How to Estimate Residential Solar Power System Size

With the cost of energy climbing and global warming and peak oil serious concerns for many people, more homeowners are considering solar power as the alternative energy of choice in the quest for an energy-efficient home. The first step in moving to residential solar power is estimating your home's average energy usage. Then you can intelligently partner with your solar power installer to design your residential solar power system.

Things You'll Need

• Electric utility bills for the past 12 months
• Calculator or pencil and paper

Instructions

1. Gather your electric utility bills from the past 12 months.

2. Add together the actual kilowatt-hours (kWh) used for each of the 12 months and divide by 12 to find the average kWh used per month.

3. Divide the average kWh used per month by 30 to find the average kWh used per day. Divide the result by 5, which is the average number of peak sun hours in the United States.

4. Multiply the result from Step 3 by 1.43 to account for system losses. The result is the size of the solar power system in kilowatts that will meet your average energy needs.

Tips & Warnings

• You can request duplicate copies of your electric utility bills from your utility company at little or no cost by calling the company's customer service department.

• If your utility company provides online access to customer accounts, you can usually find energy usage data for the trailing 12-month period there.

• Depending on your geographic location, your site may get more or less than 5 hours of peak sunlight per day. This will affect the overall size of the solar power system will need to meet your home's energy demand.

• Replacing your existing appliances and fixtures with energy efficient models may help reduce the overall size and cost of your solar power system.

• There are many federal, state and local incentives, including tax credits and rebates available to homeowners to encourage alternative energy use.

Resources

• North American Board of Certified Energy Practitioners
• The U.S. Department of Energy Efficiency and Renewable Energy
• Database of State Incentives for Renewables & Efficiency