Energy & Its Impact on Global Society Jerome K. Williams, Ph.D. Saint Leo University Dept. Mathematics & Sciences

Chapter 6: Solar Energy Renewable Energy: An Overview Characteristics of Solar Radiation History of Solar Heating Solar Heating Today

Renewable Energy: An Overview Renewable energy provides about 8% of world’s energy and 6-8% of US needs Fastest growing resources – Wind – Photovoltaics – Hydroelectric

Renewable Energy: An Overview

Rankings (Growth rates in parenthesis) Wind (55% Europe; 37% US) Photovoltaics(35% worldwide) Hydroelectric(16% worldwide) Biomass

Renewable Energy: An Overview Renewables could rise to 30-40% world’s energy source by 2050 Renewables offer advantages including: versatility, minimal environmental problems, and used with appropriate technology

Renewable Energy: An Overview Why have renewables not been used before? – Economics – Politics

Characteristics of Solar Radiation Energy from sun reaching earth per day ranges from 600 Btu/ft2/d – 2000 Btu/ft2/d Amount that reaches earth is called incident solar radiation or insolation.

Characteristics of Solar Radiation Energy falling on US is about 2000 times the energy we get from annual coal production in country Sunlight falling on home can provide 1/3 to 1/2 total annual heating needs for that house

Characteristics of Solar Radiation Power Source for Sun:Fusion Reactor – Hydrogen nuclei are converted to helium nuclei by a process called fusion – Composition of Sunlight that reaches earth’s atmosphere: (10% uv ; 40% visible; 50% infrared)

Characteristics of Solar Radiation Only 50% of incident solar energy reaches earth’s surface and is absorbed by land and oceans Albedo is the light that is reflected from the earth and its atmosphere

Characteristics of Solar Radiation Relatively constant temperature of earth is result of energy balance between incoming solar radiation and energy radiated from earth Most emitted radiation escapes into space, but some is absorbed by gases (CO 2 & H 2 O) and directed back to earth giving rise to the greenhouse effect

Characteristics of Solar Radiation

Insolation received at any location on earth ranges from W/m 2 (330 Btu/ft 2 /h) depending on latitude, season, time of day and cloudiness

History of Solar Heating Solar energy use dates back to antiquity – Heating/Cooling: Cliff dwellers (Anasazi: SW USA) – Solar desalination & heating water – Cooking Food

History of Solar Heating

Solar Heating: Cooking Food Video Preparing Chicken dinner: Minnesota in January QMg QMg

Solar Heating Today Today, radiant solar energy (residential & commercial) is used for heating swimming pools and domestic hot water (DHW). Growth rate (US Sales)5% – Much stronger growth in Asia & Europe – Solar energy boom (late 1970s – early 1980s)

Solar Heating Today Growth rate (US Sales)5% – Much stronger growth in Asia & Europe Solar energy boom (late 1970s – early 1980s) – Oil Embargo (1973) & rising oil & electricity costs – Economic incentives to upgrade – Tax Credit ended (1985); sales dropped >95%

Solar Heating Today Many states offer state tax credits for upgrading to solar systems Utility companies also offer rebates and loans to help customers upgrade – Two-thirds hot water use met by solar power – Less CO 2 released (reduce carbon footprint) – Reduce cost for utility company