What is a photovoltaic system?

Photovoltaic refers to the production of electricity (volts) from light (photons). A photovoltaic (PV) system produces electricity from sunlight using a set of solar panels. A solar panel is a collection of smaller solar cells that are wired together in the durable casing of the panel and covered with a glass surface to permit light entry. The solar cells are made of a silicon semiconductor and produce direct current (DC) electricity when they absorb light. The more light the panels absorb the more electric current they will produce. The typical residence uses alternating current (AC) electricity so the DC current produced by the solar panels must be connected to an inverter that converts DC to AC current before it can be used by your home.

What kind of PV systems are available for my house?

There are three basic kinds of PV systems that a house can use. The first is a “grid-tied” system where the solar panels produce electricity that is then run through an inverter and connected to your house via your electric meter. The solar panels provide electricity to power to your home and any excess electricity can be sold to the utility grid where it can be used by your neighbors.

The second type of PV system is a “grid-tied system with a battery backup.”  The solar panels power the house and a bank of batteries from which power can be drawn at night or in the case of a blackout. The excess electricity produced that is not used to power the home or charge the batteries can be sold to the electric utility. Batteries are relatively expensive and have short lives compared to the solar panels. A ‘charge controller’ is also required with batteries to regulate their charging and discharging.

The third type of PV system is a stand-alone or “off-grid” system that is not connected to the utility. The solar panels charge a battery bank from which electricity can be drawn directly as DC current or as AC current through an inverter.

Where are the solar panels placed?

Solar panels can be placed on the roof of the house preferably in a south facing direction in order to receive the most sunlight during the day. The solar panels are mounted on rails that are attached to the underlying roof. Other locations are ground-mounted solar panels placed on special racks that can be placed in any convenient and sunny open space. The inverter can be mounted on a wall on the inside or outside of the house or even under the solar panels in a ground-mounted PV system.

How many solar panels do I need to run my home?

That depends on several factors. How much electricity you use per month, the size of your roof and/or yard and the degree of shading at your place. Often a site assessment is needed to see what will fit and work at your residence. Check your utility bill to see how many kilowatt-hours of electricity you use per month. A PV system rated at 5 kilowatts of power (compare to a 100 Watt light-bulb in your house) will produce somewhere in the range of 400-600 kilowatt-hours of electrical energy per month if it has a clear, unshaded southern exposure in Alabama. A 5 kilowatt PV system could use as many as 28 solar panels each producing 180 Watts of power apiece or 18 panels producing 280 Watts each. An energy efficient house has the best chance of having all its electrical energy needs met with a PV system and being a ‘net-zero’ home.

How much area is needed for a PV system?

Typical residential Solar PV systems range in size from fifty to over six hundred square feet. A PV system composed of the very highest efficiency mono-crystalline cells will produce 1 kilowatt-hour for every 60 square feet. Less efficient poly-crystalline cells will require 90 to 130 square feet while thin-film systems need the largest area of all—sometimes as much as 300 square feet to generate 1 kilowatt.

How long will a PV system last?

Solar panels are very durable and degrade in performance very slowly over the years. Solar panels will often last 25 years or more and still produce 80% to 90% of their original capacity. Many systems installed in the 1970’s are still working well. Most solar panels come with a 20-25 year warranty. The inverters will probably need to be replaced in ten years or so.

How durable are solar panels in rain, sleet and hail?

Solar panels are highly durable and should endure most rain, sleet or hail without any significant damage. Most solar panels are guaranteed to withstand 3/4 inch hail balls at 120 miles per hour and are also built to withstand direct lightning strikes.

Will my PV system provide power to my home during a blackout?

If you have a grid-tied PV system, the answer is no. During a blackout, the inverter is required by law to shut down to prevent power from reaching the electric utility grid where it could harm workers working on the utility lines. This is known as the “anti-islanding” feature of inverters. A PV system with a battery back-up can still power your home by using the batteries during the blackout.