Which Roof Types Suit Solar Panels Best | Pitch, Material, Orientation

Suitable installing solar panel's roof types are: pitch 15–40's sloped roof, materials appropriately choose tiles, metal or concrete, avoid fragile materials; facing south direction can obtain whole year about 15–25% higher power generation amount, southeast or southwest second.

Pitch

Measuring pitch

Roof pitch in North American building standard's specification inside uses every 12 inches horizontal distance's vertical rise height to quantify, common's 4/12 pitch converted into physical included angle is 18.4 degrees. Using a standard tape measure to measure 3 random sample points obtained's average number of errors is usually within 0.5 inches, and using a smartphone's gyroscope app to calculate tilt angle will produce 2 to 3 degrees' standard deviation.

When the pitch reaches 6/12 time, the panel's installation angle is 26.6 degrees, this is currently the market standard on 70% mono-crystalline silicon module testing standard test conditions (STC)'s best matching variable. 8/12's roof corresponds to a 33.7-degree angle, can let sunlight penetrate the atmosphere layer's refractive index maintain at 1.1 to 1.3 between. Measuring time needs to avoid the roof's highest point 15 inches range inside's vents, to prevent local bulge causing panel's installation flatness deviation exceeding 5 millimeters.

Loss rate

In the north latitude 35 degrees' light distribution band, the photoelectric conversion efficiency's highest value appears in the panel tilt angle set at 28 degrees to 32 degrees' interval inside. Forcefully, the system will flatly paved installed on 2/12 (about 9.5 degrees)'s low pitch roof in December to next year February's winter power generation amount will plummet 18% to 22%. Pitch exceeding 10/12 (about 39.8 degrees)'s structure will let July and August's summer peak output power reduce 12.5%, due to afternoon 3 o'clock after incident light ray and glass surface's included angle will lower than 40 degrees, reflectance will from normal's 4% soar to 15% above.

· When the roof tilt angle and local latitude's difference value are controlled at an absolute value of 5 degrees within, this set photovoltaic array's whole year total power generation amount can maintain at the theoretical upper limit's 98.5% above.

· Deviation reaches 15 degrees time, in the north latitude 40 degrees region using a 10-degree tilt angle's roof, system's annualized rate of return will drop 6.3% to 7.1%.

· In order to make up this 7% production capacity gap, a originally configured 20 pieces 400 watts panels' system needs to add 2 pieces modules, hardware budget approximately will rise 550 to 650 US dollars.

Bracket and wind resistance

In pitch is 0 to 2 degrees' flat roof on constructing, installation team usually will introduce 20 degrees to 30 degrees' aluminum alloy tilt bracket to correct light receiving surface, every watt's material cost will extra increase 0.15 to 0.22 US dollars. The panel will elevate 25 degrees will increase the windward surface's air resistance, according to aerodynamics wind tunnel testing, wind speed reaches every hour 110 miles per hour, tilt bracket bottom's upward lift force (Uplift pressure) will reach every square foot 45 pounds.

· In order to resist this negative pressure value, not drilling holes' ballasted (Ballasted) installation method needs to be used for every piece size is 25 square feet's panel weight 120 to 160 pounds' concrete bricks.

· Roof's static load density will from original's every square foot 3 pounds instantly soar to every square foot 6.5 to 8 pounds, exceeded 1980 year before constructed's wood structure roof 5 pounds/square foot's load bearing limit.

· In standard 5/12 pitch's sloped roof, panel through 5.5 inches' stainless steel lag screws directly fixed on wood rafters, can resist every hour 140 miles' gust wind, newly added weight is only every square foot 2.7 pounds.

Accumulated snow sliding off

Photovoltaic glass surface's friction coefficient is approximately 0.03, the environment temperature stays at 35 Fahrenheit degrees (about 1.7 Celsius degrees), and the roof pitch reaches 8/12 (33.7 degrees), 2 inches thick's accumulated snow can slide off in 3 to 4 hours, depending on your own 40 pounds' gravity. If it is a 3/12 (14 degrees)'s gentle slope, the same snow amount needs to stay 48 to 72 hours just to completely melt. This period, the whole string panel's electricity output amount will maintain at 0% 's lowest value.

· In annual snowfall amounts exceeding 40 inches, 4/12 pitch's roof every year will lose 8% to 12% of its power generation cycle because of accumulated snow blocking.

· 9/12 above's pitch can will climate caused's machine stopping probability compress to 1.5% to 3% between.

· 45 degrees tilt angle's panel back side air flow speed compares 10 degrees tilt angle high out 0.8 meters/second, summer noon's module working temperature can drop 3 to 5 Celsius degrees, rescue back about 1.2% to 2% temperature decay rate.

Construction price increase

According to the Department of Labor's safety standard, roof pitch exceeding 4/12 (18.4 degrees) requires all construction personnel to wear load-bearing capacity reaching 5000 pounds' full body style safety harness, every day's preparation time will increase 45 to 60 minutes.

· Bumping into 7/12 to 9/12 (30 to 37 degrees)'s steep slope, installation workers' moving speed will drop 30%, the original one day can pave 25 to 30 pieces of panels' progress will be stretched long to 1.5 days.

· Efficiency loss will translate into every watt 0.10 to 0.15 US dollars' steep slope surcharge (Steep pitch fee), a 7 kW system will extra out 700 to 1050 US dollars' manual bill.

· Tilt angle breaks through 10/12 (39.8 degrees) reaching 12/12 (45 degrees) time, insurance company collected's worker compensation insurance premium rate will rise 20% to 25%, contractor will single watt installation price adjust high 0.20 to 0.30 US dollars.

· Construction team in 45-degree angle roof on moving single piece heavy reaching 45 pounds' module, muscle fatigue accumulating speed is flat ground on's 2.5 times, installing one piece panel's average consumed time from 15 minutes prolonged to 35 minutes.

Material

Choosing asphalt shingles

The North American residential market accounts for 75% of its share, and every square foot's material weight maintains at 2 to 3 pounds. Installation workers use 5/16-inch diameter stainless steel lag screws to penetrate shingle pieces, bite into below wood rafter 2.5 to 3 inches' depth, using this provide every root screw 600 to 800 pounds' pull-out resistance strength.

Drilling holes after will pave an 8 by 12-inch aluminum-made waterproof board, and at four surrounding smear polyurethane sealant, will 10 years inside's water leaking probability press down to 0.5% below. Single piece panel's installation consumed time maintained at 15 minutes around, every watt's manual expenditure is approximately 0.10 to 0.15 US dollars.

· A set rated output of 5 kilowatts (kW)'s system is expected to operate 25 years, and 10 years house age's asphalt shingles only left 5 to 10 years' remaining lifespan, midway dismantling and reinstalling panels will produce 1500 to 2500 US dollars' secondary construction cost, letting the project's overall return on investment rate drop 1.5% to 2%.

· If you can install new asphalt shingles at the same time as installing photovoltaic brackets, single-time construction can save off 200 to 300 US dollars' scaffolding erecting budget, and can apply aiming at roof renovation part 10% to 15% 's federal tax credit quota apportionment.

· Dark color asphalt shingles towards solar radiation's absorption rate high reaches 85%, July's roof surface temperature will soar to 65 Celsius degrees, photovoltaic module's backplate temperature will along with it rise to 55 Celsius degrees around, causing every day afternoon 1 o'clock to 3 o'clock's power output to produce 4% to 6% temperature decay.

Iron sheet stitching

Thickness is 24 or 26 gauge (Gauge)'s standing seam metal roof possesses 50 to 70 years' physical lifespan, perfectly covered mono-crystalline silicon solar panel 25 to 30 years' linear power decay cycle. Construction team no needs drill bit to drill holes, using high strength aluminum alloy made's S-5! U-type clamp stuck at 1 to 2 inches high's metal seam place, using a torque wrench apply 150 to 180 inch-pounds' torque just can lock tight.

· Clamp installation will single support point's working time from 15 minutes to 4 to 6 minutes, a set of 8 kilowatts' system can save 5 to 7 hours' manual work, translating into a single watt construction cost of 0.15 to 0.25 US dollars' reduction.

· Not penetrating waterproof layer's installation method will roof surface seeping water's after-sales maintenance rate drop to 0.01%, and can in every hour 160 miles' extreme wind speed under maintain system's structural integrity.

· Corrugated metal board (Corrugated metal) needs to use bringing EPDM rubber washers' fasteners to drill holes, rubber material in continuously receiving ultraviolet ray irradiation 10 to 12 years after will appear 30% above's volume shrinkage rate, every 15 years must invest 300 to 500 US dollars to replace all aging washers.

Mud tiles too heavy

Concrete tiles and clay tiles' every square foot mass reaches 9 to 15 pounds. Installation masters in pitch exceeding 4/12's roof surface on walking, slightly having no caution just will produce 5% to 10% tile stepping crushing rate, every piece replacement tile's purchasing unit price is usually between 4 and 8 US dollars. Standard's construction process requires workers first to move away tile pieces, which thickness is 0.25 inches, steel made hook fixed on bottom layer wood board, then use an angle grinder to cut tile piece back side to fit hook's protruding size.

· Single set hook base's installation consumed time reaches 30 to 45 minutes, a 24-piece panels composed's system needs to assemble 48 to 56 bases, total working hours will expand 12 to 16 hours.

· Cumbersome's cutting process will trigger every watt 0.30 to 0.50 US dollars' surcharge, causing a 6 kilowatt system's final quoted price to compare asphalt shingles high out 1800 to 3000 US dollars.

· Steel made hook will aluminum made guide rail elevate 5 to 6 inches, panel bottom's air circulation amount will lift every second 1.2 meters, midsummer season's panel working temperature can drop 3 to 4 Celsius degrees, rescue back approximately 1.2% to 1.6% of electricity amount loss.

Flat roof paving coiled materials

EPDM rubber or TPO waterproof coiled material's thickness generally between 45 and 80 mils (mil). Once used drill bit destroyed coiled material's physical layer, a long-reaching 20-year roof leak-proof warranty sheet will immediately lose effect. The installation team will adopt a counterweight block pressing style (ballast) bracket, which will be placed on a 0.5-inch thick high-density polyethylene (HDPE) protective pad, relying on single piece weight 30 to 40 pounds' concrete bricks will system press submit on roof surface.

· Counterweight design will let roof's static load density soar to every square foot 4 to 6.5 pounds, 1990 year before constructed's commercial or flat roof residence if design load bearing capacity is lower than 10 pounds/square foot, must pay 500 to 800 US dollars to issue a copy of the structural engineer's checking calculation report.

· In order to offset the 20-degree tilt angle brought by the windward surface wind pressure, needs to install an aluminum-made wind deflector board in the array's rear, which will lower the system's overall air resistance coefficient by 40%, causing every row of panels between needs to retain 1.5 feet's maintenance channel, roof area's utilization rate will drop from 85% to 65% around.

· White color TPO material towards sunlight's reflectance high reaches 70% to 80%, if on top paving bifacial power generation (Bifacial) solar panel, back side's cell piece can absorb this part reflected light, will annual total power generation kilowatt-hours lift 6% to 9%.

Old wood board shingles

Cedar wood shingles (Cedar shakes)'s fireproof rating generally stays at C level, panel bottom 1.5 to 2 inches' gap easily hoards dried out tree leaves. In rainfall amounts lower than 15 inches, the dry season, high temperatures reaching 50 Celsius degrees, the panel back side temperature will increase 15% local catching fire probability.

· Exceeding 60%'s first-line photovoltaic contractors refuse to use exceeding 10 years' wood board roof to conduct construction, looking for possessing special insurance claim settlement qualification's contractors will let installation base price skyrocketingly rise every watt 0.80 to 1.20 US dollars.

· Wood fiber's toughness will decay by 2% every year, forcefully twisting 5/16-inch fasteners has a 30% probability of causing wood shingle along grain cracks, repairing one piece 5 square inches' water leaking point at least needs to consume 120 US dollars' worth of material and manual work.

Orientation

Must face south?

A set installed at north latitude 35 degrees, full load power is 8 kilowatts (kW)'s system, if completely facing true south and not having any physical blocking, can output approximately 12500 to 13500 kilowatt-hours (kWh) of electricity every year, and the photoelectric conversion efficiency can reach nameplate nominal value's 98% above.

In the morning 9 o'clock to afternoon 3 o'clock's high radiation time period inside, true south roof every square meter can receive 1000 watts of solar radiation illuminance, guaranteed inverter can in full load capacity's 85% to 95% interval continuously operate 6 hours. Deviating true south direction 10 to 15 degrees, every year's total electricity amount loss is controlled at 1.5% to 2.5%'s extremely low level, completely can through selecting power tolerance is positive value (for example +5 watts)'s panel to offset.

Facing true south's system design median investment return cycle is usually 6.5 years to 8 years, in operating full 25 years' life cycle inside, according to average every degree electricity 0.25 US dollars' electricity bill budget, in total, can save about 75000 to 85000 US dollars' bill expenditure.

East-West facing's dispute

Facing east, the azimuth angle is 90 degrees, the maximum sunshine flux will be captured between 6 o'clock in the morning and 11 o'clock in the morning. Facing west's azimuth angle is 270 degrees, production capacity peak value concentrated between 3 o'clock in the afternoon and 7 o'clock in the evening. Compared to true south direction, pure east or pure west facing's roof whole day received's solar energy radiation total amount will reduce 15% to 22%, same 8 kilowatt array, annual power generation amount will drop to 10000 to 10800 kilowatt-hours nearby.

In order to make up for production capacity loss, the design team usually will array scale expand 20%, extra deploy 4 to 6 pieces rated power 400 watts' panels, causing hardware purchasing expenditure to rise 1200 to 1800 US dollars. Facing west panel in afternoon's high frequency output perfectly matched North American majority power grids' peak time electricity using load (peak demand), especially is in implementing time-of-use electricity price (TOU) billing mode's California state.

In the time-of-use electricity price interval inside, the afternoon 4 o'clock to evening 8 o'clock's power grid selling price is high, reaching every kilowatt-hour 0.50 to 0.65 US dollars. Facing west system in this time period outputting 1 degree electricity's financial return rate, equals to facing south system in the morning 10 o'clock non-peak time period (every degree electricity 0.20 US dollars) outputting 2.5 degrees electricity's money value.

Pure facing north, too losing

The azimuth angle is 0 degrees or 360 degrees facing north, on the roof, in the Northern Hemisphere, situated in the long-term shadow coverage area, one year inside's 365 days, almost only can receive atmosphere layer scattered light rays, unable to obtain high intensity direct light beams. Solar energy panel in this kind of diffuse reflection environment under's operating efficiency will violently drop to true south benchmark's 55% to 60% between, system whole day's average output power can barely maintain at rated parameter's 15% to 20% up and down.

Want to reach and facing south roof same's annual power generation indicator, facing north system must increase approximately 65% panel quantity, not only occupying an extremely large roof area, but will also let a set standard 5 kilowatts system's total construction cost from 15000 US dollars forcefully pulled up to 24000 US dollars above.

Return on investment rate will in facing north's design scheme inside vastly deteriorate, recovering cost's time span will from regular's 7 years prolong to 16 years to 19 years, approaching even exceeded standard string type inverter 12 to 15 years' hardware aging limit, midway large probability needs to additionally append 1500 to 2000 US dollars' equipment replacing budget.

Shadow blocking rate

If the roof east side in distance 20 feet's position has a tree height exceeding 40 feet's oak tree, every year's November to next year's February period, morning 8 o'clock to 10 o'clock's sunlight incidence angle extremely low, tree crown will in array above project out long reaching 15 feet's moving shadow. Even if only one piece of panel surface's 15% is blocked by tree leaves, in a series circuit's wooden barrel effect under, the whole strip branch circuit's current ampere number will be suppressed to the lowest point's 1.2 to 1.5 amperes, causing single string array's instantaneous power loss to high reaches 40% to 60%.

In order to resist complex facing triggered's local blocking probability, configuring every piece unit price in 40 to 60 US dollars' power optimizer (Power Optimizer) can let every piece panel independently operate, will shadow brought's annualized electricity amount discount loss rate from 35% forcedly compress back 5% to 8%'s error range inside.

Deviation angle and latitude

In north latitude 25 degrees, Florida, Miami, the sun's noon elevation angle on the summer solstice day's high reaches 88 degrees, approaching vertical irradiation. East-west facing roof and true south direction's power generation amount difference value is shrunken to merely 10% to 12%, photovoltaic system's fault tolerance space extremely large. Transferring to north latitude 45 degrees' Washington state, Seattle, winter solstice day's sun elevation angle will be low to extreme's 21.5 degrees, sunlight needs to pass through thicker atmosphere layers.

In high latitude regions, facing east or facing west's roof in winter months faces high reaching 25% to 30% production capacity cliff style dropping, system needs extra integrate capacity is 10 to 13.5 kilowatt-hours (kWh), price usually in 8000 to 12000 US dollars between lithium ion cell pack, just can in long reaching 4 to 5 days' overcast rainy low valley period maintain basic household load's stable operation.