Solar Panel Output Estimator
Estimate how much electricity your solar panels will produce. Enter your system size, state, and efficiency to get daily, monthly, and annual kWh output instantly.
System Size
The total capacity of your solar array in kilowatts (kW). A typical residential system is 6–10 kW.
State
Your location determines average peak sun hours — the key driver of solar output. Sunnier states like Arizona and Nevada produce significantly more energy.
California averages 5.5 peak sun hours/day (NREL average)
System Efficiency
Real-world efficiency accounts for losses from inverter conversion, wiring, heat, shading, and panel degradation. Most systems run at 75–85%.
Annual Output
9,636 kWh
803 kWh/month
Average U.S. home uses ~10,500 kWh/year
A 6 kW system in a sunny state typically covers 80–100% of an average home's electricity use. Output varies with roof orientation, shading, and seasonal changes.
Peak sun hours sourced from NREL (National Renewable Energy Laboratory) state averages. Actual output depends on panel orientation, roof pitch, shading, and local weather patterns.
💡About this calculator▼
Before you invest in solar — or evaluate whether your existing system is performing as expected — the most important number to know is how many kilowatt-hours your panels will actually produce. Not what the salesperson quoted. Not the nameplate rating on the panels. The real-world output, accounting for your location's sunlight and the inevitable efficiency losses every system experiences.
This estimator calculates your solar system's expected daily, monthly, and annual electricity production using three inputs: your system's size in kilowatts, your state (which determines average peak sun hours based on NREL data), and your system efficiency. Efficiency accounts for real-world losses from inverter conversion, wiring resistance, heat, and panel degradation — factors that together reduce output by 15–25% compared to laboratory ratings.
Use the result to size a battery storage system, estimate how much of your electricity bill solar will offset, or benchmark your existing system's monitoring data against what it should theoretically be producing.
Solar output is driven by three factors: how much power your panels can generate at peak conditions (system size), how many hours per day your location receives enough sunlight to run them at peak (peak sun hours), and how efficiently your system converts that potential into usable electricity (system efficiency).
Peak sun hours are not the same as daylight hours. They represent the equivalent number of hours per day when sunlight intensity reaches 1,000 watts per square meter — the standard test condition for rating solar panels. A state like Arizona gets roughly 6.5 peak sun hours per day on average, while Washington state gets closer to 3.8. This difference alone means an identical 6 kW system produces about 70% more electricity in Phoenix than in Seattle.
System efficiency captures all the losses between your panels and your electrical panel. Modern string inverters run at 93–97% efficiency, but wiring losses, temperature derating (panels lose output as they heat up), soiling, and shading push real-world system efficiency to 75–85% for most residential installations. The default of 80% is a reasonable planning assumption; well-optimized systems with microinverters and minimal shading can hit 85%, while heavily shaded or older systems may run at 70% or lower.
The calculator multiplies system size by peak sun hours by efficiency to get daily output, scales that to an annual figure (× 365 days), and divides the annual total by 12 for the monthly figure. Deriving monthly from annual this way keeps all three numbers internally consistent.
📐How it's calculated▼
Daily output (kWh) = System size (kW) × Peak sun hours (hrs/day) × Efficiency (%)
Annual output (kWh) = Daily output × 365
Monthly output (kWh) = Annual output ÷ 12
Peak sun hours by state are sourced from NREL (National Renewable Energy Laboratory) state averages. Values range from 3.0 hrs/day (Alaska) to 6.5 hrs/day (Arizona).
Example: 6 kW system in California (5.5 peak sun hours), 80% efficiency
→ Daily: 6 × 5.5 × 0.80 = 26.4 kWh/day
→ Annual: 26.4 × 365 = 9,636 kWh/year
→ Monthly: 9,636 ÷ 12 = 803 kWh/month
For reference, the average U.S. household consumes approximately 10,500 kWh per year, so this system would cover roughly 92% of average electricity needs in California.
📎Source: National Renewable Energy Laboratory (NREL) — Solar Resource Data
🔍Finding your inputs▼
System Size (kW): This is the total DC nameplate capacity of your solar array — the sum of all individual panel wattages divided by 1,000. A 20-panel system using 300-watt panels would be a 6 kW system. You can find this on your installation contract, permit documents, or utility interconnection agreement. Residential systems typically range from 4 kW (small home, low usage) to 12 kW (large home, EV charging, or pool). If you're shopping for solar, installers will size the system based on your annual kWh consumption — your utility bill shows this.
State: Your state determines the average peak sun hours used in the calculation, sourced from NREL data. Peak sun hours vary significantly — Arizona (6.5) and Nevada (6.4) are the highest; Alaska (3.0) and Washington (3.8) are the lowest. If your actual location is sunnier or shadier than the state average (e.g., southern California vs. northern California), your real output may be higher or lower than estimated. For a more precise estimate, tools like NREL's PVWatts calculator can model output for a specific address.
System Efficiency: The percentage of your panels' potential output that actually reaches your electrical panel as usable AC electricity. Losses come from four main sources: inverter conversion (3–7%), DC wiring resistance (1–2%), temperature derating (panels lose roughly 0.3–0.5% output per degree Celsius above 25°C, so hot climates see more loss), and soiling or shading (variable). The default of 80% is appropriate for a typical well-maintained system. Use 85% for a newer system with microinverters and minimal shading; use 70–75% for an older system, a heavily shaded roof, or a string inverter in a hot climate.
⚠️Special situations▼
My system is producing less than the estimate
Several factors cause real-world production to fall short of estimates. The most common: shading from trees, chimneys, or neighboring buildings that wasn't accounted for; panel soiling (dust, pollen, bird droppings) that reduces output 2–5%; inverter underperformance or clipping if the inverter is undersized relative to the array; and panel degradation (most panels lose 0.5% output per year, so a 10-year-old system runs at roughly 95% of its original capacity). If your monitoring app shows production significantly below this estimate, contact your installer for a performance audit.
Comparing this estimate to an installer's quote
Installer production estimates often use more detailed modeling tools (like NREL's PVWatts or Aurora Solar) that account for your specific roof pitch, azimuth, shading analysis, and microclimate. Those estimates will be more accurate than this calculator's state-average approach. Use this tool for quick planning and ballpark comparisons; use installer-provided modeling for final financial projections.
My roof faces east or west, not south
South-facing panels at optimal tilt produce the most output in the Northern Hemisphere. East- or west-facing panels typically produce 10–20% less than south-facing panels at the same location. If your panels don't face south, reduce the efficiency input by 10–15% to get a more realistic estimate for your orientation.
Adding an EV or pool to my home
If you're sizing a solar system to cover new loads like an electric vehicle charger or pool pump, add those loads to your current consumption before sizing the system. An EV driven 12,000 miles/year adds roughly 3,000–4,000 kWh annually. A pool pump running 8 hours/day at 1.5 kW adds about 4,380 kWh/year. Size the system to cover total projected consumption, not just current usage.
Net metering and grid export
This calculator estimates raw production, not bill savings. Whether excess production earns you full retail credit, a wholesale rate, or nothing depends on your utility's net metering policy. In states with full retail net metering (still common), overproduction rolls into a credit that offsets future bills. In states with avoided-cost net metering or no net metering, overproduction is worth significantly less — which affects the optimal system size.
❓Common questions▼
What's the difference between system size (kW) and output (kWh)?
Kilowatts (kW) measure capacity — the maximum power your system can generate at any instant under ideal conditions. Kilowatt-hours (kWh) measure energy — the total electricity produced over time. A 6 kW system running at full capacity for one hour produces 6 kWh. But panels only run near peak capacity for a few hours each day, so a 6 kW system might produce 24–36 kWh on a typical day depending on location and conditions.
How accurate are these estimates?
This calculator uses NREL state-average peak sun hours and a single efficiency factor, so it's best treated as a planning-level estimate with roughly ±15% accuracy. Factors it doesn't account for include your specific roof orientation and pitch, local microclimate variations, shading from trees or structures, and seasonal variation. For financing decisions or contract negotiations, ask your installer for a detailed site-specific model using PVWatts or similar tools.
What efficiency should I use for a system I'm planning?
For a new system with a quality string inverter and minimal shading, 78–82% is a reasonable planning assumption. If your system will use microinverters (which handle shading better and run at higher efficiency), use 82–85%. If you're in a hot climate like Arizona or Texas where heat derating is significant, use 75–78%. For battery backup systems, inverter round-trip losses add another 5–10% reduction to net usable output.
How does this compare to what a solar installer will tell me?
Installers typically use satellite imagery, shading analysis tools, and historical weather data for a specific address — producing a more precise estimate than state-average modeling. Their estimates will usually come in within 5–10% of this calculator for a south-facing unshaded roof. For complex roofs, significant shading, or non-south orientations, the gap can be wider. Use this tool to sanity-check installer quotes and understand the variables driving their numbers.
Will my solar panels still work on cloudy days?
Yes, but at significantly reduced output. On overcast days, panels typically produce 10–25% of their rated capacity. This is already baked into the peak sun hours averages used by this calculator — states with more cloud cover (Washington, Oregon, the Northeast) have lower peak sun hour values that reflect typical year-round conditions including cloudy days. The estimate represents an annual average, not a clear-sky maximum.