1. ENGR 101/ HUM 200: Technology & Society November 2, 2005

2. Agenda Mid-quarter feedback Exam Rescheduled for Tuesday 11/8 Project comments (Thursday class; Define “better,” clearly define target users, if interviewing or testing them, how identify or recruit them, multiple ways to prototype) International perspectives on energy consumption Renewable energy

3. International Issues Developing world energy sources –About one-third of world’s population lacks access to modern energy sources –Infrastructure is a significant expense –Centralized technologies require enormous investments and maintanance –Bioenergy (wood and other plant matter derivatives) is a cornerstone of sustainable energy strategy

4. Biomass Can contribute to deforestation Labor intensive work of collecting firewood Indoor smoke pollution Examples: –Residues and waste –Purpose-grown energy crops –Natural vegetation Agriculturally, balance out food and energy crops

5. Biomass Case Studies Ethanol from sugarcane in Brazil Sugarcane residue used for electricity generation Corn stalk processing for cooking fuel in China What infrastructure is required?

6. Solar Power First explored by engineers over 100 years ago (not a byproduct of the US environmental movement in the 1970s!) Appealed to people for use in Algeria and India Early initiatives bypassed in favor of ease and cheap cost of coal and wood Early parabaolic reflectors kept getting felled by weather Decentralized technology. What infrastructure is required?

7. Three Technologies for Solar Power Photovoltaic cells Concentrating solar power technologies Low-temperature solar collectors

8. Photovoltaic Cells Convert sunlight directly into electricity (photo:volt) Made of semiconductors such as crystalline silicon or various thin-film materials Also known as solar cells (put together into modules and arrays) Can provide anything from tiny amounts of power for watches to large amounts for the electric grid A PV System includes electrical connections, mounting hardware, power-conditioning equipment, and batteries that store solar energy for use when the sun isn't shining Current uses of PVs include communications satellites, water pumps, road and traffic signs

9. Photovoltaics: one cell produces 1 to 2 watts of power

10. Uses of Stand-alone PVs Replacement energy when other utilities are: –Unavailable, undesirable (no tolerance for interruption), too costly to extend power lines Can produce energy where and when it's needed, so complex wiring, storage, and control systems aren't needed Small systems produce less than 500 watts and weigh less than 68 kilograms (150 pounds); easy to transport and install Most installations take only a few hours and PV modules need only an occasional inspection and cleaning

11. Concentrating Solar Power Technologies (CSPs) Use mirrors to concentrate the sun's heat energy Drive a steam generator to produce electricity Include dish/engine systems, parabolic troughs, and central power towers

12. CSPs Relatively low cost and can deliver power when and where it is needed Excellent for satisfying need for distributed source of energy Can range from small-scale (village power, 10 kilowatts) to large-scale (grid-connected applications, 100 megawatts). Can use thermal storage during cloudy periods or at night. Can also be combined with natural gas Amount of power generated depends on amount of direct sunlight. Good for sunbelt locations. Enough electric power for the entire country could be generated by covering about 9 percent of Nevada—a plot of land 100 miles on a side—with parabolic trough systems.

13. Two Designs of CSPs Troughs Parabolic shaped reflectors concentrate the sun’s energy; pipe with oil runs down the middle and gets heated up by solar energy, which then generates electricity in a conventional steam generator Power towers Lots of large, sun—tracking mirrors that focus sunlight onto a receiver at the top of a tower; heat transfer fluid (steam, molten nitrate salt) in the receiver generates steam

14. Low-temperature Solar Collectors Absorb the sun's heat energy Heat is used directly for hot water or space heating for residential, commercial, and industrial facilities Different kinds of collectors used based on need

15. Solar Case Studies Boosting a telephone signal in Nevada Providing water for cattle in South Dakota Powering a modern home in Florida

16. Next class Make It Better activity Review of Amory Lovins video lecture Exam scheduled for Tuesday the 8 th. Review session will be Monday 5:30pm- 6:30 pm