BuildCalc Pro

Solar Panel Calculator

Calculate the ideal solar panel system size, installation costs, tax credits, and long-term savings based on your electricity usage and location.

How to Use This Calculator

1. Enter your average monthly electricity bill in dollars. 2. Enter your electricity rate (check your bill — national avg is ~$0.13/kWh). 3. Enter average peak sun hours for your area (4-6 hrs for most US locations). 4. Enter your available roof area in square feet. 5. Set the % of energy you want to offset with solar (100% = full offset). 6. Adjust panel wattage and cost per watt if desired. 7. Click Calculate to see system size, cost, and savings projections.

Solar Panel System Sizing: Everything You Need to Know

Solar energy has become one of the best investments homeowners can make, with typical payback periods of 6-10 years and systems lasting 25-30+ years. The cost of solar has dropped 70% in the last decade, making it affordable for millions of homeowners.

System sizing starts with your electricity usage. Check your utility bill for monthly kWh consumption. The average US home uses about 900 kWh/month. Divide your daily usage by peak sun hours (4-6 hours for most US locations) and system efficiency (80%) to get the kW system size needed.

Modern residential solar panels typically produce 350-450 watts each and measure about 5.5 × 3.25 feet (18 sq ft). A 6 kW system needs about 15 panels (400W each) and approximately 270 square feet of south-facing roof space. Most roofs can accommodate a 4-8 kW system.

The federal Investment Tax Credit (ITC) covers 30% of solar installation costs through 2032. This means a $20,000 system effectively costs $14,000 after the tax credit. Many states offer additional incentives — net metering policies, state tax credits, or Solar Renewable Energy Credits (SRECs) that further reduce costs.

Solar panel costs average $2.50-$3.50 per watt installed in 2024, or $12,500-$17,500 for a typical 5 kW system before incentives. Premium panels with microinverters cost more upfront but produce 5-25% more energy over their lifetime. Battery storage adds $8,000-$15,000 but provides backup power and energy independence.

Frequently Asked Questions

How many solar panels do I need for my house?

The average US home needs a 6-8 kW system, which is 15-20 panels at 400W each. Divide your annual kWh usage by 1,500 (average production per kW of solar in the US) to estimate your system size in kW. Then divide by your panel wattage.

How much do solar panels cost in 2024?

The average cost is $2.50-$3.50 per watt installed, or $12,500-$17,500 for a 5 kW system before incentives. After the 30% federal tax credit, a 5 kW system costs $8,750-$12,250. Prices vary significantly by state and installer.

How long do solar panels last?

Solar panels are warranted for 25-30 years and often produce power for 35-40+ years. They degrade about 0.5% per year, so after 25 years they still produce about 87% of their original output. Inverters may need replacement after 10-15 years ($1,000-$2,000).

Do solar panels work on cloudy days?

Yes, solar panels produce electricity on cloudy days, though at reduced output (10-25% of full capacity). They also work in cold weather — solar panels actually perform slightly better in cold temperatures. Annual production averages account for weather variations.