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).
How does a Photovoltaic (PV) system work?
The sun's energy in the form of photons release electrons from their bonds in the silicon semiconductors that make up the solar cells. When such semiconductors 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. The flow of these electrons makes up the current that will ultimately be utilized in your home or building.
What are the components of a Photovoltaic (PV) system?
A PV system is made up of different components. These include PV modules (groups of PV cells), which are commonly called PV panels; one or more batteries; a charge regulator or controller for a stand-alone system; an inverter for a utility-grid-connected system and when alternating current (ac) rather than direct current (dc) is required; wiring; and mounting hardware or a framework.
What does the inverter do?
The electricity produced by the solar modules is direct current, or DC. The inverter converts this electricity to alternating current, or AC. Most electrical devices in homes and businesses run on AC electricity.
Do I need batteries?
Batteries store direct current electrical energy in chemical form for later use. You do not need batteries if you are tied into the public utility grid. However, batteries are necessary should you need power during blackouts or if you are not connected to the grid. Since a PV system’s power output varies throughout any given day, a battery storage system can provide a relatively constant source of power when the PV system is producing minimal power during periods of reduced insolation.
What is the difference between a grid tied and off grid system?
Photovoltaic systems that are connected to the utility grid (utility-connected, grid-tie, or line-tie systems) do not need battery storage in their design because the utility acts as a power reserve. Instead of storing surplus energy that is not used during the day, the homeowner sells the excess energy to a local utility through a specially designed inverter.
Off grid systems rely on their own distinct system of solar panels, batteries, and inverters to generate electricity.
What does energy conversion efficiency mean?
Energy conversion efficiency is an expression of the amount of energy produced in proportion to the amount of energy consumed, or available to a device. The sun produces a lot of energy in a wide light spectrum, but we have so far learned to capture only small portions of that spectrum and convert them to electricity using photovoltaics. So, today's commercial PV systems are about 7% to 17% efficient, which might seem low. And many PV systems degrade a little bit (lose efficiency) each year upon prolonged exposure to sunlight. For comparison, a typical fossil fuel generator has an efficiency of about 28%.
What happens during cloudy days or in areas without plentiful sunshine?
Your solar electric system will not produce electricity without direct or diffused sunlight. It is important that you analyze your installation site and make sure you have a great solar window and that the pv system doesn’t have obstruction or shade.
What's the difference between PV and other solar energy technologies?
There are four main types of solar energy technologies:
Photovoltaic (PV) systems, which convert sunlight directly to electricity by means of PV cells made of semiconductor materials.
Concentrating solar power (CSP) systems, which concentrate the sun's energy using reflective devices such as troughs or mirror panels to produce heat that is then used to generate electricity.
Solar water heating systems, which contain a solar collector that faces the sun and either heats water directly or heats a "working fluid" that, in turn, is used to heat water.
Transpired solar collectors, or "solar walls," which use solar energy to preheat ventilation air for a building.
In what temperatures will a PV system operate? What about snow?
PV modules are generally designed to operate in temperature range of -10 to 120 degrees Fahrenheit. Heat decreases the output of the PV modules. To compensate for this, panels are usually mounted 3-6 inches off the surface of the roof to allow ventilation and cooling. Snow usually melts off the panels in a matter of hours. PV systems are designed to withstand snow, hail, rain and wind.
How long do PV systems last?
A well-designed and maintained PV system will operate for more than 20 years. The PV module, with no moving parts, has an expected lifetime exceeding 30 years. Experience shows most system problems occur because of poor or sloppy installation. Failed connections, insufficient wire size, components not rated for dc application, and so on, are the main culprits. The next most common cause of problems is the failure of electronic parts included in the Balance of Systems (BOS) - the controller, inverter, and protection components. Batteries will fail quickly if they are used outside their operating specification. In most applications, batteries are fully recharged shortly after use. In many PV systems the batteries are discharged AND recharged slowly, maybe over a period of days or weeks. Some batteries will fail quickly under these conditions. Be sure the batteries specified for your system are appropriate for the application.
How much electricity does a photovoltaic (PV) system generate?
A 10% efficient PV system in most areas of the United States will generate about 180 kilowatt-hours per square meter. A PV system rated at 1 kilowatt will produce about 1800 kilowatt-hours a year. Most PV panels are warranted to last 20 years or more (perhaps as many as 30 years) and to degrade (lose efficiency) at a rate of less than 1% per year. Under these conditions, a PV system could generate close to 36,000 kilowatt-hours of electricity over 20 years and close to 54,000 kilowatt-hours over 30 years. This means that a PV system generates more than $10,000 worth of electricity over 30 years.
Where do I begin? How can I estimate the size and cost of my system?
First, gather your electric bills to see how much electricity you use on a monthly basis. This number will be in kWh (kilowatt hours). Second, decide how much of your electricity you want to come from your PV system. Third, visit www.findsolar.com to get a rough idea of system size and costs.
Do rebates really exist?
Yes! The rebates pay for 30-35% of the installed cost. These programs are administered by the state through the California Energy Commission and California Public Utilities Commission. However, these rebates will not be around forever. The California Energy Commission buy-down program will cease to exist when the current available funds are reserved and ultimately paid out. In addition, the rebate levels decrease every six months. The sooner you install, the larger your rebate will be.
How do I apply for a solar rebate?
You must work with an Eligible Installer to apply for a solar PV rebate. Many states have created programs that reward homeowners who switch to solar power. Depending on the state in which you live, you may qualify for both state and local incentive programs. With California, New Jersey, New York, and Arizona leading the charge, other states are following suit. Visit the Database of State Incentives for Renewable Energy (DSIRE) to see what incentives your state is offering! The Eligible Installer will handle all the paperwork including the rebate application, necessary permits and utility interconnection agreement.
Why do I have to use an Eligible Installer?
Pre-qualified and certified installation companies bear the appropriate credentials, experience, insurance and financial resources to install PV systems, thus removing the risk from homeowners. Most rebates and financial incentives require that you enlist the services of a certified installation company.
Are there any tax incentives?
Yes. Homeowners may claim a first year 7.5% state income tax credit along with up to $2000 in federal investment tax credit. Businesses may claim the state tax credit, along with a first year 30% federal investment tax credit. Commercial investments are also eligible for accelerated depreciation.
This law is effective for systems placed in service by the end of 2008. New federal legislation has been introduced to extend and expand the solar tax credits.
How long until my system realizes net savings?
If you finance a large system, you may experience net savings as early as the first year. Instead of paying your monthly utility bill, you will make monthly loan payments for your PV system. You will effectively pay less for your loan over time than you currently pay your utility company.
Solar power systems usually yield an initial return on investment of 7-11%. As utility rates increase your return will also increase.
Is solar electricity really cost-effective?
Yes. Your solar electric system will supply you with electricity, which will cost you less than the rates you are currently paying. Over the course of its 30-year lifetime, a solar electric system is a great investment. It is low-risk, high-return investment that is very competitive with other types of investments (stocks, bonds, and property).
Systems will usually have a payback period of between 6-12 years. Your exact payback period will depend on your electrical usage, electric rate schedule, and cost of your system. Typically, the larger your electric bill the greater the return on investment and the faster the payback.
How does a solar electric system affect the value of my property?
According to The Appraisal Journal, Evidence of Rational Market Evaluations for Home Efficiency, a $1 decrease in your annual energy bills results in a $20 increase in your property value. Using this formula, one can estimate that your property value will increase by the net cost (after rebate) of your system.
What are Renewable Energy Credits (RECs)?
When you make electricity using clean energy, there are two products that have value. One is the electricity itself. The other is the environmental attributes of the electricity. These environmental attributes are also known as a Renewable Energy Credits (RECs). There are organizations that are willing to pay you money for the RECs that your PV system produces. Selling your RECs can provide several hundred dollars of income to you a year. Check with your installer for more information.
What happens during blackouts or other instances where the grid goes down?
If you install batteries as part of your system, you can still have electricity during power outages. Without batteries, the device that converts your solar energy into energy you use in your home (the inverter), has to disconnect from the grid and also from supplying your home with electricity. The reason for this is to protect electric utility workers who may be restoring the lines. Since your PV system produces electricity during daylight hours, it will be "live" and might produce enough electricity that could injure a linesman. CCEF will not provide a rebate for battery backup. You would need to pay for this part of the system yourself.
Will the utility company really pay me for my solar electricity?
Yes and no. Upon installation of your grid tied solar electric system, you enter into a Net Metering Agreement with your utility company. Throughout the year, you are given credit for every kWh that you produce. This credit is worth exactly what you would have been charged for that same kWh. At the end of the year, if you have produced as much as you have used, you will have reduced your electric bill to zero. You will only be responsible for paying the minimum charges for having a meter, which for most residences is $5.00 per month. However, you will not be paid for any credits remaining on your account after your 12 month billing cycle. Consequently, we size your system to meet your annual usage.
What happens to the solar electricity that I do not use?
Any excess solar electricity produced will go back into the grid through your meter, running it backwards. You are credited for each kWh produced at the same rate that you would be charged
