Physics 100 Lecture 19. Solar Thermal Energy April 9, 2018

Transcription

1 1 Physics 100 Lecture 19 Solar Thermal Energy April 9, 2018

2 2 Class Quiz Ch. 8-9: Which of the following is the most important factor in understanding the carbon cycle of the Earth? A. Absorption of carbon by plants B. Absorption of carbon by the ocean C. Production of carbon by plants D. Production of carbon by polar glaciers

3 3 Class Quiz Ch. 8-9: Which of the following is the most important factor in understanding the carbon cycle of the Earth? A. Absorption of carbon by plants B. Absorption of carbon by the ocean C. Production of carbon by plants D. Production of carbon by polar glaciers See pp of the text.

4 Reminder of the hazards of carbon-based energy Citation: Physics Today 69, 11, 48 (2016); full article Each row of the diagram represents a carbon reservoir, with the amount of carbon in each reservoir in 1870 shown in the middle column in petagrams (1 Pg = g). The boxes and arrows to the left and right depict the carbon budget16 in petagrams for the period

5 5 Some good news

6 6 Alternatives to fossil fuel energy Nuclear energy No emissions, but safety and waste disposal problems Renewable energy Solar thermal Solar electric Wind Biomass Geothermal Nuclear fusion

7 7 see also Renewable energy overview

8 8 Renewable energy trends E P 2019 P Geothermal Hydropower a Solar Waste Biomass Wind Wood Biomass Doubling time: 3.24 y 7.01 y Electricity Subtotal b Biomass-based Diesel Ethanol Biofuels Subtotal Other c Total

9 9 The Solar Constant S = 1354 W / m 2 Fluctuates from 1321 (in July) to 1412 W / m 2 (in January) due to slight change in distance from Sun Seasons are due to tilt of the Earth s axis relative to orbital plane, not the variation in the solar constant Includes infrared, visible, and ultraviolet light

10 10 Insolation The amount of solar radiation that reaches the Earth s surface is called insolation (incident solar radiation) (not to be confused with insulation, a material that impedes thermal conduction) Insolation is affected by many factors

11 11 Atmospheric absorption The surface never gets more than 1050 W/m 2 (on a clear day) due to atmospheric absorption

12 12 Energy Balance for the Earth On average (including cloudy days), only 50% of solar radiation reaches the Earth s surface. Figure 6.4 page 156

13 13 A closer look 23% 60% Atmosphere: +217% 217% = 0% net Earth s surface: +48% +163% 160% = 3% net (in reality this is very close to zero, the numbers were rounded) +23% +33% +113% 29% 105% 8% +8% 33% +21% +29% +105% 119%

14 14 The tilt of the Earth s Axis Changes how much sunlight is received by a location on the Earth throughout the year

15 15 Seasonal change to insolation The Sun s angle above the horizon changes with the seasons

16 16 The sun doesn t shine all day Stevens Point gets about 1250 Btu/ft 2 /d

17 17 Map of average solar insolation < >28

18 18 Stevens Point gets about 1250 Btu/ft 2 /d of insolation. Convert this number to kwh/m 2 /d A kwh/m 2 /d B kwh/m 2 /d C kwh/m 2 /d D. 236 kwh/m 2 /d

19 19 Stevens Point gets about 1250 Btu/ft 2 /d of insolation. Convert this number to kwh/m 2 /d 3.94 m 2 d Btu 1055 J 1 kwh 3.28 ft ft 2 d 1 Btu J 1 m 2 kwh

20 20 How much water can you heat from 20ºC to 50ºC per day using a 10 m 2, 50% efficient solar collector in Stevens Point, on average? A kg B. 565 kg C. 150 kg D kg

21 21 How much water can you heat from 20ºC to 50ºC per day using a 10 m 2, 50% efficient solar collector in Stevens Point, on average? P IA kwh m d kwh d 1 kwh 7 Q J/d c T 4190 J/kg C 30 C 565 kg 2 solar m 19.7 kwh/d J J/d m about 147 gallons!

22 22 Solar Thermal Facts Water heating is the most common application for solar energy Domestic hot water (DHW) systems are being sold with a 5% annual growth (14 year doubling time) 95% of solar heaters are for swimming pools, only 5% for DHW About two-thirds of a household s DHW load can be economically met by solar EIA web site

23 23 Solar Thermal Facts Estimated 35,464 new DHW systems installed in 2010, and 29,540 pool systems Total US capacity is over 815 MW Th (megawatts thermal equivalent) Today there are an estimated 790,000 solar pool heating systems installed in the U.S., more than any other solar technology application. SEIA Solar Industry Data graphs from 2013 report

24 24 Batch water heater

25 25 Flat-plate collector US Solar Energy Year in Review 2008

26 26 Flat-plate collector US Solar Energy Year in Review 2008

27 27 Right Here at UWSP There is a solar water heating system on the roof of many residence halls and the HEC Energy production used to be tracked on the web. There is a document about performance history of the HEC system and the eventual removal of the HEC panels in July The UWSP Sustainability site has some additional information

28 28 Solar Space Heating Three components: Insulation Solar collection Thermal storage Can reduce heating costs up to 80% Not as popular due to costs. Compare 2008 installations: 139 MW Th hot water, 762 MW Th pool heating, 21 MW Th space heating US Solar Market Insight SEIA Solar Heating & Cooling

29 29 Approximately what maximum percentage of the 40,000 Btu/h home heating needs can be met by a 700 ft 2, 50% efficient collector if the insolation is 1700 Btu/ft 2 /d? A. 25% B. 35% C. 60% D. 75%

30 30 Approximately what maximum percentage of the 40,000 Btu/h home heating needs can be met by a 700 ft 2, 50% efficient collector if the insolation is 1700 Btu/ft 2 /d? Btu h Q 40, ,000 Btu/d h d Btu E ft d Esolar % Q solar ft ,000 Btu/d 2

31 31 Concrete has a density of 2400 kg/m 3 and a specific heat of 750 J/kg/ o C. What volume of concrete can store as much heat as 10 m 3 of water (42 MJ/ o C)? A m 3 B m 3 C m 3 D m 3

32 32 Concrete has a density of 2400 kg/m 3 and a specific heat of 750 J/kg/ o C. What volume of concrete can store as much heat as 10 m 3 of water (42 MJ/ o C)? A m 3 B m 3 C m 3 D m 3 Q mc T and density m V Q mc V c solve for V : T Q T V c J/ C kg/m 750 J kg C m or about 12.7 tons of concrete!

33 33 National Solar Thermal Test Facility Albuquerque, NM Can generate about 1.5 MW of electricity Used for research and development

34 34 Solar Energy Generating Systems (SEGS) Second largest solar energy facility in the world, with 354 MW installed capacity (California Mojave Desert) Aerial view showing portions of four of the five SEGS III VII plants located at Kramer Junction Entire image courtesy Wikipedia

35 35 Ivanpah Solar Electric Generating System Commissioned 2014 CA Mojave desert Currently world s largest solar thermal facility at 392 MW List of worldwide solar thermal power stations