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| Solar Technologies |
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Faq's |
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| 1. |
What is renewable energy? |
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The United States currently relies heavily on coal, oil, and natural gas for its energy. Fossil fuels are nonrenewable, that is, they draw on finite resources that will eventually dwindle, becoming too expensive or too environmentally damaging to retrieve. In contrast, renewable energy resources – such as wind and solar energy – are constantly replenished and will never run out. |
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| 2. |
Why is energy efficiency important? |
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Energy efficiency means using less energy to accomplish the same task. By improving your energy efficiency, you reduce the size (and cost) of the renewable energy system needed to power your home. Improving your energy efficiency is the first and most important step toward adopting renewable energy.
The more efficient use of energy throughout our country results in less money spent on energy by homeowners, schools, government agencies, businesses, and industries. The money that would have been spent on energy can instead be spent on consumer goods, education, services, and products. For more information, see the American Council for an Energy-Efficient Economy and the Alliance to Save Energy Web sites.
An energy-efficient economy can grow without using more energy. In 1998, for instance, the U.S. gross domestic product increased 3.9%, while U.S. energy use decreased by 0.3%. |
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| 3. |
What are the benefits of renewable energy systems? |
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Renewable energy sources are clean and inexhaustible. The money spent on renewable energy installations tends to remain in the community, creating jobs and fueling local economies. The use of renewable energy equipment also reduces our dependence on foreign and/or centralized sources of energy, and is an important strategy in the process of creating a truly secure and sustainable energy future. |
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| 4. |
How does renewable energy help our economy? |
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Many U.S. communities have to import fossil fuels, such as oil and natural gas, to provide electricity, heating, and fuel. The cost of these fossil fuels can add up to billions of dollars. And every dollar spent on energy imports is a dollar that the local economy loses. Renewable energy resources, however, are developed locally. The dollars spent on energy stay at home, creating more jobs and fostering economic growth.
Renewable energy technologies are labor intensive. Jobs evolve directly from the manufacture, design, installation, servicing, and marketing of renewable energy products. Jobs even arise indirectly from businesses that supply renewable energy companies with raw materials, transportation, equipment, and professional services, such as accounting and clerical services.
In turn, the wages and salaries generated from these jobs provide additional income in the local economy. Renewable energy companies also contribute more tax revenue locally than conventional energy sources.
The economic advantages of renewable energy also extend far beyond the local economy. The whole country benefits. In 1997, the United States spent about $65 billion dollars outside the country to pay for fossil fuels. But as one of the world leading manufacturers of renewable energy systems, we can bring in more money with the increased use of renewable energy sources around the world. Currently, for example, the United States manufactures about two-thirds of the world photovoltaic (PV) systems. And it exports about 70% of these PV systems, mostly to developing nations, resulting in annual sales of more than $300 million. |
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| 5. |
How does renewable energy improve national security? |
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Our national energy security continues to be threatened by our dependency on fossil fuels. These conventional energy sources are vulnerable to political instabilities, trade disputes, embargoes, and other disruptions.
U.S domestic oil production has been declining since 1970. In 1973, the United States only imported about 34% of its oil. Today, our country imports more than 53%, and it is estimated that this could increase to 75% by 2010.
Most of the world oil reserves are now in the Middle East. We have witnessed this shift in economic influence through the last three sharp increases in the world oil prices: the Arab Oil Embargo in 1974, the Iranian Oil Embargo in 1979, and the Persian Gulf War in 1990. It has resulted in periods of negative economic growth and a rising trade deficit.
But with renewable energy, we can decrease our dependency on foreign oil imports. For example, the U.S. Department of Energy estimates that if we displace 10% of our petroleum use for transportation with biofuels, which are produced from organic material, we could save about $15 billion from 2000 to 2010. A 20% displacement could save us about $50 billion from 2010 to 2030. This would strengthen our energy security, as well as our economic and national security. |
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| 6. |
How fast is the use of solar energy growing? |
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Shell International predicts that renewable energy will supply 60% of the world energy by 2060. The World Bank estimates that the global market for solar electricity will reach $4 trillion in about 30 years. |
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| 7. |
What is Photovoltaics (PV)? |
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Photovoltaic (PV) cells convert sunlight directly into electricity. PV cells are the solar cells that are often used to power calculators and watches. PV cells are made of semiconducting materials similar to those used in computer chips. When sunlight is absorbed by these materials, the solar energy knocks electrons loose from their atoms, allowing the electrons to flow through the material to produce electricity. This process of converting light (photons) to electricity (voltage) is called the photovoltaic effect.
PV cells are typically combined into modules that hold about 40 cells; about 10 of these modules are mounted in PV arrays that can measure up to several meters on a side. These flat-plate PV arrays can be mounted at a fixed angle facing south, or they can be mounted on a tracking device that follows the sun, allowing them to capture the most sunlight over the course of a day. About 10 to 20 PV arrays can provide enough power for a household; for large electric utility or industrial applications, hundreds of arrays can be interconnected to form a single, large PV system. (VBE Note: One of our services is to determine how much PV can be installed at your site and to determine
what such a system can accomplish toward meeting your electrical needs.)
Some PV cells are designed to operate with concentrated sunlight. These cells are built into concentrating collectors that use a lens to focus the sunlight onto the cells. This approach has both advantages and disadvantages compared with flat-plate PV arrays. The main idea is to use very little of the expensive semiconducting PV material while collecting as much sunlight as possible. But because the lenses must be pointed at the sun, the use of concentrating collectors is limited to the sunniest parts of the country. Some concentrating collectors are designed to be mounted on simple tracking devices, but most require sophisticated tracking devices, which further limit their use to electric utilities, industries, and large buildings.
The performance of a PV cell is measured in terms of its efficiency at turning sunlight into electricity. Only sunlight of certain energies will work efficiently to create electricity, and much of it is reflected or absorbed by the material that make up the cell. Because of this, a typical commercial PV cell has an efficiency of 15% – about one-sixth of the sunlight striking the cell generates electricity. Low efficiencies mean that larger arrays are needed, and that means higher cost. Improving PV cell efficiencies while holding down the cost per cell is an important goal of the PV industry, NREL researchers, and other U.S. Department of Energy (DOE) laboratories, and they have made significant progress. The first PV cells, built in the 1950s, had efficiencies of less than 4%. |
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| 8. |
What is Concentrating Solar Power (CSP) and Solar Thermal Electric power? |
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There are (3) three main types of concentrating solar power (CSP) technologies: trough systems, dish/engine systems, and power towers. These technologies are used in CSP plants that use different kinds of mirror configurations to convert the sun's energy into high-temperature heat. The heat energy is then used to generate electricity in a steam generator.
CSP's relatively low cost and ability to deliver power during periods of peak demand—when and where we need it—mean that CSP can be a major contributor to the nation's future needs for distributed sources of energy.
For more information, please go to http://www.eere.energy.gov/solar/csp.html |
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| 9. |
What kind of warranty is typical with renewable energy? |
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Most solar photovoltaic systems come with at least 20 year warranties! |
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| 10. |
What is a solar rating? |
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The solar rating is a measure of the average solar energy (also called "Solar Irradiance") available at a location in an average year. Radiant power is expressed in power per unit area: usually Watts/sq.meter, or kW/sq.meter
The total daily Irradiation (Wh/sq-m) is calculated by the integration of the irradiance values (W/sq-m).
Click here for solar radiance maps of the US. |
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| 11. |
What are the types of PV systems? |
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There are basically 2 types of PV systems—stand-alone and grid-connected. Stand-alone systems operate independently of a utility grid and are normally used where no grid connection is possible, such as in remote areas, for portable highway signs, etc. Some stand-alone systems produce only DC power, but stand-alone systems can also produce AC power.
Prior to 2002, stand-alone PV systems were the most common, but since 2002, more PV generation has been attributed to grid-connected systems than to stand-alone systems. One reason for this transition is that fully-interactive, grid-connected, systems optimize the use of PV electricity. The reason for this is that when the grid is available for a fully interactive grid-connected PV system, none of the energy generated by the PV system is wasted. Any electricity generated by the PV system that is not used on site is sold back to the utility for someone else to use.
Grid-connected, but not interactive, PV systems use the utility grid as an auxiliary battery charger. This kind of system is common in areas where the grid connection is only available for a few hours each day. The grid provides additional battery charging to supplement that provided by the PV system. These system do not SELL energy to the grid. They just purchase it when it is needed and available. The system batteries store the purchased or PV energy for later use. If excess PV energy is produced, it is wasted.
Fully interactive grid-connected systems can either purchase energy from, or sell energy to, the utility grid. Any utility interactive system that is programmed to sell electricity to the grid must meet very stringent UL listing requirements. These systems must be capable of monitoring the condition of the utility grid and automatically disconnecting from the utility grid if the utility grid shuts down. There are two types of fully interactive grid-connected PV systems, as shown in Figure 1.
Figure 1a shows a utility interactive PV system without battery backup. Whenever the sun is shining and the utility grid is powered up, the electricity produced by the PV system is first used by the system owner and any leftover electricity is sold back to the utility grid. If the grid goes down, the PV system must also shut down. When this happens, the owner of the system will be without PV-generated electricity until the grid comes back on again.
Figure 1b shows a utility interactive PV system with battery backup. This system combines the best features of the stand-alone and the grid-connected systems by incorporating an emergency power output feature on the system inverter that continues providing power to selected circuits if grid power is lost. One set of terminals on the system inverter connects to the utility grid through the owner’s main circuit breaker panel. The other set of terminals connects to emergency loads. When grid power is available, this set of terminals will either send excess PV power back to the main circuit breaker panel or will use grid power to supply the emergency loads at night. If grid power is lost, this section of the inverter shuts down, but the emergency terminals of the inverter remain operational. When the sun is shining, power produced by the PV array is used for meeting the requirements of the emergency loads and for battery charging. As long as there are enough batteries, and as long as the PV system generates enough energy each day to meet the needs of the emergency loads, the emergency loads will be operable 24 hours a day while the utility grid is out. When the grid is restored, the system automatically reconnects to the grid and resumes normal operation.
Additional redundancy can be achieved with a PV system for cloudy days. If a fossil fuel generator is incorporated into the system, then the generator can be used to charge the batteries on cloudy days. The nice thing about this setup is that the generator will probably only need to run about 3 – 5 hours a day to provide any charge not provided by the sun.
Keep in mind that a fossil fuel generator CAN NEVER PAY FOR ITSELF, since it is only run when the utility is down. On the other hand, a utility interactive PV system will produce electricity every day over its lifetime, which can be expected to exceed 25 years. The PV modules in every system we install come with 25-year warranties. Depending upon the rebates or tax incentives available, the systems will pay for themselves before their lifetime is over. Furthermore, a 5000-watt PV system will eliminate the production of approximately 175 tons of carbon dioxide over a 25-year period |
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| 12, |
Why should I consider a PV system? |
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These systems are for those who desire to be energy independent, environmentally sensitive, protected against power outages (particularly from hurricanes), rapidly rising costs of electricity (Particularly due to shortages caused by increased worldwide demand, supply shortages and political pressure) and for those who are fascinated by the unlimited potential of solar energy. If you see yourself in this picture, then PV is probably for you, as long as you have unshaded, south-facing, east-facing or west-facing exposure on your property. |
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