How Solar Works
Think of the sun as a huge power plant that sends out waves of energy in the form of photons. These photons enter the earth's atmosphere and are responsible for the heat and light we receive.
Electricity can be converted directly from solar energy through solar cells known as photovoltaic cells—"photo" (for light) and "voltaic" (for energy). Individual cells combine to form a PV array. Normally mounted on a rooftop, the PV array components convert that solar energy into some of the electric current your home needs.
Solar produces energy during daylight hours only, so you must know when your home uses the most energy in order to make the best use of this technology. If your home is typically occupied during the daytime, and you use a lot of energy during those hours, you can benefit from solar panels. On the other hand, if your home is typically unoccupied during the daytime, and you tend to adjust your thermostat to minimize heating and air conditioning during these hours, you could end up exporting a lot of your solar electricity back to the grid. In this case, the payment you receive for exported solar will be important.
Location, Location, Location
The old real estate bromide about the importance of location applies to solar arrays, too. Most solar PV systems are installed on new or existing roofs, but they can be ground- or pole-mounted as well. Their orientation, tilt, shading and any restrictions that apply to your neighborhood are important considerations.
Roof Orientation
Southern facing roofs help maximize annual electricity production. Roofs that don’t face south have less direct sun exposure. You can get an idea of the sun's patterns by viewing your home on Internet mapping applications or any other GIS-based mapping website such as Google Maps.
As an example, the two houses shown here are on a street that runs north to south.
The house at the top has no south facing roof surface except for a small amount on the garage. Solar panels on the east facing side would only get sun in the morning, and the west facing side would only get sun in the afternoon.
The house at the bottom has a large section of south facing roof, as well as areas facing east and west.
The symbols show suitability for solar panels set flat onto the roof, but solar installers have options for lifting one end of the modules up from the roof and tilting the panels to a southern orientation.
Shading
It only takes a small amount of shading to significantly reduce a PV array's output. Ideally, a system should have no shade for at least 6 hours a day, preferably between 9 a.m. and 3 p.m.
The annual path of the sun should be considered in determining whether shading will affect the system, especially during the winter months when the sun is at a lower angle.
Tilt
The tilt of your solar PV panel is as important as the orientation. The standard practice calls for the tilt angle to be equal to the latitude, which in South Carolina is between 32 and 35 degrees.
The angle of tilt that will produce the most energy can change with the seasons. For example, if you install panels that are flatter (see summer example), you will see higher energy production during the summer months and a lower production during winter months. The period during the year when you desire the highest electricity production will drive the choice of the panel’s angle, or tilt.
The pitch of your roof could limit your ability to change the tilt. Ask your contractor what tilt is right for your PV system.
Community Restrictions
Your location may be important for another reason. Some homeowners associations (HOAs) and architectural review boards (ARBs) have rules that control whether and how solar PV systems can be installed. Before you get too far along with your solar PV system research, check with your HOA or ARB to make sure a solar PV system is allowed on the roof of your house or in your yard.
