How to Maintain Monocrystalline Solar Panels for Longevity

Maintain monocrystalline panels by monthly cleaning with soft microfiber and deionized water (30 psi max) to clear dust/bird droppings, curbing 5% monthly efficiency loss. Annually inspect wiring for corrosion; avoid abrasives to protect anti-reflective coatings.

Daily Inspection and Cleaning

Exposure to wind and sun leads to the accumulation of dust and debris on the surface, directly causing a 5%-15% decrease in power generation efficiency, and in severely polluted areas, it can even plummet by 20% or more. A thorough cleaning can instantly boost the system's output power by over 10%, equivalent to earning extra electricity for free.

If your system generates 8000 kWh of electricity per year, neglecting cleaning could result in a loss of 800 kWh of electricity annually. Calculated at 0.8 yuan per kWh, that amounts to 640 yuan per year. Adhering to at least one effective cleaning per quarter, the cumulative loss in power generation revenue over a 25-year lifespan could be as high as thousands or even tens of thousands of yuan.

Cleaning Frequency

Data shows that when panel surface contamination causes a 5% decrease in light transmittance, the system's output power loss typically ranges between 4% and 7%, rather than being a linear relationship. This means that in industrial parks with high electricity prices of 1 yuan per kWh, a 100 kW power station, if its efficiency drops by 5% due to pollution and it operates effectively for 5 hours a day, could incur a direct electricity cost loss of nearly 25 yuan per day, and 750 yuan per month, far exceeding the cost of cleaning.

Don't Just Count Days, Learn to "Read the Weather"

l Effective Rainfall: A moderate rain or higher with precipitation exceeding 15 mm, lasting for more than 30 minutes, is necessary to form effective runoff on the panel surface, washing away most loosely attached dust. Light rain (precipitation <10 mm), especially "muddy rain," can mix with dust upon evaporation to form a hardened mud film, increasing the difficulty of subsequent cleaning.

l Establish a "Rainfall-Cleaning" Correlation Table: You can record local weather forecast precipitation data. For example, if there are 30 consecutive days without effective rainfall (cumulative precipitation <5 mm), and the weather is mostly sunny and windless during this period, the dust accumulation thickness on the panels might reach 0.5 mm or more. Monitoring typically shows a power generation decrease of 8%-12% compared to the same period historically, which is a strong signal for cleaning. Conversely, if there was a heavy rain of 20 mm last week, the current cleaning cycle can be automatically postponed by 2-3 weeks.

Look Down and See How "Dirty" Your Panels Are

l Level 1 Pollution (Light Dust): The panel surface is covered with a uniform layer of gray dust; a finger swipe leaves a clear mark, but it hasn't formed clumps. Estimated light transmittance loss is 3%-5%. Response Strategy: No immediate action required; include it in the next scheduled cleaning. However, note that if there is no rain within the next 48 hours and windy conditions are forecast, the dust may worsen.

l Level 2 Pollution (Heavy Dust Accumulation + Local Stains): The dust layer thickens, possibly accompanied by dried rain stain marks (water rings), or sporadic insect corpses and tree sap spots with a diameter less than 2 cm. Estimated light transmittance loss is 6%-10%. Response Strategy: Schedule cleaning within 7-10 days. This level of pollution already has a substantive impact on power generation efficiency.

l Level 3 Pollution (Severe Shading + Scaling): Includes but is not limited to: 1. Patches of bird droppings, exceeding 3 spots on a single panel, or a single spot larger than 5 cm x 5 cm. 2. A layer of mud slurry that has hardened after being soaked by rain. 3. A large amount of autumn leaves (especially decaying leaves) covering the panels. Light transmittance loss may exceed 15%, accompanied by a high risk of hot spots (local temperature can reach 85°C or higher). Response Strategy: Emergency handling. Prioritize removal within 72 hours of discovery, especially for bird droppings and decaying matter, as their chemical corrosion is ongoing.

"Scan" Your Surrounding Environment

l High-Risk Area (Recommended Cleaning Cycle ≤1 month):

l Within 100 meters there are construction sites, cement plants, mining areas, busy main roads (traffic flow >5000 vehicles/hour): These environments generate large amounts of heavy pollutants like cement dust and metal particles, which settle rapidly. Data shows that dust accumulation speed on PV panels within 200 meters downwind of a construction site is 3-5 times that of clean areas.

l Near farmland (especially during spraying/fertilization periods): Aerosolized particles of fertilizers and pesticides can adhere to the panel surface, forming a chemical pollution film that is difficult to wash away with rain alone.

l Below bird roosts/below power lines: Bird droppings are a continuous point source pollution, requiring more frequent local spot checks and cleaning.

l Medium-Risk Area (Recommended Cleaning Cycle 1-3 months):

l Ordinary urban or rural environments, with few nearby trees and average traffic flow.

l Pay attention to spring willow/poplar catkins and autumn leaves. Temporarily increase cleaning frequency during these seasons, e.g., inspect filters and panel surfaces every 2 weeks during the high season for catkins.

l Low-Risk Area (Cleaning cycle can be extended to 3-6 months):

l Open surroundings, vegetation mainly low lawns,stay away from pollution sources and bird habitats。

l Even in such areas, it is recommended to perform two fixed cleanings: after the spring sandstorm period and after the air turns dry in autumn.

If you observe that for 3 consecutive days under similar light conditions, the actual power is 5% or more lower than the historical average for the same period or the theoretical value, and inverter malfunction has been ruled out, then there is a 95% chance that your panels need a wash.

Cleaning Operation Manual

Many people think cleaning PV panels is just about rinsing and wiping, but incorrect operations can turn a 200 yuan cleaning service into a 2000 yuan repair bill. For example, rinsing with cold water when the panel temperature is 65°C increases the risk of micro-cracks by 300%; using alkaline detergents can cause an additional 2% loss in module light transmittance over 3 years, equivalent to losing hundreds of kilowatt-hours of electricity generation prematurely.

The manual below will use specific data to tell you how to avoid the pitfalls that 99% of people fall into.

If the Timing is Wrong, All Effort is Wasted

The ideal operating window is when the ambient temperature is below 25°C and the panel temperature does not exceed 40°C. On a sunny summer noon, the temperature of black panels can easily soar to 60-70°C. 

These cracks are invisible to the naked eye but can lead to moisture ingress, causing cell oxidation and an additional annual power degradation of 1% or more. Therefore, always choose early morning, evening, or an overcast day for operations. Also, check the weather forecast to ensure at least 24-48 hours of sunny weather after cleaning, allowing residual moisture to evaporate completely and avoid water stains.

Choosing the Right Tools Saves Effort and Ensures Safety

l Water source and pressure are the primary checkpoints. Must use ordinary hose flow, with water pressure strictly controlled at 3-5 kg/cm² (approximately equivalent to normal tap water pressure). Strictly prohibit high-pressure washers, whose output pressure can be as high as 80-120 kg/cm², impacting the glass like a hammer. More dangerously, high-pressure water mist can forcibly intrude into the microscopic gaps of the junction box plug interfaces and frame sealant, compromising their IP67/IP68 waterproof rating, causing internal circuit short circuits and corrosion.

l Cleaning tools determine surface wear. The best choice is a long-handled microfiber brush roller, with fiber length preferably over 1.5 cm, soft and flexible. The second choice is a high-quality sponge mop. Strictly prohibit using hard brushes, brooms, or abrasive cleaning cloths, as they create countless micro-scratches on the glass surface's anti-reflective coating. While a single scratch is invisible, dense scratching can form a hazy film, leading to a permanent light transmittance loss of 1-3% over the long term.

l Only use "neutral" cleaning agents. Most household detergents are alkaline (pH >7). Long-term use can cause chemical reactions with the acidic anti-reflective coating on the glass surface. The correct approach is: 90% of the time, use only clean water. For stubborn organic stains (like tree sap, bird droppings), purchase a dedicated photovoltaic neutral cleaner and dilute it at a ratio of 1:300.

l A squeegee is a sharp tool for eliminating water stains. Choose a squeegee 40-45 cm wide with a smooth, undamaged rubber blade. When squeegeeing, ensure the blade is at a 30-45 degree angle to the glass surface, scraping in one pass without going back and forth.

Step by Step, Don't Rush

1. Step One: Safety Power Off. This is not a suggestion, it's a rule. Before operation, you must turn off the DC switch on the inverter to reduce the voltage to a safe range. Working on live modules risks electric shock, and abnormal signals generated by hot panels contacting water may trigger inverter fault codes.

2. Step Two: Pre-rinse. Use a gentle water flow, starting from the upper left corner of the panel array, fanning towards the lower right corner. The goal is to rinse off over 90% of the dust particles. Never start wiping directly, otherwise the dust particles will act like "sandpaper," scratching the glass during wiping.

3. Step Three: Apply Cleaning Solution. Apply the diluted cleaning solution evenly over the panel surface using the soaked mop, moving from top to bottom in an "S" pattern, ensuring coverage of all areas. For stubborn stains, let the solution sit for 1-2 minutes to soften, but do not let it dry on the surface in sunlight.

4. Step Four: Second Rinse and Squeegee Dry. Rinse off all cleaning solution and dirt thoroughly with clean water. This is the most critical step: Immediately squeegee dry. During operation, press one end of the squeegee firmly against the frame, ensure the blade makes full contact with the glass, and scrape from top to bottom in one smooth motion, overlapping each pass by 5 cm. This "squeegee drying" step prevents mineral deposits in the water from forming stains after drying, increasing the benefit of this cleaning by at least 15%.

5. Step Five: Final Inspection. Quickly inspect the panels after cleaning. Focus on areas below the junction box and the seams between the frame and glass for water streaks or residual droplets. Ensure all moisture is completely removed.

These "Stupid Things" Must Never Be Done

l Do not stand on the panels! The static load capacity of a single module is typically 5400 Pa (approximately 540 kg per square meter), but the dynamic pressure of stepping creates huge point pressure,It is very easy to cause internal cell cracks.

l Do not wipe the surface directly when it is dry. 

l Do not use unknown "strong stain removers". There have been cases where using acidic toilet cleaner to wash a power station caused the entire array's power to degrade by over 20% within six months, resulting in significant losses.

Inspection Checklist

The loosening amplitude of an M8 bracket screw from 1 mm to 3 mm can increase the stress borne by the fixing point by 5 times when encountering a level 8 gale, potentially causing bracket deformation or even module fall.

A barely visible glass micro-crack 3 cm long can lead to moisture seepage during the rainy season, causing that module's power to degrade by over 10% within 6 months, and it cannot be replaced for free.

Panel Surface Condition

l Best Inspection Light: Conduct inspections under low-angle oblique light conditions, such as early morning or evening. When light grazes the panel surface, any tiny irregularities, cracks, and stains are magnified by shadows, becoming clearly visible.

l Inspection Path: Scan along the panel frame, with your line of sight at a 30-45 degree angle to the panel surface. Key checks include:

l Micro-cracks: Look for hairline cracks (width less than 0.1 mm), with lengths potentially ranging from 2 cm to spanning the entire cell. Cannot be felt by touch.

l Hot Spots: The cell area in a hot spot is usually darker than other areas, as if baked, sometimes accompanied by bubbles 1-2 cm in size or delamination of encapsulant material. 

l Coating Corrosion: Check if there are large areas on the panel surface that appear map-like with a frosted texture. This is usually caused by strong acids or alkalis (e.g., bird droppings, cleaning agents) corroding the anti-reflective coating, leading to a permanent 3%-5% decrease in light transmittance in that area.

l Obstructions

l Quantify Shading Area: Take a photo with your phone and estimate the percentage of the panel's total area shaded by the obstruction's projection. For example, 5 fallen leaves might only shade 0.5%, while a clump of bird droppings 15 cm in diameter might shade 0.2%.

l Establish "Shading-Loss" Correlation: A shadow from a branch only 2 cm wide, if it spans 6 cells across three strings of cells, can cause the entire module's output power to drop by 30%-50% during the time the shadow persists. Record the time of day the shadow appears and its duration. If it exceeds 2 hours, the source of the shade must be removed.

Mounting Structure and Grounding

l Shake Test: Apply moderate force (about 5 kg of push) to try to shake the main uprights and rails of the mounting structure. Observe the amplitude of movement; if visible sway exceeds 2-3 mm, it indicates that the connection points (usually M8 or M10 bolts) have loosened and need tightening.

l Corrosion Assessment: Don't panic when you see rust; first assess the grade. Surface rust (can be scraped off with a fingernail) can be derusted and repainted. But if there is pitting deeper than 0.5 mm on a 2 mm thick angle iron, or the corroded area exceeds the size of a coin, professional structural reinforcement or replacement is needed.

l Quick Grounding Continuity Check: Check that the green grounding wire from the structure to the grounding flat bar is securely connected. Pull on it by hand to confirm the M6 grounding screw is not loose. If the grounding wire is found cut or severely corroded (copper wire blackened/greenened), the system loses lightning protection and must be repaired immediately.

Junction Box and Cables

l Junction Box Status: A normal box has uniform surface color. If local yellowing, blistering, or bulging is found on the box surface, it indicates that internal diodes or solder joints have overheated, possibly exceeding 100°C. After cooling, gently touch the box surface with the back of your hand; if it feels significantly warmer than other boxes (temperature difference >10°C), it also indicates a fault.

l MC4 Connectors: Check if the plugs are fully inserted (a "click" should be heard). Gently rotate the connection point of the male and female plugs; there should be no looseness. Disconnect the plug (ensure power is off first!), and observe that the internal metal terminals should be bright silver, without black burn marks or green patina.

Regular Inspection

A 10kW home system represents an investment of about 40,000-50,000 yuan. If neglect of inspection leads to an annual efficiency loss exceeding 2% (far above the normal 0.5-0.8%), the lost electricity revenue over the 25-year lifespan could amount to tens of thousands of yuan.

The core of regular inspection is to identify and resolve small issues (like a loose bolt, a small patch of bird droppings) before they escalate into costly repairs (like replacing an entire panel or inverter, costing thousands of yuan) or permanent power generation decline.

Visual and Mechanical Structure Inspection

The mounting structure of a 10kW system bears over 1000 kg of wind pressure and snow load daily. Loosening of any installation bolt can trigger a chain reaction. Data shows that over 60% of abnormal power generation efficiency decreases originate not from core electrical faults, but from the accumulation of "minor issues" like mechanical loosening, shading, or corrosion.

A panel tilt angle deviation exceeding 3 degrees can cause an annual loss of nearly 3% in power generation revenue at 40 degrees north latitude, equivalent to generating 200-300 kWh less electricity. This type of inspection doesn't require advanced skills but needs a keen eye and an accurate measuring tape, best performed in clear weather with wind speeds below level 3.

1. The Panel's "Face": Glass, Cells, and Obstructions

Start with the panels themselves. A standard 550W monocrystalline panel measures about 2.2 meters long and 1.1 meters wide. Inspect it as carefully as you would a car windshield.

l Glass Inspection: Focus on finding two types of marks. First, cracks, even hair-thin (less than 0.3mm), especially within 5cm of the frame edges. These could be due to installation stress or hail and need marking for professional review within a month. Second, wear of the anti-reflective coating. Look against the light; if irregular frosted, hazy areas appear locally, covering more than 5% of the panel area, it will cause reduced light transmittance, and power generation will be over 5% lower than normal panels.

l Cell Inspection: Mainly look at color. Normal cells are uniformly dark blue. The appearance of bright spots (hot spots, temperature may exceed 80°C), dark spots (failure due to micro-cracks), or rainbow patterns (EVA aging) are signs of problems.

l Obstruction Grading and Cleaning: Bird droppings, mud, pollen – it's not just about wiping them off; consider the impact. Temporary dust might affect generation by less than 2%, but hardened bird droppings shading an area larger than a coin must be cleaned immediately. This localized shading can cause a local temperature difference exceeding 40°C at summer noon, being the prime cause of hot spots. Leaving it unaddressed long-term will permanently reduce cell performance.

Table: Common Panel Surface Issues and Handling Urgency

2. Mounting Structure and Foundation: Is the Power Station's "Skeleton" Stable?

l Bolt Tightness Spot Check: Don't trust "looks tight." Use a torque wrench to spot check 10% of the bolts according to the torque values specified in the installation drawings (e.g., C-channel column connection bolts often require 40-50 N·m). If over 10% of the bolts have torque values below 70% of the standard, a comprehensive tightening is needed. Loose bolts cause structural sway, leading to wear and deformation at fixation points over time.

l Corrosion Assessment Standard: The galvanized layer thickness is generally required to be greater than 65μm. During inspection, white powder (zinc oxide) is normal, but if you see base material (iron-red) rust spots, and a single spot area is greater than 1cm², or the total corroded area at a connection exceeds 5%, anti-rust treatment is needed.

l Foundation Stability: For ground-mounted stations, check concrete foundation piers for cracks wider than 2mm or significant tilting. For rooftop stations, press on different parts of the structure to feel for abnormal "soft" movement.

3. Angle and Spacing: Don't Let Installation Errors "Steal" Your Electricity

Minor installation deviations are magnified into significant generation losses over 25 years.

l Tilt Angle Accuracy: Use an inclinometer (smartphone app accuracy is sufficient). Taking the optimal tilt angle of 35 degrees in North China as an example, if the actual tilt is 32 or 38 degrees (3-degree deviation), the annual total generation might lose 2.5%-3%. If the deviation exceeds 5 degrees, the annual loss could reach over 5%.

l Row Spacing Verification: Pay special attention in autumn/winter when the sun is low. Ensure the shadow from the front row does not fall on the rear row. On the critical Winter Solstice, ensure the rear panels are completely unshaded between 9 AM and 3 PM true solar time. Spacing calculation usually requires at least 4 hours of unshaded time on the Winter Solstice. Insufficient spacing can lead to 15%-20% generation loss in winter.

Electrical Connection and Safety Inspection

Statistics show that over 80% of PV fires can be traced back to electrical connection faults. A seemingly ordinary loose MC4 connector can see its contact point resistance surge from the normal 0.5 mΩ to over 50 mΩ. Under an 8A operating current, local power loss jumps from 0.03 W to over 3 W, instantly generating temperatures of several hundred degrees Celsius, enough to melt insulation and cause a fire.

DC-side voltage can be as high as 600V-1000V, and arc faults are powerful and cannot self-extinguish like AC. Therefore, electrical inspections must follow the principles of "power-off operation, from surface to interior, data verification". Recommended frequency is routine visual inspection every 6 months, and loaded inspection by professionals using thermal imagers and clamp meters every 2 years.

1. DC Connectors

l Mating Feel and Appearance: When disconnecting, there should be a distinct "click" and some resistance. If it feels loose, the internal spring contacts may be fatigued, increasing contact resistance. Look closely at the internal metal parts of the male/female connectors for blackening or melting points from electrical erosion, or dulling from oxidation. Check if the rubber seal is aged or cracked (gently pull to check for permanent deformation or cracks), a precursor to waterproofing failure.

l Torque is the Lifeline: Use a torque screwdriver to check the torque on the cable crimping screws. For 4mm² or 6mm² PV cable, this torque is typically between 2.0-2.5 N·m. Insufficient torque causes poor contact; excessive torque can damage the terminal.

l Resistance Measurement (Advanced): With the system completely powered off, use a milliohm meter to measure the contact resistance of a single connector. New connectors should be <0.5mΩ; if in operation it exceeds 2mΩ, it must be replaced. Compare the resistance of all connectors in a string; the difference should not exceed 20%.

Table: Common DC Connector Fault Diagnosis

2. Junction Box

l Sealing and Waterproofing: After opening the box cover, first check if the silicone seal is still elastic, sticky, or permanently flattened. Look inside the box for moisture, water droplets, or rust. Use a megohmmeter to measure the insulation resistance of the junction box to ground; the insulation resistance after wet leakage test should be no less than 1MΩ.

l Diodes and Cable Connections: Observe the bypass diodes for bulging or cracking. Under normal operation, quickly touch the diode casing to feel its temperature. If noticeably hot to the touch (estimated over 70°C), it may be frequently conducting. Check its forward voltage drop with a multimeter (typically 0.3V-0.6V); if significantly off or shorted/open, replace immediately. Check internal cable terminal crimps are secure, and check for discoloration (bluing) of lugs due to overheating.

3. Cables

l Sheath and Shielding: Feel along the cable sheath for bulges, cracks, or hardening. Especially parts passing through eaves, metal conduits, check for wear or burrs. For armored cables, check for visible rust on the armor. Any damage exposing the copper core is highest risk, require immediate power-off handling.

l Temperature and Ampacity: During full system load (sunny noon), scan the cable surface with an infrared thermometer. The surface temperature of PV1-F 4mm² cable in 25°C ambient should not exceed 60°C during continuous operation. If temperature exceeds limits, it could be undersized cable or insulation aging.

l Wiring Standards: Ensure DC and AC cables are laid separately, with a minimum spacing of 30cm to avoid interference. Check that cables in trays are neat; excessive bending (bend radius less than 6x cable diameter) damages insulation.

4. Grounding and Lightning Protection

l Grounding Continuity: Use a ground resistance tester to measure the system's overall ground resistance. For home PV systems, this must be strictly controlled below 4Ω. Use a multimeter to measure resistance between panel frame and ground bus; should be less than 1Ω.

l Lightning Arrestor (SPD) Status: Check the status window on the SPD; green is normal, red or black means failed and needs replacement. Check the cross-section of the ground wire connected to the SPD; should not be less than 6mm².

Performance Data Deep Analysis

System Performance Ratio (PR) is the key metric. A well-performing station typically has a PR between 80%-85%. If your 10kW station's theoretical generation for a month should be 1200 kWh (based on local irradiation data), but it only produced 960 kWh, then the PR is 80%.

If this value is below 78% for three consecutive months or decreases by more than 5% compared to the previous period, it indicates a significant system problem. These problems are often gradual, like current mismatch due to a slight micro-crack in a panel within a string, potentially causing a loss of only tens of kWh per month, hard to notice, but accumulating to hundreds of kWh per year.

1. Understanding the Inverter, the "Chatty" Machine

Every data point on the inverter screen tells you the real story; don't just look at total generation.

l DC Side Voltage/Current: Record data during peak sunlight (e.g., noon to 1 PM). For an inverter with 3 strings, the DC voltages of the 3 strings should be very close, deviation usually not exceeding 5V. If one string's voltage is consistently over 10V lower than others, bypass diodes in that string might be shorted or there's severe shading. Look at DC current; values for each string should be basically the same, maximum deviation should not exceed 2%. If one string's current is significantly lower, it could indicate severe performance degradation in that string, poor connector contact, or shading.

l AC Power and Grid Voltage: The inverter's AC output power should be close to "DC Power × Efficiency". If AC power fluctuates frequently or drops to zero during good sunlight, note the grid voltage at that time. When grid voltage consistently exceeds 260V (single-phase) or 450V (three-phase), the inverter will derate or shut down to protect the grid. This might be due to high line voltage in your area, requiring contact with the utility to adjust transformer taps, not a device fault.

Table: Common Generation Anomalies and Corresponding Data Clues

2. Calculate the "System Efficiency" Yourself

PR doesn't require complex software; you can calculate it with Excel.

1. Get Data: Find the "Global Horizontal Irradiation" (monthly cumulative, kWh/m²) for your location from a weather website. Then, convert it to irradiation on your panel's tilted surface ("Plane of Array Irradiation") using a formula, or use direct data from some monitoring platforms.

2. Theoretical Generation: Multiply this POA irradiation by your system's capacity (kW). E.g., monthly POA irradiation 150 kWh/m², 10kW system theoretical generation = 150 * 10 = 1500 kWh.

3. Calculate PR: Divide the actual generation recorded by your meter by the theoretical generation. E.g., actual 1275 kWh, PR = 1275 / 1500 = 0.85 (85%).

4. Trend Comparison: Calculate PR monthly and plot the values. If the curve shows a declining trend for 3 consecutive months or more, even if the absolute value is above 80%, it's a warning sign indicating slow system performance degradation.

3. Correct Summer's "Inflated" Generation for Temperature

Don't be fooled by strong summer sun; high temperatures reduce panel output.

l The panel power temperature coefficient is typically -0.35% to -0.45%/°C. When panel temperature reaches 65°C (common in summer), compared to standard test conditions (25°C), output power decreases by approximately (65-25) * (-0.4%) = -16%.

l So, when comparing July and April efficiency, don't just look at absolute values. July might have stronger irradiation, but high temperatures cause efficiency loss. Focus more on PR; if July's PR is much lower than April's, it might indicate poor heat dissipation or other issues.

4. Give Your System a "Thermal Imaging Check-up"

Infrared thermal images are great for finding hidden faults; recommended on a windless, sunny summer noon.

l Normally operating panels have even temperature distribution, overall temperature might be 25-35°C above ambient.

l If you find one or more bright white spots on a panel, 20-30°C hotter than surrounding areas, it's likely a "hot spot" caused by micro-cracks, internal short, or cell defect. This cell not only doesn't generate power but consumes power from others, heating up like a resistor.

l If a junction box or MC4 connector appears abnormally bright white in the image, much hotter than others, it indicates high contact resistance, serious heating, a fire hazard, and must be addressed immediately.

Common Mistakes That Must Be Avoided

A panel can theoretically last 25-30 years, but one careless mistake can cause its efficiency to permanently drop by over 5% within 1 year, or even trigger hot spots causing local temperatures to exceed 80°C, rendering it completely useless. Repairing or replacing a single panel, including labor and parts, can cost 15% to 20% of the initial investment, not including lost generation revenue during downtime.

Using Wrong Cleaning Tools

Industry tracking data shows that improper tools and cleaning methods cause an average annual solar panel performance degradation of 2%-5%. In severe cases, peak power output can permanently decrease by 8% or more within a year.

A panel worth 1500 yuan could see its long-term generation revenue reduced by over 30% due to a few high-pressure washer cleanings, potentially amounting to thousands of yuan in cash.

Using a High-Pressure Washer: Convenient but Potentially Sealing-Destroying

Water pressure over 80 Bar is essentially gambling with the panel's sealing lifespan. The pressure resistance of the sealant around the panel and the backsheet material has clear design limits, typically able to withstand instantaneous water pressure up to 30-40 Bar. Household handheld pressure washers easily reach 80-120 Bar or higher.

What does this pressure mean? It's equivalent to continuously impacting the panel's most vulnerable sealed edges with a force of 8-12 kg per square centimeter. One rinse might be fine, but doing this every month accelerates fatigue damage to the sealant. Moisture can infiltrate the interior as vapor through microscopic, invisible gaps. Once internal humidity exceeds limits, it can trigger Potential Induced Degradation (PID), an irreversible chemical degradation process. Experimental data shows that at 85% relative humidity and ambient temperatures above 25°C, PID can cause module power degradation exceeding 30% within 6 months.

The correct method is: Use a standard garden hose with natural water flow. The pressure, roughly equivalent to the pressure of water falling freely from a height of 1 meter from the tap (about 0.3-0.5 Bar), is sufficient to rinse off dust and absolutely safe.

Using Hard Brushes/Scrapers to Wipe Dust is Like "Sanding" the Glass

Panel glass is coated with an anti-reflective layer 100-200 nanometers thick, optimizing light refraction to increase transmittance from about 91% for ordinary clear glass to over 94%. Don't underestimate this 3% difference; it directly corresponds to a similar proportion of power generation.

When you use hard-bristled brushes, rough brooms, or even scrapers to remove bird droppings or stubborn dust, the Mohs hardness of these tools (often over 5.0) is much higher than the coating's hardness (about 4.0). Each scrape creates countless micron-sized scratches on the coating. A single scratch's effect on light transmission is negligible, but wiping monthly for a year will create a uniform "frosted surface" from these scratches, greatly increasing light diffusion.

Measured data shows that after 36 months of incorrect wiping, panel glass transmittance can decrease by 2.5%-4%. This means a panel rated at 400 watts might only have a maximum output of about 384 watts three years later. This lost 16 watts is permanent and irrecoverable. For a 10kW system, it's like permanently losing 400 watts of capacity, generating about 500 kWh less per year.

The correct tools are: Materials with Mohs hardness below 3.0, like sponges, soft cloths, or professional silicone squeegees. Always soak and soften dirt with water before cleaning, adhering to the principle of "rinse first, then mop, never dry-wipe".

Misusing Cleaners: Chemical Corrosion is an Invisible Killer

The aluminum frame, silicone sealant, and glass of panels are sensitive to pH. Their long-term safe use pH environment is generally between 6 and 8, neutral.

Many people use dish soap, laundry detergent water, or even window cleaner for convenience. Common dish soap has a pH around 8-9 (weakly alkaline), laundry detergent can be as high as 10-11 (alkaline), and some strong glass cleaners can be as low as 3-4 (acidic). Occasional use might be fine, but using these cleaners quarterly or every two months allows residual chemicals to slowly corrode the aluminum frame (reacts with both acid and base), accelerate silicone sealant aging (saponification), and leave a hard-to-rinse chemical film on the glass. This film itself affects light transmission, causing an annual generation loss of about 0.5%-1%, and the material corrosion is cumulative.

The safest choice is: Use plain water. For sticky stains, use a professional solar panel cleaner with a neutral pH (6-8), formulated to be residue-free, non-corrosive, and often containing ingredients that aid evaporation, reducing water spots.

Pouring Cold Water on Hot Surfaces: Thermal Shock Crack Risk Increases 10x

Solar panels under direct summer noon sun can easily reach surface temperatures of 65-75°C or higher. Pouring cold water below 20°C at this time causes the glass surface to contract violently due to rapid cooling.

Glass is a poor heat conductor. When the surface cools and contracts, the interior remains hot and expanded. This temperature difference creates enormous thermal stress. Ordinary tempered glass can typically withstand a thermal shock difference (ΔT) of about 150°C, but under ideal conditions. Installed panels have inherent installation stress, and the glass itself may have tiny, invisible stress concentration points.

When a ΔT of over 50°C is instantly applied to the glass, the probability of micro-cracks increases by a factor of 10 compared to rinsing at ambient temperature. These micro-cracks start thinner than a hair, hard to see, but will gradually expand with daily temperature cycles and panel bending from wind pressure, potentially developing into through-cracks within 1-2 years, causing module failure.

The only correct cleaning time is: Early morning, evening, night, or overcast/rainy days, ensuring the panel temperature is close to the air temperature. The temperature difference is minimal, ensuring safety.

Ignoring Partial Shading

Tests show that a palm-sized (about 20cm²) bird dropping, shading just 1%-2% of a single cell's area, can cause the output power of an entire 365W module to plummet by over 60% within 30 minutes. 

More dangerously, the shaded cell instantly becomes a heating resistor, its local temperature soaring to 120-150°C within an hour, far exceeding material safety thresholds.  Long-term neglect of partial shading leads not only to annual generation losses of 5%-15% but is also a direct cause of permanent panel damage.

Hot Spot Effect: The Shaded Cell "Overheats" or Even "Burns Out"

Cells in a solar panel are connected in series, like Christmas lights; the current is limited by the narrowest path. When a small part is shaded by a leaf or bird dropping, that cell can't generate electricity and instead acts as a resistor in the current path.

When current is forced through this "resistor," electrical energy converts to heat. During normal operation, cells operate about 20-30°C above ambient. Once shaded, the unfortunate cell's temperature rises sharply, easily 40-60°C higher than neighboring, normally generating cells. If the ambient temperature is 30°C, the shaded cell can heat up to over 85°C within half an hour.

This temperature already exceeds the long-term tolerance limit of the EVA encapsulant. The EVA will begin to yellow and carbonize, causing permanent loss of light transmission. If the shading persists and the temperature continues to rise to 120-150°C, an avalanche effect occurs: the cell's solder ribbons melt and detach due to overheating, causing an open circuit. More severely, the cell itself (monocrystalline silicon) can experience "thermal runaway" at high temperatures, forming irreversible damage points, visibly appearing as dark burn marks – the "hot spot." Once a hot spot forms, that cell is essentially ruined, and the hot spot can spread like rust, potentially causing the entire module to fail within 6 months.

Power Loss: 1% Shading Can Wipe Out Half Your Power

This sounds counterintuitive but is a basic characteristic of series circuits. A standard module typically has 60 or 72 cells in series. Current must flow through every cell, its magnitude determined by the least illuminated cell.

A partially shaded cell not only stops generating but also creates a "reverse bias," acting like a barrier in the current path. To pass this barrier, the voltage across the string redistributes, and the system operating point deviates severely from the Maximum Power Point (MPP).

The exact loss depends on the shading location and area. If a shadow completely covers half a cell (about 0.4% of the module area), this half-cell forces the other, normally functioning half-cell in parallel to also stop working, potentially reducing the module's power output by one-third instantly. If the shadow is linear, crossing several cells, forming a "hard shadow," the power drop can easily exceed 50%.

Inspection revealed that the shadow of a mere 2 cm diameter clothesline, between 9-10 AM daily, fell diagonally across one module, just shading the edge of three cells. This thin shadow caused the system's average daily generation to be 12% lower than expected for a whole month.

Which Shades Are Most Insidious? Bird Droppings, Leaves, and Dust are the Top Three Culprits

l Bird Droppings: The "Concrete Spot." Fresh droppings are soft, less problematic. But once dry, they harden like cement, causing almost 100% shading. Their danger lies in their small area, high concentration, making them typical "ignition sources" for hot spots. A dried dropping 3-4 cm in diameter, if covering the cell's main gridline, is highly likely to cause visible hot spot damage within a week.

l Leaves: The Seasonal "Power Killer." Autumn is peak season for leaves. A single plane tree leaf can cover 1/8 of a module. Leaves aren't uniform like dust; they cause 100% full shading. If not cleared promptly, a leaf left on the module for 3-5 days can already create hot spot risks underneath. More importantly, leaves accumulate on the module's lower frame. If not removed, damp, decaying leaves can corrode the aluminum frame and become a breeding ground for mold, further affecting edge light transmission and sealing.

l Frame Dust Accumulation: The Silent "Performance Pest." If dust isn't cleaned long-term, it accumulates around the module's aluminum frame edges, forming a "dust wall." This dust might not cause immediate hot spots but will act like a picture frame, gradually reducing the module's effective light-receiving area. Year after year, this shadow slowly encroaches inward, causing an additional average annual efficiency loss of about 0.2%-0.3% – a significant figure over a decade.

Rough Handling of Snow and Foreign Objects

In northern winters, 20 cm of snow on panels adds a continuous pressure of 20-30 kg per square meter. But this isn't the deadliest part. What often destroys panels is rough handling during snow removal.

A standard monocrystalline silicon cell is only 180 microns (0.18 mm) thick, not much thicker than a sheet of A4 paper (about 100 microns). When you strike ice with a hard shovel, the local pressure at the impact point can instantly exceed 5 MPa, enough to create micron-sized micro-cracks in the extremely brittle silicon wafer.

One reckless snow shoveling session can create dozens of invisible cracks inside the panel. These cracks expand over subsequent 50+ daily temperature cycles, eventually causing cell breakage, permanent power degradation of over 15%, and this damage is not covered by warranty.

Using a Hard Shovel to Break Snow is Like "Planting Landmines" Inside Your Panel

When snow compacts and turns to ice, the first instinct for many is to use a shovel, broom, or even a stick to break the ice.

The impact force isn't evenly distributed. Tapping the glass might feel gentle, but the force transmits as a wave through the glass and the cells beneath. The contact area of a shovel edge or stick with the glass might be only 0.5 cm². If you apply 5 kg of force, the instantaneous pressure at the contact point is 10 kg/cm² (about 1 MPa). Tempered glass is strong and might withstand it, but the cells underneath are extremely fragile.

This is how micro-cracks form. Monocrystalline silicon cells are like thin biscuits, very brittle. The huge impact stress causes microscopic cracks, thinner than a thousandth of a hair, inside the cell. Crucially, these cracks are initially completely invisible; the panel seems fine, with a power loss of maybe 1%-3%, unnoticeable. But micro-cracks are permanent and progressive. As the panel expands and contracts daily with temperature changes (amplitude up to 1-2 mm per meter) and bends slightly from wind pressure (amplitude up to several cm), these micro-cracks constantly "open and close," slowly expanding like a fatigue test. Within 6 months to a year, multiple micro-cracks may connect into a larger crack, causing partial or complete failure of that cell and a sudden sharp power drop. By then, it's too late.

The correct tool is a long, soft snow rake. Made of soft foam or plastic, it has a large contact area with the glass, distributing pressure across the entire panel surface and avoiding stress concentration.

Standing on Panels to Work is Gambling They Won't Break Immediately

Installers or owners sometimes step directly on panels for roof access or inspection.

A person's weight concentrated on the soles creates immense

pressure. A 75 kg adult, standing with shoe contact area about 400 cm², exerts an average pressure of about 0.19 kg/cm². But when standing on a tilted PV panel, balancing concentrates force on heels or toes, reducing the actual contact area to less than 100 cm², skyrocketing local pressure to over 0.75 kg/cm².

Panels are not designed for load-bearing. Although modules undergo mechanical load testing (e.g., frontal 5400 Pa, approx. 550 kg/m²) before leaving the factory, this test applies pressure evenly across the entire surface. Stepping with one foot is a classic point load, completely different from test conditions. This causes invisible bending deflection in the glass (possibly over 2 cm), and the cells underneath this bending state have a 99% probability of developing new micro-cracks or accelerating existing ones.

Stepping on the edges is even more dangerous. The area within 15 cm of the module edge is the structurally weakest part.

Safety regulations require using compliant walkways or tread pads. Maintenance access should be planned during installation design. If panel contact is unavoidable, use tread pads specifically designed for solar panels, which distribute your weight over a square meter or more, ensuring safety.

Picking Bird Droppings by Hand: Local Stress Can Directly "Detonate" Micro-cracks

Dry, hardened bird droppings are like little cement dots. Many people instinctively pick at them with fingernails or hard objects. This action is also dangerous.

Picking generates complex shear and peeling forces. The dropping adheres to the glass over a tiny area. Prying it with a fingertip applies force sideways, not vertically. This creates a moment, trying to "lift" the dropping, while applying huge peeling stress to the tiny spot of glass underneath.

This local stress can be the last straw. If the glass underneath happens to have a pre-existing, micron-sized micro-crack tip, this seemingly minor local stress can exceed the material's fracture toughness limit, causing the crack to instantly propagate by millimeters, even across the entire cell. The probability isn't 100%, but the risk is real. A module worth thousands of yuan could see its lifespan end with this one "diligent" cleaning attempt.

The safest method is to "soften" it with water. Place a wet cloth over the dropping for 10-15 minutes to let it absorb water and soften. Or, in the early morning when there's dew, rinse it continuously with low-pressure water for a few minutes; the dropping will dissolve and fall off. The principle is always to let the contaminant separate naturally, not force removal.

Ignoring Loose Mounting: Small Movement Leads to Big Trouble

Panels aren't absolutely static; mounted on structures, they micro-move due to wind pressure and thermal expansion/contraction. Typically, designed allowable longitudinal frame displacement within ±3 mm is safe.

But if mounting bolts loosen, or the structure weakens from corrosion, the situation changes. At wind speeds of 15 m/s (Force 7), a loose panel's sway amplitude can increase to ±1 cm or more. This large-amplitude, high-frequency repeated flexing imposes continuous fatigue stress on the cells.

The principle of metal fatigue applies to silicon wafers too. Under prolonged swaying, internal micro-cracks accelerate. A single windy event can make a 1 mm long crack grow to 10 mm. Regularly checking the mounting bolt torque is crucial; use a torque wrench to tighten to the value specified in the manual (e.g., 15-20 N·m). Also check the paint on steel structures for integrity and rust, especially at welds. A tiny rust spot can become a structural hazard within 3-5 years.