How the SMA PID Box protects your solar panels against PID

Crystalline silicon solar panels are currently the most widespread technology in the world. However, a phenomenon largely unknown to the general public can significantly reduce their performance: PID (Potential Induced Degradation) . The good news is that SMA has developed a reliable and accessible solution: the SMA PID Box , also known as the PV Offset Box.

What is PID and why is it a problem?

Potential Induced Degradation (PID) is a form of degradation that affects crystalline silicon photovoltaic cells (monocrystalline and polycrystalline). This phenomenon occurs when solar modules are subjected to a negative electrical potential relative to ground .

Under these conditions, electrons gradually migrate from the photovoltaic cells to the metal frame of the panel. This migration creates an internal polarization that progressively reduces the power produced by the installation.

"Without protection against PID, the loss of efficiency can reach up to 30% in just a few years, with a direct and measurable impact on the profitability of a solar installation." — Fraunhofer ISE, Solar Energy Research Institute

Aggravating factors of PID

Several conditions favor the appearance and acceleration of the PID phenomenon:

• High humidity : humid environments accelerate electron migration
• High temperatures : heat increases conductivity and worsens the phenomenon
• High system voltage : installations with high negative voltage (>600V) are more at risk
• Transformerless inverters : Modern (and more efficient) transformerless inverters create a negative potential
• Lack of grounding : technical configuration favorable to PID

Examples of manufacturers and models historically involved

PID is not a theoretical problem. Many manufacturers and installations have been affected:

• Evergreen Solar : first documented cases of PID from 2005-2007
• Solon SE : In 2010, this German manufacturer officially introduced the term "PID" after identifying and studying the phenomenon.
• Standard c-Si panels (type-p) : a large part of the global market is potentially exposed, except for modules specifically tested and certified as "PID-resistant"
• Fraunhofer ISE study (2013) : out of 23 major manufacturers tested, only 4 offered modules insensitive to PID

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How does the SMA PID Box work?

The PID Box SMA , also known as the PV Offset Box , uses an intelligent nighttime regeneration principle to counteract and reverse the effects of PID.

Operating principle

The system operates primarily at night, when the photovoltaic installation is inactive:

1. Automatic detection : the PID Box detects the voltage drop of the photovoltaic array after sunset
2. Reverse voltage application : it applies a positive reverse voltage (between +400 V and +1000 V relative to ground) to the modules
3. Cell regeneration : this process reverses the polarization created during the day and allows the affected cells to gradually regenerate.
4. Continuous cycle : the process repeats every night for continuous protection

"The SMA PID Box restores panel performance approximately twice as fast as the initial rate of degradation. It's a simultaneous preventative and curative solution." — SMA Solar Technology Technical Documentation

Technical advantages of the SMA PID Box

• Gradual restoration of performance : recovery of lost efficiency, approximately twice as fast as the initial degradation
• Negligible electricity consumption : less than 3W drawn from the grid during the night (virtually no impact on the bill)
• Universal compatibility : usable with the majority of solar inverters on the market, including transformerless models.
• Simple installation : easy integration into new or existing installations
• Zero maintenance : autonomous operation without intervention required
• Continuous protection : ongoing preventative action against the onset of PID

Comparison of PID solutions: which option to choose?

Faced with the problem of PID, several solutions exist on the market. Here is a detailed comparison to help you choose:

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Economic analysis: what is the return on investment for the PID Box?

The ROI (return on investment) analysis of the PID Box SMA demonstrates its economic relevance, particularly in Belgium and France where residential solar kits represent a significant investment.

Calculation of lost revenue due to PID

Let's take a concrete example of a typical residential installation in Belgium:

• Installation : 6 kWp (standard solar kit)
• Initial investment : €7,500 (average price 2024-2025)
• Annual production : 5,400 kWh (900 kWh/kWp in Belgium)
• Annual savings : €1,620 (rate €0.30/kWh)
• PID loss : 20% after 3 years (average estimate)
• Annual loss of earnings : €324 per year

ROI of the SMA PID Box

Economic conclusion: With an ROI of less than 3.5 years and a cumulative gain of more than €5,000 over the lifetime of the installation, the SMA PID Box offers an excellent cost-benefit ratio, far superior to the complete replacement of modules or the installation of a transformer inverter.

Installation and compatibility of the SMA PID Box

Compatible installations

The SMA PID Box can be installed on:

• Residential installations : from 3 kWp to 10 kWp
• Commercial installations : up to 30 kWp (multiple PID Boxes in parallel if necessary)
• Single-phase and three-phase configurations
• Systems with transformerless inverters (SMA, Fronius, SolarEdge, Huawei, etc.)
• New and existing installations

Technical prerequisites

• Network connection : 230V power supply available (for nighttime operation)
• Access to the PV field : possibility of electrical connection to the modules
• Manufacturer validation : agreement from the panel and inverter manufacturer is recommended

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Frequently Asked Questions (FAQ) about the SMA PID Box

1. Which solar panels are sensitive to PID?

P-type crystalline silicon photovoltaic panels (monocrystalline and polycrystalline) are the most susceptible to PID. This technology represents approximately 90% of the global market. Recent modules certified "PID-resistant" or "PID-free" are specifically designed to resist this phenomenon. Thin-film technologies such as CdTe or CIGS are generally less affected.

2. Does the SMA PID Box consume a lot of power?

No, the PID Box's energy consumption is less than 3 W during its nighttime operation (approximately 8-10 hours per night). This represents an annual consumption of around 10 kWh, or less than €3 per year. This cost is completely negligible compared to the gains achieved in terms of restoring photovoltaic efficiency.

3. Can a PID Box be installed on an existing installation?

Yes, absolutely! The SMA PID Box can be easily added to existing photovoltaic systems, whether they are a few months or several years old. Installation simply requires an electrical connection to the PV array and a 230V grid connection. It is recommended to obtain approval from the panel and inverter manufacturers before installation, although compatibility is generally excellent with modern inverters.

4. Are there other solutions to the PID problem?

Yes, several alternatives exist, but with different trade-offs. The main solutions are: using transformer-based inverters with grounding (effective prevention but lower efficiency and high cost), replacing modules with PID-resistant certified panels (a radical but very expensive solution), or initially choosing PID-free modules for new installations. The SMA PID Box offers the best compromise between cost, efficiency, and simplicity, particularly for existing installations.

5. How can I tell if my installation is suffering from PID?

Several indicators can reveal a PID problem: a gradual decrease in yield not explained by soiling or shading, a production decrease exceeding normal degradation (0.5-0.7% per year), production discrepancies between strings (panel chains), or modules exhibiting visible dark areas (visual inspection or thermography). A professional diagnosis with IV curve measurements can confirm PID.

6. Does the PID Box require maintenance?

No, the SMA PID Box operates completely autonomously and requires no special maintenance. Once installed and configured, it operates automatically every night without human intervention. It is simply recommended to check annually during general system maintenance that the operating indicator is active and that power consumption remains stable.

Conclusion: The SMA PID Box, essential protection for your photovoltaic investment

Potential Induced Degradation (PID) represents a real and underestimated threat to crystalline silicon photovoltaic installations. With yield losses reaching up to 30% in just a few years, this phenomenon can seriously compromise the profitability of a solar investment.

The SMA PID Box offers an elegant solution to this problem: efficient, economical, and easy to implement. With a return on investment (ROI) of less than 4 years and potential savings of several thousand euros over the installation's lifetime, it represents a sound investment for both residential and commercial properties.

Whether you are planning a new installation or want to protect an existing system, Wattuneed will assist you in choosing and integrating the SMA PID Box that is suitable for your configuration.

Wattuneed SPRL
Rue du Commerce 102, 1040 Brussels, Belgium
Telephone: +32 87 45 00 34
Email: info@wattuneed.com
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