Solar energy is energy that is converted fairly directly from sunlight to whatever form we use it in. Sunlight can heat air and water, and it can be used to generate electricity. For basic information on solar energy, you can visit the U.S. Department of Energy.
Photovoltaic (PV) cells, also called solar cells, convert light directly to electricity. PV systems are modular in nature, and solar energy is more evenly distributed around the world than any other renewable energy resource. For these reasons PV is practical on a much smaller scale and possible in many more locations than any other renewable energy resource. PV cells are usually wafers of silicon, or thin films deposited on glass, metal, or plastic.
Here are some web sites where you can learn more about photovoltaics:
The following are some of the technical issues that affect photovoltaic systems.
Solar Cells — Solar cells, or photovoltaic cells, are semiconductor electronic devices that convert light into electric power. They work somewhat like a battery, except that in a battery the energy comes from a chemical reaction, while in a solar cell it comes from the light that is hitting the cell.
For more information on how solar cells work:
Solar Panels — Solar panels are groups of solar cells that are wired together and mounted on a supporting surface. Most panels sandwich the cells between protective layers, and are also sealed around the edges. Some panels have metal frames around the edges.
The efficiency of a solar panel is the ratio of the electric power it produces to the light power that hits it. Solar panels are available in a wide variety of sizes and efficiencies.
For more information on solar panels:
Installation Issues — A good site for a photovoltaic system should have no surrounding structures or trees that can cast a shadow on the solar panels. In the northern hemisphere it should be either flat or facing approximately south. Supports can be built on a flat roof so that the panels face south. When the panels face the sun on a clear day, a typical system will produce about 100 watts for each square meter of panels, or about 10 watts for each square foot. For more information, consult a photovoltaic system installer.
To calculate the expected performance of a photovoltaic system connected to the electric grid, use the PVWATTS program. You can also get a list of photovoltaic installers who are participating in SDF’s PV program.
Inverters — Inverters convert the DC electricity that is produced by solar panels into AC electricity, which is used by the electric utility grid and most household appliances. Many types and sizes of inverters are available.
Some inverters are intended for solar energy systems that are connected to a large electric utility grid. Others are intended for solar energy systems that are not connected to the grid, and also control the batteries that are used at night or in bad weather.
Interconnection Issues — Connecting a photovoltaic system to the electric utility grid requires following laws and standards on the design of the system and the equipment. It also requires careful coordination with the electric utility company, which owns the grid. To find out more, discuss the issue with a qualified photovoltaic system installer in your area.
A typical photovoltaic system costs $8 to $12 per peak watt. The system continues operate with little maintenance for about 20 years, generating electricity whenever the sun is shining on it. Solar electricity is very competitive today for small-scale off-grid electricity, such as houses in remote areas.
To estimate electricity you can generate with a specific sized photovoltaic system, and the value of this electricity at the rate you are paying, go to www.nrel.gov/ncpv.
Learn more about SDF’s Solar PV Grant Program.
To find out about financial incentives for renewable energy in various states, visit the Database of State Incentives for Renewable Energy. In the mid-Atlantic states, special energy loans for installing a solar energy system are available from the AFC First Financial Corp.
Sunlight is used in many parts of the world to heat water for homes, offices, and swimming pools. Solar water heating is cost effective in the Philadelphia area and many other parts of the country when offsetting a more expensive water heating fuel such as electricity. A variety of systems are available for installation.
Solar thermal collectors capture the sun's heat for heating water. Here is some more information on technical issues related to designing and installing a solar water heating system.
Design Strategies for Homes.
Design Strategies for Swimming Pools.
Design Strategies for Commercial Buildings.
Solar water heating is most cost effective when offsetting an expensive energy source such as electric water heat. In southeastern Pennsylvania it is now cost effective to replace an electric water heater with a solar water heater. Solar water heaters, if properly maintained, can be expected to last for 20 years or more.
The installed cost of a solar water heating system will vary depending on the type of system and its size. A typical drain back system or a propylene glycol system will run from $3,500 to $5,000 installed. For more information visit these sites:
Other Good Solar Water Heating Sites:
Almost since the dawn of human civilization, we have used the sun's energy to make our homes warmer and brighter. Today we use both active and passive solar energy systems to maximize the use of the sun's energy for heating, cooling and daylighting. By using solar energy, we can make our homes more comfortable and healthier, while saving money and improving our environment.
Active systems are characterized by the presence of solar collector panels, most commonly located on the roof of a building, although other locations are possible. An active system requires mechanical devices such as pumps or fans to transport solar-heated air or liquid to its point of use or to storage.
Passive systems have no solar panels but rather rely on design or construction materials to collect or shed the sun's heat. Passive systems have few, if any, mechanical devices and depend primarily on natural processes such as radiation, convection, or conduction to transport the collected heat. Passive systems use windows, doorways, greenhouses, or skylights as solar collectors. Good passive solar architecture can reduce the energy consumption of a building by 50% or more without adding any cost to the construction.
The following websites provide information on solar space heating:
For information on technical issues related to designing and installing solar space heating systems, visit the following websites.
Learn more about economic issues related to designing and installing solar space heating systems.
To learn more about how sunlight can be used for daytime lighting, visit the US Department of Energy.