Trade-Offs for Hydroelectric power AdvantagesDisadvantages Moderate to high net energyHigh construction costs High efficiency (80%)High environmental impacts from flooding to form reservoir Low-cost electricityHigh evaporation water loss in tropical areas No CO 2 emissionsLots of methane generation initially, especially in tropical reservoirs Can provide flood control below the damDanger of collapse Provides irrigation waterUproots people Reservoir useful for fishing and recreationDecreases fish harvest below dam Decreases flow of natural fertilizer (silt) below dam Can cause problems for migrating species (salmon)

Trade-Offs for Wind Power AdvantagesDisadvantages Moderate to high net energy yieldSteady winds needed High efficiencyBack-up system needed when winds are low Moderate capital costHigh land use for wind farm Low electricity cost (and falling)Visual pollution Very low environmental impactNoise when located near populated areas No CO 2 emissionsCan kill birds and interfere with flights of migratory birds Quick construction Easily expanded Can be located at sea Land below turbines can be used to grow crops or raise livestock

Trade-offs of Geothermal Energy AdvantagesDisadvantages Very high efficiencyScarcity of suitable sites Moderate net energy at accessible sitesCan be depleted if used too rapidly Lower CO2 emissions than fossil fuelsEnvironmental costs not included in market price Low cost at favorable sitesCO 2 emissions Low land use and disturbanceModerate to high local air pollution Moderate environmental impactNoise and odor (H 2 S) High cost except at most concentrated and accessible sources

Trade-offs of Hydrogen AdvantagesDisadvantages Can be produced from plentiful waterNot found as H 2 in nature Low environmental impactEnergy needed to produce fuel Renewable if produced from renewable sources CO 2 emissions if produced from methane No CO 2 emissions if produced from waterEnvironmental cost not included in price Good substitute for oilNon-renewable if generated with electricity from fossil fuels or nuclear Competitive price if fossil fuel environmental and health cost added in High costs Easier to store than electricityWill take 25 to 50 years to phase in Safer than gas and natural gasShort driving range for current fuel cell cars NontoxicNo fuel distribution system in place High efficiency (45 – 65%) in fuel cellsExcessive hydrogen leaks may deplete ozone in the atmosphere