Frequently asked questionsQ: What is photo Voltaic (solar electricity) or “PV”? or What do we mean by photo Voltaic?
A:The word itself helps to explain how photo voltaic (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, photo voltaics could literally be translated as light-electricity. And that’s just what photo voltaic materials and devices do; they convert light energy to electricity, as Edmond Becquerel and others discovered in the 18th Century.Q: How can we get electricity from the sun?
A: 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 photo voltaic (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).Q: What are the components of a photo Voltaic (PV) system?
A: 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.Q: How long do photo Voltaic (PV) systems last?
A: 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 and can last more than 30 years. 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.Q: What’s the difference between PV and other solar energy technologies? A: There are four main types of solar energy technologies:
1. Photo Voltaic (PV) systems, which convert sunlight directly to electricity by means of PV cells made of semiconductor materials.
2. 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.
3. 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.
4. Transpired solar collectors, or “solar walls,” which use solar energy to preheat ventilation air for a building.Q: Can I use photo Voltaic (PV) to power my home?
A: PV can be used to power your entire home’s electrical systems, including lights, cooling systems, and appliances. PV systems today can be blended easily into both traditional and nontraditional homes. The most common practice is to mount modules onto a south-facing roof or wall. For an additional aesthetic appeal, some modules resemble traditional roof shinglesQ: Can I use photo Voltaic (PV) to power my business?
A: PV systems can be blended into virtually every conceivable structure for commercial buildings. You will find PV being used outdoors for security lighting as well as in structures that serve as covers for parking lots and bus shelters, generating power at the same time.Q: How do I know if I have enough sunlight for PV?
A: A photo Voltaic (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. Most PV modules are angled to catch the sun’s rays, so any snow that collects on them usually melts quickly. There is enough sunlight to make solar energy systems useful and effective nearly everywhere in California.Q: How big a solar energy system do I need?
A: The size of solar system you need depends on several factors such as how much electricity or hot water or space heat you use, how, 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 suit your needs.Q: Why should I purchase a PV system?
A: People decide to buy solar energy systems for a variety of reasons. For example, some individuals buy solar products to preserve the Earth’s finite fossil-fuel resources and to reduce air pollution. Others would rather spend their money on an energy-producing improvement to their property than send their money to a utility. Some people like the security of reducing the amount of electricity they buy from their utility, because it makes them less vulnerable to future increases in the price of electricity. If it’s designed correctly, a solar system might be able to provide power during a utility power outage, thereby adding power reliability to your home. Finally, some individuals live in areas where the cost of extending power lines to their home is more expensive than buying a solar energy system.Q: How is a solar electric system designed, installed, and maintained?
A: You could install a photo Voltaic (PV) or solar electric system yourself. But to avoid complications or injury, you will probably want to hire a reputable professional contractor with experience in installing solar systems. PV systems have few moving parts, so they require little maintenance. The components are designed to meet strict dependability and durability standards so they can stand up to the elements. However, they are fairly sophisticated electric systems, so installation usually requires the knowledge and experience of a licensed electrical equipment contractor.Q: Where can I find someone who designs, installs, and maintains photo Voltaic (PV) systems?
A: We suggest you look for a PV installer or equipment provider in the telephone directory under “Solar Energy Equipment and Systems Dealers.” It is a good idea select a designer or installer of solar energy systems from the list in your local yellow pages by first asking for information from several of them about their experience with PV systems as well as how much their services and products cost. With a system designer, you can discuss power requirements or hot water needs for your building, sunlight availability, and other important factors, and determine the type of system that’s needed to meet your needs. System designers and installers should be able to provide you with cost estimates and other pertinent information. If your house is not yet designed or built, it is important to make the building as energy efficient as possible to reduce your PV system’s energy requirements.Q: How much does a solar energy system cost, and how much will I save on utility bills?
A: Some of the following documents are available as Adobe Acrobat PDFs. Download Acrobat Reader. Unfortunately, there is no single or simple answer. But a solar rebate and other incentives can reduce the cost of a PV system. This cost depends on a number of factors, such as whether it is a stand-alone system or is integrated into the building design, the size of the system, and the particular system manufacturer, retailer, and installer. For solar water heaters and space heaters, you also have to consider the price of the fuel used to back up the system. In most cases, you would have to add the cost of natural gas or electricity to get a more accurate estimate of how much you can expect to pay for a solar energy system. It is also difficult to say how much you will save with a solar energy.
Q: How often should I clean my Solar Panels?
When someone gets a new rooftop solar installation, the second question they always ask is “how often do I need to clean my solar panels.” We’ll answer that question on this week’s show — taking into account the different effects of rain, dust and electric rates (BTW, the first question people always ask is “how do I read my electric bill;” but that’s a topic for another show).
Rooftop solar panels get dirty primarily from wind-blown dust and pollen. Birds are usually not a problem unless your last name is Hitchcock and you live in Bodega Bay. As panels get dirtier, their output declines. A small amount of soiling — say a light dusty film — may only cause a 5 percent output decline. However, when panels get very dirty — perhaps in an agricultural area or location that does not get regular rainfall — the output decline can be greater than 20 percent. A good heavy rainstorm will usually wash away most of the accumulated soiling. I use the term “usually” because on panels that are tilted at about 5 degrees or less, the rain may leave a puddle of muddy debris along the lower edge of the panel. When this puddle dries, sometimes a thick layer of dirt accumulates along the lower row of cells (sometimes moss and weeds may even grow in these areas). Depending on the design of the system, this small accumulation of dirt can cause a very significant decrease in output. So the answer to the question: “how often should I clean my solar panels” really depends on five factors: your location (does it rain regularly or only during certain months), the tilt angle of your panels (steeply tilted panels tend to stay much cleaner than panels that are close to horizontal), the amount of wind blown dust, your electric rate (if your electric rate is high then it is more worthwhile to clean your panels), and the cost to clean your panels. For more about cleaning your solar panels, please Listen Up to this week’s edition of the Energy Show.