Solar Array Size Calculator
Calculate the right solar array size, total capacity, number of panels, roof space required and installation cost for your home or business energy needs.
Solar Array Size Calculator
Enter your energy usage and system details to calculate the ideal solar array size, panel count, roof area and total cost.
How to Use Solar Array Size Calculator
Follow these steps to calculate the right solar array size, total panels, roof area, installation cost and payback period for your home or business:
- 1Enter Monthly Energy Consumption. Find your monthly kWh usage on your electricity bill. The US household average is 900 kWh per month. Enter your exact figure for an accurate array size.
- 2Enter Peak Sun Hours. Input the average daily peak sunlight hours for your location. Southwest US averages 6–7, Northeast US averages 3–4 and the UK averages 2–3 peak sun hours per day.
- 3Set System Efficiency. Enter your expected system efficiency percentage. The default of 80% accounts for inverter losses, wiring resistance, panel temperature derating and soiling. Most residential systems operate at 75%–85%.
- 4Select Panel Wattage. Choose the wattage rating of the individual solar panels you plan to install. Higher wattage panels produce the same total power from fewer panels and less roof space.
- 5Enter Installation Cost per Watt. Input the price per watt quoted by your solar installer. The US national average ranges from $2.50 to $3.50 per watt fully installed including hardware, labor and permits.
- 6Set Tax Credit Percentage. Enter your applicable solar tax credit. The US federal Investment Tax Credit (ITC) is 30% through 2032. Enter 0 if no credit applies in your region.
- 7Select Array Configuration. Choose whether you are installing a single-face roof array, a dual-face array on two roof slopes, a ground-mount system or a flat-roof ballasted array.
- 8Click Calculate. Press Calculate Solar Array Size to instantly view required array size in kW, total panels, array wattage, roof area, gross cost, net cost after tax credit, annual output and payback period.
How to Calculate Solar Array Size
What Is a Solar Array?
A solar array is a group of solar panels wired together to form a complete power-generating system. Array size is measured in kilowatts (kW) of peak power capacity, which determines how much electricity the system can produce under standard test conditions. Residential arrays typically range from 3 kW to 20 kW, while commercial arrays range from 20 kW to several megawatts.
Step 1 — Calculate Daily Energy Requirement
Divide your monthly electricity consumption by 30 days to find your average daily energy usage.
Example: 900 kWh ÷ 30 = 30 kWh/day
Step 2 — Find Raw Solar Capacity Needed
Divide daily energy requirement by peak sun hours to get the minimum solar capacity before accounting for system losses.
Example: 30 ÷ 5 = 6.0 kW
Step 3 — Adjust for System Efficiency
Real solar systems lose energy through inverter conversion (3%–8%), wiring resistance (1%–3%), panel temperature derating in hot weather (5%–10%) and soiling (2%–5%). Dividing by efficiency gives the actual array size needed to reliably meet your consumption.
Example: 6.0 ÷ 0.80 = 7.5 kW
Step 4 — Calculate Number of Panels
Divide total required array wattage by the wattage of each individual panel. Always round up to ensure complete energy coverage.
Example (400W panels): (7.5 × 1,000) ÷ 400 = 18.75 → 19 panels
Step 5 — Calculate Roof Area Required
Standard residential solar panels measure approximately 65 × 39 inches (5.4 sq ft active area, roughly 22 sq ft with mounting clearance per 400W panel). Required area scales proportionally with panel wattage.
Total Roof Area = Panels × Area per Panel
Example: 19 × (400 × 0.055) = 19 × 22 = 418 sq ft
Step 6 — Calculate Cost and Payback
Multiply total array wattage by the installed cost per watt for gross cost. Apply the tax credit for net cost. Divide net cost by annual savings to find the payback period.
Net Cost = Gross Cost × (1 − Tax Credit ÷ 100)
Annual Savings = Annual Output (kWh) × Electricity Rate
Payback = Net Cost ÷ Annual Savings
Example: 7,500 × $2.80 = $21,000 gross
$21,000 × 0.70 = $14,700 net
10,950 kWh × $0.13 = $1,423/yr savings
$14,700 ÷ $1,423 = 10.3 years payback
Solar Array Size Chart
Use the tables below to quickly estimate the required solar array size, panel count, roof area and installation cost for different home energy usages and locations.
Solar Array Size by Monthly Energy Consumption
| Monthly Usage | Daily Usage | Array Size | Panels (400W) | Roof Area | Gross Cost | Net Cost* |
|---|---|---|---|---|---|---|
| 300 kWh | 10 kWh | 2.5 kW | 7 panels | 154 sq ft | $7,000 | $4,900 |
| 500 kWh | 16.7 kWh | 4.2 kW | 11 panels | 242 sq ft | $11,760 | $8,232 |
| 700 kWh | 23.3 kWh | 5.8 kW | 15 panels | 330 sq ft | $16,240 | $11,368 |
| 900 kWh | 30 kWh | 7.5 kW | 19 panels | 418 sq ft | $21,000 | $14,700 |
| 1,200 kWh | 40 kWh | 10.0 kW | 25 panels | 550 sq ft | $28,000 | $19,600 |
| 1,500 kWh | 50 kWh | 12.5 kW | 32 panels | 704 sq ft | $35,000 | $24,500 |
| 2,000 kWh | 66.7 kWh | 16.7 kW | 42 panels | 924 sq ft | $46,760 | $32,732 |
*Net cost after 30% federal ITC at $2.80/watt, 5 peak sun hours, 80% efficiency, $0.13/kWh rate.
Solar Array Size by Peak Sun Hours
| Peak Sun Hours | Array Size | Panels (400W) | Annual Output | Best Regions |
|---|---|---|---|---|
| 2.5 hrs/day | 15.0 kW | 38 panels | 10,950 kWh | UK, Northern Europe, Pacific NW |
| 3.0 hrs/day | 12.5 kW | 32 panels | 10,950 kWh | Northeast US, Germany, Canada |
| 4.0 hrs/day | 9.4 kW | 24 panels | 10,950 kWh | Midwest US, Central Europe |
| 5.0 hrs/day | 7.5 kW | 19 panels | 10,950 kWh | Southeast US, Mediterranean |
| 6.0 hrs/day | 6.3 kW | 16 panels | 10,950 kWh | Southwest US, Middle East |
| 7.0 hrs/day | 5.4 kW | 14 panels | 10,950 kWh | Arizona, Nevada, Texas West |
| 8.0 hrs/day | 4.7 kW | 12 panels | 10,950 kWh | Sahara, Arabian Peninsula |
Based on 900 kWh/month, 80% system efficiency, 400W panels. All rows sized to meet the same annual energy target.
Solar Array Size by Home Size
| Home Size | Avg. Monthly Use | Recommended Array | Panels (400W) | Roof Area Needed | Est. Net Cost* |
|---|---|---|---|---|---|
| Under 1,000 sq ft | 400–500 kWh | 3–4 kW | 8–11 panels | 176–242 sq ft | $8,000–$11,000 |
| 1,000–1,500 sq ft | 600–800 kWh | 5–7 kW | 13–18 panels | 286–396 sq ft | $12,000–$16,000 |
| 1,500–2,000 sq ft | 800–1,000 kWh | 7–9 kW | 18–23 panels | 396–506 sq ft | $15,000–$19,000 |
| 2,000–2,500 sq ft | 1,000–1,300 kWh | 9–11 kW | 23–28 panels | 506–616 sq ft | $18,000–$22,000 |
| 2,500–3,000 sq ft | 1,300–1,700 kWh | 11–14 kW | 28–36 panels | 616–792 sq ft | $22,000–$29,000 |
| Over 3,000 sq ft | 1,700–2,500 kWh | 14–21 kW | 36–53 panels | 792–1,166 sq ft | $29,000–$43,000 |
*Net cost after 30% federal ITC at $2.80/watt, 5 peak sun hours, 80% efficiency.
Panel Count by Array Size and Panel Wattage
| Array Size | 300W Panels | 350W Panels | 400W Panels | 450W Panels | 500W Panels |
|---|---|---|---|---|---|
| 3 kW | 10 panels | 9 panels | 8 panels | 7 panels | 6 panels |
| 5 kW | 17 panels | 15 panels | 13 panels | 12 panels | 10 panels |
| 7 kW | 24 panels | 20 panels | 18 panels | 16 panels | 14 panels |
| 10 kW | 34 panels | 29 panels | 25 panels | 23 panels | 20 panels |
| 12 kW | 40 panels | 35 panels | 30 panels | 27 panels | 24 panels |
| 15 kW | 50 panels | 43 panels | 38 panels | 34 panels | 30 panels |
| 20 kW | 67 panels | 58 panels | 50 panels | 45 panels | 40 panels |
Panel counts rounded up to nearest whole panel. Higher wattage panels reduce count and roof space for the same total array output.
Mono vs. Poly vs. Thin-Film Options for Solar Array Size
Choosing the correct cell technology determines the efficiency and spatial footprint of your Solar Array Size installation. Monocrystalline panels offer the highest efficiency (20%+), followed by polycrystalline (15-18%) and thin-film (10-13%):
| Technology | Typical Efficiency | Temperature Tolerance | Space Required |
|---|---|---|---|
| Monocrystalline | 20% - 22% | Excellent (-0.37%/°C) | Minimal |
| Polycrystalline | 17% - 19% | Moderate (-0.41%/°C) | Moderate |
| Thin-Film (Amorphous) | 11% - 13% | Superb (-0.20%/°C) | High |
Monocrystalline panels are highly recommended when roof space is constrained, whereas thin-film is suited for flexible surfaces or hot climates due to its superior temperature coefficient.
Solar Tilt, Azimuth, and Seasonal Sizing for Solar Array Size
For maximizing the seasonal or annual output of a solar PV array running Solar Array Size calculations, panel orientation and tilt angle must be carefully optimized. The optimal tilt angle is primarily determined by your geographic latitude, while the azimuth determines the direction the panels face (South in the Northern Hemisphere, North in the Southern Hemisphere):
For fixed-tilt Solar Array Size systems, setting the tilt equal to the local latitude is generally the best year-round compromise. In locations with higher cloud cover during winter, bias the angle slightly toward summer parameters to maximize performance during peak generation months.
Temperature Derating Factors in Solar Array Size PV Systems
Solar panels are rated at a Standard Test Condition (STC) of 25°C. However, real-world panel temperatures in Solar Array Size arrays frequently reach 45°C to 65°C. Because silicon cells lose efficiency as they heat up, a temperature coefficient must be applied to calculate actual power output:
Standard monocrystalline panels lose approximately 0.35% to 0.45% of power per degree Celsius above 25°C. Account for this thermal derating factor to ensure your inverter isn't under-sized during hot summer afternoons.
Frequently Asked Questions (FAQs)
To calculate the ideal array size, review past monthly electricity bills to find your average daily kilowatt-hour consumption. Divide this daily energy usage by the average peak sun hours in your geographic location, then account for typical energy losses to estimate your perfect array capacity.
A typical residential solar array size ranges from five to eight kilowatts, which covers the electricity needs of a standard American home. However, the perfect size depends completely on your family's personal energy consumption, the size of your roof, and local climate and sunlight conditions.
Yes, available roof space is a crucial factor when sizing a solar array. Each standard panel occupies roughly eighteen square feet. If your roof is relatively small or shaded, you might need to invest in highly efficient premium panels to hit your required daily electrical production target.
A standard five-kilowatt solar array generally requires between twelve and seventeen individual solar panels, assuming you use panels rated between three hundred and four hundred watts each. This setup typically demands around three hundred square feet of unshaded, south-facing roof real estate.
Oversizing your array helps compensate for inevitable system inefficiencies, unpredictable cloudy weather, and natural panel degradation over time. Producing slightly more power than you currently use also prepares your home for future electrical additions like a new electric vehicle or a heat pump.