Solar Energy

From Lauraibm

Current revision as of 09:11, 19 July 2007

MI Summary

Solar Energy

Solar energy from the sun is a source of renewable energy and is in widespread use around the world. It has many benefits, as solar electric generation has the highest power density among all the renewable energy sources. It is also pollution-free, so it doesn't harm the Earth's atmosphere and environment. Also, after the initial set-up costs, the operating costs are very low. However, solar electricity is for the consumer expensive to buy, compared to normal grid electricity.

However, it could be considered expensive compared to the normal grid electricity and the main down-side is that it is obviously unavailiable at night and in poor weather conditions. As well as the poor weather, recently there has been a concern about global dimming, an effect of pollution allowing less sunlight to reach the Earth's surface, which will result in lowering the power density that could be achieved from solar energy.

Introduction

Solar power (also known as solar energy) uses Solar Radiation emitted from our sun. Solar power, a renewable energy source, has been used in many traditional technologies for centuries, and is in widespread use where other power supplies are absent, such as in remote locations and in space.

Energy From the Sun

Solar radiation reaches the Earth's upper atmosphere at a rate of 1366 watts per square meter (W/m2). The first map shows how the solar energy varies in different latitudes.

Map of global solar energy resources. The colours show the average available solar energy on the surface (as measured from 1991 to 1993). For comparison, the dark disks represent the land area required to supply the total primary energy demand using PVs with a conversion efficiency of 8%.

While traveling through the atmosphere, 6% of the incoming solar radiation (insolation) is reflected and 16% is absorbed resulting in a peak irradiance at the equator of 1,020 W/m². Average atmospheric conditions (clouds, dust, pollutants) further reduce insolation by 20% through reflection and 3% through absorption. Atmospheric conditions not only reduce the quantity of insolation reaching the Earth's surface but also affect the quality of insolation by diffusing incoming light and altering its spectrum. The second map shows the average global irradiance calculated from satellite data collected from 1991 to 1993. For example, in North America the average insolation at ground level over an entire year (including nights and periods of cloudy weather) lies between 125 and 375 W/m² (3 to 9 kWh/m²/day). This represents the available power, and not the delivered power. At present, photovoltaic panels typically convert about 15% of incident sunlight into electricity; therefore, a solar panel in the contiguous United States on average delivers 19 to 56 W/m² or 0.45 - 1.35 kWh/m²/day.

While average insolation and power offer insight into solar power's potential on a regional scale, locally relevant conditions are of primary importance to the potential of a specific site.

After passing through the Earth's atmosphere, most of the sun's energy is in the form of visible and Infrared radiations. Plants use solar energy to create chemical energy through photosynthesis. Humans regularly use this energy burning wood or fossil fuels, or when simply eating the plants.

A recent concern is global dimming, an effect of pollution that is allowing less sunlight to reach the Earth's surface. It is intricately linked with pollution particles and global warming, and it is mostly of concern for issues of global climate change, but is also of concern to proponents of solar power because of the existing and potential future decreases in available solar energy. The order of magnitude is about 4% less solar energy available at sea level over the timeframe of 1961–90, mostly from increased reflection from clouds back into outer space.

Advantages and disadvantages of solar power

Advantages

• The 89 petawatts of sunlight reaching the earth's surface is plentiful compared to the 15 terawatts of average power consumed by humans. Additionally, solar electric generation has the highest power density (global mean of 170 W/m2) among renewable energies.
• Solar power is pollution free during use. Production end wastes and emissions are manageable using existing pollution controls. End-of-use recycling technologies are under development.
• Facilities can operate with little maintenance or intervention after initial setup.
• Solar electric generation is economically competitive where grid connection or fuel transport is difficult, costly or impossible. Examples include satellites, island communities, remote locations and ocean vessels.
• When grid-connected, solar electric generation can displace the highest cost electricity during times of peak demand (in most climatic regions), can reduce grid loading, and can eliminate the need for local battery power for use in times of darkness and high local demand; such application is encouraged by net metering. Time-of-use net metering can be highly favorable to small photovoltaic systems.
• Grid-connected solar electricity can be used locally thus minimizing transmission/distribution losses (approximately 7.2%).
• Once the initial capital cost of building a solar power plant has been spent, operating costs are low compared to existing power technologies.

Disadvantages

• Solar electricity is expensive compared to grid electricity.
• Solar heat and electricity are not available at night and may be unavailable due to weather conditions; therefore, a storage or complementary power system is required for most applications.
• Limited power density: Average daily insolation in the contiguous U.S. is 3-9 kW·h/m2 usable by 7-19.7% efficient solar panels.
• Solar cells produce DC which must be converted to AC when used in currently existing distribution grids. This incurs an energy loss of 4-12%.

Source

• Wikipedia