Chapter 16: Renewable Energy

Germany

• National policy to transition to renewable energy

• Goal: 80% of power from renewables by 2050

• 2023: 55% of electricity production was renewable

• Renewable Energy Act ensures priority grid access for renewable electricity

• Individuals can sell excess electricity

• Currently Leader In Renewable Energy

Costs of Renewables

• Economic & environmental costs of switching systems

• Intermittent supply (fluctuations) challenges require system coordination

• Germany's progress:

  • Lowered greenhouse gas emissions

  • Reduced reliance on imported fuels

  • Renewable energy cost matches fossil fuels

  • Increased research and job opportunities

  • Still work to be done

Renewable Energy

• 2023: 9% of total energy & 21% of electricity in the U.S.

• Obama’s goal: 80% renewable electricity by 2035

• Global: Over 30% of electricity comes from renewable sources

• U.N. target: 80% reduction in fossil fuel use by 2050

• Other sources must replace fossil fuels

Renewable Energy Use In the US. (2013)

• Biomass energy: 49.0%

• Hydropower: 28.0%

• Wind: 17.4%

• Solar: 3.5%

• Geothermal: 2.2%

• Total: 9.14 quadrillion BTU units (10% of U.S. energy use in 2013)

Why Switch?

• Fossil fuels increase \CO_2 \ in the atmosphere

• Pollutants other than \CO_2 \ are released when burning fossil fuels; Acid Rain

• Oil & gas reserves are finite (non-renewable)

• Over 1 billion people lack access to electricity

Can We Switch?

• Modern society is built around fossil fuels

• Infrastructure took 70–100 years to develop

• Government subsidies heavily favor fossil fuels:

  • \\\$20 \ billion annually to fossil fuels

  • \\\$15.6 \ billion to renewable energy

• Building renewable infrastructure requires massive government support

Solar Energy

• Solar constant: all wavelengths of sunlight; Biggest Opportunity

  • 30% reflected

  • 20% absorbed by the atmosphere

  • 50% reaches Earth's surface

• The Sun provides 10,000 times the energy we use

Solar Difficulties

• Does not change the biosphere's energy balance

• Solar energy is abundant but diffuse (spread out)

• Varies with season, latitude, and atmospheric conditions (stronger closer to the equator)

• Collection, conversion, and storage are challenging

• Must be cost-effective (otherwise others won’t use it)

Solar Heating of Water

• Flat-plate collector: thin, broad box with a black bottom

  • Black bottom absorbs sunlight and heats water in tubes

  • Glass top prevents heat loss

• Active systems: pumps move heated water

• Passive systems: gravity and convection move water

• 60 million solar hot-water systems exist globally

• Initial costs are high, but solar systems are cheaper over time

• China leads the world in solar thermal systems (18 million households)

Solar Space Heating

• Flat-plate heaters can be used for space heating (heats air rather than water)

• Passive solar heating is less expensive and can be homemade

• Air circulates through collector boxes

• Mounting collectors to allow convection increases efficiency

Solar Buildings

• Buildings can act as their own collectors

• Design and insulation are crucial

• Deciduous plants block summer sun but allow winter sun

• Evergreen hedges protect from wind on the shady side

• EPA Energy Star program:

  • Labels buildings that use 40% less energy than others in their class

  • By 2014, 25,500 buildings earned the label

Criticism of Solar Heating

• Requires a backup heating system

• Good insulation minimizes this need

• Reduces dependency on conventional fuels

• Reduces fuel demand and economic/environmental costs

Solar Electricity

• Photovoltaic cells convert sunlight into electricity

• Structure:

  • Wire attached to top and bottom of wafer

  • Sunlight creates an electric current

• Efficiency: 15–20%

• Durable: No moving parts, lasts up to 30 years

• Silicon is the main material used in solar cells

  • Abundant element on Earth

Net Metering

• Inverters act as an interface between PV modules and the electric grid

• Converts DC to AC

• Detects and responds to fluctuations in voltage or current

• Costs have declined but remain substantial

• Compensations for extra electricity production

Cost of PV

• Close to other electricity sources

• New technology improves efficiency and cost-effectiveness

• Fastest-growing energy technology globally

Utilities Moving to PV Use

• Large-scale PV plants are being developed (Hard to convince individuals to pay upfront cost)

• Rooftops are the most promising future for PV use

• Utilities offer incentives for home use

• 2008 Emergency Economic Stabilization Act: Tax credits for 30% of system costs

• Germany leads the world in rooftop PV installations

New PV Technology

• Thin-film PV cells can be applied to roofing tiles or glass

• 3D silicon cells capture 25% of light energy

• Light-absorbing dyes transmit energy to solar cells

• Flexible plastic polymer cells are being developed

Concentrated Solar Power (CSP)

• Mirrors focus light onto a receiver

• Receiver transfers heat to a turbogenerator

• Works well in sunny areas with ample space

• Requires water to cool the steam generated

• Types:

  • Solar troughs: Reflect light onto a center pipe

  • Power towers: Focus light onto a centrally located tower with a receiver

Solar Future

• Disadvantages:

  • Technology is more expensive than traditional energy sources (Biggest Turn Off For People)

  • Backup energy sources or batteries are needed

  • Many areas are not sunny in winter

  • Birds can be incinerated by CSP systems

  • Production of PV cells generates some pollution

• Despite challenges, solar PV energy is growing

Demand & Use

• Solar can be used for daytime electricity, conventional sources at night

• Air conditioning is the second-largest power use after refrigeration

• Solar and wind together can replace coal and nuclear energy

Indirect Solar Energy: Hydropower

• Many power sources derive energy from the Sun

• Hydropower:

  • Hydroelectric dams use water under pressure to drive turbogenerators

  • Falling water can turn paddle wheels

• Statistics:

  • 6.2% of electrical power in the U.S.

  • 16% of electrical power worldwide

Dams

• Benefits:

  • Eliminate cost and environmental impacts of fossil fuels

  • Provide flood control and irrigation water

  • Offer recreation and tourist opportunities

  • Pumped water dams store water until high demand requires release

• Drawbacks:

  • Loss of land flooded by reservoirs

  • Displacement of populations

  • Impede or prevent migrating fish

  • Reservoirs increase evaporation rates, reducing downstream water supplies

  • Water supplies can become saltier

Dams: Challenges

• Few sites remain for new dam construction

• Dams are controversial due to ecological and sociological impacts

• Projected benefits may not justify the costs

Indirect Solar Energy: Wind Power

• Statistics:

  • 8% of global electricity in 2023

  • China is the world leader in wind energy

• Wind farms consist of multiple wind turbines in the same location

• Wind-driven blades are directly geared to a generator

Wind Power: Benefits

• Reliability and efficiency have reduced costs

• Immense potential for wind energy capture

• Wind farms in the Midwest could meet U.S. energy needs

• Farmers are paid to install turbines on their land

• Could provide 20% of U.S. electricity by 2030

Wind Power: Challenges

• Intermittent winds require backup systems or batteries

• Can be visually unappealing and noisy

• Can harm birds and bats

• Offshore wind farms may address some issues

• Power needs to be transported, as wind farms are often far from users

Indirect Solar Energy: Biomass Energy

• Derived from present-day photosynthesis

• Ahead of hydropower in U.S. renewable energy use

• Most commonly used for heat

• Sources include:

  • Burning wood

  • Municipal waste

  • Generating methane

  • Producing alcohol

Firewood

• Main cooking and heating source for 2.6 billion people

• 2.5 million U.S. homes use wood stoves for heat

• Pellet stoves use compressed pellets from wood waste

• Can be sustainable if forests are sufficient and users are limited

Fuelwood Crisis

• People forage for wood in developing countries

  • Conversion to charcoal provides income

  • Used for personal cooking and heating

• Can degrade local forests and woodlands

• Fuelwood use peaked in the 1990s

  • Declining as people switch to fossil fuels

• More efficient stoves reduce wood use

Burning Waste

• Electricity can be produced by burning:

  • Municipal waste

  • Wood waste from sawmills and woodworking companies

  • Cane waste from sugar refineries

• Coal power plants can be converted to biomass power

• May meet only a small percentage of electrical needs

• Any reduction in fossil fuel use is beneficial

Methane

• Biogas: Anaerobic digestion of sewage produces methane

• Can also produce nutrient-rich fertilizer

• Common in China and India using animal dung

Energy for Transportation

• Critical for a sustainable energy future

• Biofuels produce ethyl alcohol and biodiesel

• 2.5% of global transportation fuels come from biofuels

• Ethanol:

  • More expensive than oil unless oil exceeds \\\$55 \ per barrel

  • Federal tax credits make it cost-competitive

  • U.S. uses 14.3 billion gallons per year (2/3 the energy of gasoline)

Corn and Ethanol

• 1/3 of U.S. corn is dedicated to ethanol production

• Not available for corn oil or livestock feed

• Renewable Fuel Standards (RFS) guide production

• Brazil uses sugarcane to produce ethanol

• U.S. leads the world in ethanol production

• Biofuels account for 8% of U.S. fuel consumption

Enviromental Impact of Ethanol

• Fossil fuels are used to produce ethanol

• Growing corn and processing releases greenhouse gases

• Ethanol reduces greenhouse gas emissions by 12–18%

• Land-use changes to grow more corn increase \CO_2 \ emissions

• Corn-based ethanol offers no net environmental benefit

Second-Generation Biofuels

• Derived from crop residues, grasses, logging residues, fast-growing trees, etc.

• High in cellulose or sugar

• Technology uses enzymes to break cellulose

• Cheaper and more energy-efficient

• Less competition for land and food

• Tax credits are needed to continue development

Hydrogen

• Hydrogen is not a fuel but an energy carrier (like electricity)

• Must be generated using another energy source

• Only by-product of burning \H_2 \ is water

• No pure hydrogen gas exists naturally; it must be manufactured

• Electrolysis extracts hydrogen from water but requires energy input

Challenges of Hydrogen

• Hydrogen can be obtained from hydrocarbon fuels

• More energy is required to produce \H_2 \ than is contained in \H_2 \

• Better to use hydrocarbons directly

• Using hydrogen requires a cheap, abundant, non-polluting energy source (e.g., solar energy)

• Technology exists but is expensive

Hydrogen Storage

• Difficult to store enough hydrogen for long-distance travel

• Compressing hydrogen requires energy into a liquid

• Hydrogen can be combined with metal hydrides to absorb and release \H_2 \

• Most hydrides are too heavy

• Hydrogen can be converted into liquid formic acid by combining with \CO_2 \

Fuel Cells

• Produce electricity to power an electric motor (mostly in buses)

• Hydrogen joins with oxygen to produce electricity (no burning)

• Emissions are water and heat

• Efficiency: 45–60% (combustion engines: 20%)

• Fuel cells power buses worldwide

• Passenger cars exist but face challenges due to lack of education

Hydrogen Economy

• Requires infrastructure development

• Still decades away

• Other renewable energy options are available sooner

Geothermal Energy

• Uses naturally heated water or steam to heat buildings or produce electricity

• Enhanced Geothermal Systems (EGS) generate electricity

• U.S. has widespread underground heat resources

• Not available to everyone, everywhere

• Can only be part of a renewable energy solution

Heat Pumps

• Use Earth as a heat exchange system (relative stable temperature below the surface)

• Ground extracts heat in winter and absorbs it in summer

• Reduce or eliminate air conditioning and furnaces

• Geothermal Heat Pump (GHP): Loops of buried pipes filled with antifreeze

• Upfront costs are paid off in 6–8 years

• Most cost-effective, energy-saving system available

Tidal and Wave Power

• Tides contain large amounts of energy

• Tidal barrage: Dam built across the mouth of a bay; tides turn turbines

  • 30 locations globally have tides high enough for this use (e.g., Bay of Fundy)

• Adverse environmental impacts exist

• More possible locations exist (costal)

• part of the solution, not the whole thing

Ocean Thermal Energy Conversion (OTEC)

• Most oceans have thermal gradients between surface and deeper waters

• OTEC uses this temperature difference to produce power

• Currently has low economic promise

• Could be coupled with other operations, such as cooling seaside buildings

Policy

• Global targets aim to stabilize greenhouse gas levels

• Focus on energy conservation and efficiency:

  • Increase mileage standards for vehicles

  • Improve energy efficiency in lighting, appliances, and buildings

• Public policy must encourage renewable energy use and conservation

• Requires action at both national and international levels

U.S. Policy

• Key legislation:

  • Energy Policy Act (2005)

  • Energy Independence & Security Act (2007)

  • American Recovery & Reinvestment Act (2009)

• Supply-side policies:

  • Fund research and development

  • Provide tax credits for renewable power in any form

• Demand-side policies:

  • Promote energy conservation and efficiency

  • Support development of hybrid and hydrogen fuel cell vehicles

  • Build infrastructure for renewable energy

  • Encourage waste-energy recovery

  • Reduce or stop subsidies for non-renewable energy

International Policy

• 67 countries have renewable energy targets

• International cooperation can increase renewable energy use

• European Union (EU) initiatives:

  • 2007 plan to promote efficiency, develop renewables, and lower greenhouse gases

  • Energy market development

• Energy Union's 2014 plan:

  • Aim for energy independence and diversification

  • Transition to conservation and renewables as costs of old practices rise

  • Support developing countries in adopting renewable energy

• Germany serves as a model for renewable energy transition