ENS 201 Chapter 20, Spring 2008

Chapter 20: Sustainable Energy Aurora IV, built by students @ Minnesota Uni, 1999 The complex problems we face today will not be solved by the same level of thinking that created them, Albert Einstein Outline: • Energy History • Current Energy production and use • Conventional energy sources: fossil fuels and nuclear power • Introduction to renewable energy • Tapping Solar Energy – Passive Solar Heat vs. Active Solar Heat • High Temperature Solar Energy: Parabolic Mirrors • Photovoltaic Cells and storage of electrical energy • Energy From Earth’s Forces • Energy From Biomass • Conservation – Utilization Efficiencies – Energy Conversion efficiency Energy History • Fire: The first human energy technology • Muscle (domestic animals) Wind & water power: important since dawn of agriculture 10,000 years ago. • Coal (19th century): promoted by the invention of steam engine and wood shortage • Oil (20th century): liquid fuels are ease to ship, store and burn Current Commercial Energy Sources • Fossil Fuels (petroleum, natural gas, and coal): ~ 86% • Nuclear power: ~ 6% • Renewable: – Hydroelectric dams: ~ 7% – Others (wind, solar, geothermal, biomass): < 3% • In poorer countries: biomass provides more than 90% of the energy used for cooking and heating Worldwide Commercial Energy Production Fossil fuel: Coal • Fossilized plant material preserved by burial in sediments (286 million to 360 million years ago) and changed by geological forces into carbon-rich fuel • Mining operations are highly hazardous  • accidents • lung diseases due to coal dusts Coal Pollution • Coal burning releases: – Radioactivity and heavy metals into the atmosphere – Sulfur (if not removed) which oxidizes to sulfur dioxide or sulfate – Nitrogen oxides and CO2 • Drainage from coal mine and piles is acidic and highly toxic  water pollution Fossil fuel: Oil • Like coal, petroleum is formed from organic material buried in sediment and subjected to anaerobic bacterial decomposition • At least half of total deposit is usually uneconomical to pump out Fossil Fuel: Natural Gas • World’s third largest commercial fuel – Produces half as much CO2 as equivalent amount of coal – Most rapidly growing energy source – Difficult to ship long distances, and to store in large quantities Nuclear Power • Most commonly used fuel is U235, a naturally occurring radioactive isotope of uranium • Radioactive wastes management is highly hazardous and expensive Nuclear waste Underground burial – In developed countries: luxurious lifestyle is dependent on a limited, unsustainable oil supply that cannot last forever – In developing countries: major debt burdens that still hold back – price shocks + Pollution lead to   awareness about energy conservation & renewable energy sources Oil Economical Implications the sun serves as a giant nuclear furnace in space Passive Solar gain: South-oriented, earth-sheltered homes • Orienting homes so that living spaces have passive solar gain on the winter and are shaded by trees or roof overhang in the summer • Earth-sheltered homes built into a slope or protected by earth maintain relatively stable subsurface temperature => exceptionally efficient energy savers Summer ventilation and High double-glazed windows giving light to the back of the house In the winter Passive Solar Heat: Greenhouse • glass-walled on the south incorporating massive energy- storing material that slowly release heat at night Superinsulated straw-bale constructed houses • High insulating qualities => high energy efficiency for heating and cooling • Efficient sound insulators • Low cost and long duration Passive Heat Absorption: Use of stationary absorptive structures to gather & hold heat: Adobe Dwellings • Slowly collect the heat during the day and slowly release it at night • After cooling at night, the massive buildings maintain a comfortable day temperature, even as they absorb external warmth Solar Box Cookers • An insulated box with a black interior and a glass or plastic lid serves as passive solar collector (~ 120oC): • fuel is free, hours spent on hunting fuel wood are saved Firewood/solar cooker (2 billion people around the world now have no access to electricity) Active solar heat: systems that pump heat- Parabolic Mirrors • Parabolic mirrors are curved reflective surfaces that track the sun and collect light and focus it onto a concentrated point • The energy absorbed drive a steam-turbine electric generator Photovoltaic Cells • One of the new promising technology: collectors made of amorphous silicon with boron impurities => • Suitable as solar roof tiles: that are enough for a house & any surplus can be sold back to the utility company =>more cost efficient