where Q is the average daily radiation received at the surface location, S is the number of hours of sunshine recorded at the site per day and So is the maximum possible number of hours of sunshine at the site per day (unobstructed horizon), and a and b are constants (Table 1). The average value of Qo is equal to 429 BTU/hr/ft2 multiplied by the cosine of the latitude angle.
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Motors for direct current are of one type only and have no special name or type. They are suitable for any general purpose work. The speed is usually around 1800 but the speed varies considerably more than in alternate current motors, and varies considerably with the voltage.
Source :
Richter, H. P. Wiring Simplied, Published by Park Publishing Co., Minneapolis MN, 18th Edition. (c) 1946. (Page 116)
Currently available cadmium sulfide/cuprous sulfide cells similarly degrade, but from exposure to moisture in the air. SES (a Shell subsidiary) is selling cadmium sulfide/cuprous sulfide modules hermetically sealed in glass cases. These extremely reliable devices are as expensive as silicon cells, but recently Photon Power Corporation (jointly owned by a French oil company and Libbey-Owens-Ford) announced for the third time the impending availability of CdS/Cu2S modules at a price of $5 per watt. By the time these devices are in the hands of consumers - with aluminum cases replacing the wooden ones - the price in units of one will probably be only slightly less than present silicon solar cell modules.
Source :
Davidson, Joel and Komp, Richard The Solar Electric Home : a photovoltaics how-to handbook, published by aatec publications, Ann Arbor MI. (c) 1983. (Page 11)
A solar cell is made by placing a thin layer of phosphorous-doped silicon in intimate contact with a layer of boron-doped silicon. When light falls on the cell, photons are absorbed and electrons are set free. The excess electrons accumulate in the phosphorous-doped silicon, which is called n-silicon because electrons have negative charge. If one end of a wire is attached to this top layer and the other end connected to the layer beneath, electrons will leave the upper layer, flow through the wire, and be absorbed by the boron-doped silicon, which is called p-silicon, meaning positive.
Fig. 2-5 "How a Photovoltaic Cell Works" (600 x 634 pixels) Caption
The electrons flowing through the external wire circuit can be used to light a light or turn a motor, just as electricity from any other source. Thus, the solar photovoltaic cell, using light only, generates electricity.
Source :
Maycock, Paul D. and Stirewalt, Edward N. Photovoltaics : Sunlight to Electricity in One Step, Published by Brick House Publishing Company, Andover MA. (c) 1981. (Pages 26 - 27)
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The number of hours of sunshine per day can be measured by the Campbell-Stokes sunshine recorder which uses a lens to focus direct sunshine onto a heat-sensitve paper chart. A discolored line is produced when the solar disc is focused onto the paper. The length of the discolored line divided by the total length of the chart corresponding to the time between sunrise and sunset is the percent possible sunshine for the day.
Regular measurements of sunshine duration and cloudiness are made at numerous weather stations throughout the world, and these records usually cover periods of 20 to 60 years or more. The average daily radiation is a function of sunshine duration at the particular location, and is correlated with the amount received outside the atmosphere Qo by
Q = Qo (a + b (S/So))
Table 1 Climate Constants
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Location S/So a b
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Atlanta GA 0.59 0.38 0.26
Madison WI 0.58 0.30 0.34
El Paso TX 0.84 0.54 0.20
Albuquerque NM 0.78 0.41 0.37
Table 1 from Angstrom, A. "Solar and Terrestrial Radiation," Journal of the Royal Meterological Society, Vol. 50, No. 121, (c) 1924.
Climate Constants from Lof, G.O.G., Duffie, J.A. and Smith, C.O., World Distribution of Solar Energy, in Solar Energy, Vol. 10, No. 1, pp. 27-37, (c) 1966.
NOTE : sites more remote from our location are not included in Table 1
Source :
Williams, J. Richard. Solar Energy : Technology and Applications, Published by Ann Arbor Science Publishers, Inc., Ann Arbor MI, Second Printing, 1975. (c) 1974. (Pages 5 - 6)
Caption for Figure 2-5 (Maycock/Stirewalt) :
Schematic diagram of single crystal silicon solar cell. Sunlight penetrating into the silicon frees electrons, which filter upward through the cell junction, concentrating in the n-silicon layer. From there the electrons flow through the metallic fingers into the wire, finally completing the circuit by returning through the baseplace to the p-silicon layer.
The thin crystal silicon wafers, sawn from a solid ingot, are typically 3-6 inches in diameter. This was one of the earliest commercial solar cells, widely used on space satellites since the 1950s. Silicon cells of this general type still constitute the mainstay of the commercial solar photovoltaic business, although now rectangular in shape in order to provide more compact arrays.
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