What Factors Determine Solar Panel Size | Energy Use, Roof Space, Sunlight Availability

Panel quantity by daily power consumption quantity, sunshine duration, and roof area decided.

If the family's daily power consumption is 12 degrees, local sunshine 4 hours, need install a 3 kW system.

Actual measure time according to 400W single block panel occupying land 2 square meters, need at least reserve 15 square meters no block towards south space.

Energy Use

Check bill

Flip open the past 12 months' electricity fee bill, you need to put above every month's kilowatt-hour (kWh) value, all sum up, get out the whole year's 365 days' total power consumption quantity. Assume your home's 1st month consumed 850 degrees of electricity, and in the 7th month, the refrigeration peak period power consumption quantity soared to 1,420 degrees of electricity. These two extreme values' difference amount reached 570 degrees of electricity, reflecting an out-of-reach seasonal energy fluctuation rate as high as 67%.

Power companies usually according to 30 days as one billing cycle, your monthly receipt will clearly print with one daily average power consumption quantity index, for example, every day 32.5 degrees electricity. If your home uses a 15-minute data sampling frequency smart meter, you can go to the power company website and download a 35,040 data points' annual CSV format table. This copy data sample can let you use a spreadsheet to calculate the whole year's power consumption median value, excluding off every year about 14 days go out on vacation, and every day drop to 5 degrees electricity's abnormal lowest value interference.

According to the USA Energy Information Administration (EIA) 2023 year's statistical sample, one set area at 2,000 square feet's single family villa, as long as lived 3 to 4 months, its annual average power consumption quantity will usually be stable at 10,649 degrees electricity's level up down float. If the annual total degree number exceeds 15,000 degrees electricity, explain this residence's energy density is lean high, your photovoltaic module procurement budget then needs to be adjusted according to proportion up to 40% to 50%.

Dismantle big piece

Calculate out 365 days' power consumption total quantity after, you must put this 10,000 degrees electricity's physical index dismantle to at least 5 high power's family appliance loads on.

l One unit refrigeration capacity is 3 tons' central air conditioning. If the energy efficiency ratio (SEER) is only 12, in the air temperature exceeds 32 degrees Celsius in the summer season, every day full load operates 8 hours, then a single day will burn off 28 degrees electricity.

l One capacity is a 50-gallon electric water heater. If the water temperature is set at 120 Fahrenheit degrees (about 49 degrees Celsius), every day, the complete 3 times full capacity heating cycle, the whole year cumulative power consumption will reach 3,500 degrees to 4,000 degrees electricity's interval.

l If your garage is inside a park with one unit equipped with 75 kilowatt-hours of cell pack's electric vehicle, according to every year's commute drive 12,000 miles' frequency, every mile consumes electricity 0.3 degrees, then the whole year will produce 3,600 degrees of electricity's newly added load demand.

l The kitchen's full-size side-by-side door refrigerator even if it has 24-hour plug electricity, its power usually only fluctuates between 150 watts and 400 watts, and the whole year contributes 800 degrees electricity's fixed base number.

l One unit power reaches 5,000 watts' electric oven, every week opens 3 times, every time bake set at 400 Fahrenheit degrees operate 1.5 hours, one year down will consume about 1,170 degrees electricity.

Calculate time

Analyze power consumption quantity cannot only look at every year's 10,000 degrees electricity's total volume, also need to put every day's 24 hours' time axis slice out different's billing rate multiplier. If your location's power grid implements time-of-use electricity prices (TOU) mode, the afternoon 4 o'clock to night 9 o'clock's 5 hours usually be demarcated as the highest peak value time period, and the electricity fee unit price may reach per degree 0.35 US dollars. In the night, from 10 o'clock to the early morning of the next day, 6 o'clock, the 8-hour trough period, the same one degree electricity unit price will suddenly drop 65%, drop to per degree 0.12 US dollars.

USA family daily 70% of photovoltaic system electricity generation quantity concentrates in the morning from 10 o'clock to 3 o'clock, this 5 hours. This time, the roof receives solar radiation intensity reach per square meter 1,000 watts' physical peak value. You daytime extra generate out come's 10 degrees electricity, if according to 1:1's net metering (Net Metering) full amount rule, transport back power grid, can obtain 10 full price's bill credit points. But in promoting NEM 3.0 policy's billing region, daytime on grid's electricity fee purchase price plummets 75%, from per degree 0.30 US dollars to per degree 0.08 US dollars.

Installed capacity must accurately match your home's daytime appliance operating time of 2 kilowatts to 3 kilowatts' basic load, or you have to increase your budget by 7,000 to 10,000 US dollars to purchase one block of 13.5 kilowatt-hours' family use energy storage lithium cells, use to put noon overflow's 10 degrees electricity flat shift to night 8 o'clock to offset expensive's peak value unit price.

Measure increment

The electricity quantity index cannot only stay at the past 365 days' statistical regression analysis on, must superimpose future 10 years to 25 years cycle's equipment electricity use growth rate. Photovoltaic panel every year inevitably will produce 0.5% physical attenuation rate, this then requires at 1st year design time, panel's nominal power total sum must compare history actual total power consumption quantity high out 110% to 115% calculation allowance. If you plan at 2 years inside your home's gas boiler with a heat pump heating system for two years, in the winter season, outdoor temperature lower than 5 degrees Celsius, the heat pump's operating load will make your home 1st month and 2nd month's electricity quantity sudden increase 30% to 45%.

Home inside if have 2 not reach 5-year-old children, along with their age growth step into the teenager stage, electronic equipment's hold rate and hot water consumption frequency will according to proportion increase, family annual total power consumption quantity's long-term compound growth rate about maintain at 1.5% to 2.5%'s amplitude. Standby power supply every day will swallow up the whole building's total electricity use quantity's 5% to 10%, according to one year's 10,000 degrees electricity's base number calculate, no reason lose's electricity quantity at 500 degrees to 1,000 degrees between.

In order to offset this part every day, 24 hours, every hour about 50 watts to 100 watts' continuous power loss, your roof needs at least extra lay 1 to 2 blocks rated power 400 watts' solar energy panel. When you put electric vehicle charging pile's output power from 1 level (1.4 kilowatts) to 2 level (7.2 kilowatts), charging speed jumps to 5 times, but every time you charge, the instant current exerted by the family electrical box will fierce increase to 30 amperes.

Reduce burden

In calculating out 120%'s total capacity expansion rate after, still need to execute this energy consumption equation inside execute 20%'s hardware energy efficiency reduction coefficient. Spend 300 US dollars to put whole house 40 incandescent light bulbs all change into 9 watts' LED lights, every month at least can cut off 150 degrees electricity's invalid load. If your home has one unit that already serves exceed 15 years' old style pulsator washing machine, its single time wash power consumption quantity compares current Energy Star (Energy Star) standard drum product high out 75%.

Clean up refrigerator condenser back accumulated 3 millimeters thick's dust, can make compressor's refrigeration efficiency in 24 hours inside elevate 15% to 20%, every day help you save down 0.5 degrees electricity. At the wall body thermal insulation layer inside, an additional 6 inches of glass fiber cotton is added, which can forcefully shorten the air conditioning's operating time by 25%, equivalent to giving this photovoltaic system a reduction of 800 degrees electricity's electricity generation pressure. Put window glass from single layer upgrade to fill in argon gas's double layer Low-E glass, solar radiation heat's transmittance will suddenly drop 60%, summer season air conditioning overall load quantity follows it drop 12% to 18%.

At select photovoltaic panel specification before completing this batch, the total cost not reach 2,000 US dollars' micro adjustment, can put your home's future annual power consumption quantity baseline from 12,000 degrees to 10,500 degrees. Total electricity use base number drop 1,500 degrees, you can buy less 4 blocks unit price 350 US dollars' photovoltaic module, thereby saving 1,400 US dollars' initial capital expenditure, at the same time saving down roof on about 6.8 square meters' physical area to avoid exhaust pipe cast down's shadow.

Roof Space

Measure size

One block rated power 400 watts' monocrystalline silicon photovoltaic module, its standard physical specification is usually length 1.72 meters, width 1.13 meters, single block surface area reach 1.94 square meters. If your home's power consumption median value needs to configure one set of 8 kilowatts' photovoltaic system, according to 20 blocks module calculate, the roof must carve out at least 38.8 square meters' absolute flat space. According to the USA National Fire Protection Association (NFPA) formulate's residential building code, solar energy panel matrix's edge distance roof ridge must forcefully reserve 0.91 meters (36 inches)'s smoke exhaust channel.

Side roof eaves and adjacent building's boundary need to leave out 0.45 meters to 0.9 meters' setback distance, building survey map's gross area therefore will produce a 20% to 30% reduction rate. The building area is 2,000 square feet's single-family house. Its double-slope roof's single side projection area is about 92.9 square meters. Deduct exhaust pipe and skylight occupy's 5.5 square meters volume obstacle after, net lay rate usually be compressed at 65%'s theoretical upper limit inside.

Calculate angle

Photovoltaic module's electricity generation efficiency and roof's tilt angle present a high degree of non-linear correlation. The North America region obtains the highest sunshine intensity's best tilt parameter distribute at 30 degrees to 45 degrees' numerical interval. If the roof's slope drops to 15 degrees below, the panel's rainwater runoff rate will suddenly decrease by 40%, leading to surface dust accumulation's thickness and mass increase, whole year's photoelectric conversion efficiency will follow it produce 3% to 5% negative deviation.

Direction angle (azimuth angle)'s data index towards overall output's interference rate higher, towards due south (azimuth angle 180 degrees)'s roof at noon time receives solar radiation intensity can reach per square meter 1,000 watts' physical peak value. When the panel is towards due east or due west, due to missing sunshine frequency, the strongest's 4 hours, the annual total electricity generation quantity's average number will plummet 15% to 20%. Towards the north's roof slope surface will lose reach as high as 30% to 45% of incident light intensity, project investment return cycle will be pulled long to 14.5 years above. Own flat roof's residence need to increase per watt 0.15 US dollars to 0.25 US dollars' extra construction budget, to procure tilt angle is 10 degrees to 20 degrees' aluminum alloy fixed bracket, artificially manufacture out 30%'s sunlight intercept increment.

Look at load bearing

Standard's glass backplane photovoltaic module add-on aluminum guide rail will exert per square foot 2.5 pounds to 4 pounds' continuous static physical downward press weight. The local weather bureau's historical statistical sample shows the winter season maximum snowfall quantity once reached 24 inches, snow density brings extra instantaneous load, which will soar to per square foot 20 pounds' limit peak value. One building house age reaches 18 years' wood structure house, its original asphalt waterproof roll material usually already passed through 25 years' design life cycle's 72%.

At old tile, the forcefully drive in diameter is 0.31 inches' stainless steel fixed bolt, future 5 years inside rainwater leak's probability will present exponential level fierce increase, reach normal statistical value's 400%. Dismantle old tile and change to a 30-year warranty period's new type anti-weathering composite asphalt material. Need to expend per square foot 3.5 US dollars to 5.5 US dollars' replacement cost, single time amount high reach 10,000 US dollars' fee must be counted into the photovoltaic project's initial financial budget total table. Structure engineer on-site survey finds attic inside's 2x4 inches wood crossbeam appears exceed 0.5 inches' sink deflection, house owner must add additional 1,500 US dollars to 3,000 US dollars' wood reinforce material fee.

Hide shadow

Photovoltaic cell cells at circuit board usually adopt series connection structure, one tree height is 45 feet's oak tree at 2 o'clock in the afternoon will shadow project at array inside 10% 's area on, whole string 10 blocks panel's real-time output power will produce cliff style drop, drop amplitude high reach 30% to 50%. Install personnel use carry 360-degree fisheye lens's sunshine path analyzer, can accurately measure out whole year's 8,760 hours inside's shadow block percentage error. The roof on the existing height exceeds 1.5 feet's brick built chimney or diameter is 8 inches' ventilation pipe. Time, morning 9 o'clock and afternoon 3 o'clock will produce a length exceeding 4 feet's move blind zone.

Put shadow cause's energy attenuation rate to compress to 5%'s tolerance threshold below, need for 7 kilowatts' system extra procure unit price is 50 US dollars to 80 US dollars' micro inverter (Microinverters). Increase 20 independent micro inverters will make the hardware procurement list's total amount expand from 1,200 US dollars to 1,600 US dollars, retrieve back every year about 800 degrees electricity's output loss quantity. According to per degree electricity 0.18 US dollars' retail unit price, micro inverter brings yield rate can at 8.5 years to 11 years' financial cycle inside realize profit loss balance point. Weather data model calculates tree every year with 0.5 meters to 1.5 meters' average speed continuous growth, at system expected's 25 years life inside not execute every year spend 300 US dollars' tree crown trim plan, 15th year's overall electricity generation quantity benefit median will be diluted off at least 12.5%.

Sunlight Availability

Calculate effective light

Every day, the sun rises and falls 12 hours, not equal to the physical meaning of electricity generation time. Photovoltaic engineering design introduces peak sunshine hour number (PSH) as a quantitative index, it strictly defines solar radiation intensity reaching per square meter 1,000 watts' standard time length. Utilize USA National Renewable Energy Laboratory (NREL) long-reach 30 years' historical weather data sample conduct regression analysis. Arizona state Phoenix city's annual average peak sunshine reaches every day 5.7 hours, and Washington state Seattle's statistical median value is only every day 3.2 hours.

Assume at two places respectively procure and install one set capacity is 8 kilowatts' same specification photovoltaic system, equipment hardware add-on manual budget is 24,000 US dollars. Phoenix city's system is able to output about 16,644 degrees of electricity, Seattle's system total output will large amplitude slide drop to 9,344 degrees of electricity. Two places annual electricity generation total quantity's dispersion degree high reach 43.8%, high latitude rainy region's users must will purchase panel's quantity increase at least 75%, extra pay 18,000 US dollars' equipment and construction fee, just can match sunshine sufficient region single family residence's normal energy output scale.

Measure high low trough

Earth revolution trajectory causes sunshine intensity fluctuation in the north latitude 40 degrees above region will present extreme periodic distribution difference. On June 21st's summer solstice day, the sun's height angle approaches 73 degrees' highest value, light rays penetrate the atmosphere's path shortest, and the single day's effective sunshine hour number may break through 6.5 hours' highest parameter. Arrived on December 21st's winter solstice day, the sun's height angle suddenly dropped to 26 degrees, an extremely low value. Not only did the daytime physical time length shorten to not reach 9 hours, but the slant shoot light ray at pass through thick heavy cloud layer time's refractive index and absorption rate large amplitude climb, daily average peak sunshine will cliff style drop to 1.8 hours below.

Retrieve past 20 natural years' weather station measure sample, winter season continuous overcast rainy weather leads to every week average electricity generation quantity drop break theoretical calibrated value 20% below's probability high reach 68.5%, system total output's single month standard deviation at 12th month and 1st month reach whole year statistical wave peak.

If your home's 1st month's heating power consumption quantity reaches 1,500 degrees electricity, only rely on every day's 1.8 hours' peak sunshine to cover that month's 100% electricity use load, reverse deduce out's system theoretical install demand will expand to surprising's 27.7 kilowatts. At not possess full amount net metering (Net Metering) policy's power grid jurisdiction region, you need to advance withdraw exceed 75,000 US dollars' excess capital budget to cope with that kind of seasonal energy deficit, or spend 25,000 US dollars to purchase 3 groups of capacity is 13.5 kilowatt-hours' energy storage lithium cells, use this to balance long-reach 90 days' winter season trough period output deviation.

Check temperature meter

Leave factory specification book on mark's 400 watts rated power, is at laboratory standard test condition (STC), namely panel surface temperature accurately controlled at 25 degrees Celsius, time measured's highest ideal value. Monocrystalline silicon panel's power temperature coefficient universally set at -0.35%/°C's industry parameter range inside, representing panel temperature every exceed 25 degrees Celsius increase 1 degree Celsius, system's real-time output power then will face 0.35%'s physical attenuation.

In California's south part's 7th month, noon outdoor environment air temperature climbs to 38 degrees Celsius, roof surface dark color asphalt tile absorbs radiation heat, which will put photovoltaic module's actual working temperature to 65 degrees Celsius, physical extreme value range.

Compared to 25 degrees Celsius' laboratory baseline, a 40 degrees Celsius temperature difference multiplied by 0.35% attenuation ratio will lead to system's instantaneous electricity generation efficiency suffering a high reach 14% hard deduction.

At noon, the sunshine intensity is highest from 12 o'clock to 2 o'clock, and the roof on one block 400 watts' panel can only transport 344 watts' direct current towards the inverter. Heat attenuation not only reduces low voltage amplitude, but will also accelerate the internal cable's insulation layer aging rate. Long-term stay at 60 degrees Celsius above high temperature environment's module, its 25-year life cycle's overall electricity quantity attenuation median will compare temperate weather zone's data sample high out 1.5% to 2.2%.

Look at air value

Air quality index (AQI) and earth surface environment factor towards incident photon's transmittance play a strict's weaken role. Every year, the autumn season on the west coast of the USA, frequent mountain fires will release large amounts of high concentration suspended particulate matter. When the air in the PM2.5 concentration index continues to break through 150 micrograms/cubic meter, solar radiation is smoke large area scatter and absorb, and the earth's surface receives visible light intensity will follow a sudden drop of 15% to 25%.

Continuous drought for 60 days after, the panel glass surface accumulated a 2.5-millimeter thickness dust layer, which will make light transmittance produce about 7.5% normalized negative deviation, the whole set of 8 kilowatts system's electricity generation benefit will therefore lose 18 US dollars to 25 US dollars' cash value.

According to the weather department's rainfall quantity frequency distribution statistics, every 45 days, one time rainfall quantity exceeds 0.5 inches' strong precipitation, able to wash off mud and sand attachment on panel surface 95%, making the system's output power in 24 hours inside rapid return to rated parameter's 98% above.

In annual snowfall quantity exceeds 40 inches in the north cold zone region, snow accumulates completely cover panel time, single day electricity generation quantity will instantly return zero, but procure carry with bifacial electricity generation (Bifacial) specification's high level module, able to utilize white snow ground high reach 80% 's high reflectivity (Albedo), from back surface glass absorb environment scatter light, in clear's winter day inside provide extra 8% to 12% output increment premium.