Chapter Thirteen: Renewable Resources

Potentially Renewable

Can be regenerated indefinitely as long as its not overharvested - biomass

Nondepletable

Cannot be used up in the span of human time

Renewable

An energy source that is either potentially renewable or nondepletable

Biomass Examples

Wood, charcoal, animal products, manure, plant remains, and municipal solid waste

Biofuels

Liquid fuel created from processed or refined biomass (ethanol, biodiesel) - used in developed countries

Modern Carbon vs. Fossil Carbon

Modern carbon is in biomass that was recently in the atmosphere (net zero) - fossil carbon is the carbon stored in fossil fuels

Carbon Neutral

When an activity doesn’t change the atmospheric CO2 concentration

Solid Biomass

Typically used for heating in developing countries - wood, charcoal, and manure

• Fuelwood - only sustainable if growth keeps up with removal (net removal is unsustainable, select removal is good)

• Charcoal - more expensive but produces less smoke - charcoal production clears the land of trees

• Manure - burning helps to remove microorganisms, releases pollution

Ethanol

Made by converting starches and sugars from plants into alcohol and CO2 (fermentation) - the US is the world leader in ethanol production - usually mixed with gasoline - E-85 is used in flex-fuel vehicles - bad because it uses fossil fuels and land to produce it, has a lower energy content, and we need to find alternatives to corn

Biodiesel

More expensive than ethanol - diluted to B-20 (20% biodiesel, 80% petroleum) for modified engines - mostly found from soybean oil and processed vegetable oil, algae is another alternative - fewer emissions, modern carbon

Hydroelectricity

2nd most common form of renewable energy - electricity derived from the kinetic energy of moving water - run-of-the-river or water-impoundment dams

Run-of-the-River Dam

Water is retained behind a low dam or no dam - little environmental damage - typically smaller - energy is intermittent - less common than water-impoundment dams

Water Impoundment

Water is stored in a reservoir behind a dam - more common form of hydroelectricity

Tidal Systems

Use gates and turbines similar to run-of-the-river systems - not in many locations because the difference between high and low tide is not big enough to spin the turbines

Passive Solar Design

Use of solar radiation without the use of active technology - windows on south-facing wall - double-paned windows - dark or light materials on the roof/exterior (depending on where you live) - overhanging roof - window shades - thermal mass - concrete, bricks, stone, and tile absorb sunlight

Types of Active Solar Energy

1. Solar Water Heaters - flat plate collectors, only for heating water

2. Photovoltaic Cells - converts sun’s energy to electricity

3. Concentrating Solar Thermal Systems (CSP) - solar farms

Pros and Cons of Active Solar Energy

• Pros: no air pollution, produces electricity when needed most, can be economically feasible (long term)

• Cons: expensive, lots of energy to make cells, batter storage can lead to environmental damage, uses heavy metals, potential solar fires

Wind Energy

Energy derived from the kinetic energy of moving air - wind turbines convert this kinetic energy to electricity (wind farms) - nondepletable - batteries to store electricity - cons are bird deaths, land use, and habitat fragmentation

Geothermal Energy

Source of heating and cooling (heat pumps) and electricity (power plants) - ground source heat pumps, hot water heat pumps

Ground-Source Heat Pumps

Geothermal energy transfers heat from ground to a building

Hot Water Heat Pumps

Extracts heat from the air in a garage/basement and transfers it to a hot water tank

Hydrogen Fuel Cells

An electrical-chemical device that converts hydrogen into an electrical current - reactants are continually added to the cell - generated by the reaction between hydrogen and oxygen - electrolysis can be used as an alternative method

Our Energy Future

Efficiency - conservation - development of renewable and nonrenewable resources (a balance) - need innovation and technological advances - nations need to commit to support the development of renewable resources - improve the electrical grid (smart grid) - need to address the cost and storage of renewable resources