Energies solar

Solar energy can also be directly converted into electrical energy by photovoltaic and photogalvanic cells or transformed into gaseous fuels such as hydrogen by the photoelectrolysis or photocatalytic (solar) decomposition of water. 

The Sun consists of about 80% hydrogen, 20% helium, and about 1% carbon, nitrogen, and oxygen. The fusion of hydrogen into helium, which accounts for the energy liberated, can occur several ways. Two probable mechanisms are  

Both reactions occur, though the Bethe mechanism requires a higher temperature and therefore predominates in the central regions of large stars. 

The solar constant is 2.0 cal/cm min or 1,370 W/m above the Earth s atmosphere and about 1.1 kW/m normal to the Sun s beam at the equator. At other latitudes, this value is reduced due to the filtering effect of the longer atmospheric path. 

Ideal sites for solar energy collection are desert areas such as one in northern Chile which has low rainfall (1 mm/year) and 364 days/year of bright sunshine. The Chile site (160 x 450 km ) receives about 5 X 10 kJ/year (1 kJ/m /h x 60 min/h x 8 h/day x 365 day/year x 72,000 km x 10 m /km ). This is about a third of the world s use of energy in 1995. Thus, theoretically, the desert areas or nonarid lands could be used to supply the world with all its energy requirements, and there is no doubt that before the next century has passed solar energy will probably dominate a large portion of the world s energy sources. 

The use of wind as a renewable energy source involves the conversion of power contained in moving air masses to rotating shaft power. These air masses represent the complex circulation of winds near the surface of Earth caused by Earth s rotation and by convective heating from the sun. The actual conversion process utilizes basic aerodynamic forces, ie, lift or drag, to produce a net positive torque on a rotating shaft, resulting in the production of mechanical power, which can then be used directly or converted to electrical power. 

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 

On the positive side, the three-dimensional nature of the resource provides it with a distinct advantage compared to other solar technologies. Specifically, because siting usually involves placing the individual turbines as high as possible, typically spacing turbines about 2 to 3 blade diameters apart crosswind and 10 diameters apart downwind, only a small fraction of a wind farm area is actually occupied. The rest of the land remains available for other appHcations, such as crop production or Hvestock grazing. 

Achievement of development goals is expected to lead to cost reductions such that cost-effective machines at a good site should produce electricity at - 0.05/kWh. 

Our planet receives as much solar energy in 30-40 minutes as humankind uses in a year. Solar energy is the most abundant energy source on the planet. It is already being used as the energy source of space vehicles and space stations. (The energy source on the International Space Station is an acre-size solar collector receiving an insolation of 1.37 kW/m2.) The capacity of a collector is expressed in terms of its peak power production (wp).  

The global total of installed solar collector capacity today (2008) is about 60 GW and according to Emerging Energy Research and the Prometheus Institute, it will reach about 300 GW by 2020. As to their size and design distribution, the small (10-100 kW) photovoltaic (PV) units will total 170 gW, the medium-sized (1-10 mW) concentrating PV (CPV) units about 6 gW, the 

This is the amount of electric power that a PV module is able to generate when it receives 1,000 W/m2 of solar irradiation at 25°C. Therefore, the actual rate of power generation can be much less when the insolation is low, such as at night. 

Post-Oil Energy Technology After the Age of Fossil Fuels 

Another application of converting light to electricity is photovoltaic cells. This will be discnssed in Section 9.4.1.2 on solar energy applications. 

4 RENEWABLE SOURCES OF ENERGY IN THE 21st CENTURY AND BEYOND 

In order to reduce reliance on fossil fuels, new technologies that take advantage of renewable sources of energy are needed. Several clean sources of electricity, such as solar, wind, and geothermal, may be appropriate depending on the application. Hydropower represents a traditional renewable energy source. These renewable sources are described in this section. 

CURRENT AND FUTURE STATE OF ENERGY PRODUCTION AND CONSUMPTION 

The sun is categorized as a renewable source of energy since it has emitted radiation for billions of years, independent of how much of this energy humans have used and are currently using. There are many ways to use solar energy either in the form of heat (solar-thermal energy) or in the form of electricity (solar-photovoltaic energy). 

The Sun provides warmth. This is essential for all organisms most of which can survive only within a narrow temperature range. At high temperature (above 40°C), the biomolecules start to break down, at low temperatures (near 0°) the chemical reactions for metabolism occur too slowly. The organisms stop to grow and reproduce. Two important factors help to moderate and maintain temperatures on Earth the earth s atmosphere and the oceans. 

At the top of our atmosphere 1.372 kW/m (i w = 1 J/s) solar energy is received. More than half of the incoming sunlight may be reflected or absorbed by clouds, dust and gases. Short wavelength radiation is Altered out (e.g. UV by ozone) and cannot reach the surface. 

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A. J. Nozik, in Photovoltaic and Photoelectrochemical Solar Energy Conversion, F. Cardon, W. P. Gomes, and W. Dekeyser, eds.. Plenum, New York, 1981. 

There is a large volume of contemporary literature dealing with the structure and chemical properties of species adsorbed at the solid-solution interface, making use of various spectroscopic and laser excitation techniques. Much of it is phenomenologically oriented and does not contribute in any clear way to the surface chemistry of the system included are many studies aimed at the eventual achievement of solar energy conversion. What follows here is a summary of a small fraction of this literature, consisting of references which are representative and which also yield some specific information about the adsorbed state. 

Much use has been made of micellar systems in the study of photophysical processes, such as in excited-state quenching by energy transfer or electron transfer (see Refs. 214-218 for examples). In the latter case, ions are involved, and their selective exclusion from the Stem and electrical double layer of charged micelles (see Ref. 219) can have dramatic effects, and ones of potential imfKntance in solar energy conversion systems. 

Pleskov Y V 1994 Semioonduotor photoeleotroohemistry for a oleaner environment utilisation of solar energy Environmental Oriented Eleotroohemistry (Studies in Environmental Soienoe 59) ed C A C Sequeira (Amsterdam Elsevier)... 

Hydrogenated amorphous silicon has shown promise in producing economical cells for converting solar energy into electricity. 

The capture of solar energy as fixed carbon in biomass via photosynthesis is the initial step in the growth of biomass. It is depicted by the equation... 

X 10 Btu/short ton), the solar energy trapped in 17.9 x 10 t of biomass, or about 8 x 10 t of biomass carbon, would be equivalent to the world s fossil fuel consumption in 1990 of 286 x 10 J. It is estimated that 77 x 10 t of carbon, or 171 x 10 t of biomass equivalent, most of it wild and not controlled, is fixed on the earth each year. Biomass should therefore be considered as a raw material for conversion to large suppHes of renewable substitute fossil fuels. Under controlled conditions dedicated biomass crops could be grown specifically for energy appHcations. 

The maximum efficiency with which photosynthesis can occur has been estimated by several methods. The upper limit has been projected to range from about 8 to 15%, depending on the assumptions made ie, the maximum amount of solar energy trapped as chemical energy in the biomass is 8 to 15% of the energy of the incident solar radiation. The rationale in support of this efficiency limitation helps to point out some aspects of biomass production as they relate to energy appHcations. 

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