PVWatts Solar Calculator
Estimate the energy production and savings from your solar panel installation.
Solar radiation data is based on your location. For this demo, we use data for Phoenix, AZ.
The total DC power rating of your solar panels. A typical residential system is 4-10 kW.
‘Premium’ modules have higher efficiency and better performance in high temperatures.
Tracking systems follow the sun to increase output but have higher costs.
Angle of the array relative to horizontal. For fixed systems, often equal to latitude.
Direction the array faces. 180° is South, 90° is East, 270° is West.
Total losses from soiling, shading, wiring, degradation, etc. Typically 10-20%.
The average cost you pay for electricity, used to calculate savings.
Estimated Annual AC Energy Production
Annual Savings
Avg. Solar Radiation
Performance Ratio
| Month | Solar Radiation (kWh/m²/day) | AC Energy (kWh) | Energy Value ($) |
|---|
Formula Used: AC Energy = DC Size × Solar Radiation × Days × (1 – Losses) × Efficiency
What is a PVWatts Solar Calculator?
A pvwatts solar calculator is a tool designed to estimate the electricity production and financial viability of a grid-connected solar photovoltaic (PV) system. Originally developed by the National Renewable Energy Laboratory (NREL), PVWatts allows homeowners, installers, and researchers to make informed decisions by providing reliable performance estimates based on location and system design. This calculator simplifies complex variables into an easy-to-use interface, making solar energy estimation accessible to everyone. Whether you’re considering a small residential setup or a larger commercial installation, a pvwatts solar calculator is the first step toward understanding your potential energy output and savings.
PVWatts Solar Calculator Formula and Explanation
The core of this pvwatts solar calculator relies on a fundamental formula to estimate energy production. While the official NREL model is highly complex, our calculator uses a simplified, yet effective, method:
AC Energy (kWh) = System Size (kW) × Solar Radiation (kWh/m²/day) × Days in Month × (1 – System Losses / 100) × DC to AC Efficiency
This formula provides a clear and powerful estimation of what a system can produce. For those looking to dive deeper, you can find more information on NREL’s official site or explore our guide on advanced solar modeling tools.
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| System Size | The total nameplate power of the solar panels. | kW (kilowatts) | 4 – 15 kW |
| Solar Radiation | The amount of solar energy that strikes the surface of your panels. | kWh/m²/day | 2.0 – 7.5 |
| System Losses | Combined percentage of energy lost due to factors like heat, wiring, and dirt. | % | 10% – 20% |
| DC to AC Efficiency | Efficiency of the inverter converting DC from panels to usable AC for the home. | % | 95% – 98% |
Practical Examples
Example 1: Standard Residential System in a Sunny Climate
- Inputs:
- System Size: 6 kW
- Location: Phoenix, AZ (High Solar Radiation)
- Tilt: 20°, Azimuth: 180° (South-facing)
- System Losses: 14%
- Results:
- This system would likely produce approximately 10,000 kWh per year. The high solar radiation in Phoenix significantly boosts output, making it an ideal location for solar.
Example 2: Residential System in a Northern Climate with Tracking
- Inputs:
- System Size: 6 kW
- Location: Boston, MA (Moderate Solar Radiation)
- Array Type: 1-Axis Tracking
- System Losses: 16% (higher due to potential snow)
- Results:
- This system might produce around 7,500 kWh per year. The 1-axis tracking system helps compensate for the lower solar radiation by following the sun’s path, improving overall efficiency compared to a fixed array in the same location.
How to Use This PVWatts Solar Calculator
- Enter Your Location: This is the most critical input, as it determines the amount of sunlight your panels will receive.
- Define Your System Size: Input the total DC kilowatt capacity of your desired solar array.
- Select Module and Array Type: Choose the panel technology and mounting system (fixed or tracking).
- Set Tilt and Azimuth: Optimize these angles for your location to maximize sun exposure. A south-facing array (180° azimuth) is usually best in the Northern Hemisphere.
- Estimate System Losses: Account for real-world inefficiencies. 14% is a standard starting point.
- Input Utility Rate: Enter your cost per kWh to calculate your potential savings.
- Calculate: Click the button to see your monthly and annual energy production estimates. Explore our solar financing calculator to understand the investment side.
Key Factors That Affect Solar Panel Output
- Solar Irradiance: The single most important factor. It’s a measure of the sun’s power reaching a specific area and varies significantly by location and time of year.
- Panel Orientation (Tilt & Azimuth): The angle and direction of your panels directly impact how much sunlight they capture. Sub-optimal orientation can reduce output by 25% or more.
- Shading: Even small shadows from trees, buildings, or chimneys can disproportionately decrease the output of an entire solar array.
- Temperature: Solar panels are less efficient in high heat. As panel temperature rises, voltage drops, reducing power output. This is why a hot, sunny day may produce less power than a cool, sunny day.
- System Losses: A catch-all term for real-world factors that reduce efficiency, including dirt on panels (soiling), power loss in wiring, inverter inefficiency, and age-related degradation.
- Module Type: Premium monocrystalline panels generally perform better in high heat and low light compared to standard polycrystalline or thin-film panels.
- For a complete analysis, consider our solar panel degradation calculator.
Frequently Asked Questions (FAQ)
1. What does a pvwatts solar calculator do?
It estimates the annual and monthly electricity production (in kWh) of a grid-connected solar panel system based on its location, size, and equipment specifications.
2. How accurate is this calculator?
This calculator provides a good initial estimate for planning purposes. For precise, investment-grade analysis, you should use NREL’s official PVWatts tool or consult a professional solar installer who can perform a detailed site assessment.
3. Why is my location so important?
Solar energy production is entirely dependent on the amount of sunlight received (solar irradiance), which varies greatly by geographical location, climate, and weather patterns.
4. What are “System Losses”?
System losses are the unavoidable reduction in energy output due to real-world conditions like dirt on panels, wiring resistance, inverter inefficiency, and gradual degradation of the panels over time.
5. Does a higher temperature mean more power?
No. Counterintuitively, solar panels are most efficient in cool, sunny conditions. High temperatures decrease their efficiency and power output.
6. What is the difference between Azimuth and Tilt?
Azimuth is the compass direction your panels face (e.g., 180° for South). Tilt is the vertical angle of your panels relative to the ground. Both are crucial for maximizing sun exposure.
7. Is a tracking system worth it?
It depends. Tracking systems increase output by 15-45% but add cost and complexity. Their value is greater in areas with high direct sunlight. Check with our solar ROI calculator for more details.
8. How do I choose the right system size?
The right size depends on your electricity consumption, available roof space, and budget. You can start by looking at your annual kWh usage on your utility bill.