4.+HARVESTING+THE+SUN

=CHAPTER 3= =Electricity from the sun=

__Electricity from The Sun __ __Making power from Sunlight __ -Electricity can be produced from sunlight in two main ways; by producing heat that powers an electricity generator or by converting sunlight directly to electricity using solar cells. -The first approach, concentrated solar thermal (CST), uses sunlight to heat liquids that are used to power electricity generators.  *Requires using mirrors to concentrate sunlight. -There are several ways to do this. Some CST plants use curved mirrors (parabolic trough mirrors) that track the movement of the sun across the sky and focus sunlight on a pipe, heating water or other liquid. Other designs use longs rows of nearly flat, rotating mirrors to accomplish basically the same result with lower-cost materials. -CST plants are large, utility-scale installations that require substantial capital investments.  -They use steel, glass, and concrete- and they do not require any precious or rare materials- they are usually not vulnerable to strategic bottlenecks in the supply of materials needed to scale up their size. As a result, CST plants could be used immediately to provide larger amounts of electricity. -These plants are connected to the existing transmission and distribution grids. However, this technology is most efficient in areas with the most direct sunlight, and the desert areas that qualify are far away from the population centres where most of the electricity is needed. As a result, full utilization of this potential will require the building of new high-technology transmission lines that connect to a smart grid distribution.

How Concentrated Solar Thermal Power Works -At CST plants, solar energy is concentrated by mirrors, which focus the sun’s rays on a pipe filled with synthetic oil called Therminol or water, heating it to several hundred degrees Fahrenheit. Photovoltaic Power The second way to produce electricity light is by using solar cells  -This is made of materials with special properties to convert the energy of photons in the sunlight directly into electricity.  -No stream turbines are involved. These photovoltaic (PV) cells semiconductor devices like transistors. <span style="font-family: 'Arial Rounded MT Bold','sans-serif';">They are more efficient as well as possibly cost advantages over electricity generated by fossil fuels. <span style="font-family: 'Arial Rounded MT Bold','sans-serif';">How does it work? <span style="font-family: 'Arial Rounded MT Bold','sans-serif';">They PV cells make electricity directly without a turbine. When sunlight hits the panel, usually made of semiconducting silicon, the photons in the sunlight free electrons from the atoms in the PV material, so they flow out of the cell as electrical current. <span style="font-family: 'Arial Rounded MT Bold','sans-serif';">An inverter is needed to convert the direct current into the alternating current we use in our homes.

<span style="font-family: 'Arial Rounded MT Bold','sans-serif';">Space-Based Solar Power <span style="font-family: 'Arial Rounded MT Bold','sans-serif';">-There is a proposal for space based solar energy that has been debated for decades. <span style="font-family: 'Arial Rounded MT Bold','sans-serif';">-In space, there is no intermittency problem, and therefore solar energy is stronger. <span style="font-family: 'Arial Rounded MT Bold','sans-serif';">-Sunlight that hits rooftop solar panels in North America, carries around 125-375 watts per square meter, delivering about one kilowatt-hour of electricity a day. <span style="font-family: 'arial rounded mt bold','sans-serif';"> -In theory it is possible to put into orbit a large array of photovoltaic cells about 22,300 miles above the earth where solar radiation is more than 8 times stronger. <span style="font-family: 'arial rounded mt bold','sans-serif';"> -Scientists propose placing several satellites. A single photovoltaic array in space could collect six to eight times the daily power collection as one on Earth, and the orbit would be able to support thousands of arrays.

<span style="font-family: 'Arial Rounded MT Bold','sans-serif';">The Intermittency Problem <span style="font-family: 'Arial Rounded MT Bold','sans-serif';">-Unlike fossil fuel or nuclear plants, solar electric plants can produce a constant electrical current only when the sun is shining. <span style="font-family: 'arial rounded mt bold','sans-serif';"> -Even though the fuel-sunlight-is free, there is no sun at night, and passing clouds during the day affect the flows of solar electricity. <span style="font-family: 'Arial Rounded MT Bold','sans-serif';">-The intermittency problem requires utilities to think differently about the role played by solar electricity. <span style="font-family: 'Arial Rounded MT Bold','sans-serif';">-One advantage of solar electric plants it the energy generated is at the peak when the sun is hottest. <span style="font-family: 'Arial Rounded MT Bold','sans-serif';">-PV cells do not generate heat in the production of electricity, they cannot use thermal storage. Most photovoltaic plants have gas-fired generators on stand—by in order to solve their intermittency problem. <span style="font-family: 'Arial Rounded MT Bold','sans-serif';">-Another partial solution is the completion of unified notional smart grid as when it is spread out over a large geographic area, the intermittency challenges in one location will usually be offset by the availability of sunlight elsewhere. <span style="font-family: 'Arial Rounded MT Bold','sans-serif';">The Future of Solar Power <span style="font-family: 'Arial Rounded MT Bold','sans-serif';">-Today all forms of solar electricity are still priced higher than electricity from the burning of coal or gas, largely because of the enormous costs associated with greenhouse gas pollution or excluded from calculations of the true value of electricity from those latter sources. <span style="font-family: 'Arial Rounded MT Bold','sans-serif';">-Whenever oil prices reach a peak, there is a surge of public support for alternative sources of energy. But when oil prices come back down again, that support has tended to dissipate fairly quickly. <span style="font-family: 'Arial Rounded MT Bold','sans-serif';">Solar Resources in the United States <span style="font-family: 'Arial Rounded MT Bold','sans-serif';">-The available solar energy resources varies from region to region <span style="font-family: 'arial rounded mt bold','sans-serif';"> -the hot desert regions have the potential for solar power, and that is where most utility-scale installations have been built.

<span style="font-family: 'Arial Rounded MT Bold','sans-serif';">Once the world chooses to set ambitious goals forscaling up solar-electricity development,and commits to the investments necessary to further improve technologies involved, there is no question that solar energy will provide a mojor percentage of the world’s electricity.