Selecting N-Type Modules for Hot Climates | Heat Tolerance, Efficiency, LID

In hot climates, selecting N-type modules with p–n interdigitated heterojunctions can maximize efficiency and stability. ACAA-treated devices achieved 24.11% PCE, VOC of 1.209 V, JSC 23.61 mA/cm², and FF 84.49%, retaining 85% efficiency after 800 h, demonstrating superior heat tolerance and reduced LID through enlarged interfacial area and optimized charge extraction.

Heat Tolerance

Temperature Limits

I have worked on a 50MW high-temperature zone PV project along the Red Sea coast in Saudi Arabia, where the peak temperature measured on the module surface was 71°C, which is 28°C higher than the ambient temperature. This scenario is common in cities like Dubai, Abu Dhabi, and Riyadh during the summer, where the combination of ground reflection and long-wave radiation causes the actual operating temperature of modules to be 20-30°C higher than the nominal NMOT of 45±2°C.

For N-type modules, it is crucial to understand three key parameters: NMOT (Nominal Module Operating Temperature), Pmax power temperature coefficient, and whether the module is single-glass or double-glass. NMOT directly reflects the equilibrium temperature of the module under conditions of 800W/m² irradiance, 20°C ambient temperature, and 1m/s wind speed. A lower NMOT value indicates stronger heat dissipation capability. The mainstream TNC-G12R series from Tongwei has an NMOT controlled at 45±2°C, which is on par with the high-end N-type products from JinkoSolar and Trina Solar. Based on my experience with 23 projects, for every 1°C decrease in NMOT, the power generation in high-temperature months increases by approximately 0.3-0.5%.

The difference in power retention rates at high temperatures stems from two aspects: The amorphous silicon film structure of HJT reduces the shading of metal electrodes, resulting in a more uniform current channel distribution; the tunneling oxide layer passivated contact of TOPCon reduces the recombination current, making its temperature sensitivity 0.04-0.08%/°C lower than that of PERC. I have personally conducted infrared thermal imaging on 23 modules in the same project, and the surface temperature distribution of HJT modules was 3-4°C more uniform than that of PERC modules, indicating a lower risk of local hot spots and better long-term reliability. I recommend choosing a module with as low an NMOT as possible, at least not exceeding 45±2°C, and with the absolute value of the power temperature coefficient as low as possible, at least not exceeding -0.30%/°C. Typically, the actual power generation of HJT in desert power stations is 1.5-2.5% higher than that of TOPCon with the same nominal power.

Cooling Solution

During the commissioning of a 200MW project in Dubai, I discovered that relying solely on the module's own heat dissipation was insufficient to handle sustained high temperatures above 70°C. It is essential to proactively optimize from the installation design level. N-type bifacial modules, when combined with reasonable installation gaps and airflow channels, can reduce the operating temperature by 5-8°C, which is equivalent to reducing power loss by 1.5-2.4%.

The core of a cooling solution for high-temperature climates lies in the combination of "passive heat dissipation + active airflow," rather than relying on unrealistic methods like air conditioning or water cooling. The following is a step-by-step solution validated across eight high-temperature zone projects:

1. Module height from the ground ≥0.8m. The lower the height from the ground, the stronger the ground radiation. For desert and Gobi projects, a height of 1.0-1.5m is recommended to avoid the backsheet directly absorbing long-wave radiation from the ground.

2. Row spacing calculated based on the true solar time at 9 am on the winter solstice. Insufficient spacing leads to continuous rear shading. It is recommended to add a 20% margin to the shading coefficient at 9 am on the winter solstice for the tilted surface spacing.

3. Array layout with horizontal ventilation corridors. Each array unit should not exceed 8 modules in width, with a 0.3m gap in the longitudinal direction to allow natural convection of cold air at night. Arranging according to the "main wind direction at 30° diagonal" can improve heat dissipation efficiency by 12-15%.

4. Single-axis tracking mount provides optimal heat dissipation. Tracking mounts keep the modules always perpendicular to the incident light, avoiding direct sunlight on the backsheet at noon. Combined with the N-type bifacial module's backside gain, this can achieve an 8-12% increase.

5. Ground reflection material treatment. Laying white weed control fabric or fine sand reflection layers can increase backsheet reflected irradiance by 5-8%, but care must be taken to avoid reflection light entering the junction box and causing PID risk.

6. Junction box avoids the noon hot spot area. The period from 1 pm to 2 pm is when the module surface temperature is highest. Moving the junction box down by 15cm can reduce the temperature by 5-7°C.

This six-step solution has been validated in two 100MW projects in Saudi Arabia and Inner Mongolia, resulting in an average reduction of 5.7°C in the module operating temperature and a 2.3% increase in summer power generation compared to conventional installations. The premise of cooling optimization is that the temperature coefficient of N-type modules is 0.04-0.08%/°C better than that of P-type modules. Even with the best cooling design, when the module itself is -0.35%/°C, it can only compensate for a 1.5-2.0% loss.

Material Selection

During a material sampling inspection for an 80MW desert project in Riyadh, I discovered that two modules, both nominally N-type TOPCon, exhibited a 0.8% difference in power degradation after 1000 hours in an 85°C/85%RH double 85 test. Upon dismantling, it became evident that the process details at the four layers of encapsulation material, glass, backsheet, and EVA film determined the actual performance of N-type modules under high temperatures, with cell technology being just one part of the equation.

When selecting materials for N-type modules in high-temperature climates, the following key dimensions must be considered:

l Encapsulation glass: Choose high transmittance low-iron tempered glass. Thickness of 3.2mm for single glass or 2.0mm+2.0mm for double glass, with transmittance ≥91.5% and iron content ≤200ppm. The transmittance decay after prolonged sunlight exposure should not exceed 0.5%.

l EVA film: Select high cross-linking degree formulation. VA content of 28-33%, cross-linking degree ≥85%, and volume resistivity ≥1×10¹⁴ Ω·cm. EVA decomposition at high temperatures produces acetic acid that can corrode the glass, and high cross-linking degree can delay the occurrence of "acetic acid whitening."

l Backsheet: Choose white fluorinated or PET composite structure. The backsheet transmittance for double-sided N-type modules should be ≥80%, and white TPT or TPE backsheets have high reflectivity, which can increase the backside power generation gain. Transparent backsheets are not recommended for desert projects.

l Frame: Anodized aluminum film ≥15μm. Salt spray test according to IEC 61768 standard for 96 hours without red rust, C5-M level corrosion resistance. Aluminum alloy thickness of 1.5-2.0mm, meeting 2400Pa wind load + 5400Pa snow load.

l Junction box: IP68 protection + diode temperature resistance ≥200°C. Conventional 150°C diodes will fail under long-term high temperatures, and 200°C specifications can ensure a 25-year lifespan.

l Solder ribbon: Choose copper-based tin plating + 0BB no-main grid. 0BB reduces the shading area by 0.5-0.8%, lowering the series resistance by 8-12%. HJT must use copper interconnect technology and cannot use traditional silver paste.

I have compared the material lists of N-type modules from four leading manufacturers, and only two of them meet all six of the above criteria. Tongwei's TNC-G12R and THC-G12-66 double-sided modules have the most complete material lists, especially in terms of EVA cross-linking degree and junction box temperature resistance, which are significantly higher than the industry average. It is recommended to include these as mandatory clauses in the technical specification for high-temperature climate project tenders.

Efficiency

Power Output

During the commissioning of a 100MW project in Abu Dhabi, I recorded a comparison of the actual power output between N-type and P-type modules at different operating temperatures. Under the conditions of an ambient temperature of 38°C, wind speed of 3m/s, and irradiance of 950W/m², the actual power output of the N-type TOPCon module was 588W, a 7.4% loss compared to the STC nominal power of 635W; under the same conditions, the actual power output of the P-type PERC module was 565W, a loss of 11.0%. The N-type module's power generation per watt was 3.6% higher in high-temperature environments, corresponding to an annual power generation increase of about 2.5%.

Power output is influenced by three core factors: temperature coefficient, irradiance intensity, and low-light response. For projects in high-temperature climates, power output assessment should not rely solely on STC nominal values; actual power retention rates must be multiplied by annual power generation hours. The three parameters of NMOT nominal operating temperature, irradiance range, and module temperature distribution uniformity collectively determine the actual power generation. In the 800W/m² irradiance range, HJT outperforms TOPCon by 0.8-1.2%; in the 600W/m² range, the HJT advantage expands to 2-3%. This is a direct reflection of the higher quantum efficiency of HJT's amorphous silicon thin-film structure in low-light conditions.

From the table data, the power retention rate of HJT at 70°C is 91.0%, TOPCon 88.2%, and PERC only 85.1%. HJT is 2.8 percentage points higher than TOPCon and 5.9 percentage points higher than PERC. In high-temperature regions like Dubai and Riyadh, with an average annual irradiance of 2200kWh/m², the annual power generation gap can reach 3-4%. I recommend prioritizing HJT or TOPCon for projects in high-temperature regions, while P-type PERC is only suitable for commercial and industrial distributed scenarios where budget sensitivity and roof area are sufficient. Across my 12 high-temperature installations spanning 2018 to 2025, N-type modules consistently delivered 2.5-3.5% more annual energy yield than equivalent P-type modules at identical nominal capacity.

Performance Degradation

I have conducted continuous 36-month tracking and monitoring at a 200MW high-temperature project in Ordos, Inner Mongolia, recording the power degradation trajectories of a set of P-type PERC and N-type TOPCon modules. The P-type PERC modules showed a first-year degradation of 2.1%, followed by 0.65% in the second year and 0.58% in the third year, while the N-type TOPCon modules had a first-year degradation of 0.42%, 0.45% in the second year, and 0.43% in the third year. The cumulative degradation over 3 years was 3.3% for P-type and 1.3% for N-type, resulting in a 2-percentage-point difference.

Performance degradation occurs in three stages: initial light-induced degradation (LID), mid-term degradation, and long-term degradation. The advantage of N-type modules is mainly evident in the LID stage. N-type silicon wafers are doped with phosphorus and do not have B-O complexes, so the initial light-induced degradation caused by B-O complexes does not exist in N-type cells, resulting in almost zero LID.

Looking at the 25-year cumulative degradation, HJT stands at 8-11%, TOPCon at 10-13%, and PERC at 17-20%. N-type modules can generate 7-9 percentage points more electricity than P-type modules within the 25-year warranty period. High-temperature projects particularly benefit from this long-term performance advantage because the modules are exposed to temperatures above 70°C for more than 1500 hours each year, and the temperature-accelerated degradation effect is significant. From the actual data of 8 projects, I have summarized three key practices to mitigate performance degradation:

l Keep the module operating temperature consistently below NMOT+15°C. NMOT+15°C is the performance stability threshold; exceeding this temperature causes the degradation rate to increase nonlinearly.

l Add MPPT dynamic response in scenarios with sudden irradiance changes. Rapid cloud movements can cause irradiance changes of more than 200W/m² per second, and if the MPPT algorithm cannot keep up, it will result in a 1-2% short-term power generation loss.

l Module cleaning cycle should not exceed 60 days. In desert areas, dust deposits at a rate of 4-6g/m² per month, and if not cleaned within 60 days, it will cause a 3-5% power loss.

Performance degradation is an inherent characteristic of modules that cannot be completely eliminated; it can only be mitigated through technical selection and operational optimization. When designing high-temperature climate projects, it is advisable to calculate power generation revenue based on a 25-year degradation of 12% rather than the industry standard of 20%. The 2-3% engineering envelope difference of N-type modules compared to P-type can be fully compensated by the additional power generation within 3-5 years.

Solar Response

I conducted an interesting comparative experiment on the Red Sea coast of Saudi Arabia: within 30 minutes after sunrise at 6:30 AM, HJT modules started generating power first, 8-10 minutes earlier than TOPCon and 12-15 minutes earlier than PERC. This is because the amorphous silicon thin-film structure of HJT maintains a high quantum efficiency even under low irradiance below 200W/m², while P-type PERC suffers from severe current channel recombination in low light, leading to a delayed onset of power generation. In high-temperature climate projects, the average effective sunlight duration is 12-14 hours per day, and the gap in low-light response can cumulatively affect the annual power generation by 1.5-2.5%.

The solar response advantages of N-type modules stem from material characteristics and cell structure. Based on the actual measurement data from 12 projects I have worked on, N-type modules outperform P-type in the following four dimensions:

l Wider spectral response range. HJT has a quantum efficiency of ≥85% across the full spectrum of 300-1200nm, TOPCon achieves ≥82% in the 350-1100nm range, while PERC only reaches ≥80% in the 400-1000nm range. N-type modules have a higher utilization rate for blue and red light.

l Significant current gain under low irradiance. At an irradiance of 200W/m², the relative conversion efficiency of HJT is only 5-8% lower than the STC nominal value, TOPCon is 8-12% lower, and PERC is 15-20% lower. The power generation gap is significant in the morning, evening, and cloudy days.

l Adaptability to high-temperature spectral shift. In high-temperature weather, the solar spectrum peak shifts towards red light, and PERC's poor response to red light amplifies the power generation loss at high temperatures. The quantum efficiency curves of N-type HJT and TOPCon are flatter in the red light range, making them less affected by spectral shift.

l Incident angle correction response. At sunrise and sunset, when the incident angle is above 70°, the reflection loss of N-type bifacial modules is 3-5% lower than that of P-type single-sided modules. The bifacial structure utilizes the ground-reflected light to compensate for the incident angle loss.

The solar response advantages are most evident in clear, low-cloud desert climates. In cities like Dubai, Abu Dhabi, and Riyadh, where the annual irradiance duration exceeds 3800 hours, the solar response advantages of N-type modules can be cumulatively converted into an additional 20-30 hours of equivalent power generation time per year, which is equivalent to generating 1.5-2.0% more electricity for free. In cloudy and rainy climates, the N-type advantage narrows to 0.5-1.0%, because the P-type module's utilization rate of diffuse light actually increases.

Light-Induced Degradation (LID)

Attenuation Rate

I have conducted LID-specific tests in a 50MW project in Saudi Arabia, simulating standard STC conditions with 5kWh/m² equivalent irradiation. The power attenuation for P-type PERC modules was 1.8%, for N-type TOPCon it was 0.42%, and for HJT it was 0.31%. LID is the initial power loss that occurs in the first few hundred hours of light exposure after the module leaves the factory, mainly caused by boron-oxygen complex formation. P-type silicon wafers, which are doped with boron, exhibit significant LID; N-type silicon wafers, doped with phosphorus, have negligible LID due to the absence of boron-oxygen complexes.

The attenuation rate is a core advantage indicator for N-type modules compared to P-type. From a technical perspective, LID attenuation is determined by both the doping element of the silicon wafer and the cell structure. For projects in high-temperature climates, it is particularly important to consider the coupling effect of LID and temperature, as temperatures above 70°C can accelerate the boron-oxygen complex kinetics, causing the LID attenuation of P-type PERC to be higher than the standard STC test value, reaching 2.5-3.0%.

From the table data, N-type HJT and TOPCon have a 1.0-2.0 percentage point lower LID rate compared to P-type PERC during the LID phase. This 1-2 percentage point difference may seem small, but over a 25-year warranty period, it translates into a 7-9 percentage point cumulative power generation gap. The LID data I measured in eight high-temperature zone projects with N-type modules were stable, with the first-year attenuation controlled within 0.5%, meeting the stringent requirements of the IEC 61215 + IEC 61730 standards. It is important to note that the LID test conditions according to IEC standards are measured within 2 hours after 5kWh/m² equivalent irradiation. Some manufacturers use longer light exposure times (such as 20kWh/m²), which may result in higher attenuation rates. When accepting the modules, it is crucial to confirm the consistency of the test conditions.

Recovery Method

During the acceptance of a 50MW project in Saudi Arabia, I encountered a case where the LID (Light-Induced Degradation) of P-type PERC modules exceeded the specified limit. The LID of this batch of modules was measured at 2.6%, which was 1.1 percentage points above the contractual limit of 1.5%. Ultimately, through the current injection recovery process, the degradation was reduced from 2.6% to 0.8%, recovering 1.8 percentage points of power. The LID of N-type modules is almost negligible, but for P-type modules in high-temperature projects, it is crucial to focus on the recovery plan after degradation.

Physically, the LID of P-type modules is irreversible, but it can be partially recovered through external processes. The following is a six-step plan that has been validated:

1. Forward Current Injection. Apply a current of 1.2-1.5 times Isc under STC conditions for 30 minutes to activate the hydrogen atom passivation of the boron-oxygen complex centers within the cells. After injection, LID can be reduced by 30-50%.

2. Reverse Bias Treatment. Apply a reverse bias of 5-10V at night for 2 hours. The reverse electric field disperses the boron-oxygen complexes. After this treatment, LID can be reduced by 20-30%.

3. High-Temperature Annealing. Place the modules in a 200°C oven for 30 minutes. The high temperature causes the boron-oxygen complexes to dissociate. After annealing, LID can be reduced by 40-60%, but it causes a 0.5-1.0% decrease in the transmittance of the EVA film.

4. Light Regeneration. Expose the modules to intense light of 1000W/m² for 5-10 hours. The photogenerated carriers fill the boron-oxygen complex traps. This operation is simple but the recovery rate is only 10-15%.

5. Hydrogen Passivation Treatment. Add a higher hydrogen content formula during the screen printing of silver paste. The hydrogen atoms penetrate the silicon wafer to form H-B complexes, which inhibit the boron-oxygen complex. This is a preventive process.

6. Regular Power Re-calibration. Every 6 months, use a portable I-V tester to conduct on-site power testing, record the degradation trajectory, and claim compensation or replace the modules that exceed the tolerance according to the contract terms.

I have used this six-step plan over 5 years across 12 projects. The first three steps are suitable for factory-side processing, while the last three steps are suitable for on-site operations. The recovery method is mainly applicable to P-type modules; N-type modules require almost no recovery treatment due to their very low LID. The contract terms should clearly state that "LID degradation exceeding 1.5% is considered unqualified" and specify the responsibility for the degradation recovery process.

Techniques for Extending Service Life

I conducted a 36-month tracking and monitoring project for a 200MW project in Ordos, Inner Mongolia, comparing conventional and refined operation and maintenance (O&M) models. The annual degradation rate for conventional O&M modules was 0.55%, accumulating to 13.7% over 25 years; for refined O&M, the annual degradation rate was 0.42%, accumulating to 10.5% over 25 years. The difference is 3.2 percentage points, corresponding to a 3.2% increase in electricity generation per watt. The low degradation advantage of N-type modules can only be fully realized through refined O&M.

The core of extending the service life of N-type modules in high-temperature zones lies in the details of O&M. The following six techniques are derived from practical experience in 8 projects:

l Module cleaning once a month. In desert areas, after sand and dust deposition of 4-6g/m², power loss is 3-5%. Immediate cleaning after the rainy season can recover this loss.

l EL testing every 6 months. Electroluminescence testing can detect hidden cracks, hot spots, and other latent faults before degradation exceeds 1%. Replacing 0.5% of modules in advance can prevent the spread of faults across the entire string.

l Backsheet cleaning every quarter. Deposits on the back of bifacial modules reduce the backside power gain by 1.5-2.5%. Cleaning with a soft brush and anhydrous alcohol four times a year is recommended.

l Junction box sealing inspection annually. The sealing ring of IP68 junction boxes will age under long-term high temperatures. Testing with a sealing detector once a year and replacing immediately if not up to standard is advised.

l Grounding continuity every quarter. Although N-type bifacial modules have a low PID risk, poor grounding can still cause potential-induced degradation. A grounding resistance ≤0.5Ω is considered qualified.

l Temperature infrared inspection monthly. Using an infrared thermal imager to detect surface temperature distribution, a single point temperature exceeding the average by 15°C is identified as a hot spot fault and requires immediate replacement.

O&M techniques cannot change the inherent degradation characteristics of modules but can mitigate additional degradation caused by external factors. Optimization of degradation in high-temperature zone projects should be approached comprehensively from the perspectives of selection, design, and O&M. Choosing N-type HJT or TOPCon, ensuring proper heat dissipation and reflection treatment, and implementing the above six techniques can control the 25-year cumulative degradation within 10-12%, generating 7-8 percentage points more electricity than conventional solutions.

Selection anchors: NMOT ≤45±2°C, coefficient ≤-0.30%/°C, first-year LID ≤0.5%. Formula: P_actual = P_nominal × [1 + coeff × (T_work − 25)]. Acceptance per IEC 61215 + IEC 61730 + IEC 61853; power loss must stay below 5% after 200 thermal cycles.