Renewable and Nonrenewable Energy Sources

6.1 Renewable vs. Nonrenewable Energy Sources

• Learning Objective: ENG-3.A
  • Identify differences between nonrenewable and renewable energy sources.
• Suggested Skill: 1.C Concept Explanation
  • Explain environmental concepts, processes, or models in applied contexts.
• Essential Knowledge:
  • ENG-3.A.1 Nonrenewable energy sources are those that exist in a fixed amount and involve energy transformation that cannot be easily replaced.
  • ENG-3.A.2 Renewable energy sources are those that can be replenished naturally, at or near the rate of consumption, and reused.
• Renewable Energy Sources
  • Can be replenished naturally, at or near rate of consumption & reused.
  • Depletable renewables can run out if overused
    • Ex: Biomass (wood, charcoal, ethanol)
  • Nondepletable renewables do not run out if overused
    • Ex: Solar, wind, hydroelectric, geothermal
• Nonrenewable Energy Sources
  • Exist in fixed amounts on earth & can’t easily be replaced or regenerated
  • Fossil Fuels
    • Fossilized remains of ancient biomass that take millions of years to form
    • Coal, Oil, Nat. Gas
  • Nuclear: energy generated from uranium or other radioactive fuels
• Key to Renewable Energy Rate of Consumption
  • Rate of use must be at or below rate of regeneration for renewables
  • Fossil fuels will run out because they take far longer to regenerate than the rate we use them
• FRQ 6.1: Explain whether or not biomass is a renewable energy source. Justify your answer

6.2 Global Energy Consumption

• Learning Objective: ENG-3.B
  • Describe trends in energy consumption.
• Suggested Skill: 6.C Mathematical Routines
  • Calculate an accurate numeric answer with appropriate units.
• Essential Knowledge:
  • ENG-3.B.1 The use of energy resources is not evenly distributed between developed and developing countries.
  • ENG-3.B.2 The most widely used sources of energy globally are fossil fuels.
  • ENG-3.B.3 As developing countries become more developed, their reliance on fossil fuels for energy increases.
  • ENG-3.B.4 As the world becomes more industrialized, the demand for energy increases.
  • ENG-3.B.5 Availability, price, and governmental regulations influence which energy sources people use and how they use them.
• Developed vs. Developing Countries
  • Developed nations use more energy on a per capita basis, but developed nations use more energy in total (higher pop.)
  • Developing nations are still industrializing & pop. is still growing rapidly
    • It will also increase on a per/person basis as their economies industrialize & residents achieve higher standards of living
  • The avg. US resident uses 5x as much energy as the world avg.
• Fossil Fuels: Most Used Energy Source
  • Fossil fuels are by far the most common fuel source globally
  • Hydroelectric energy (dams used to create electricity) are second largest source
    • Water spins a turbine which generates electricity
  • Oil gasoline = main fuel for vehicles
  • Coal = main fuel for electricity gen.
  • Nat. gas = secondary fuel for electricity gen. & main fuel for heating
  • Nuclear is the third largest source
    • Uranium fission releases heat to turn water into steam to turn a turbine to gen. electricity
• Development Increases FF Consumption
  • Many residents of less developed nations depend on subsistence fuels - biomass that they can easily gather/purchase
    • Ex: wood, charcoal, dried animal manure. Can drive deforestation
  • As developing nations develop, fossil fuel consumption will increase
    • Oil → Gasoline for vehicles
    • Coal & Nat. gas → electricity
      • Electricity demand for homes & manufacturing
  • Econ. development → affluence (wealth) → higher per capita GDP → energy use
• Factors That Affect Energy Source Use
  • Availability: Fossil fuel use depends on discovered reserves & accessibility of these reserves
  • Price: FF Prices fluctuate dramatically with discovery of new reserves or depletion of existing ones
    • Fracking opens new NG reserves, increasing availability, decreasing price, increasing use
  • Gov. Regulation: gov. can mandate certain energy source mixes (25% renewable by 2025)
  • Gov. CANNOT directly raise or lower prices of energy sources (ex: raise gas to $10/gallon)
  • Gov. CAN use:
    • Taxes increases to discourage companies from building FF power plants
    • Rebates, or tax credits to encourage companies building renewable energy power plants
• Practice FRQ 6.2
  • From 2005 to 2018, the annual investment in renewable energy sources in the United States increased from $11.4 billion to $46.5 billion. Calculate the percent change in renewable energy investment in the US from 2005 to 2018.
  • Experts estimate that for the US to reach 100% renewable energy in 2050, it will require $7.8 trillion. Calculate the percent change this would represent from the 2018 investment level of $46.5 billion.

6.3 Fuel Types and Uses

• Learning Objective: ENG-3.C
  • Identify types of fuels and their uses.
• Suggested Skill: 1.A Concept Explanation
  • Describe environmental concepts and processes.
• Essential Knowledge:
  • ENG-3.C.1 Wood is commonly used as fuel in the forms of firewood and charcoal. It is often used in developing countries because it is easily accessible.
  • ENG-3.C.2 Peat is partially decomposed organic material that can be burned for fuel.
  • ENG-3.C.3 Three types of coal used for fuel are lignite, bituminous, and anthracite. Heat, pressure, and depth of burial contribute to the development of various coal types and their qualities.
  • ENG-3.C.4 Natural gas, the cleanest of the fossil fuels, is mostly methane.
  • ENG-3.C.5 Crude oil can be recovered from tar sands, which are a combination of clay, sand, water, and bitumen.
  • ENG-3.C.6 Fossil fuels can be made into specific fuel types for specialized uses (e.g., in motor vehicles).
  • ENG-3.C.7 Cogeneration occurs when a fuel source is used to generate both useful heat and electricity.
• Subsistence Fuels
  • Wood (and charcoal) are two of the most common fuel sources in developing nations
    • Wood is free/cheap to cut down and utilize as fuel; can cause deforestation & habitat loss
  • Peat is partially decomposed organic matter (often ferns or other plants) found in wet, acidic ecosystems like bogs and moors
    • Can be dried and used as a biomass fuel source
  • Biomass fuel sources that are easily accessible (can be found and gathered by hand); often used in developing countries as a home heating or cooking fuel
  • Charcoal is made by heating wood under low oxygen conditions for a long time
• Coal Formation
  • In order of energy density & quality: lignite → bituminous → anthracite
    • Because higher energy density means more energy released when a fuel source is burned, anthracite is the most valuable form of coal (highest quality)
  • The deeper a coal reserve is buried, the more pressure from overlying rock layers & the more energy dense
  • Pressure from overlying rock & sediment layers compacts peat into coal over time
  • Coal is burned to heat water into steam, to turn a turbine that generates electricity
    • More dense coal = hotter/longer fire = more steam = more electricity
• Natural Gas
  • Natural gas is mostly methane (CH4) and is found on top of trapped oil (petroleum) deposits
  • Considered the “cleanest” fossil fuel (produces the fewest air pollutants & least CO_2 when burned)
  • Forms when oil is trapped in a porous, sedimentary rock, underneath a harder, impermeable rock layer that doesn’t let the gas escape
  • Decaying remains of plants & animals (mostly marine life) are buried under layers of rock & converted by pressure into oil (petroleum) and natural gas over time
  • Produces about ½ as much CO_2 as coal when burned to generate electricity
  • Produces virtually no PM (ash/soot)
  • Produces far less SOx, NOx than coal or oil, and NO MERCURY
• Crude Oil (petroleum)
  • Extracted by drilling a well through the overlying rock layers to reach the underground deposit and then pumping liquid oil out under pressure
  • Can also be recovered from tar sands (combination of clay, sand, water, and bitumen)
  • Decaying organic matter trapped under rock layers is compressed into oil over time
  • Bitumen is a thick, sticky, semi-solid form of petroleum (not liquid)
  • Extracting & using oil from tar sands is extremely energy and water intensive
    • Lots of water needs to be heated (requiring energy) to create steam that’s piped down into the tar sand to melt the bitumen into a liquid that can flow up a pipe
    • Lots more water is used to separate the oil from all of the impurities (sand, clay) at the refinery
• Fossil Fuel Products
  • Crude oil (petroleum) is converted into lots of different products through the process of fractional distillation
  • Crude oil is burned in a furnace and vapor passes into a column where different hydrocarbons are separated based on their boiling points
  • Hydrocarbons w/lower boiling points gather at the top of the column, higher boiling points gather at bottom
  • Different hydrocarbons within petroleum are used for different products
    • Petroleum gas
    • Gasoline (fuel for cars)
    • Naphtha (used to make plastic)
    • Jet fuel
    • Diesel fuel
    • Motor oil
    • Bitumen (asphalt for roads)
• Practice FRQ 6.3: Natural gas is considered to be a better fossil fuel for the environment than coal is. Explain TWO environmental benefits of using natural gas as a fuel compared to using coal.

6.4 Distribution of Natural Energy Resources

• Learning Objective: ENG-3.D
  • Identify where natural energy resources occur.
• Essential Knowledge: ENG-3.D.1
  • The global distribution of natural energy resources, such as ores, coal, crude oil, and gas, is not uniform and depends on regions geologic history.
• Suggested Skill: 2.B Visual Representations
  • Explain relationships between different characteristics of environmental concepts, processes, or models represented visually: In theoretical contexts, In applied contexts
• FF Energy Reserves
  • Coal
    • 1. US 2. Russia 3. China 4. Australia ~100-150 Years
  • Natural Gas
    • 1. Russia 2. Iran 3. Qatar 4. US 5. Saudi Arabia ~50-60 Years
  • Oil
    • 1. Venezuela 2. Saudi Arabia 3. Iran 4. Canada 5. Iraq ~50 Years
• Fracking & Shale Gas
  • Hydraulic fracturing (aka fracking) is a method of natural gas extraction that has extended access to natural gas
    • Gas trapped in semi-permeable, sedimentary rock layers, such as shale, is released by cracking the rock with pressurized water
  • Fracking natural gas from shale rock increases & extends supply of natural gas
• Shale Gas Reserves
  • FFs are non-renewable, and will eventually be depleted, but short-term economic profit still drives extraction & use
    • Discovered, but unharvested reserves represent economic benefit to countries
• Tar/Oil Sands
  • Tar or oil sands are bitumen deposits where crude oil can be recovered, but with higher water & energy inputs
  • Canada (Alberta region) = world’s largest oil sands reserve
  • Just like fracking, tar/oil sands extraction extends the world’s supply of crude oil
• FRQ 6.4: Identify a region of the United States that is likely to be a large producer of natural gas. Describe the geological features associated with natural gas reserves.

6.5 Fossil Fuels

• Learning Objective: ENG-3.E
  • Describe the use and methods of fossil fuels in power generation.
• Essential Knowledge:
  • ENG-3.E.1 The combustion of fossil fuels is a chemical reaction between the fuel and oxygen that yields carbon dioxide and water and releases energy.
  • ENG-3.E.2 Energy from fossil fuels is produced by burning those fuels to generate heat, which then turns water into steam. That steam turns a turbine, which generates electricity.
  • ENG-3.E.3 Humans use a variety of methods to extract fossil fuels from the earth for energy generation.
• Learning Objective: ENG-3.F
  • Describe the effects of fossil fuels on the environment.
• Essential Knowledge: ENG-3.F.1
  • Hydrologic fracturing (fracking) can cause groundwater contamination and the release of volatile organic compounds.
• Suggested Skill: 7.A Environmental Solutions
  • Describe environmental problems.
• Fossil Fuel Combustion
  • Combustion is a step in the CARBON cycle: hydroCARBONS (FFs) are burned to release energy & the carbon stored in them reacts with O2 in the air to form CO2
    • Methane (natural gas), gasoline, propane, butane, coal are all fossil fuels (hydrocarbons) that release energy in the same way
    • Wood and biomass work the same, carbon is burned & reacts with O2 to form CO2 & give off energy
  • Reaction between Oxygen (O2) & fossil fuels (hydrocarbons) that releases energy as heat and produces CO2 & H_2O as products
• FF to Generate Electricity
  • These steps of electricity gen. are the same, no matter what you’re burning to produce the initial heat
    • Heat → Water into Steam → Steam turns a turbine → Turbine powers generator → Generator produces electricity
  • Coal, oil, natural gas, biomass, and trash can all be burned to drive this same process
  • Even nuclear energy work similarly, with nuclear fission producing the initial heat
  • The #1 source of electricity production globally is coal, followed by natural gas
• Environmental Consequences: Coal
  • Habitat destruction to clear land for mining
  • Produces pollutants & releases CO_2 (GHG → global warming)
    • Releases more CO_2 than any other FF when burned for electricity gen.
    • Releases PM (soot, ash) which can irritate respiratory tracts of humans/animals
    • Produces toxic ash contaminated with lead, mercury, and arsenic
      • Taken to landfills or stored in ash ponds; both can leak into ground/surface waters, or into soil
    • Releases SOx & NOx (sulfur and nitrogen oxides) which irritate resp. systems, and contribute to smog and acid precipitation
• Generating Electricity
  • Much of the energy “lost” or not converted into electricity escapes as heat
  • Cogeneration: when the heat produced from electricity generation is used to provide heat (air & hot water) to a building; CHP (Combined Heat and Power) systems are close to 90% efficient (much better than coal/NG alone)
  • Coal is ~30% efficient as a fuel source for generating electricity (30% of energy from the bonds in the hydrocarbons are converted to electricity)
    • Nat. Gas is ~60% efficient when it’s burned to generate electricity
• Oil/Petroleum Extraction
  • Extracted by drilling a well through the overlying rock layers to reach the underground deposit and then pumping liquid oil out under pressure
  • Can also be recovered from tar sands (combination of clay, sand, water, and bitumen)
  • Bitumen is a thick, sticky, semi-solid form of petroleum (not liquid)
  • Extracting & using oil from tar sands is extremely energy and water intensive
    • Lots of water needs to be heated (requiring energy) to create steam that’s piped down into the tar sand to melt the bitumen into a liquid that can flow up a pipe
    • Lots more water is used to separate the oil from all of the impurities (sand, clay) at the refinery
• Environmental Consequences: Tar Sands
  • Habitat destruction to clear land for: roads, drilling equipment, digging through ground surface to reach deposits (biodiv. loss)
  • Ground or nearby surface water depletion (H_2O needed for steam & for washing impurities from bitumen at refinery)
  • Water contamination: tailing ponds (holes dug for storing wastewater) can overflow & run into nearby surface waters, or leach into groundwater (Benzene (carcinogen) salts, acids, hydrocarbons, bitumen)
    • All toxic to plant and animals
  • CO_2 released by machinery during extraction, transport, refinement
• Environmental Consequences: Crude Oil/Petroleum
  • Possibility of spill (either from tanker ships or pipelines breaking
  • Habitat loss or fragmentation when land is cleared for roads, drilling equipment, pipelines
  • Spills in water = crude oil covering sun, clogging fish gills, suffocating many ocean animals, sticking to bird feathers
  • Spills on land = toxic to plant roots, surface or groundwater contamination (with hydrocarbons/crude oil)
• Fracking (Hydraulic Fracturing)
  • Used to extract natural gas from sedimentary rock
    • Vertical well is drilled down to sed. rock layer, then turns horizontally into the rock layer
    • Perforating gun cracks (fractures) the rock layer around hor. well, making it more permeable
    • Fracking fluid (water, salt, detergents, acids) is pumped into well @ very high pressure to crack the rock even more & allow natural gas to flow out
    • Nat. gas is collected @ surface & shipped for processing/use
    • Flowback water (used fracking fluid) flows back out well & is collected and stored in containers or ponds nearby
• Environmental Consequences: Fracking
  • Possibility of well leaking & contaminating groundwater with fracking fluid (salt, detergents, acids) or hydrocarbons
  • Depletion of ground or surface waters nearby (as they’re drawn from for fracking fluid)
    • Ponds can overflow or leach into ground & contaminate surface or ground waters with fracking fluid (salt, detergents, acids)
    • Can be toxic to plants & animals that rely on these water sources
  • Increased seismic activity (earthquakes) linked with wastewater injection wells (storing fracking fluid deep underground)
  • Hab. loss/fragment
  • CH_4 (GHG) release
• FRQ 6.5 Explain one environmental consequence of tar sands petroleum extraction. Explain a different environmental consequence of hydraulic fracturing.

6.6 Nuclear Energy

• Learning Objective: ENG-3.G
  • Describe the use of nuclear energy in power generation.
• Essential Knowledge:
  • ENG-3.G.1 Nuclear power is generated through fission, where atoms of Uranium-235, which are stored in fuel rods, are split into smaller parts after being struck by a neutron. Nuclear fission releases a large amount of heat, which is used to generate steam, which powers a turbine and generates electricity.
  • ENG-3.G.2 Radioactivity occurs when the nucleus of a radioactive isotope loses energy by emitting radiation.
  • ENG-3.G.3 Uranium-235 remains radioactive for a long time, which leads to the problems associated with the disposal of nuclear waste.
  • ENG-3.G.4 Nuclear power generation is a nonrenewable energy source. Nuclear power is considered a cleaner energy source because it does not produce air pollutants, but it does release thermal pollution and hazardous solid waste.
• Learning Objective: ENG-3.H
  • Describe the effects of the use of nuclear energy on the environment.
• Essential Knowledge:
  • ENG-3.H.1 Three Mile Island, Chernobyl, and Fukushima are three cases where accidents or natural disasters led to the release of radiation. These releases have had short- and long-term impacts on the environment.
  • ENG-3.H.2 A radioactive element's half-life can be used to calculate a variety of things, including the rate of decay and the radioactivity level at specific points in time.
• Suggested Skill: 2.B Visual Representations
  • Explain relationships between different characteristics of environmental concepts, processes, or models represented visually: In theoretical contexts, In applied contexts
• Nuclear Fission & Radioactivity
  • A neutron is fired into the nucleus of a radioactive (unstable) element, such as Uranium
    • Nucleus breaks apart and releases lots of energy (heat) + more neutrons that break more nuclei apart, releasing more energy (chain reaction)
  • Radioactivity refers to the energy given off by the nucleus of a radioactive isotope (Uranium-235)
    • Radioactive nuclei decay, or breakdown and give off energy (radiation) even without fission; nuclear fission just releases tons of energy all at once
    • Radioactive Half-Life = the amount of time it takes for 50% of a radioactive substance to decay (breakdown)
      • Ex: ½ life of Cobalt-60 isotope = 5.27 yrs
      • In 5.27 yrs, ½ of a Co-60 sample would be Gone (decayed)
• Generating Electricity
  • Same electricity generation process as with FFs, just uranium fission to heat water into steam
    • Heat → Water into Steam → Steam turns a turbine → Turbine powers generator → Generator produces electricity
      • U-235 stored in fuel rods, submerged in water in reaction core; heat from fission turns H_2O → steam…
    • Control rods are lowered into reactor core to absorb neutrons and slow down the reaction, preventing meltdown (explosion)
    • Water pump brings in cool water to be turned into steam and also cools reactor down from overheating
    • Cooling tower allows steam from turbine to condense back into liquid and cool down before being reused (this gives off H_2O vapor)
• Nonrenewable, but cleaner than FFs
  • Nuclear energy is NONRENEWABLE because radioactive elements like Uranium are limited
    • No air pollutants (PM, SOx/NOx) or CO2/CH4 released when electricity is generated; mining of uranium & plant construction still release GHGs
    • Only gas released from elec. gen. is water vapor (which is technically a GHG, but stays in atm, very briefly)
  • Other drawbacks of nuclear energy include possibility of meltdown & radioactive contamination
    • Spent Fuel Rods: used fuel rods remain radioactive for millions of years & need to be stored in lead containers on site @ Nuclear PPs
    • Mine tailings: leftover rock & soil from mining may have radioactive elements that can contaminate water or soil nearby
    • Water use: nuclear PPs require lots of water and can deplete local surface or groundwater sources
  • Thermal Pollution: hot water from PP released back into surface waters can cause thermal shock (decreased O_2 & suffocation)
• Nuclear Meltdowns
  • Three Mile Island (US), Fukushima Japan, and Chernobyl Ukraine = 3 most famous nuclear meltdowns
    • Three Mile Island (US): partial meltdown due to testing error; radiation released but no deaths or residual cancer cases
    • Fukushima (Japan): an earthquake and tsunami triggered cooling pump failure that lead to a meltdown (explosion of reactor core) & widespread radiation release
    • Chernobyl (Ukraine): stuck cooling valve during test lead to complete meltdown (explosion of reactor core), several deaths, and widespread radiation release
  • Environmental consequences of meltdowns: genetic mutations & cancer in surrounding people, animals, and plants due to radiation released from reactor core
    • Contaminated soil: radiation can remain in soil and harm plants and animals in the future (genetic mutations)
    • Radiation spread: radiation can be carried by the wind over long distances, affecting ecosystems far from the meltdown site
• Practice FRQ 6.6 Identify and describe one letter in the diagram that is common to both nuclear and fossil fuel electricity production. Identify and describe one letter in the diagram that is found ONLY in nuclear power plants.

6.7 Energy From Biomass

• Learning Objective: ENG-3.1
  • Describe the effects of the use of biomass in power generation on the environment.
• Essential Knowledge:
  • ENG-3.1.1 Burning of biomass produces heat for energy at a relatively low cost, but it also produces carbon dioxide, carbon monoxide, nitrogen oxides, particulates, and volatile organic compounds. The overharvesting of trees for fuel also causes deforestation.
  • ENG-3.1.2 Ethanol can be used as a substitute for gasoline. Burning ethanol does not introduce additional carbon into the atmosphere via combustion, but the energy return on energy investment for ethanol is low.
• Suggested Skill: 7.B Environmental Solutions
  • Describe potential responses or approaches to environmental problems.
• Biomass vs. Biofuels
  • Biomass: organic matter (wood/charcoal, dried animal waste, dead leaves/brush) burned to release heat - primarily for heating homes/cooking.
    • Also can be burned in PPs to generate electricity (less common than FFs)
  • Biofuels: liquid fuels (ethanol, biodiesel) created from biomass (corn, sugar cane, palm oil).
    • Used as replacement fuel sources for gasoline, primarily in vehicles
    • Utilized primarily in developing world for heating homes & cooking food. Easy to harvest, available, cheap/free (subsistence fuel)
• Modern vs. Fossil Carbon
  • Biomass burning releases CO2, but doesn’t increase atmospheric CO2 levels like FF burning does
    • Burning biomass releases modern carbon (CO_2 that was recently sequestered, or taken out of the atmosphere) whereas FF burning releases fossil carbon that had been stored for millions of years
    • Biomass burning is considered “carbon neutral”
    • Think of spending a dollar someone just gave you vs. withdrawing from your long-term savings account to spend
• Human health & Env. Consequences of Biomass Burning
  • Biomass burning releases CO, NO_x, PM, and VOCs - all respiratory irritants
    • 3 billion people globally cook on open, biomass fires, mostly in developing world
  • Lack of environmental protection laws & financial resources for other fuels lead to more biomass deforestation in developing nations (Hab. loss, soil erosion, loss of CO2 sequestration, air & H2O filtration)
    • Biomass burn. indoors for heat/cooking worsens effects (pollutants trapped & conc.)
      • Worsened asthma, bronchitis, COPD, emphysema, eye irritation
  • Environmental consequences = deforestation & air pollutants
    • NO_x, VOCs, and PM all contribute to smog formation
• Biofuels: Ethanol & Algae
  • Corn & sugar cane are fermented into ethanol which is mixed w/ gasoline
    • Corn grain/sugar cane broken down & yeast ferment sugars → ethanol
    • E85 or flex fuel = 51-83% ethanol + gasoline mix; used in flex-fuel vehicles
      • Decreases oil consumption for transport, but is less efficient than pure gasoline
    • Soil erosion, hab. loss, GHG release (ag. soils, tractors, fertilizers) H_2O use. Lots of corn needed, relative to petroleum; can compete w/human cons. of corn. “renewable” only to the extent that the production of corn is sustainable (sugar cane is a perennial, and is more sustainable)
    • Environmental consequences = all the neg. consequences of monocrop ag.
  • Algae produce oils that can be used as biofuels more sustainably than corn
• Biodiesel
  • Liquid fuels produced specifically from plant oils (soy, canola, palm)
    • Palm oil biodiesel has been found to produce 98% MORE GHGs than FFs, due to clearing of forest for palm plantations, and if already cleared land is used, or if plantations are continually replanted (however, also causes all the env. impacts of ag), CO2 release, Loss of hab, Soil erosion, Loss of air/H2O filtration
    • Can be more sustainable
• Practice FRQ 6.7 Explain why biodiesel fuels have a different effect on atmospheric carbon levels than fossil fuels do. Describe TWO environmental benefits of using algae for biofuel production, rather than corn, palm oil, or sugarcane.

6.8 Solar Energy

• Learning Objective: ENG-3.J
  • Describe the use of solar energy in power generation.
• Essential Knowledge:
  • ENG-3.J.1 Photovoltaic solar cells capture light energy from the sun and transform it directly into electrical energy. Their use is limited by the availability of sunlight.
  • ENG-3.J.2 Active solar energy systems use solar energy to heat a liquid through mechanical and electric equipment to collect and store the energy captured from the sun.
  • ENG-3.J.3 Passive solar energy systems absorb heat directly from the sun without the use of mechanical and electric equipment, and energy cannot be collected or stored.
• Learning Objective: ENG-3.K
  • Describe the effects of the use of solar energy in power generation on the environment.
• Essential Knowledge: ENG-3.K.1
  • Solar energy systems have low environmental impact and produce clean energy, but they can be expensive. Large solar energy farms may negatively impact desert ecosystems.
• Suggested Skill: 5.C Data Analysis
  • Explain patterns and trends in data to draw conclusions.
• Active vs. Passive Solar Energy
  • Passive solar: absorbing or blocking heat from the sun, w/out use of mechanical/electrical equip.
    • Using sun’s heat to cook food in a solar oven
    • Orienting building design to block sunlight in warmer months & allow sunlight in during colder months
    • Double paned windows, southern facing windows w/roof overhang, deciduous shade trees, skylight to decrease elect. use, dark colored sunlight abs. floor
  • Active solar: use of mechanical/electrical equip. to capture sun’s heat (solar water heaters or CST - concentrated solar thermal), or convert light rays directly into electricity (PV cells)
    • Solar water heaters capture sun’s heat in water or circulating fluid & transfer heat to warm water for home - in place of electric/gas water heater
• Photovoltaic Cells (PV)
  • Aka “solar panels”; contain semiconductor (usually silicon) that emits low voltage electrical current when exposed to sun
    • Photons (particles carrying energy from sun) cause separation of charges between two semiconductor layers (n & p); electrons separate from protons & flow through circuit to load, delivering energy (as electricity)
  • A drawback is intermittency (solar energy can only be generated during the day)
    • Could be solved by cheaper, larger batteries that can store energy generated during the day for use at night, Currently these aren’t cost-effective yet
    • PV cells on a roof can directly power the building, or send excess electricity back to the grid for other users (earning you a credit from your utility company)
• Concentrated Solar Thermal (CST)
  • Heliostats (mirrors) reflect sun’s rays onto a central water tower in order to heat water to produce steam to turn a turbine → electricity
  • A drawback is habitat destruction & light beams frying birds in mid air
• Community (solar farm) vs. rooftop solar
  • FRQ tip: don’t just say “solar panels” differentiate between rooftop (individual home/business) solar and community or large-scale solar farms
    • Large-scale solar “farms” can generate lots of electricity, but do take up land and cause habitat loss/fragmentation
    • Rooftop solar doesn’t take up land, but only produces a little electricity
• Solar Energy Pros
  • No air pollutants (PM, SOx, NOx) released to gen. electricity
  • No CO_2 released when gen. electricity. Renewable, unlike FFs which will run out
    • Semiconductor metals (silicon) still need to be mined to produce PV cells (solar panels)
      • This can disrupt habitats & pollute water with mine tailings, air with PM
  • No mining of fossil fuels for electricity production
• Solar Energy Cons
  • Solar panel farms can displace habitats
  • Silicon is a limited resource
• Practice FRQ 6.8 Explain the relationship between the tracking ability of a solar PV system and its energy production. Given a graph of simulated energy production for solar PV in Los Angeles, what conclusions can be drawn?

6.9 Hydroelectricity

• Learning Objective: ENG-3.L
  • Describe the use of hydroelectricity in power generation.
• Essential Knowledge:
  • ENG-3.L.1 Hydroelectric power can be generated in several ways. Dams built across rivers collect water in reservoirs. The moving water can be used to spin a turbine. Turbines can also be placed in small rivers, where the flowing water spins the turbine.
  • ENG-3.L.2 Tidal energy uses the energy produced by tidal flows to turn a turbine.
• Learning Objective: ENG-3.M
  • Describe the effects of the use of hydroelectricity in power generation on the environment.
• Essential Knowledge: ENG-3.M.1
  • Hydroelectric power does not generate air pollution or waste, but construction of the power plants can be expensive, and there may be a loss of or change in habitats following the construction of dams.
• Suggested Skill: 7.F Environmental Solutions
  • Justify a proposed solution, by explaining potential advantages.
• Hydroelectricity Basics
  • Kinetic energy of moving water → spins a turbine (mechanical energy) → turbine powers generator
    • Water moves either with natural current of river or tides, or by falling vertically through channel in a dam
  • By far the largest renewable source of electricity globally
  • China, Brazil, and US = 3 biggest hydroelectricity producers
• Water Impoundment (Dams)
  • Dam built in a river creates a large artificial lake behind the dam (reservoir)
    • Damming the river enables operators to allow more or less water through the channel in the dam, increasing or decreasing electricity production (water flows