How to Make a Design for Solar Panels on a Home

Solar panel array installed on a home roof

According to an abstract of a 2008 article in "Environmental Science and Technology," when you replace traditional energy sources with solar you can reduce air emissions by up to 89 percent. Not only is solar energy cleaner than traditional fossil-fuel energy sources, it is also relatively simple to understand and implement at your own home.



When designing a home solar system, the main issues you need to consider are how much electricity you use, and where you will install the solar panels.

Instructions

1. 

   If you are connected to the utility grid, excess electricity generated from your solar panels goes back into the power lines.

   Decide if your home solar system will be off the grid or if it will be tied into your existing utility (on-grid). An on-grid system feeds the electricity produced by your solar panels back into the utility; when your panels are not producing, you receive electricity from other sources on the grid. If you choose to be off-grid, you will need to install a battery to store energy for times when your panels are not directly producing (e.g., at night).

2. Look at your home electric bills from the past year and determine how much energy you use, on average, per month. According to the U.S. Energy Information Administration, the 2008 average monthly energy consumption per household was 920 kilowatt-hours (kWh).

3. Visit PVWatts.org and use their “Solar Power Calculator” to find out how large a system you will need, or use an equivalent PV energy calculator or formula. Enter your zip code, how much of your electricity you want to offset (e.g., 75 percent) and either your monthly kWh usage or your average electric bill. The calculator will return an estimate of your ideal system size in kilowatts (kW). For instance, if you live in San Francisco and use 920 kWh of electricity per month, your solar panels need to produce about 7 kW if you want to offset 100 percent of your electricity.

4. 

   Notice the individual cells that make up this small photovoltaic module.

   Use the estimated system size of your system (e.g., 7 kW) to find out how many solar panels you will need. Solar panels, or modules, are composed of many photovoltaic cells, each producing 1 to 2 watts of power. Modules come in a wide variety of sizes and are combined to form a solar array.

5. Figure out where the solar array will fit on your home. You will need approximately 100 square feet of space per kW of photovoltaic system–for example, a 7 kW system requires about 700 square feet. Your roof is a common and practical place to install solar panels. The most important design consideration here is the aspect, or orientation, of the mounting surface to the sun. Ideally, you should place your solar panels on a south-facing aspect.

6. 

   This solar array is mounted at a much greater angle than the roof.

   Determine the tilt for your solar modules. The optimum tilt is equal to your latitude, e.g., if your latitude is 39°N, then you want your panels to be tilted at a 39° angle to the ground. Your roof may be less tilted than necessary–you can compensate for this by constructing an angled mounting rack.

Tips & Warnings

• Find out about state and local incentives for installing solar at the Database of State Incentives for Renewables and Efficiency at www.dsireusa.org.

References

• U.S. Dept. of Energy: Solar Energy Technologies
• U.S. Energy Information Administration: FAQ
• "Environmental Science and Technology"; Emissions from Photovoltaic Life Cycles; Vasilis M. Fthenakis, Hyung Chul Kim, Erik Alsema; Feb. 2008

Resources

• Database of State Incentives for Renewables and Efficiency
• PV Watts: Solar Power Calculator