Solar Energy: Understanding Renewable Energy Sources and Consumption, Slides of Energy and Environment

Download Solar Energy: Understanding Renewable Energy Sources and Consumption and more Slides Energy and Environment in PDF only on Docsity! Solar Energy Introduction to renewable energy Energy from the sun 2xQ Docsity.com Renewable Energy Consumption  Energy Source QBtu / % (1994) QBtu / % (2003) QBtu / % (2011) Hydroelectric 3.037 / 3.43 2.779 / 2.83 3.171 / 3.26 Geothermal 0.357 / 0.40 0.314 / 0.32 0.226 / 0.23 Biomass 2.852 / 3.22 2.884 / 2.94 4.511 / 4.64 Solar Energy 0.069 / 0.077 0.063 / 0.06 0.158 / 0.16 Wind 0.036 / 0.040 0.108 / 0.11 1.168 / 1.20 Total 6.351 /7.18 6.15 / 6.3 9.135 / 9.39 much room for improvement/growth, but went backwards from 1994 to 2003! Docsity.com Input flux (average properties) Solar radiation incident on atmosphere 100% Up-scatter RT from clouds Up-scatter 25% , from atmosphere | Atmospheric 9% I absorption Absorption yY % Down-scatter | 10% \rer atmosphere Direct solar 6% 24% Diffuse down-scatter from clouds 17% Ground 7) 7 tevel Figure 4.2. Absorption and scattering of solar radiation in the atmosphere. The values shown are for average weather, and are averaged over all seasons and latitudes. Docsity.com Making sense of the data  • We can infer a number of things from the  previous figure:  – 52% of the incoming light hits clouds, 48% does not  • 25% + 10% + 17%  – in cloudless conditions, half (24/48) is direct, 63%  (30/48) reaches the ground  – in cloudy conditions, 17/52 = 33% reaches the ground:  about half of the light of a cloudless day  – averaging all conditions, about half of the sunlight  incident on the earth reaches the ground  – the above analysis is simplified: assumes atmospheric  scattering/absorption is not relevant when cloudy  2Q Docsity.com A naturally balanced budget EARTH'S ENERGY BUDGET Reflected by Reflected Reflected from - atmosphere by clouds earth's surface 6% 20% 4% Radiated to space from clouds and atm osphere Absorbed by atmosphere 16% Radiat ed directly to space from earth ® Docsity.com Average Insolation  • The amount of light received by a horizontal surface (in W/m2)  averaged over the year (day & night) is called the insolation  • We can make a guess based on the facts that on average:  – half the incident light reaches the ground  – half the time it is day  – the sun isn’t always overhead, so that the effective area of a horizontal  surface is half it’s actual area  • half the sphere (2R2) projects into just R2 for the sun  • twice as much area as the sun “sees”  • So 1/8 of the incident sunlight is typically available at the  ground  – 171 W/m2 on average  Docsity.com Insolation variation  • While the average insolation is 171 W/m2,  variations in cloud cover and latitude can  produce a large variation in this number  – A spot in the Sahara (always sunny, near the  equator) may have 270 W/m2 on average  – Alaska, often covered in clouds and at high  latitude may get only 75 W/m2 on average  – Is it any wonder that one is cold while one is hot?  Q Docsity.com Average daily radiation received  divide by 24 hr to get average kW/m2 ranges in W/m2: < 138 138–162 162–185 185–208 208–231 > 231 Docsity.com Which is best?  • To tilt, or not to tilt?  • If the materials for solar panels were cheap,  then it would make little difference (on flat  land)  • If you have a limited number of panels (rather  than limited flat space) then tilting is better  • If you have a slope (hillside or roof), then you  have a built‐in gain  • Best solution of all (though complex) is to  steer and track the sun Docsity.com Orientation Comparison Steered collector pointed at sun 1000 7Sianted ~~ ‘ Z stationary \ = surface 500 " Horizontal surface 0 | BAM. 12 noon 4PM. Time Figure 4.4 Solar power incident on three types of collectors for a typical winter day at 40° N latitude. The energy collected each day is given by the area under each curve. Docsity.com Numerical Comparison: winter at  40º latitude  Date Perpendicular (steered, W/m2) Horizontal (W/m2) Vertical S (W/m2) 60º South (W/m2) Oct 21 322 177 217 272 Nov 21 280 124 222 251 Dec 21 260 103 216 236 Jan 21 287 125 227 256 Feb 21 347 186 227 286 Mar 21 383 243 195 286 overall winner better in summer good in winter 2nd place based on clear, sunny days Docsity.com Making sense of these big numbers  • How much area is this per person?  – U.S. is 9.361012 m2  – 1/75th of this is 1.251011 m2  – 300 million people in the U.S.  – 416 m2 per person  4,500 square feet  – this is a square 20.4 meters (67 ft) on a side  – one football field serves only about 10 people!  – much larger than a typical person’s house area  • rooftops can’t be the whole answer, especially in cities  Q Docsity.com Ways of using solar energy Direct heating of flat panel (fluids, space heating) Passive heating of well-designed buildings Thermal power generation (heat engine) via concentration of sunlight Direct conversion to electrical energy Docsity.com My Plans for Your Brain  real world stuff stuff you learn in school this is your brain… stuff you learn in school real world stuff phys 12 …this is your brain after physics 12 Docsity.com