Monthly Production Simulation
A Monthly Production Simulation is a detailed energy modeling process that predicts how much electricity a solar PV system will generate each month over a year. Instead of relying on a single annual total, this simulation breaks production into monthly segments, accounting for seasonal variations in sunlight, shading patterns, weather, tilt, azimuth, and system performance.
Monthly Production Simulation is essential for accurate proposal estimates, system sizing, financial modeling, ROI projections, and validating long-term production guarantees. Solar designers, installers, EPCs, and sales teams use it to produce realistic, customer-ready outputs, especially when working inside software tools like Solar Designing and performance modeling engines.
It also plays a key role in proposal creation, utility interconnection studies, payback calculations, and monthly revenue forecasting for solar businesses.
Key Takeaways
- Monthly Production Simulation provides accurate, season-based solar output prediction.
- Accounts for shading, tilt, weather, temperature, losses, and inverter efficiency.
- Critical for proposals, ROI modeling, and financial evaluations.
- Helps EPCs and installers set realistic customer expectations.
- Enhances accuracy compared to annual-only energy estimates.
What Is a Monthly Production Simulation?
A Monthly Production Simulation calculates a solar system’s expected monthly energy output (kWh) by modeling:
- Local solar irradiance
- Seasonal daylight changes
- Temperature effects
- Shading variations
- System losses (soiling, mismatch, wiring, inverter efficiency, etc.)
- Plane-of-array (POA) irradiance
- Module orientation and tilt
Unlike annual simulations, monthly modeling delivers more granular, realistic, and bankable production data, which is crucial for both residential and commercial project evaluation.
Monthly outputs are typically used in proposals, financial models, cashflow projections, and performance comparisons.
Related foundational terms include Performance Simulation, POA Irradiance, and Solar Savings Calculator.
How Monthly Production Simulation Works
1. Importing Local Solar Data
Weather datasets include irradiance, temperature, wind speed, and albedo values.
2. Modeling System Geometry
Tilt, azimuth, module spacing, and row orientation influence seasonal performance.
See Solar Layout Optimization.
3. Shading Analysis Over Seasons
Winter months produce longer shadows; summer months produce shorter ones.
See Shading Analysis.
4. Applying Monthly Loss Factors
Including:
- Soiling
- Module degradation
- Snow losses
- Temperature losses
- DC/AC clipping
5. Running the Simulation Engine
The model calculates hourly irradiance → monthly POA → system output for each month.
6. Producing 12-Month Output Table
Month-by-month kWh is generated, forming the basis of proposals and ROI calculations.
7. Export to Proposal or Financial Tool
Often delivered inside proposal software or tools like the Solar ROI Calculator.
Types / Variants of Monthly Production Simulation
1. Hourly-to-Monthly Simulation
Converts hourly irradiance into monthly totals for high accuracy.
2. Monthly Averaged Simulation
Uses long-term climate averages—faster but less detailed.
3. POA-Based Monthly Simulation
Uses plane-of-array irradiance factoring tilt and orientation.
4. Shading-Adjusted Simulation
Integrates shade profiles for each month of the year.
5. DC/AC-Optimized Monthly Models
Includes clipping assessments, inverter efficiency, and ILR behaviors.
How It’s Measured
Monthly Production Simulation outputs include:
Monthly Energy (kWh)
The primary metric for evaluating system performance.
POA Irradiance (kWh/m²)
Solar energy received on the tilted plane.
Performance Ratio (PR)
See Performance Ratio.
System Loss Breakdown (%)
Wiring loss, soiling, shading, mismatch, inverter, and thermal loss.
Monthly Peak Sun Hours
Affects production and seasonal energy trends.
Monthly DC/AC Clipping
Shows if inverter limits reduce output in summer months.
Practical Guidance for Solar Designers & Installers
1. Avoid relying only on annual estimates
Monthly simulation provides realistic customer expectations.
2. Use monthly shading data for accuracy
Integrate Shadow Analysis to avoid overestimating winter production.
3. Ensure tilt & azimuth are optimized for seasonal balance
See Sun Angle Calculator.
4. Verify DC/AC ratio behavior seasonally
High DC/AC ratios produce more summer clipping.
5. Use tools like SurgePV for automated modeling
Solar Designing generates monthly outputs instantly.
6. Include monthly simulation in proposals
Monthly kWh builds trust and transparency with customers.
7. Adjust for snow & soiling variation
Monthly loss factors prevent over-optimistic estimates.
Real-World Examples
1. Residential Home in California
A 7 kW rooftop system produces:
- 940 kWh in July
- 420 kWh in December
- Monthly simulation helps the homeowner understand realistic expectations.
2. Commercial Rooftop in India
A 150 kW system shows high output from Feb–May and reduced production during monsoon months.
The simulation allows the EPC to propose better financial structuring.
3. Utility Ground-Mount in Europe
Simulation shows long winter losses but strong summer performance due to steep tilt.
Investors rely on monthly profiles for cashflow forecasting.
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