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You’re ready for a highly efficient solar system on your roof. How much solar power will you need? What size solar panel system should you have?
Most homes need 15–25 solar panels to meet most of their energy needs.
Your exact number of solar panels will vary based on your energy consumption, how much sunlight hits your roof, and the wattage of the panels you choose.
Every household is going to be different depending on several factors. That’s why our solar experts are here to help you sort through all the technical stuff.
Understanding your energy needs
Check your electric bills to see how many kilowatts you use daily. We’ll also review your home’s energy usage to determine its kilowatt-hour consumption. Your system's production ratio and how much electricity your solar panels produce compared to the system’s size will help us calculate how many panels you may need to meet your household’s energy demand.
The solar panel’s power output will directly influence how many solar panels you need to meet your requirements. Systems with lower-wattage solar panels may require more panels to achieve the same electricity output as those with higher-wattage solar panels.
Simple formula to calculate your ideal solar system size
Follow these five steps for a quick estimate using this solar power calculator logic:
Gather your annual usage (kWh). Example: 10,800 kWh.
Find your average daily peak sun hours. Example: 4.5 hrs/day (Midwest).
Select a system efficiency factor. Engineers often use 0.8 (80%).
Note your panel wattage. Example: 400 W (0.4 kW).
Run the math:
Panels Needed = Annual kWh ÷ (Sun Hours × 365 × Efficiency) ÷ Panel Wattage
Plugging in the example:
Panels Needed = 10,800 ÷ (4.5 × 365 × 0.8) ÷ 0.4
= 10,800 ÷ (1,314) ÷ 0.4
= 8.22 ÷ 0.4
≈ 20.5 panels
So you’d round up to 21 panels, a roughly 8.4 kW system.
Key Insight: While the DIY formula is a great starting point, professional 3-D shade modeling and on-site surveys provide the precise data needed to maximize your system.
Real-world examples and panel-count tables
Panel count by home size and monthly usage
Home Size | Avg. Monthly kWh | System Size (kW) | Panel Count* |
1,500 ft² | 750 | 7.0 | 18 |
2,000 ft² | 1,000 | 9.5 | 24 |
2,500 ft², all-electric | 1,400 | 13.0 | 33 |
*Assumes 400 W panels, 80% system efficiency, 4.5 sun hrs.
System size benchmarks
DC System Size | Typical Panel Count (400 W) |
5 kW | 12-14 |
6 kW | 15-17 |
10 kW | 24-27 |
15 kW | 36-40 |
How single appliances affect panel needs
Refrigerator upgrade ➜ ~1 panel
EV adoption ➜ ~5-6 panels
Pool pump ➜ ~2 panels
Key factors that change your solar panel count
1. Your annual electricity use (kWh)
The fastest way to see how much power you need is to total the kilowatt hours (kWh) on the last 12 months of utility bills. This is your annual electricity consumption.
Higher-than-average homes: Electric vehicles, heat-pump HVAC, pools, or larger square footage can push annual use well above 15,000 kWh.
Lower-than-average homes: Small, energy-efficient, or part-time residences may use under 6,000 kWh.
If you plan to buy an EV or switch from gas to electric appliances, add that future consumption now so your system is future-proof.
2. Peak sun hours in your location
“Peak sun hours” reflect the quality of sunlight your roof can capture, with one peak sun hour equaling 1 kW of solar energy per square meter.² The number of solar panels you need depends on how much solar radiation reaches the ground where you are.
Believe it or not, residential solar panels can work well even in overcast conditions. However, areas that consistently receive more direct sunlight may require fewer solar panels to meet their energy needs.
Additionally, solar panel efficiency and wattage play an essential role. Higher solar panel wattage means each panel can generate more electricity, reducing the total number of panels required.
U.S. Region | Typical Peak Sun Hours/Day* |
Southwest (AZ, NV, CA deserts) | 6-7 |
South (TX, FL) | 5-6 |
Midwest | 4-5 |
Northeast & Pacific Northwest | 3-4 |
*Source: NREL PVWatts®
Use the free NREL PVWatts tool to find the figure for your ZIP code.¹
3. Panel wattage and efficiency
Most modern residential panels have a solar panel wattage of 370-450 W and 19-22% efficiency. Higher efficiency panels produce more power in the same roof area, meaning you need fewer solar panels.
Higher wattage panels produce more power in the same roof area, meaning you need fewer panels.
All systems experience 15-20% energy losses from factors like the inverter, temperature, and wiring. Professional designs often automatically account for this.
4. Available roof space, angle, and shading
A typical 400 W panel covers roughly 18 sq ft. Multiply that by your estimated panel count to see if your roof has enough surface area.
Consider these key factors:
Orientation (south-facing is best in North America).
Tilt (15-40° is common).
Shading from chimneys, trees, or neighboring buildings.
HOA rules or historic-district guidelines.
In general, you’ll need 100 square feet of south-facing roof space for every kilowatt of power.³ It’s not just about the size of your roof but also the peak sunlight hours your specific location receives.
The number of solar panels needed depends on how much sunlight your home receives, as more solar panels may be required to generate the same amount of electricity.
Clouds? No problem, the sun can handle it. Shadows from chimneys, trees, or taller buildings are a bigger obstacle to the sun’s rays. But do not worry; we can assess your home’s sun exposure and find the ideal layout for installing solar panels.
5. Future lifestyle changes
Electrifying your life means adding new loads to your home's energy consumption. Planning for future energy needs is crucial.
Upgrade | Extra Annual kWh | Approx. Additional Panels (400 W) |
EV (12,000 mi/yr) | 2,900 kWh | 5-6 |
Heat-pump water heater | 1,830 kWh | 3-4 |
Home battery add-ons (e.g., Tesla Powerwall) | 5,000 kWh | 6-9 |
Planning ahead avoids paying for another installation later.
Pro Tip: When sizing your system, always consider future energy needs, such as an EV or electric appliances.
People also ask
How many solar panels do I need for a 2,000 sq ft home?
A typical 2,000 sq ft house that consumes around 1,000 kWh per month would need roughly 24 high-efficiency panels. This is approximately a 9.5 kW system in a location assuming 4.5 peak sun hours. Check your actual utility bills and sun hours for a refined answer.
How many panels make a 5 kW system?
With 400 W panels, the math is simple: 5,000 W ÷ 400 W/panel = 12.5. So expect 12-13 panels. Panels below 400 W will raise that count slightly.
How much roof space is required?
Each 400 W panel is about 3 ft × 6 ft (18 sq ft). Multiply by your panel count: 24 panels × 18 sq ft = 432 sq ft. You should also add about 10% clearance for walkways and fire setbacks.
Can I power my whole house with solar alone?
Yes, if your roof fits enough panels to meet 100% of your annual usage and your utility allows net metering. Pairing solar with a solar battery enables night-time and backup power, inching closer to full energy independence.
How many panels for 1,000 kWh per month?
1,000 kWh × 12 months = 12,000 kWh/year. Using the formula with 4.5 sun hours and 400 W panels, you would need about 23 panels. We recommend rounding up to 24 panels to ensure you have enough power to cover your needs.
Limitations, next steps, and peace-of-mind solutions
Even a perfect DIY estimate can’t see every variable.
Roof structure limits (truss spacing, load ratings).
Local permitting rules or utility interconnection caps.
Shade surprises—a neighbor’s future remodel or tree growth.
Professional installers use drone mapping, lidar, and 3-D shade modeling to eliminate these unknowns. They also design systems that integrate smart inverters, monitoring apps, and energy storage options. Sunrun, for example, partners with automakers like Ford so an F-150 Lightning can power your home during an outage.
Key Insight: A modern solar installation is more than just panels. It's an integrated system with smart inverters, monitoring apps, and battery storage for true energy independence and security.
Points for the professional solar power installer
Even if you don’t have the exact answers to all these questions, it doesn’t hurt to give them some thought. You’ll be all the more prepared and know the right questions to ask during your free solar consultation (and thoroughly impress our solar experts).
Consider them as a starting point towards solar success. And don’t worry, we’ll tell you how many solar panels you need, explain how much energy your system could generate for your home’s needs, and guide you through how to choose the best solar panels for your home.
Schedule a free, no-obligation solar assessment with a trusted provider. A quick call and a copy of your utility bill are all it takes to receive a personalized solar energy plan, subscription options, and an expert-designed system monitored right from your phone, including insights into your system’s real-time energy production.