What is photovoltaics (solar electricity) or "PV"?

What do we mean by photovoltaics? The word itself helps to explain how photovoltaic (PV) or solar electric technologies work. First used in about 1890, the word has two parts: photo, a stem derived from the Greek phos, which means light, and volt, a measurement unit named for Alessandro Volta (1745-1827), a pioneer in the study of electricity. So, photovoltaics could literally be translated as light-electricity. And that's just what photovoltaic materials and devices do; they convert light energy to electricity, as Edmond Becquerel and others discovered in the 18th Century.

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How can we get electricity from the sun?

When certain semiconducting materials, such as certain kinds of silicon, are exposed to sunlight, they release small amounts of electricity. This process is known as the photoelectric effect. The photoelectric effect refers to the emission, or ejection, of electrons from the surface of a metal in response to light. It is the basic physical process in which a solar electric or photovoltaic (PV) cell converts sunlight to electricity.

Sunlight is made up of photons, or particles of solar energy. Photons contain various amounts of energy, corresponding to the different wavelengths of the solar spectrum. When photons strike a PV cell, they may be reflected or absorbed, or they may pass right through. Only the absorbed photons generate electricity. When this happens, the energy of the photon is transferred to an electron in an atom of the PV cell (which is actually a semiconductor).

With its newfound energy, the electron escapes from its normal position in an atom of the semiconductor material and becomes part of the current in an electrical circuit. By leaving its position, the electron causes a hole to form. Special electrical properties of the PV cell—a built-in electric field—provide the voltage needed to drive the current through an external load (such as a light bulb).

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How long do photovoltaic (PV) systems last?

A PV system that is designed, installed, and maintained well will operate for more than 20 years. The basic PV module (interconnected, enclosed panel of PV cells) has no moving parts. The best way to ensure and extend the life and effectiveness of your PV system is by having it installed and maintained properly. Experience has shown that most problems occur because of poor or sloppy system installation.

 

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How does a residential solar electric system work?

Solar cells in the modules mounted on your roof convert sunlight directly into DC power. A component called an inverter converts this DC power into AC power that can be used in your home. The system is interconnected with your utility. During the day, if your solar system produces more electricity than your home is using, your utility may allow net metering or the crediting of your utility account for the excess power generated being returned to the grid. Your utility would provide power as usual at night and during the day when your electricity demand exceeds that produced by your solar system. Systems are also available with a battery backup. Part of the power produced by your solar system during the day is used to charge the batteries, which provide power for your critical loads in the event of a power outage.

 

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How do I know if I have enough sunlight for PV?

A photovoltaic (PV) system needs unobstructed access to the sun's rays for most or all of the day. Shading on the system can significantly reduce energy output. Climate is not really a concern, because PV systems are relatively unaffected by severe weather. In fact, some PV modules actually work better in colder weather.

 

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How big a solar energy system do I need?

The size of solar system you need depends on several factors such as how much electricity, hot water or space heat you use, the size of your roof, and how much you're willing to invest. Also, do you want the system to supply your complete energy usage or to supplant a portion of your higher cost energy usage? You can contact a system designer/installer to determine what type of system would best suit your needs.

 

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Can my HOA or neighbors prevent me from installing a solar system?  

In a lot of cases, no. Many states have solar access laws that provide varying degrees of protection against restrictions that can be imposed on you.  Please contact us for more information.

 

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Will my system work at night?

No. Sunlight must be present for your solar modules to produce power. At night, you draw power from your utility.

 

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Will my system work on cloudy days?

Yes, though they produce less electricity. Under a light overcast sky, panels might produce about half as much as under full sun.

 

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Will my system continue to produce energy if the grid goes down?

Grid-tied solar systems are required by code to shut down upon loss of grid power.  The primary reason for this is to protect repair crews working to restore normal grid operation. Stray or unknown sources of current could be harmful to utility workers if solar PV systems remain on.  Once the grid is operating normally for 5 minutes the system will automatically begin producing power.  Batteries charged by a solar system or backup generators can be integrated to provide power to critical loads during grid outages.

 

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How can I get the most energy out of a solar PV system?

Solar PV systems perform the best when the PV modules face due south at a tilt close to the latitude of their location. Any variance from this and annual energy production will decrease.

 

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What is a typical payback on a solar PV system?

The current payback for most systems is between 6 and 10 years, where a combination of utility and tax incentives exists.  The exact payback will depend on the specific system components, type of application, as well as current and escalated utility rates over time.

 

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What incentives exist to help me offset the cost of installing solar?

Incentives vary by region and by customer type. Please see the list below to determine which incentives may apply to you.

•    Federal Investment Tax Credit: This is a dollar for dollar tax credit that is calculated at 30% of the system cost. The system cost used to calculate the value of the credit may need to be adjusted if other incentives were received and passed along to the installer to reduce the sell price of the system.

•    Utility Incentives: Incentives can be in the form of cash rebates offered at the time of installation or performance based incentives paid periodically based on the actual energy generated by the system. Major utilities in Texas who have historically had programs are Oncor, TNMP, Entergy, Austin Energy, CPS and CoServ. Incentive amounts and program availability change often.

•    Modified Accelerated Cost Recovery System (MACRS). This incentive allows commercial, taxpaying entities to fully depreciate the solar asset according to a 6 year schedule. Actual cash value of the depreciation will be based on the marginal tax rate.

•    Grants: Historically, grants have been accessible for certain customers. Public entities, such as state agencies, ISD’s and municipalities have been able to apply for funding through the State Energy Conservation Office to install renewable energy systems. The USDA also has a grant program available to rural businesses.

 

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How much does an average PV system cost?

Residential systems can vary between $2.50 per watt on the low end to $4.50 per watt on the upper end. This would be for a typical, roof attached, residential installation. Costs can increase above this threshold depending on the type of mounting and PV technology implemented. Larger commercial systems are on the lower end and can even go below this scale.

 

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How long will a PV system continue to produce energy?

Most PV modules warranty that production in year 25 will be no less than 80 percent of nameplate rating. Typical useful life is considered to be 30 years, but the system will continue produce energy well beyond that point.

 

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What is net metering? Is net metering available where I live and work?

Net metering is a policy that allows homeowners to receive the full retail value for the electricity that their solar energy system produces. The term net metering refers to the method of accounting for the photovoltaic (PV) system's electricity production. Net metering allows homeowners with PV systems to use any excess electricity they produce to offset their electric bill. As the homeowner's PV system produces electricity, the kilowatts are first used for any electric appliances in the home. If the PV system produces more electricity than the homeowner needs, the extra kilowatts are fed into the utility grid.