What Challenges Do Solar Panels Face in Winter | Snow, Temperature, Daylight

Winter challenges include snow block (can drop power generation 30–80%), sunshine time length reduced by about 40–60%, low temperature although raises efficiency, but inverter needs anti-freeze; suggest timely clearing snow, increase tilt angle to 40° above, check line insulation.

Snow

Block light rate

In a piece nominal power is 400W's standard monocrystalline silicon photovoltaic module surface, if covered with 0.5 centimeters thick dry powder snow, this time light penetration rate will maintain at 85%. In standard test conditions (1,000 W/m²'s light intensity), this module is still able to output 310 W to 320 W's instantaneous power, voltage drop amplitude usually controlled at 5% within.

When snow thickness accumulates to 2.5 centimeters, sunlight's physical transmittance will suddenly drop to 15%, and the illuminance on the monocrystalline silicon piece's surface will not be enough 150 lux (Lux). When snow thickness breaks through 5 centimeters, the transmittance of snow layer's illuminance will be lower than 50 lux. At this time, the module's working current will slide down to 0.1 amperes below, a piece area is 1.9 square meters's panel power generation power approaches 0W.

A 10-piece panel series composed, total installed capacity is 4,000W's string, usually need inverter startup voltage reach 250V. If the array middle has 2 pieces of panels 10 centimeters thick's snow completely covered, the module's internal bypass diode will automatically conduct, leading to the whole string's operation voltage down adjust 20%, to 200V. In this voltage parameter under, a unit rated power is 3,000W's inverter unable to reach the lowest wake-up threshold, as long as 8 hours's effective sunshine window period inside, this string's cumulative power generation amount will maintain at 0 kWh.

Snow has how heavy

The International Electrotechnical Commission released IEC 61215 test standard, which regulates qualified photovoltaic modules must pass a 5400 pascals (Pa) forward static mechanical load test. 5400 Pa converted into physical weight, equivalent to every square meter's glass surface able to endure 550 kilograms's vertical downward press load.

Nature snowfall's density span extremely big, just fallen's dry snow density at 50 kilograms/cubic meter to 100 kilograms/cubic meter; passed 24 hours settle's wet snow density will increase to 200 kilograms/cubic meter to 300 kilograms/cubic meter; and in multiple times freeze-thaw cycles after formed's ice snow mixture, density highest can reach 400 kilograms/cubic meter to 500 kilograms/cubic meter. Below is a size of 1.7 meters multiplied by 1.0 meters (surface area 1.7 square meters), thickness is 35 millimeters's aluminum alloy frame standard module, in face different snowfall forms time's load data distribution:

Self slide down

Residential roof's slope usually set at 30 degrees to 45 degrees between. The photovoltaic panel surface's use's thickness is 3.2 millimeters's anti-reflection coating tempered glass, dry snow, and this kind of glass surface's static friction coefficient is about 0.15. When the ambient air temperature rises back to 2℃ time, the glass and snow's contact surface will melt to form a layer 0.1 millimeters thick of water film, and the friction coefficient along with it drops to 0.02 below. A piece of area is 2 square meters, carries 15 kilograms of weight (about 4 centimeters thick) snow, and, under the effect of gravity, will move downward at a speed of 0.5 meters/second and slide down.

Monocrystalline silicon panel surface possesses 5% extremely low albedo, able to absorb 95% ultraviolet and infrared radiation heat. In an environment with a temperature is -5℃'s sunny day, if the panel's top end has 20% area not covered by snow and receives 400 W/m²'s solar radiation, the silicon piece's internal temperature will in 45 minutes inside rise to 10℃. About 15 W's heat energy will be transmitted through the thermal conductivity of 205 W/(m·K)'s aluminum alloy frame downward, making the bottom ice snow layer's melt speed raise 30%.

Bifacial photovoltaic module able to absorb snow from the back and reflect sunlight. Winter snow ground's albedo is high, up to 80% to 90%, back receiving diffuse light can for a piece 400W's bifacial panel bring 20W to 45W's extra heat input. With single facial module comparison, bifacial module in snow thickness is 8 centimeters's situation under, completely melt snow fall off's time cycle will shorten 1.5 to 2 hours.

Clear snow calculate account

A installed capacity is 12 kilowatts (kW), contains 30 pieces photovoltaic panels's standard family system, at roof occupy's project area about is 50 square meters. If you hire a professional roof maintenance company, they clear 15 centimeters thick snow, single time service fee quote usually at 150 dollars to 250 dollars. Two workers use a 6-meter-long glass fiber telescopic pole to operate, finish clear need consume time 1.5 hours. Assume this 12 kW system on the 1st month's sunny day, the single day's highest power generation amount is 35 degrees (kWh). According to every degree electricity 0.15 dollars's retail electricity price, and the single-day power benefit is 5.25 dollars. Pay 200 dollars's clear snow fee, need system with highest power continuous operate 38 days then can smooth out this item artificial cost.

If you self-purchase a handle equipped with a 60-centimeter wide polyethylene foam scraper, the length is 9 meters's telescopic snow removal rake, equipment purchase cost between 70 dollars and 120 dollars. For eaves height is 3.5 meters's single-layer residence, use this tool will single time snow removal consume time compress to 45 minutes. Operate time, foam scraper needs with panel's aluminum alloy frame maintain 10 centimeters to 15 centimeters's safe distance, in order to prevent exceed 50 joules's mechanical impact force transmitted to panel center. This kind of magnitude's physical collision has a 3% probability of leading to internal 156 millimeters multiply 156 millimeters's silicon piece produce micro cracks, thereby triggering every year 0.8% above's power extra attenuation.

Temperature

Photovoltaic module's standard test condition usually set at 25℃'s environment temperature under, match 1000 W/m²'s light intensity test output power. The market share of monocrystalline silicon panels reached 80%, and its power temperature coefficient is usually calibrated at -0.34%/℃ to -0.40%/℃ between. When the outdoor air temperature drops to -15℃, the panel's actual working temperature compared to 25℃'s baseline produces a 40℃ temperature difference deviation.

According to -0.35%/℃'s temperature coefficient median value, this 40℃'s temperature drop will convert into a 14% output power increment. A piece factory nominal power is 400W's solar panel, in -15℃'s early morning, receiving 900 W/m²'s radiation intensity, its actual instantaneous power is able to climb to 456W. Silicon semiconductor material in low temperature state under, internal electron cross 1.12 electron volts (eV) band gap needed's free energy reduced about 12%. Electron move resistance's lower let photoelectric conversion efficiency from normal temperature under's 20% highest raise to 22.8%. Inverter at input end receives direct current power average every day extra out about 1.5 kWh, a unit design life is 15 years's 8 kW inverter process high power load time's heat dissipation rate dropped 40%.

Careful high voltage

· Temperature drop will lead to open circuit voltage (Voc) according to -0.28%/℃'s rate straight line rise. Take nominal open circuit voltage as 37.5V's panel as an example. In -20℃'s extreme cold current, a single piece panel's peak voltage will dash high to 41.2 V.

· Household energy storage systems often adopt every string by 15 pieces panels series's design specification. This time, this string's total voltage will skyrocket from 562.5V to 618V. The North America area requires household single-phase inverter's highest direct current input voltage safe range must be controlled at 600V within.

· 618V's actual load voltage exceeds the inverter's rated highest value by 3%, will lead to equipment internal overvoltage protection relay in 0.2 seconds inside cut off direct current busbar. Once the inverter trigger lock state, in the next 6 hours' effective sunshine time period, the whole 5 kW system's power generation amount drop amplitude will reach 100%.

· Installation engineer in design drawing time, need utilize meteorology library middle past 50 years within's lowest extreme air temperature as multiplier factor calculate, will every string panel's series upper limit quantity reduce 10% to 15%. Every string panel quantity from 15 pieces to 13 pieces, the system's total open circuit voltage will be mandatory limit at 535V's average value interval inside, and the probability of downtime accidents drops to 0.05%.

Glass carry freeze?

Thickness is 3.2 millimeters' photovoltaic panel surface cover has a layer of high light transmittance tempered glass, its thermal expansion coefficient is 9×10⁻⁶/℃. Frame adopts 6063-T5 anodized aluminum alloy, thermal expansion coefficient high up to 23×10⁻⁶/℃. In daytime, receive 700 W/m² sunlight irradiation time, panel surface temperature can reach 15℃, and night air temperature often in 3 hours inside suddenly drop to -25℃. Face high up to 40℃'s day-night temperature difference fluctuates, length is 2 meters, width is 1 meter's aluminum alloy frame will produce 0.92 millimeters's physical cold shrink deformation.

Glass panel and aluminum frame between exist's deformation difference value will produce about 15 megapascals (MPa)'s shear stress. Fill in the gap middle's ethylene-vinyl acetate copolymer (EVA) film in a -10℃ below's low temperature environment, its physical elastic modulus will increase 200%. Film becomes hard will make buffer deformation ability drop 30%, trigger frame sealant appear 0.1 millimeters tiny crack's probability rise 4%. Standard module's mechanical structure in our factory before passed 200 times -40℃ to 85℃'s extreme thermal cycle test, in 25 years' warranty cycle inside, glass break's actual measure probability still maintain at 0.01% below.

Cable afraid suffer freeze

Connect each panel's PV1-F specification direct current cable, outside wrap with thickness is 1.5 millimeters's cross-linked polyethylene (XLPE) insulation layer. When the environment temperature is lower than -30℃ time, high molecular polymer material's molecular chain activity ability drops 80%, and cable's bending radius limit from diameter's 4 times increase to 6 times. If workers in -15℃'s environment under with greater than 90 degrees's fold angle force pull drag diameter is 4 square millimeters (4 mm²) cable, insulation layer surface appear 0.5 millimeters depth crack's risk will soar 50%.

Exposed in the air middle's crack will let exposed's copper core and melt's snow water contact, system exist greater than 500 milliamperes (mA) leakage current's electrical hidden danger. Inverter's leakage current detect module once in 0.1 seconds inside detect to exceed 300 mA's current leakage amount, then will immediately close stop single unit power is 10 kW's equipment. Replace a piece length is 15 meters's damaged direct current cable, material cost about is 25 dollars, and need pay an artificial fee of 150 dollars.

Standard construction manual mandatory regulate, cable lay operation environment temperature must not be lower than -5℃, according to specification, operate can will outer skin freeze crack's physical damage rate reduce 98% above. Exposed at roof outdoor's cable still needs sleeve on diameter is 20 millimeters's anti ultraviolet corrugated pipe, able to resist at least 15 kilograms's ice drop impact force.

Daylight

Daytime really not enough

In the northern hemisphere's high latitude area, 12th month's average daytime time be compressed to 9.2 hours, and really able to let photovoltaic panels full load operate's effective sunshine time (Peak Sun Hours) only has 2.4 hours to 2.8 hours. Compare under, 7th month's effective sunshine time usually can reach 5.8 hours. Every day, reduce near 3 hours' high efficient working interval, let a set installed capacity be 10 kW's family standard photovoltaic power station's single day power generation amount from summer's 55 degrees (kWh) large margin drop to 22 degrees. If according to every degree of electricity, the 0.16 dollars's grid repurchase price is calculated, single-day power benefit from 8.8 dollars shrinks to 3.52 dollars.

In order to make up for the physical gap in sunshine time length, install equipment with lithium iron phosphate cell household energy storage cell system has become a common plan. A unit capacity is 13.5 kWh's household cell pack, can in morning 9 o'clock to afternoon 2 o'clock this segment only has's 2.4 hours peak period inside, with 5 kW's continuous charge power will surplus's 12 degrees electricity store up, arrived afternoon 5 o'clock sun drop mountain after, again with 3 kW's discharge power toward house inside's heat take equipment transmit 4 hours's electricity load.

Meteorology and energy monitor statistics show that when the solar elevation angle is lower than 15 degrees, the atmosphere layer between wavelengths at 380 nanometers and 780 nanometers will break through 60% of the visible light absorption rate. This time, the photovoltaic panel's surface's diffuse reflection light proportion will exceed 75%, and the normal single-facial module's diffuse reflection light's absorption efficiency is only 12% to 18% of direct light.

Shadow be pulled long

Light incidence angle becomes low, bringing another physical phenomenon: buildings and trees' shadows being multiplied and pulled long. A tree height is 12 meters's oak tree, at a distance of 8 meters direct north, place's single layer residential roof on, summer noon project's shadow length is only 3.5 meters, completely touch not to photovoltaic array's edge. Arrived 12th month 21st day, same time point project's tree shadow length will extend to 24 meters, shadow area cover rate high up to photovoltaic panel total area's 45%.

When a piece area is 1.9 square meters's panel by tree shadow blocked bottom 15%'s cell piece time, whole string by 12 pieces panels series connect's module current will be forced limit at suffer block panel's lowest current level, total output power's drop amplitude will instant reach 85% above. In order to cope with long shadow trigger's power sudden drop, roof-top install micro inverter or power optimizer become mandatory option. Give every piece of manufacturing cost is 250 dollars's panel independent equipment, a unit price of about 80 dollars's direct current power optimizer, can will shadow block cause's system overall power generation amount loss rate from 40% to 8% within.

Adjust adjust tilt angle

Normal residence's fixed style roof bracket usually with 35 degrees's fixed angle install, whole year not make any intervention. If the bracket will replace the hydraulic push rod or manual adjust bolt's adjustable style mechanical bracket, in the 11th month, early will panel tilt angle upward adjust to local latitude add on 15 degrees's number value, for example, in the 45 degrees area of the north latitude, adjust to 60 degrees, then can let the panel surface and winter low's solar light ray maintain close to 90 degrees's vertical angle.

Light ray vertical incidence can reduce the tempered glass surface's reflectance from 12% to 3.5%, let the silicon piece's effective photon quantity increase by about 8.5%. Rely on 15 degrees to 25 degrees's angle adjust, whole array in 11th month to 2nd month's 90-day long cycle inside, cumulative power generation amount can solid solid ground raise 12% to 15%. A set of 8 kW's system through adjust angle, in winter can extra squeeze out about 360 degrees electricity, convert into electricity fee benefit about 57 dollars, offset adjust angle bracket early period extra input's 300 dollars hardware cost, about need 5 winter's return cycle.