Frequently Asked Questions About Solar PV Systems and Solar Thermal Systems

Consult this Solar PV Systems and Solar Thermal Systems FAQ for common questions about solar photovoltaics, photovoltaic (PV) systems and solar water heating systems.

Q: What is photovoltaics (PV) or solar electricity?
A: Photovoltaics is a way of creating electrical power by converting energy from the sun into direct current electricity. It is a way to produce electricity from a clean, infinitely renewable resource, and it is based on the photovoltaic effect.

The photovoltaic effect (which is the creation of electricity in a material when that material is exposed to light) was first discovered in the 1800s by Alexandre-Edmond Becquerel, a French physicist, and it is now the basic operating principle of the modern solar cell.

Although the word photovoltaics may look strange, it literally means “light-electricity,” and is a combination of the Greek word “phos” (which means light) and “volt” (which is a unit of measurement named for Alessandro Volta, an Italian physicist who invented the battery during the 1800s).

Q: How is light energy turned into electricity?
A: To transform solar energy into electricity, a semiconducting material that exhibits the photovoltaic effect is used. Typically, that semiconducting material is silicon, but other materials that release electricity when exposed to sunlight may be used as well.

To get electricity from the sun, this semiconducting material (also called a PV cell or a solar cell) is placed in sunlight. As the photons (or particles of energy) that make up sunlight strike the PV cell, some of the photons are absorbed by the photovoltaic cell, and their energy is transferred to that PV cell. In addition, electrons that are released from the PV cell flow, creating electrical current.

Due to the special electrical properties of solar cells, thus captured, flowing solar energy provides the voltage needed to drive the current through an electrical circuit or external load (such as a calculator or light bulb).

Q: What is a photovoltaic system made of?
A: What parts a PV system has depends on the type of photovoltaic system used. Depending on whether a PV system is an off-grid system or a utility-grid-connected system, it may include photovoltaic panels (which are groups of PV cells, or PV modules), one or more storage batteries, a charge regulator or controller (for stand-alone photovoltaic systems), an inverter (which converts direct-current electricity to alternating current electricity), wiring, a framework, and mounting hardware.

Q: How long will a photovoltaic system last?
A: A properly designed, installed and maintained PV system may last for decades. In fact, because a basic PV module (which is an interconnected, enclosed photovoltaic panel) has no moving parts, it requires little maintenance and can last for nearly 40 years.

Typically, PV modules don’t “die” due to old age. Instead, the amount of energy that they produce starts to diminish. (This is why it is important to check system data regularly. That way, if there is a drop in output, it can be detected right away.)

The best way to extend the life and efficiency of a photovoltaic system is to make sure that it is properly installed and properly maintained. Luckily, PV systems are relatively maintenance-free, and most PV system malfunctions are due to substandard PV system installation.

Q: What makes photovoltaic systems different from other solar energy technologies?
A: The main types of solar energy technologies are:

  • PV systems, which use PV cells made of semiconducting materials to turn sunlight into electricity.
  • Solar water heating systems, which use solar collectors that face the sun to either heat water or heat a “working fluid” that is then used to heat water.
  • Concentrating solar power systems (CSP systems), which use reflective devices such as mirror panels or lenses to generate heat that is then used to generate electricity.
  • Transpired solar collectors (also known as “solar walls”), which use solar power to preheat air that is used in a building ventilation system.

Q: Can I use photovoltaics (PV) to power my house?
A: Yes. Depending on the PV panels you choose, the size of your home, how your roof and panels are positioned, and how much sunlight is available in your area, the electricity created by a PV system could be used to power your entire house (including appliances, cooling systems and lights).

Typically, PV modules are mounted onto south-facing roofs or walls (to give them the best access to sunlight). And for those who are concerned about the look of their homes, solar shingles (which are PV cells designed to look like roof shingles) are also available.

Q: Can I use a solar energy system to power my business building?
A: Yes. Depending on the photovoltaic panels you choose, the size of your business building, how much sunlight is available, and how your roof and PV panels are positioned, a solar energy system could be used to power commercial property. Not only are PV panels already used outdoors to power street signs, security lighting, and bus shelters, PV systems are easily concealed and can be blended into nearly any commercial structure.

Q: How much sunlight do you need for a PV system?
A: How much sunlight a PV system needs primarily depends on how much electricity it needs to generate. Obviously, an energy-efficient home needs a solar energy system with fewer photovoltaic panels than a house that consumes more energy. Fortunately, because PV systems work anytime the sun is shining, direct sunlight isn’t actually needed for a photovoltaic panel to generate electricity. In fact, even PV modules in shaded areas can produce electricity (although they do not generate nearly as much electricity as PV cells exposed to direct sunlight), and some PV panels even work better in colder weather.

Q: How big should my solar energy system be?
A: How big your solar electricity system needs to be depends on many factors. For instance:

  • How much power do you need to generate?
  • How much roof space do you have on which to mount your PV panels?
  • How much space heat and hot water do you use?
  • How much money do you want to invest in a new PV system?
  • How much direct sunlight will your solar electricity system get?

All of these factors and more can affect how big your photovoltaic system needs to be.

Q: How much does a PV system cost?
A: How much a solar energy system costs depends on how it is designed, and how it is designed depends on a number of factors. Because the size and type of photovoltaic system needed for any structure depends on specifics related to that structure (for instance, how much energy is needed, how much sunlight is available, how much PV panel space is available, and more), there is no one answer for this question.

To get an idea of how much a solar electricity system may cost for you, consult a professional installer. You can also consult a sustainable construction company for insights on how building design can be used to maximize space for solar panels, for capturing passive solar energy, and for integrating other energy-efficient design choices into your home.

Q: What is net metering?
A: Net metering (also known as “net energy billing”) is a solar energy system policy that allows private electricity producers to essentially sell their surplus solar electricity to a utility company.

For solar system users to benefit from net metering, their solar systems must be connected to a public-utility power grid. This way, any surplus electricity that their solar system produces is then fed into the grid, where other customers can use it.

Whether solar system users can use net metering to further offset their utility bills depends on the net metering laws of the municipalities in which they live. Because net metering laws change, it is best to contact your local utility company to find out if net metering is available in your area.

Q: How much will a solar energy system help me save on my utility bills?
A: This largely depends on how much energy your building needs, how much you pay for utilities already, how efficient your PV system is, and how much your utility company will pay you for any surplus energy that your solar system generates (which is known as “net metering”).

Q: Should I buy a photovoltaic system?
A: Like most purchasing decisions, whether or not to buy a PV system is a personal decision. Typically, those who buy solar electricity systems are motivated by a desire to use sustainable, renewable resources, and to reduce their reliance on fossil fuels. Because PV systems do not create air or noise pollution, solar panel systems are also typically bought by those who want to reduce their impact on the environment.

Investing in a photovoltaic system may be right for you if you want to:

  • Reduce your carbon footprint.
  • Reduce your reliance on a utility company.
  • Protect yourself from potential price hikes in the cost of electricity.
  • Use an environmentally-friendly energy source.
  • Have a sustainable emergency power source should there be a utility power outage in your area.

Q: Can I install and maintain a solar electric system myself?
A: Unless you are a PV installer or solar electricity equipment provider, you probably shouldn’t try to install your PV system yourself. Although solar energy systems are practically maintenance-free, they are fairly sophisticated, and their efficiency and life expectancy can be significantly impacted by whether or not they are properly designed and installed.

In addition, whenever electricity is involved, there is the potential for injury, and this is particularly true with PV system installation. Because solar electricity systems use high-voltage direct current (DC) wire, there is a real risk for fatal injury due to electrocution.

Q: How do I find someone who designs, installs and maintains PV systems?
A: One of the easiest ways to find someone who works with PV systems would be to go online and try searching for “green home construction” or for a “progressive home builder” in your area. If you would like to learn more about green building and progressive home design, you can also call P.E.A. Builders at 262-506-96916 or visit www.peabuilders.com.

When you find a PV installation company that you think you want to work with, be sure you discuss your power needs, sunlight availability, roof space and other key factors that will impact the effectiveness of your solar energy system. You will also want to discuss pricing and their level of experience installing solar panels and PV systems.

Solar Thermal Systems

Q: How does a solar thermal system with solar water heaters work?
A: A solar thermal system may be an active solar water-heating system or a passive one. In active solar water-heating systems, pumps are used to circulate household water, and a heat exchanger may or may not be used. In passive solar water-heating systems, natural convection or household water pressure is used to circulate water that has been heated in a solar collector that faces the sun. In either case, most thermal systems work together with conventional electric or gas water-heating systems, and all use some sort of storage tank or solar collector.

At P.E.A Builders, we often use flat plate solar collectors. You may also use evacuated tube solar collectors. Typically, four or five flat-plate collectors will provide enough hot water for a family of four. While evacuated tube collectors may cost twice as much per square foot as flat plate collectors, they can still operate at temperatures as low as -40°F.

Q: Can a solar water heater replace a gas or electric water heater?
A: No, not completely. Typically, a conventional electric or gas water heating system is still needed even when a solar water heating system is in place. However, this is generally only to provide hot water when the sun has not shined for several days. So, while both systems are still needed, a solar water heating system can often provide up to 80% of a home’s hot water annually.

Q: Can I heat my swimming pool with solar panels?
A: Yes, absolutely. In fact, using a solar heating system to heat a swimming pool is fairly common. This may be because solar pool-heating systems can increase an unheated pool’s temperature by 10°F or more, and using solar swimming pool heaters can extend the swimming season by two to three months. One of our preferred types of solar collectors, the flat plate solar collector, is typically used for solar pool heating.

Q: Are there benefits to using solar energy to heat water in the home?
A: Yes, absolutely. First, when you use solar energy to heat water for your home, your fuel is free, so there are no monthly utility bills for costs associated with heating your water. Secondly, solar water heaters are a non-polluting and infinitely renewable source of hot water. Unlike water heaters that rely on fossil fuels, solar water-heating systems do not rely on ever-diminishing resources or add any dangerous chemicals to the environment (such as carbon dioxide, sulfur dioxide, or nitrogen oxides).

Q: How much does a home solar heating system cost?
A: How much a solar heating system will cost depends on many factors, including the size of solar thermal system needed, the type of solar heating system used, installation costs, and more. If solar rebates are available in your area, you may be able to use them to reduce the total cost for installing a solar heating system in your home. You will also want to consider the fuel costs associated with whatever gas or electric water heater system you use to back up your solar thermal system.

Q: How much money can I save with a solar heating system?
A: How much money you can save by having a solar heating system installed in your home depends on several factors, including how much you already pay to heat your water, how much hot water you use, how often you need to use your conventional, backup system, and more.

Passive Solar Energy

Q: What is passive solar energy?
A: Passive solar energy is an environmentally-friendly home design technique that uses architectural design to help capture heat from the sun and use it to meet a building’s energy needs.

Q: How does passive solar design work?
A: Passive solar heating designs use window placement, landscaping elements, and other architectural design elements to passively trap and store thermal energy from the sun. Typically, passive solar energy designs use windows to amplify solar energy and floors, walls, and roofs made of heat-absorbing materials to collect it.

Q: What are the parts of a passive solar design?
A: According to the U.S. Department of Energy, a successful passive solar home design will include the following elements:
South-facing windows. Typically, windows that collect solar energy should face within 15 degrees of true south. They should also be shade-free during the heating season from at least 9 a.m. to 3 p.m. every day. (During the summer, spring and fall, however, the windows should be shaded. This is to avoid overheating during warmer times of year.)
Thermal mass. Thermal mass is any material in passive solar home design that is used to absorb heat from the sun. Commonly used thermal mass materials such as concrete, brick, stone, and tile are popular because they also provide structural and/or finish material. Darker color thermal mass materials tend to absorb more heat than lighter colors, and are commonly used in passive solar energy architecture.
Distribution mechanisms. Distribution mechanisms are those mechanisms used to transfer solar heat from where it is collected (the windows) and stored (the thermal mass) to different areas of the structure or house. Passive solar design distribution mechanisms may include fans, sun-heated floors, and sunspaces.
Control strategies. Control strategies are used to provide shade and prevent overheating during warm periods. Common passive solar design control strategies include roof overhangs, electronic control devices, differential thermostats, shutters, blinds, and awnings.

Q: What is direct solar gain design? How does it differ from indirect solar gain design?
A: Direct solar gain design and indirect solar gain design are two different passive solar design strategies for passively capturing and storing solar energy.

  • In a direct solar gain design, solar energy directly enters the living space through a window (as sunlight) and strikes a thermal mass (such as a tile floor or concrete wall) that absorbs and stores the heat. In this way, the living space itself acts as a solar collector.
  • In an indirect solar gain design, the heat-absorbing thermal mass is situated between the sun and the living space, and the absorbed solar energy is transferred to the living space by conduction.

Q: What is isolated gain design?
A: Isolated gain design is a passive solar energy design strategy that uses isolated spaces called sunspaces (also called sunrooms, solar rooms, or solariums) to collect and store solar energy. The sunspace is attached to the living space, but can be closed off with doors, windows, and other adjustable openings so that captured heat can be transferred when desired.

Q: What are the benefits of using passive solar design for my home?
A: There are many benefits to living in a home that has been designed to use passive solar energy. Not only are passive homes exceptionally energy-efficient, they can often keep a comfortable interior climate without using an active heating or cooling system. Passive solar homes also leave a carbon footprint that is much, much smaller than less efficiently designed structures, and can result in dramatic annual energy savings.

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