PV Module vs Panel What’s the Difference | Structure, Output, Usage

The main difference between PV Module and PV Panel lies in the structure and usage.

PV modules are composed of multiple PV modules (solar cells) in series or parallel, with standard power usually being 250W to 400W and output voltage between 30V to 40V.

PV panels are units of modules used for installation and power generation; a panel usually consists of 60 to 72 cells.

Structure

The outermost layer of a conventional individual PV module is covered with low-iron ultra-white embossed tempered glass with a thickness of up to 3.2 mm. The front light transmittance must reach a high standard of 91.5% to 93% in the wavelength range of 380 nanometers to 1100 nanometers. In order to cope with strong winds of up to 130 kilometers per hour or the impact of 25 mm diameter hail at a speed of 23 meters per second, the static load bearing capacity of the outer glass surface needs to reach 5400 Pascals. The surface anti-reflection coating thickness is usually controlled between 100 nanometers and 120 nanometers, which can reduce the overall light reflectivity by about 2.5% and increase the overall power generation of a single module by 1.5% to 2%.

· On the actual production line, the weight of a single piece of glass with an area of about 2.58 square meters reaches about 22.5 kilograms.

· Single-layer glass accounts for an absolute proportion of 72.5% of the 31-kilogram total weight of a single finished module.

Encapsulation Film

Closely below the tempered glass is EVA or POE polymer encapsulation film with a thickness usually of 0.45 mm to 0.5 mm. After the encapsulation film is heated at 145 degrees Celsius to 155 degrees Celsius for 15 minutes in the workshop laminator, the cross-linking index must exceed 75% to effectively block 99% of external water vapor from penetrating into the internal circuit. As the market share of bifacial power generation modules exceeds 45%, POE film with a water vapor transmission rate lower than 1 gram per square meter per day and a volume resistivity greater than 10 to the 16th power ohm-cm allows the service life of individual modules to extend from 20 years to 30 years.

· The yellowing index (YI) of EVA film with a UV blocking rate of 99% is strictly required to be controlled below 2 during the 25-year outdoor light attenuation cycle, to prevent each increase of 1 YI value from causing the short-circuit current to drop by 0.15 amperes.

· The film material, with a cost of about 1.2 US dollars to 1.5 US dollars per square meter, accounts for only 4% to 5% of the overall module manufacturing cost, yet it undertakes the physical insulation function for a 1000-volt DC system voltage.

Thin Silicon Wafers

As the carrier of photoelectric conversion, monocrystalline silicon cell thin wafers have had their thickness reduced from 170 microns to the current 130 microns in the past 5 years, reducing silicon material volume consumption by 23.5%. On a standard-sized 182 mm by 182 mm M10 cell, 130 silver paste main grid lines with a width of only 25 microns to 30 microns are printed on the surface, and the silver paste consumption reaches 60 mg to 75 mg per piece. In the series splicing process, an automated layout machine can connect 3600 silicon wafers with an area of 331 square centimeters per hour into ultra-long strings of 72 or 78 pieces using solder ribbons with a width of 0.2 mm and a thickness of 0.25 mm.

· A set of 144 half-cell structure modules has a maximum working current passing through it as high as 13.5 amperes to 14 amperes under standard test conditions of 25 degrees Celsius.

· The internal series resistance of the module is compressed to below 1.5 ohms, and the photoelectric conversion efficiency during full-load operation is stable at 22.5% to 23%.

Backsheet Material

The bottom encapsulation of single-sided power generation modules uses a fluorine-containing composite polymer backsheet with a total thickness between 0.3 mm and 0.35 mm, with a single sheet weighing less than 0.5 kg. After being placed continuously for 1000 hours in a double-85 accelerated aging test box with a relative humidity of 85% and a temperature of 85 degrees Celsius, the tensile strength retention rate of the backsheet must be maintained above 80%, and the interlayer peel strength must not be lower than 40 Newtons per centimeter.

In order to ensure the safety of power station operation and maintenance personnel when contacting the 1500-volt maximum system voltage, the partial discharge voltage of the backsheet must exceed 1000 volts DC, and the leakage current requirement during pressure testing is less than 50 microamperes per square meter of area.

· The internal white titanium dioxide reflection layer can reflect 5% to 8% of the missed light penetrating through the silicon wafer gaps back to the bottom of the cell, adding an extra 2 to 3 watts to the rated output power of each module.

· The backsheet, with a purchase unit price of about 1.8 US dollars per square meter, is required to withstand more than 3000 hours of xenon lamp UV radiation testing on its surface, with the thickness shrinkage rate strictly controlled within the 1.5% range.

Aluminum Alloy Frame

The anodized aluminum alloy frame that tightly wraps the above-mentioned 5-layer structure has standard cross-section heights divided into two specifications, 30 mm or 35 mm, with the thickness fluctuating between 1.2 mm and 1.5 mm. The physical weight of the overall aluminum material plus the junction box is about 2.5 kg to 3 kg, the yield strength is mandatory to be greater than 210 MPa, and the tensile strength needs to exceed 250 MPa. When workers assemble the frame, 30 to 40 grams of two-module silicone sealant will be injected into the U-shaped groove. After the matching glue is cured for 24 hours at a room temperature of 25 degrees Celsius, the Shore hardness reaches 35A to 45A, and the tensile shear strength is greater than 1.2 MPa per square centimeter.

· Oval installation holes with a length of 14 mm and a width of 9 mm are reserved on the outside of the frame, located at distances of 400 mm and 1200 mm from the upper and lower edges of the module.

· The fixed installation hole spacing can ensure that the bearing stress distribution variance when fixed with 8 bolts remains in the low range of 0.05.

Panel Rails

When 3 to 15 independent modules are transported to the roof and combined into a large panel system, C-shaped steel or aluminum alloy rails with thicknesses ranging from 2.5 mm to 4 mm must be installed at the bottom. On a residential roof with an inclination angle set at 20 to 30 degrees, every 1 meter of rail extension needs to bear a system self-weight of 15 kg to 18 kg, plus an additional winter snow weight of 50 kg to 80 kg per square meter locally. When using M8 specification, 40 mm long stainless steel inner hexagon bolts combined with middle pressure blocks and side pressure blocks to fix the modules on the bracket, the torque of the electric wrench needs to be accurately set at 16 Newton-meters to 20 Newton-meters.

· The ground clearance supported by the bracket under the panel is usually 15 cm to 20 cm, and the bottom ventilation space can maintain the air flow rate at 0.5 meters to 1.5 meters per second.

· Air circulation can reduce the array temperature during summer full-load operation by 3 to 5 degrees Celsius, recovering about 1.5% of power generation loss.

· For a panel array containing 20 independent modules, the purchase budget for bracket materials plus logistics costs is in the range of 300 to 450 US dollars, accounting for 8% to 11% of the total system hardware budget.

Output

When measuring the nameplate power of a single PV module in a laboratory environment, the industry standard is Standard Test Conditions (STC). Above the test bench, a solar irradiance of 1000 watts per square meter will be simulated, the spectral distribution must comply with the AM 1.5 air mass standard, and the physical temperature of the cell itself is strictly locked at 25 degrees Celsius by a constant-temperature air conditioner.

When the factory label is printed with a peak power of 550 watts, it refers to the maximum DC power a single device can output under the aforementioned extremely ideal conditions. Once moved to an outdoor roof, environmental parameters will lean toward the Nominal Operating Cell Temperature (NOCT). At this time, the test irradiance drops to 800 watts per square meter, the ambient air temperature is set at 20 degrees Celsius, and the surface wind speed is maintained at 1 meter per second.

· Under NOCT conditions, a single module originally rated at 550 watts will actually have its measured output power fall back to the range of 410 watts to 415 watts, with the book data shrinkage rate reaching 24.5% to 25.5%.

· The open-circuit voltage (Voc) of a single module is measured at 49.8 volts in the laboratory, but under real outdoor light, it usually drops to around 47.2 volts.

· The short-circuit current (Isc) will drop proportionally with the weakening of light intensity from 14.05 amperes under STC conditions to 11.35 amperes, with the standard deviation of current fluctuations generally controlled within 0.15 amperes.

Single Unit Limit

Stripping away external environmental interference, the current mainstream N-type monocrystalline silicon independent modules on the market usually have a single area of about 2.58 square meters, and the photoelectric conversion efficiency brought by their internal 144 half-cells is stable between 22.3% and 22.8%. When the sun rises in the morning and the photon flux irradiated on the surface of the tempered glass exceeds 150 watts per square meter, the PN junction inside the single module begins to generate an electromotive force sufficient to overcome the 0.5-ohm internal series resistance, and the module enters a working state.

At this time, the working voltage at the maximum power point (Vmp) of a single device is about 41.5 volts, and the working current (Imp) is about 13.2 amperes. As the intensity of ultraviolet and infrared rays increases at noon, the internal electron transition frequency speeds up, and the peak hourly power generation of a single device approaches 0.55 kWh of direct current.

· For a plain area with median light resources, the theoretical total DC-side power generation of a single 550W module within 365 days a year can reach 720 to 750 kWh.

· In the first year of the equipment's life cycle, affected by the initial light-induced degradation effect, the output power will be fixedly lost by 1% to 1.5%, and subsequently, the linear power decline rate each year is limited by contract within 0.4%.

Wiring and Grid Connection

When installation workers connect 10 independent 550W modules head-to-tail through 4 square millimeter PV cables with MC4 connectors to assemble a panel array, the electrical characteristics of the system will undergo a double-style physical superposition.

In this pure series circuit topology, the total working current of the panel system is still limited by the individual module with the worst performance, maintained at a level of 13.2 amperes, but the working voltage at the system DC end will grow linearly, rising from 41.5 volts for a single piece all the way to 415 volts. If two such 10-piece series panels are then wired in parallel, the total output current at the combiner box will double to 26.4 amperes, and the total rated power reaches 11000 watts (11 kilowatts).

Lost Electricity

When the panel system operates at full load in an outdoor open-air environment, the increase in backsheet temperature will cause irreversible discount to the output power. The power temperature coefficient of monocrystalline silicon material is usually marked as negative 0.30% per degree Celsius. When high summer temperatures cause the panel surface temperature to reach 65 degrees Celsius, which is 40 degrees Celsius higher than the laboratory baseline of 25 degrees Celsius, the actual output power of the entire system will be forcibly reduced by 12%. A rooftop panel array rated at 5500 watts will have its highest real output capability compressed to about 4840 watts at this time.

· When fallen leaves in autumn or the shadow of a chimney cover only 10% of the panel area, due to the barrel effect, if the 3 internal bypass diodes do not conduct in time, the output current of the entire panel string will instantly plummet by 30% to 40%.

· Dust particles with a thickness of 0.5 mm accumulated on the module surface will cause the light transmittance to drop by about 2.5%, and the monthly power generation loss at the panel end caused by this is distributed between 1.5% and 3%.

· The internal resistance variance and maximum power point deviation between 10 modules will generate system-level mismatch losses, and this part of electrical friction usually eats up 0.8% to 1.2% of the total power generation.

Usage

Taking Loose Stock

The independent application scenarios of single PV modules in the retail market are usually limited to small off-grid electricity needs. RV camping enthusiasts or small yacht owners will purchase one to two single-sided power generation modules with rated power between 400 watts and 450 watts, laying them flat on the top of the vehicle or cabin deck with an area of less than 5 square meters. The short-circuit current output by a single independent module is usually between 10 amperes and 13 amperes, and the open-circuit voltage is maintained at a level of 35 volts to 40 volts.

Users need to configure an MPPT (Maximum Power Point Tracking) solar charge controller that supports a maximum input voltage of 50 volts and a maximum rated current of 20 amperes to convert the 36-volt DC generated by the module into 14.4-volt constant-voltage DC, which is stored in a 12-volt lithium iron phosphate deep-cycle cell with a capacity of 200 Ah to 300 Ah. The retail terminal price for purchasing a single 400-watt module usually fluctuates between 140 US dollars and 180 US dollars, pushing the purchase unit price per watt to 0.35 US dollars to 0.45 US dollars, far exceeding the wholesale purchase average price of 0.12 US dollars per watt for large ground power stations.

The size of an independent module is usually standardized for production at 1722 mm by 1134 mm, and the weight of a single piece is about 21.5 kg. A physically strong adult, in the absence of auxiliary lifting equipment, can at most independently carry one module for a distance of 15 to 20 meters; improper operation has a 20% probability of causing backsheet scratch loss.

Batch Shipping

Large manufacturing workshops will arrange 36 pieces of 30 mm thick aluminum frame modules vertically and sideways, putting them into a corrugated paper reinforced packaging box with a length of 2290 mm, a width of 1130 mm, and a height of 1250 mm. The gross weight of a single fully loaded packaging box is as high as 1150 kg, with standard forklift holes with a height of 120 mm reserved at the bottom.

An electric counterbalanced forklift with a rated load of 3 tons can only lift one complete packaging pallet steadily at a time. When deploying a row of 40-foot high-cube containers for sea transport, the internal volume of the container is 76 cubic meters, and the maximum cargo weight is limited to 26 tons. Logistics planners will stuff 20 standard pallets into the container in a way of stacking two layers up and down, and a single full container can accommodate exactly 720 independent modules with a rated power of 550 watts, reaching a total book installed capacity of 396 kilowatts.

During the bumpy 30 to 45 days of sea transportation, the relative humidity inside the container occasionally soars to 95%. The 1.5 kg of environmentally friendly desiccant placed in the packaging box can control the environmental water vapor absorption rate below 5%, ensuring that the physical compressive strength of the carton will not suffer a cliff-like drop, preventing the modules located at the bottom from bearing gravity extrusion exceeding 7000 Pascals, which would cause micro-cracks in the internal silicon wafers.

Going on the Roof

Once batches of modules are transported to townhouses in urban suburbs, the goal of the construction team is to assemble the scattered modules into a grand panel system that can be connected to the grid for power generation. On a south-facing sloping roof with an available area of 45 square meters, three installation technicians holding high-voltage electrical operation certificates need to spend about 6 to 8 hours of working time to splice 16 independent modules with a power of 500 watts into a complete panel array with a total power reaching 8000 watts using metal rails.

In order to resist gusts of up to 110 kilometers per hour that may appear locally, installation workers must drill holes every 1.2 meters on the roof's load-bearing wooden beams and drive in 80 mm long stainless steel lag screws to fix the L-shaped aluminum hooks. The physical gap between adjacent modules must be accurately locked at 22 mm with a torque wrench, and the aluminum alloy thickness of the middle pressure block must not be lower than 4 mm to absorb the metal thermal expansion deformation generated when the daytime air temperature in summer is as high as 40 degrees Celsius.

After being combined into a large panel, 16 modules are connected head-to-tail in the electrical circuit. The maximum working voltage of the system at noon will surge to around 650 volts, and the rated output current is maintained at 12.5 amperes. The panel system generates a peak daily DC power of more than 45 kWh, which needs to be transported all the way along the exterior wall of the house through a 25-meter-long 6-square-millimeter flame-retardant PV cable to the inverter end in the garage.

Daily Troubleshooting

Within the 25-year life cycle of a standard panel system, daily monitoring is carried out at the macro panel system level, while physical maintenance is accurate to the individual module level. If the data collector in the inverter background finds that the overall power generation of a certain input circuit today has abnormally dropped by more than 15% compared to the same time period yesterday, maintenance personnel will control a quadrotor drone equipped with a thermal imaging lens to rise to an absolute height of 15 meters above the roof for infrared scanning.

On the infrared temperature distribution heat map sent back by the drone, if it shows that within the 35-square-meter panel array area, a rectangular area of about 2.58 square meters has a surface temperature reaching 75 degrees Celsius, which is 15 degrees Celsius higher than the surrounding area, it indicates that a hot spot effect has occurred inside that independent module.

After the maintenance workers arrive at the scene, there is no need to dismantle and rebuild the entire panel system weighing up to 340 kg. Just cut off the front-end DC isolation circuit breaker, loosen the 4 pressure blocks around the faulty module with an inner hexagon wrench, unplug the positive and negative MC4 waterproof plugs, and spend 45 minutes to pull out the single module that has lost power generation capability and replace it with a brand new module of the same specification with a working voltage of 41 volts and a short-circuit current of 13 amperes, and the system will immediately restore 100% of the rated power output.