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Unformatted text preview: Page 1 of 11 MT 518 Solar Energy – Theory and Application Mid–Term Test Solutions (10 points) 1. Explain the advantages and limitations of solar energy. List five (5) different factors in each category to support your argument. Advantages: • Renewable • Plentiful • No lethal radiation • Not centralized • Non pollutant Disadvantages: • Ignorance of the American public about what solar energy is able to do. • If people want solar equipment they do not know where to find it. • Most buildings that use solar energy for space heating have been custom built at a relatively high cost. • Financing the initial cost is particularly difficult when building costs are high, and when mortgage money is difficult to obtain. • Shortage of contractors and architectural engineering designers who are equipped to handle the present complexity of solar energy designs. Page 2 of 11 (10 points) 2. Calculate the declination, the zenith angle, and the azimuth angle of the sun for New York City (Lat. 40.8ºN) on October 1 at 2:00 pm solar time. Solar Declination, δ S : δ S = 23.45 ⁰ sin[360(284+n)/365] ( ⁰ Ref. Slide #3.3) n = 274 (October 1) Therefore, δ S = 23.45 ⁰ sin[360(284+274)/365] ⁰ δ S =  4.22º Zenith Angle, z : Solar Time = 14.00 hours (2:00 pm) Solar Hour Angle, h s = 15º x Hours from local solar noon = 15(14 – 12) = 30º sin α = sin L sin δ s + cos L cos δ s cos h s (Ref. Slide #3.22) = (sin 40.8º)(sin 4.22º) + (cos 40.8º)(cos 4.22º)(cos 30º) = 0.606 α = 37.3º z = 90º – α = 90º – 37.3º (Ref. Slide #3.20) z = 52.7º Azimuth Angle, α s : sin α s = cos δ s sin h s / cos α (Ref. Slide #3.22) sin α s = (cos 4.22º)( sin 30º) / cos 37.3º = 0.627 α s = 38.8 º Page 3 of 11 (20 points) 3. Two rows of flat plate collectors are mounted on a flat roof at a 40º angle with the horizontal (see sketch) and are facing true south. What should the minimum distance “D” between collectors be such that they do not shade each other on the shortest day of the year when shadows are longest, December 21, between 10:00 am and 2:00 pm solar time. The installation is at 40ºN Lat.at 40ºN Lat....
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 Spring '11
 Cohn
 Thermodynamics, Heat, rock bed

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