Solar Power Calculator
Calculate real-world solar panel output accounting for temperature, irradiance, shading, soiling, and inverter losses. Free power output tool, no signup.
Solar Power Production Calculator
Enter system size, location, tilt, and azimuth. Get daily, monthly, and annual kWh production with a month-by-month breakdown, CO2 offset, and tree equivalents.
Ready to design solar projects
in minutes, not hours?
SurgePV combines AI-powered 3D roof modeling, bankable energy simulation, and white-label proposals in one platform. Used by solar installers to close deals faster.
What This Tool Covers
The Solar Power Calculator estimates how much electricity a solar system will produce - by day, month, and year. Enter system size, location, tilt, and orientation and get a production profile that accounts for efficiency losses, panel degradation, and seasonal irradiance variation.
Inputs You Provide
- • System size (kW DC)
- • Location or US state for irradiance data
- • Panel tilt angle (degrees)
- • Azimuth (compass direction panels face)
- • System efficiency / derate factor
- • Annual panel degradation rate (%)
Outputs You Get
- • Daily average energy production (kWh)
- • Monthly production (kWh/month)
- • Annual production (kWh/year)
- • Month-by-month production chart
- • CO₂ offset (metric tons/year)
- • Equivalent trees planted
Features
Goes beyond simple kW × PSH math to model real-world production losses and degradation over time.
Monthly Production Profile
See how production varies across all 12 months based on location-specific irradiance data - not just an annual average.
Degradation Modeling
Apply an annual degradation rate (typically 0.5% per year) to see 25-year production decline and how it affects lifetime energy output.
CO₂ & Environmental Impact
Converts annual production to CO₂ offset in metric tons and tree equivalents - useful for customer proposals and grant applications.
How It Works
Production estimates follow NREL PVWatts methodology, adjusted for tilt and azimuth corrections.
Enter System Size
Input DC system size in kilowatts. This is the sum of panel wattages - not the inverter AC output rating.
Select Location
Choose a US state or city. The tool pulls monthly irradiance values (kWh/m²/day) for that location from solar resource data.
Set Tilt & Azimuth
Enter tilt angle (0° = flat, 90° = vertical) and azimuth (180° = true south for Northern Hemisphere). The tool applies correction factors to reduce irradiance for non-optimal orientations.
Apply Efficiency Derate
Enter system efficiency (default 0.80). This derate accounts for inverter losses, wiring losses, soiling, mismatch, and temperature effects on panel output.
Review Monthly & Annual Production
Results show daily, monthly, and annual kWh output, plus CO₂ offset and tree equivalents. Compare against utility consumption to see offset percentage.
Use Cases
Customer Proposals
Show homeowners exactly how much energy their system will produce each month. Month-by-month data builds credibility compared to a single annual estimate.
Tilt & Azimuth Optimization
Run multiple scenarios to find the tilt angle and compass orientation that maximizes annual production for a given location - useful for ground mount and carport design.
Utility Bill Offset Verification
Compare annual kWh production against a customer's utility bill to determine what percentage of consumption the proposed system offsets before finalizing size.
Calculation Methodology
Based on NREL PVWatts v8 methodology, the industry standard for US solar energy production estimates.
Daily Production
Daily kWh = System kW × PSH × System Efficiency
PSH is adjusted monthly based on location irradiance data. System efficiency (derate) is typically 0.78–0.85 for grid-tied systems.
Tilt & Azimuth Correction
Adjusted PSH = PSH × Tilt Factor × Azimuth Factor
Optimal tilt ≈ latitude. Azimuth factor peaks at 180° (true south); east/west orientations reduce output by 10–15%.
Annual Degraded Production
Year N Production = Year 1 Production × (1 − Degradation Rate)^(N−1)
Standard degradation is 0.5%/year. After 25 years at 0.5%/year, panels produce about 88% of their original rated output.
CO₂ Offset
CO₂ (metric tons) = Annual kWh × 0.000386
The EPA grid emission factor for US average is approximately 0.386 kg CO₂ per kWh. This varies by state - coal-heavy grids have higher factors.
Pro Tips
Use 0.80 Derate as Your Default
NREL's PVWatts default is 0.86, but real-world installs with soiling, slightly suboptimal wiring, and inverter clipping land closer to 0.78–0.82. Use 0.80 for conservative proposals.
Optimal Tilt Equals Your Latitude
For maximum annual yield, set panel tilt equal to the site latitude. In Phoenix at 33°N, a 33° tilt is optimal. Tilting 15° steeper maximizes winter production; 15° flatter maximizes summer.
East/West Splits Can Match South Production
An east/west split array produces about 80–85% of a south-facing system annually, but the production curve is flatter - less morning and evening peaking, better for self-consumption without batteries.
Check December vs. June Production
Monthly data matters when your customer has a time-of-use rate. If December production barely offsets their winter load, they may need a larger system or battery storage - flag this before the proposal is signed.
Frequently Asked Questions
How accurate is this calculator vs. PVWatts?
This tool uses the same core methodology as NREL PVWatts but with simplified location inputs. For the same location, tilt, and derate, results will be within 3–5% of PVWatts output. For final engineering estimates, use PVWatts with exact GPS coordinates and TMY3 weather data.
What derate factor should I use?
Use 0.80 for a conservative real-world estimate. PVWatts' default is 0.86, which assumes clean panels and optimal conditions. Real installs with roof-mount temperature penalties, occasional soiling, and modest wiring losses perform closer to 0.78–0.82.
What azimuth value should I use for south-facing panels?
True south is 180°. Southeast is 135°, southwest is 225°. Note this is true azimuth, not magnetic azimuth - no compass correction needed. For most US locations, panels within 30° of true south lose less than 5% annual production.
Why does production vary so much by month?
Solar irradiance varies by 2× or more between summer and winter at most US latitudes. In Minnesota, December sees about 2.5 PSH/day while July hits 5.5 PSH/day. This is why month-by-month data is more useful than an annual average alone.
What degradation rate should I enter?
Standard monocrystalline panels degrade at 0.5%/year - the NREL-documented industry median. Premium panels with linear power warranties often guarantee no more than 0.4%/year degradation. Use 0.5% as a safe default for proposals.
Does this include shading losses?
No. The calculator assumes an unshaded installation. For sites with tree, chimney, or neighboring building shading, use a dedicated shading analysis tool or shade reduction factor (typically 0.90–0.97) applied as an additional derate before entering system efficiency.
Related Tools
System Size Calculator
Size a system from annual energy consumption and location.
Solar Savings Calculator
Turn production estimates into dollar savings over 25 years.
Sun Angle Calculator
Find optimal tilt angles and solar position for any date and location.
CO2 Savings Calculator
Calculate lifetime carbon offset from a solar installation.
Ready to Turn Production Data into a Full Solar Proposal?
SurgePV turns your production estimate into a complete solar proposal - annual generation reports, financial modeling, incentive calculations, and e-signatures in one platform.
No credit card required · Full access · Cancel anytime
