Which Panels Work Best with Photovoltaic Systems | Compatibility, Efficiency, Design

When choosing panels compatible with photovoltaic systems, need to consider efficiency, design and performance. High-efficiency monocrystalline silicon panels efficiency can reach 22-23%, suitable for places where space is limited; polycrystalline silicon panels cost-performance ratio is high, efficiency is between 16-18%. When choosing, should do balance according to the lighting conditions of the installation location and budget.

Compatibility

Check panel voltage

A piece of nominal 500W solar panel, under standard test conditions 25°C's open-circuit voltage usually floats between 48.5V to 51.2V. When winter air temperature drops to minus 15°C, calculated according to the voltage temperature coefficient of -0.28%/°C, the panel's actual output voltage will instantly climb 11.2%.

Using a single-phase inverter whose maximum DC input voltage limit is at 600 V, connecting 12 pieces of 500 W panels in series at 25°C the total voltage is 582 V, located below the 600 V red line. Once the air temperature drops to minus 15°C, the whole string voltage will violently surge to 647.1 V, immediately crossing the 600 V physical limit leading to equipment short-circuit protection shutting down.

· Inverter's lowest startup voltage is generally set floating between 80V and 120V.

· Morning when the sun just rises, environmental irradiance is only 50 W/m² to 100 W/m².

· At this time, three pieces of panels with voltage at 35 V connected in series can output 105 V's voltage, crossing the 90 V startup threshold to start processing electrical energy.

Calculate current upper limit

Current 210 mm size large silicon wafer bifacial power generation modules, front side's short-circuit current nominal value universally reached 14.5A to 15.3A's range. Installed on flat roofs paved with white reflective film, the backside absorbed scattered light can provide 15% to 20% of extra current gain, causing the panel's actual output current to soar to 17.4A or even 18.3A.

Old model inverters with service time exceeding 3 years, single route MPPT's maximum allowed input current usually stuck at 12.5A or 13A's upper limit. Inserting 18A's large current panel into 13A's interface, the 5A current exceeding the upper limit will be forcibly cut off by the inverter motherboard hardware, causing nearly 27% of power waste every day.

· New model inverters supporting large current already have MPPT input terminals' tolerance current elevated to 20A to 22A's specification.

· Under the situation where the environmental temperature is as high as 45°C full load operating 300 days, the 20A specification's terminal temperature rise can be controlled within 40°C.

· Every time the terminal working temperature lowers 10°C, the probability of thermal burn down drops above 95%.

Inverter proportion

Inside the industry, the ratio of DC side panel total power and AC side inverter rated output power is controlled between 1.2 to 1.3 times. A set of systems whose rated AC output power is 10 kW, the actual paved panel total power on the roof can be increased to 12.5 kW. When noon 12 o'clock to afternoon 2 o'clock, the sun's irradiance reaches 1000 W/m²'s peak value, panel output power might reach 11.5 kW. The 1.5 kW electricity quantity exceeding the inverter processing upper limit will be dissipated as waste heat in the form of peak shaving, cut-off loss approximately occupies 1.5% to 2.1% of the whole year's total power generation.

At low irradiance time periods of the first 3 hours after sunrise and 3 hours before sunset, as well as the whole year up to 120 days' cloudy and rainy weather inside, the extra installed 2.5 kW panels can hardly pull the system's working load rate from 45% high to above 65%. Experiencing 365 days' cycle statistics, system configured with 1.25 times proportion, whole year effective total power generation compared to 1 to 1 configured system increased 7.3% to 8.5%.

Pick micro inverter

Micro inverters usually adopt 1-drag-1, 1-drag-2 or 1-drag-4's physical wiring architecture, putting each piece module's independent MPPT tracking efficiency fixed at 99.8% numerical value. Inside a tilted roof environment, when 2 pieces of panels are blocked by leaves losing 40% of the lighting area, the remaining 18 pieces of panels can still maintain 100% full-speed full-load operation. Although per watt's procurement budget increased 0.3 US dollars to 0.5 US dollars, within 25 years' warranty cycle, total power generation data's positive deviation stably maintains at 5.5% to 7% range.

· Micro inverter's startup threshold is extremely low, only needs 22V to 25V to activate motherboard chip to work.

· Every day morning and evening's effective grid-connection time altogether extended 45 minutes to 60 minutes.

· Single-phase 240V AC cable's transmission loss is only 33% of DC high voltage cable loss.

· Within 100 meters, the AC voltage drop is strictly suppressed below 1.5%.

Connect storage cell

When matching a 48V low voltage lithium iron phosphate cell pack, the inverter needs to largely step down the panel end's 350V high voltage DC power. The stepping down process's electrical energy conversion efficiency loss is between 4% to 5.5%. Wanting to use 5 kW's constant power to charge a low voltage cell, the sustained current passing inside the connection cable will be as high as 104 A. Must use pure copper wire whose cross-sectional area is at least 35 square millimeters to prevent metal from heating up.

· Inverter matching 350V to 400V high voltage cell pack, the voltage difference between panel voltage and cell end voltage is shrunk to within 50V.

· Charge and discharge round-trip loop's comprehensive conversion efficiency soared to 96% to 97.5% echelon.

· Calculated by frequency of circulating charge and discharge 1 time every day, households using high voltage matching system inside 10 years' cell attenuation cycle extra recover 2500 degrees to 3200 degrees of electrical energy.

Efficiency

Pick silicon wafer structure

The highest photoelectric conversion numbers measured inside a laboratory often stay in the ideal state above 26%. At the factory assembly line's actual mass production delivery stage, P-type PERC cell panel's average conversion numerical value stably fluctuates around 21.4%. In the last two or three years, the mass production average numerical value of N-type TOPCon cell panels leaped to 22.5%, and higher manufacturing cost HJT heterojunction cell panels pushed this number high to 23.2%.

Putting a piece of monocrystalline silicon panel whose area is 2.58 square meters tiled flat on the roof, under 1000 W/m²'s standard solar radiation intensity, 21.4% numerical value P-type panel every hour can output 552 W's electrical energy. Changing to a 23.2% numerical value HJT panel, under the same area, every hour's electrical energy output increased to 598 W. This 46 W's power difference seems weak, but inside a family system whose installed total capacity is 10 kW, adopting HJT panels can on the same 50 square meters roof usable area, lift total system output power to above 10.8 kW.

· HJT cell's silicon wafer thickness has already been reduced to within 130 micrometers to 150 micrometers' range.

· Extremely thin silicon wafer lowered the probability of internal electrons and holes recombination, letting carrier lifetime extended from 2 milliseconds to 3 milliseconds.

· Surface deposited amorphous silicon thin film layer towards ultraviolet waveband's light absorption rate vastly lifted 12% to 15%.

· In the morning and evening's low weak light environment, high conversion rate panel's startup working time advanced 25 minutes to 35 minutes.

Summer afraid of heat?

All solar panels' various test parameters marked when leaving the factory are all obtained inside a 25°C's standard constant temperature laboratory. Arriving in July and August's hot summer season, when the environmental air temperature reaches 35°C, after dark colored panels absorb heat, the surface actual working temperature will rapidly climb to 65°C to 70°C's high position. P-type module's temperature attenuation coefficient generally stuck on -0.34%/°C's scale. When the panel temperature is 40°C higher than the standard test temperature, the whole piece panel's instantaneous output power will be reduced by 13.6%.

Nominal 500W panel at extreme heat noon can barely output 432W's electrical energy. N-type TOPCon panel's temperature coefficient lowered to -0.29%/C, under the same high temperature environment's power drop width narrowed to 11.6%, output power maintained at 442W. HJT panel possesses better physical temperature stability, temperature coefficient is only -0.26%/C, under high temperature state's power drain amount is compressed to 10.4%. Inside a 120-day summer high temperature cycle, low temperature coefficient panel's total power generation is 4.5% to 6.2% more than conventional panels.

Time's loss

Polycrystalline silicon or P-type monocrystalline panel within the first 300 hours after installation complete and exposed to the sun, internally contained boron-oxygen complexes will undergo a chemical reaction, causing the first year's absolute output power to drop 2% to 2.5% diving style. Arriving at 2nd year to 25th year's service period inside, panel power every year will continuously decline with 0.55%'s fixed rate. When service fully reaches 25 years, a piece of nominal output 500W P-type panel can only emit 424W's electrical energy, the remaining number is 84.8% of the initial nominal value.

N-type panel at manufacturing processing link used phosphorus element to replace boron element, first year light-induced attenuation amplitude is forcibly pressed down to within 1%'s warning line. Subsequently, 30 years' year-by-year attenuation rate maintained on 0.4%'s standard line. When the service period reaches 30 years, the N-type panel can still maintain 87.4% of its power generation ability.

At coastal zones where environmental humidity year-round exceeds 80%, water vapor seeping into panel interior easily triggers potential-induced degradation effect, leading to leakage current increasing from 1.5 milliamperes to 2.2 milliamperes. Adopting double layer 2.0 mm thickness tempered glass encapsulated module, water vapor transmission rate is close to 0 grams/square meter/day.

Bifacial light absorption rate

Paving on roof white TPO waterproof membrane whose reflectivity reaches 80%, panel backside's received light amount can reach 15% to 22% of front side direct light intensity. Module backside's photoelectric conversion ability is not completely equal with front side. P-type bifacial panel's backside conversion ability usually only has 70% to 75% of front side. N-type module's backside conversion ability can reach 80% to 85% of the front side.

When the front side outputs 500W power, under the blessing of a white roof environment, the N-type bifacial panel's backside can supply 60W to 75W's incremental power, and the whole piece panel's total output power is pushed high to above 560W.

Dust blocked it

Continuous 3 months no rainfall dry season, panel surface accumulated 2 millimeters to 3 millimeters thickness dust layer, will make effective light flux penetrating glass reaching silicon wafer reduce 4% to 7%. Bird droppings or autumn falling tree leaves if block panel top's merely 10 square centimeters area, will cause blocked part's silicon wafer resistance instantly surge 80 times above. Current cannot pass through high impedance area, is forced to bypass from panel backside's 3 bypass diodes. This physical action will lead to the whole piece panel's one-third area stopping working, single piece panel's output voltage violently plummets from 40V to around 26V.

The remaining 10 pieces of panels connected in series at the same group will also because of the short board effect, overall current output forced to lower 25% to 35%. Every six months, arrange one time water wash cleaning, clearing surface attached 0.5 grams/square meter's particulate matter, can let the whole set system's photoelectric conversion numbers rapidly recover 4.5% to 6.8% of normal level. Cleaning operations must be chosen before 7 o'clock in the morning or after 6 o'clock in the evening to conduct, preventing 15°C's cold water contacting glass whose surface temperature is as high as 55°C triggering thermal stress burst.

Design

Orientation: How to arrange

On the northern hemisphere's geographical location, installing a panel facing due south that is also at an azimuth angle of 180 degrees' position, is able to obtain 100% of the annual total radiation amount baseline value inside the theoretical calculation model. If limited by building structure, paving panel on roof surface facing due east or due west, namely azimuth angle 90 degrees or 270 degrees, the whole year's total power generation data will slide down 15% to 22% compared to the due south baseline value.

Adopting east-west dual-direction alternating tilted back-to-back arrangement on flat commercial or residential roof surfaces, thoroughly saved the 1.5 meters wide row spacing that must be reserved during north-south single-direction arrangement, letting panel installed density on every square meter usable roof area sharply increase 110% to 120%. Within the morning 10 o'clock to afternoon 2 o'clock's time period, the solar irradiance peak value received by the due south-facing panel maintains at 950W/m² to 1050W/m²'s range.

Putting orientation deliberately rotated 45 degrees towards the southwest direction, will let panel's every day full load peak output window period pushed back backwards to around 3:30 in the afternoon. Putting power generation peak period and family's electricity usage peak period at afternoon 4 o'clock to night 8 o'clock overlap, will press down metering numbers of buying electricity from the power grid by 30% to 40%.

Calculate tilt angle

On a north latitude 35 degrees' coordinate position, adopting a 35 degrees tilt angle fixed panel can capture up to 98.5% of the theoretical limit annual solar radiation total amount. Putting installation tilt angle adjusted down to 15 degrees, the whole year's total power generation will along with it reduce 4.2% to 5.8%, aerodynamic wind resistance coefficient borne by panel vastly dropped 35%.

On flat roof structures, must maintain 10 degrees above the lowest installation tilt angle, relying on earth gravity and rainfall's scouring action, washing away glass surface continuously accumulated 0.5 millimeters to 1.2 millimeters thickness particulate dust layer. When carrying out fitting style flat paving installation on an asphalt shingle roof whose slope is 22 degrees, between the panel backplate and the roof wooden board, a 10-centimeter to 15-centimeter air interlayer is preserved. Relying on the natural convection phenomenon of air heated up rising, in summer afternoons when the air temperature is as high as 35°C, air circulation can lower the panel's actual working temperature 4°C to 6°C.

Leave out shade avoidance distance

According to general roof fire safety code requirements, installation array edge distance to roof surrounding edges must preserve a 0.9-meter wide barrier-free maintenance channel, and the roof ridge both sides' highest points also need to leave out 0.45 meters' smoke exhaust and heat dissipation gap, forcibly occupying 15% to 20% of the total usable roof area.

Winter solstice day noon's solar altitude angle drops to the whole year's lowest 21.5 degrees. Distance to ground 0.6 meters high standard size panel, at noon on December 21st, projected shadow length reaches 1.52 meters. Between the front row panel's upper edge and the back row panel's lower edge, the actual interval distance must be set at above 1.6 meters. If spacing is compressed to 1.2 meters, the front row shadow at 3 o'clock in the afternoon will block the back row bottom 3 rows' solar cells, triggering the bypass diode's conduction mechanism, leading to a single piece panel's output voltage instantly cliff-style plummet from 42V to 28V, whole string panels' electrical energy output cut off 33%.

Roof load-bearing weight

Standard double-glass solar panel whose area is 2.58 square meters and net weight is 32 kilograms. Adding 4 kilograms of weight's aluminum alloy guide rails and stainless steel fasteners, the average newly added constant load indicator exerted on the roof structure falls within the 14.5 kilograms to 18.2 kilograms per square meter range. Conventional asphalt shingle roof adopting wooden framework, its design redundancy's remaining load-bearing capacity indicator is usually 25 kilograms to 30 kilograms per square meter, completely able to bear panel's weight.

On flat roof, unable to punch holes and penetrate using ballasted installation bracket system, inside each installation base tray needs to place 12 kilograms to 18 kilograms' cement counterweight block, used to offset aerodynamic upward lifting pulling force generated by strong wind.

At category 3 hurricane frequent occurrence areas where wind speed reaches 210 kilometers per hour, the counterweight block's weight indicator is forced to double increase to 45 kilograms to 60 kilograms per square meter. In sloped roof installation, 8-millimeter diameter stainless steel bolts are used, and the depth of penetration of the roof wooden main beam must reach 63.5 millimeters, ensuring that the single root bolt's pull-out resistance strength indicator maintains above 180 kilograms to 220 kilograms' safety threshold.

Fire prevention and snow resistance

All DC high voltage cables penetrating the roof entering the indoor must pass through galvanized metal conduit whose nominal wall thickness size reaches 2.5 millimeters, and addly install DC fast fuse hardware switch whose rated cut-off current is 25A within 1.5 meters spatial range away from inverter, ensuring within 0.2 seconds extremely short time of occurring arc fault thoroughly cut off 600V's transmission voltage.

Load-bearing structure design included extreme weather variables met within up to 25 years equipment life cycle. Panel models passing high snow load certification, inside mechanical stress test laboratory are able to bear 5400 Pascals' static downward pressure, equal to every square meter area bearing 550 kilograms of accumulated snow weight.

In order to prevent the aluminum alloy frame from occurring mechanical bending deformation under this 550 kilograms weight, the bottom's metal support guide rail must accurately lock at panel long edge size's one-fourth and three-fourths' scale position. Panel backside's wind pressure resistance test standard then requires bearing 2400 Pascals' dynamic upward pulling force, ensuring panel under 35 meters per second gust impact will not occur structural tearing.

All black appearance

Residential roof installation highly regards visual integration degree of panel and existing building appearance. Standard industrial panels use silver anodized aluminum alloy frame and white polymer plastic backplate, reflectivity indicator towards visible light is between 12% to 18%. All black panels replaced the white backplate with a black polymer coating, and used electroplated black metal frames, forcibly pressing down surface light reflectivity to a numerical value of 3% to 5%.

Pure black surface and dark colored asphalt shingles or gray cement flat tiles on vision maintained highly consistent dark colored color block. Black backplate extra absorbed 8% to 12% of infrared heat energy, leading to panel internal working temperature elevating 2.5°C to 3.8°C when noon lighting is strongest. Temperature rise brought power attenuation penalty on physical performance, letting all black panel's daily average power generation indicator reduce 0.4% to 0.6% compared to white backplate panel. Residents inside the high-end real estate market are willing to pay an extra 0.08 US dollars to 0.12 US dollars' procurement premium to make up for this 0.6% electricity loss.