from direct lightning surges to induced surges, suitable for large-scale ground-mounted power station projects with high lightning protection requirements.
Type 2 DC SPD meets Class II protection requirements, installed at the DC input of the inverter, specifically intercepting line-conducted surges and switching operation overvoltages. With features such as fast response speed, high clamping accuracy, and easy installation, it is the standard choice for DC-side protection in distributed photovoltaic projects.
Step 2: Verify three key parameters
Uc (maximum continuous operating voltage) must be greater than 1.2 times the system’s maximum open-circuit voltage Uoc. If chosen too low, the SPD will continuously heat up under normal conditions, accelerating aging or even leading to failure.
For the nominal discharge current (In), it is recommended to choose ≥ 20 kA (8/20 µs) for Type 2 products. In areas with frequent thunderstorms or large-scale projects, it is advised to select 40 kA or higher to provide sufficient margin for the system.
The lower the Up (protection level voltage), the better, and it must be lower than the insulation impulse withstand voltage on the DC side of the inverter. A higher Up indicates that surge clamping is not precise enough, and equipment may still suffer damage.
LSP Solar DC SPD Solution
LSP Company began producing surge protectors in 2010. The company is dedicated to creating safe and high-quality products for solar systems. LSP has a professional laboratory and implements strict quality control at every stage of production.
LSP serves over 1,200 companies in 35 countries. Many consumers trust the LSP brand for its reliability and high customer satisfaction. LSP surge protectors comply with IEC standards and are certified by TUV, CB, and CE. These certifications demonstrate that LSP’s products are safe, reliable, and of superior quality. LSP consistently upholds its commitment to quality, reliability, and innovation.
LSP DC SPD Product Highlights
LSP offers a variety of DC surge protectors for solar systems. The main products include Type 1+2 and Type 2 DC surge protectors suitable for solar panels, photovoltaic arrays, and inverters. These devices can prevent excessive voltage during lightning strikes or switching surges and divert excess current to the ground.
LSP’s DC surge protector (SPD) has some important features in solar applications:
Adopts LKD brand metal oxide varistor (MOV) technology for rapid response.
Capable of withstanding high discharge currents (Iimp, In/Imax) with high safety.
Maintains low voltage to protect equipment.
Features a clear status window (green indicates normal, non-green indicates abnormal), making inspection convenient.
Compact size, easy to install near photovoltaic arrays, combiner boxes, and inverters.
Conclusion: Maximizing Solar ROI with Reliable DC Surge Protection
From the perspective of investment return, the procurement cost of DC SPDs typically accounts for only 1% to 3% of the price of photovoltaic inverters, representing a very small proportion of the entire system and hardly imposing any significant pressure on initial investments. However, this small expenditure can continue to play a role over several years or even throughout the lifecycle of the system: by effectively suppressing lightning strikes and operational surges impacting DC-side equipment, it significantly reduces the probability of downtime caused by surge-induced failures in key components such as inverters, combiner boxes, and monitoring devices. This indirectly lowers operation and maintenance costs by reducing unnecessary repairs and spare part replacements.
Frequently Asked Questions
What is a DC Surge Protective Device for solar?
A DC Surge Protective Device (SPD) for solar is a critical safety component designed to shield photovoltaic systems from transient overvoltages. It intercepts sudden high-voltage spikes—caused by lightning strikes or electrical switching, and safely diverts them to the ground. By installing SPDs on the DC side, you protect expensive inverters and panels from catastrophic failure.
Where should installers place DC SPD in a solar energy system?
Installers should place DC SPDs at key entry points: first, in the combiner box near the solar array to intercept surges at the source. Second, at the DC input of the inverter to safeguard sensitive power modules. If the distance between panels and the inverter exceeds 10 meters, SPDs must be installed at both ends.
Why is grounding important for DC SPD?
Without a solid earth connection, a DC SPD cannot divert excess voltage away from sensitive solar components. Proper grounding ensures the device shunts thousands of amperes safely to the earth, preventing catastrophic inverter failure and fire hazards. This drainage system is essential for shunting lightning energy.
How often should users inspect DC SPD?
Users should visually inspect DC SPDs every six months, or quarterly in high-lightning regions. Routine checks are crucial to verify the status indicator: green signifies protection, while red indicates a failed module requiring immediate replacement. Additionally, always perform a specialized inspection after major thunderstorms to detect potential damage.
What parameters should users check when selecting DC SPD?
Users must verify three critical parameters: Maximum Continuous Operating Voltage (Ucpv), which must be at least 1.2 times the system’s open-circuit voltage; Discharge Current (In / Imax), indicating durability against lightning strikes; and Voltage Protection Level (Up), which should remain below the inverter’s withstand limit.
