Solar Panel Calculator

The Four Key Inputs for Your Solar Calculation

To get a reliable estimate, the Solar Panel Calculator relies on four critical pieces of information. Understanding them is the first step to planning your system.

• Average Electricity Consumption: This is the most important factor. It's the amount of electricity your home uses, typically measured in kilowatt-hours (kWh) per month or day. You can find this on your monthly utility bill. The higher your consumption, the larger your solar system needs to be.
• Peak Sun Hours Per Day: This is NOT just the number of daylight hours. It's the average number of hours per day that your location receives sunlight at an intensity of 1,000 watts per square meter. Locations in the sunny Southwest might get 5-6 peak sun hours, while locations in the Northeast might only get 3-4.
• Single Solar Panel Wattage: This refers to the power output of an individual solar panel under standard test conditions. Common residential panels today range from 350 to 450 watts. Higher wattage panels mean you'll need fewer of them to achieve your target system size.
• System Efficiency Buffer: Solar systems are not 100% efficient. The calculator automatically includes a 1.25 multiplier (a 25% buffer) to account for real-world energy losses from the inverter, wiring, panel temperature, and dirt accumulation.

Practical Example: Sizing a System for a Typical Home

Let's walk through an example to see how these inputs come together.

• Average Consumption: 900 kWh per month.
• Peak Sun Hours: 4.5 hours per day (a common US average).
• Panel Wattage: 400-watt panels.

Here’s how the calculator processes this information:

1. Calculate Daily Need: 900 kWh/month ÷ 30 days/month = 30 kWh/day.
2. Determine Base System Size: 30 kWh/day ÷ 4.5 peak sun hours = 6.67 kW or 6,667 watts. This is the raw power needed.
3. Adjust for Inefficiency: 6,667 watts × 1.25 (efficiency buffer) = 8,334 watts. This is the realistic system size you should aim for.
4. Calculate Number of Panels: 8,334 watts ÷ 400 watts/panel = 20.8 panels. Since you can't have a fraction of a panel, you round up.

Beyond the Numbers: Other Important Factors

This calculator provides a great starting point, but a professional solar installer will consider several other factors:

• Roof Space and Orientation: Do you have enough usable, south-facing (in the Northern Hemisphere) roof space to fit the required number of panels?
• Shading: Are there trees or buildings that will cast shadows on your roof during the day? Shading can significantly reduce a system's output.
• Local Regulations and Net Metering: Your local utility's policies on connecting to the grid and getting credit for excess power (net metering) can affect the financial viability of your system.
• Battery Storage: Do you want to store excess energy in a battery for use during power outages or at night? This adds cost and complexity but increases energy independence.

Frequently Asked Questions (FAQ)

Q: Where do I find my "peak sun hours"?

A: You can find maps and data from the National Renewable Energy Laboratory (NREL) or various online solar resources. Searching for "peak sun hours map [your state/country]" is a good start. A solar installer will have precise data for your specific location.

Q: Is it better to buy higher-wattage panels?

A: Higher-wattage panels are more efficient, meaning you need fewer of them to achieve the same total system size. This is ideal for homes with limited roof space. However, they are often more expensive per panel. The best choice depends on your roof size and budget.

Q: Will this system cover 100% of my electricity bill?

A: The goal of this calculation is to size a system that generates, on average, the same amount of energy you consume (a 100% offset). However, your actual bill savings will depend on your utility's net metering policies and any fixed fees they charge.

Q: What happens if I use more or less energy than I calculated?

A: Your system will still work perfectly. If you use less energy, you may export more power to the grid, potentially earning a credit. If you use more, you will simply draw the extra power you need from the grid as you do now.