ENGR 101/ HUM 200: Technology & Society

November 2, 2005

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

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

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

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?

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?

Three Technologies for Solar Power

• Photovoltaic cells

• Concentrating solar power technologies

• Low-temperature solar collectors

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

Photovoltaics: one cell produces 1 to 2 watts of

power

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

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

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.

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

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

Solar Case Studies

• Boosting a telephone signal in Nevada

• Providing water for cattle in South Dakota

• Powering a modern home in Florida

Next class

• Make It Better activity

• Review of Amory Lovins video lecture

• Exam scheduled for Tuesday the 8th. Review session will be Monday 5:30pm-6:30 pm