6.1 - Renewable V.S. Nonrenewable Energy Sources

Renewable V.S. Nonrenewable

• Renewable Energy Sources

  • Can be replenished naturally, at or near rate of consumption & reused.

  • Depletable renewables can run out if overused

    • Ex: Biomas (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

6.4 - Distribution of Natural Energy Resources

• Coal

  • US

  • Russia

  • China

  • Australia

  • ~100-150 years

• Natural Gas

  • Russia

  • Iran

  • Qatar

  • US

  • Saudi Arabia

  • ~50-60 years

• Oil

  • Venezuela

  • Saudi Arabia

  • Iran

  • Canada

  • Iraq

  • ~50 years

Fracking and 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

Crude Oil (Petroleum)

• Decaying organic matter trapped under rock layers is compressed into oil over time

• 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

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)

6.3 - Fuel Types and Uses

Subsistence Fuels

• 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

• 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

  • Charcoal is made by heating wood under low oxygen conditions for a long time

• 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

Coal Formation

• Pressure from overlying rock & sediment layers compacts peat into coal over time

• In order of energy density & quality: lignite → bituminous → anthracite

• The deeper a coal reserve is buried, the more pressure from overlying rock layers & the more energy-dense

• Because higher energy density means more energy released when a fuel source is burned, anthracite is the most valuable form of coal (highest quality)

  • 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

• 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

• Natural gas is mostly methane (CH4) and is found on top of trapped oil (petroleum) deposits

  • Forms when oil is trapped in a porous, sedimentary rock, underneath a harder, impermeable rock layer that doesn’t let the gas escape

• Considered the “cleanest” fossil fuel (produces the fewest air pollutants & least CO2 when burned)

  • Produces about ½ as much CO2 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

• Decaying organic matter trapped under rock layers is compressed into oil over time

• Extracted by drilling a well through the overlying rock layers to reach the underground deposit and then pumping liquid oil out under pressure

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)

6.5 - Fossil Fuels

Fossil Fuel Combustion

• Reaction between Oxygen (O2) & fossil fuels (hydrocarbons) that releases energy as heat and produces CO2 & H2O as products

• Remember: 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

Fossil Fuels to Generate Electricity

• The #1 source of electricity production globally is coal, followed by natural gas

• 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 and create energy.

  • Even nuclear energy works similarly, with nuclear fission producing the initial heat

Environmental Consequences: Coal

• Habitat destruction to clear land for mining

• Produces pollutants & releases CO2 (GHG → global warming)

  • Releases more CO2 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

• 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

• 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)

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)

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 (H2O 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

  • CO2 released by machinery during extraction, transport, refinement

Environmental Consequences: Crude Oil/Petroleum

• Possibility of spill (either from tanker ships or pipelines breaking

  • 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)

• Habitat loss or fragmentation when land is cleared for roads, drilling equipment, pipelines

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

  • 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

• Depletion of ground or surface waters nearby (as they’re drawn from for fracking fluid)

• Increased seismic activity (earthquakes) linked with wastewater injection wells (storing fracking fluid deep underground)

• Hab. loss/fragment

• CH4 (GHG) release

6.6 - Nuclear Energy

Nuclear Fission and 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 H2O → 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 H2O vapor)

Nonrenewable, but cleaner than Fossil Fuels

• ⛰ 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 O2 & 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 case

  • 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

6.7 - Energy From Biomass

Biomass VS. Biofuels

• Biomass: organic matter (wood/charcoal, dried animal waste, dead leaves/brush) burned to release heat - primarily for heating homes/cooking

  • Utilized primarily in developing world for heating homes & cooking food

    • Easy to harvest, available, cheap/free (subsistence fuel)

  • Can also 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

Modern VS. Fossil Carbon

• Biomass burning releases CO2, but doesn’t increase atmospheric CO2 levels like FF burning does

  • Burning biomass releases modern carbon (CO2 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 and Environmental Consequences of Biomass Burning

• Biomass burning releases CO, NOx, PM, and VOCs - all respiratory irritants

  • 3 billion people globally cook on open, biomass fires, mostly in developing world

  • Biomass burn. indoors for heat/cooking worsens effects (pollutants trapped & conc.)

    • Worsened asthma, bronchitis, COPD, emphysema, eye irritation

• Environmental consequences = deforestation & air pollutants

  • 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

  • NOx, VOCs, and PM all contribute to smog formation

Biofuels: Ethanol and 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

  • “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.

  • Soil erosion, hab. loss, GHG release (ag. soils, tractors, fertilizers) H2O use

  • Lots of corn needed, relative to petroleum; can compete w/human cons. of corn

  • 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

    • Can be more sustainable if already cleared land is used, or if plantations are continually replanted (however, also causes all the env. impacts of ag.)

6.8 - Solar Energy

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)

  • 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)

• 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

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 and Cons

• Pros

  • No air pollutants (PM, SOx, NOx) released to gen. electricity

  • No CO2 released when generating electricity

  • Renewable, unlike FFs which will run out

  • No mining of fossil fuels for electricity Production

• Cons

  • Semiconductor metals (silicon) still need to be mined to produce PV cells (solar panels)

    • This can disrupt habitats and pollute water with mine tailings, air with PM

    • Silicon is a limited resource

    • Solar panel farms can displace habitats

6.2 Global Energy Consumption

Developed VS. Developing Countries

• Developed nations use more energy on a per capita basis, but developing nations use more energy in total (higher pop.)

• The avg. US resident uses 5x as much energy as the world average.

• 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

Fossil Fuels: Most Used Energy Source:

• Fossil fuels are by far the most common fuel source globally

  • Oil ⇒ gasoline = main fuel for vehicles

  • Coal = main fuel for electricity gen.

  • Nat. gas = secondary fuel for electricity gen. & main fuel for heating

• Hydroelectric energy (dams used to create electricity) are second-largest source

  • Water spins a turbine which generates electricity

• 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

• Econ. development → affluence (wealth) → higher per capita GDP → energy use

• As developing nations develop, fossil fuel consumption will increase

  • Oil → Gasoline for vehicles

  • Coal & Nat. gas → electricity

    • Electricity demand for homes & manufacturing

Factors That Affect Energy Source Use

• Availability: fossil fuel use depends on discovered reserves and accessibility of these reserves

  • use of fossil fuels varies heavily with availability

• Price: fossil fuel 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

6.9 Hydroelectricity

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 through channel, turns turbine, turbine powers generator → ⚡)

  • Also allows for control of flow downstream, prevention of seasonal flooding due to high rainfall

  • Reservoirs are also a source of recreation money (boating fees, tourism, increased property values, fishing, etc.)

  • 2 big impacts = flooding of ecosystems behind dam & sedimentation (buildup of sediments behind dam)

Run of River System and Tidal Energy

• A dam diverts the natural current of a river through man-made channel beside the river

  • Natural current of the river turns the turbine...powers the generator...⚡

  • Less impactful to surrounding ecosystem since no reservoir is formed & ecosystems behind dam aren’t flooded

  • Doesn’t stop natural flow of sediments downstream like water impoundment systems do

  • Doesn’t generate nearly as much power & may be unavailable in warmer seasons when river water levels are lower

  • Tidal power comes from tidal ocean flow turning turbine (coastal areas only

Drawbacks of Hydroelectric Dams

• Ecological:

  • Reservoir floods habitats behind dam (forst/wetlands are gone; river becomes a lake)

    • Prevents upstream migration of fish like salmon, that need to swim up to spawning grounds to reproduce

    • Sedimentation changes upstream and downstream conditions

      • upstream becomes warmer (less oxygen) and rocly streambed habitats covered in sediment

      • downstream loses sediment (important nutrient source), decreased water level, loses streambed habitat

    • downstream wetlands especially suffer since nutrients in sediment don’t reach them

• Environmental:

  • fossil fuel combustion during dam construction, increased evaporation due to the larger surface area of the reservoir, and methane release due to the anaerobic decomposition of organic matter in reservoir

• Economic:

  • human homes and businesses must be relocated due to reservoir flooding, initial construction is very expensive (does create long-term jobs though), sediment buildup must be dredged (removed by crane) eventually

    • loss of ecosystem services from downstream wetlands, and potential loss of fishing revenue if salmon breeding is disrupted

Fish Ladders

• Cement “steps” or series of pools that migratory fish like salmon can use to continue migration upstream, around or over dams

  • Enables continued breeding for salmon, food source for predators like large birds, bears, and fishing revenue for humans

  • “Salmon cannon” is a similar alternative that enables salmon to be captured or directed into a tube that carries them over the dam

Benefits of Hydroelectric Dams

• No GHG emissions when producing electricity (initial construction does require cement

  • Reservoir & dam can be tourist attractions

  • Jobs are created to maintain the dam

  • Reliable electricity source generated for surrounding area

  • No air pollutants released during electricity generation (no PM/SOx/NOx)

• Allows for control of downstream seasonal flooding

  • In US, only 3% of dams are for hydroelectricity; 37% are for recreation/scenic purposes; 2nd most common purpose is flood control (allowing humans to build closer to rivers in floodplains that would normally be flooded seasonally)

    • This flood prevention is good for humans, but deprives river flood plains of nutrient-rich sediment that supports plant growth & nearby wetland habitats

6.10 Geothermal Energy

Geothermal Basics

• Natural radioactive decay of elements deep in earth’s core gives off heat, driving magma convection currents which carry heat to upper portion of mantle, close to earth’s surface

  • Water can be piped down into the ground and heated by this heat from the mantle

    • Hot water can be converted into steam → turbine → elect. or be used to heat homes directly

• Geothermal for electricity: naturally heated water reservoirs underground are drilled into & piped up to the surface (or water can be piped down into naturally heated rock layers

  • The heat from magma turns the water into steam, which is forced through pipes to spin a turbine

  • Water is cooled in cooling tower & returned to the ground to start the process over

  • Renewable since heat from earth’s core won’t run out; but only if groundwater is returned after use

Ground Source Heat Pump

• Often referred to as “geothermal” but technically the heat does not come from geologic activity (comes from the ground storing heat from the sun)

  • More accurate name is “ground source heat pump”

    • 10 feet down, the ground stays a consistent 50-60o due to holding heat from sun (not warmed by geothermal energy from magma - so not technically geothermal energy)

    • Heat absorbing fluid is pumped through a pipe into the ground where it either takes on heat from the ground, or gives off heat to the ground

      • In summer, heat from home transfers to liquid & liquid transfers heat to the ground, cooling house

      • In winter, liquid takes heat from ground & transfers it to the house, warming house

Geothermal Heating

• True geothermal heating involves piping water deep into ground to be heated by magma & then transfering heat from water to the building

  • Different than ground source heat pump

  • Well must go thousands of meters (kms) down into the ground to reach heated water reservoir

  • Heated water is piped up to surface & sent to homes or businesses to heat them

Geothermal Pros and Cons

• Pros

  • Potentially renewable, only if water is piped back into the ground for reuse

  • Much less CO2 emission than FF electricity

  • No release of (PM/SOx/NOx/CO) as is case with FFs

• Cons

  • Not everywhere on earth has access to geothermal energy reaching close enough to surface to access it

  • Hydrogen sulfide can be released, which is toxic and can be lethal to humans & animals

  • Cost of drilling that deep in the earth can be very high initially

    • Sometimes so high that it’s not even worth it

6.11 Hydrogen Fuel Cell

Hydrogen Fuel Cell Basics

• Use hydrogen as a renewable, alternative fuel source to fossil fuels

  • H2 gas and O2 are the inputs used to generate electricity; H2O is given off as a waste product

• H2 gas enters fuel cell where it’s split into protons (H+) and electrons (e-) by an electrolyte membrane that only lets protons pass through

  • Electrons take an alternative route (circuit) around the membrane, which generates an electrical current

  • O2 molecules enter fuel cell break apart into individual O atoms and combine with two hydrogens (H+) to form H2O as a by product (only emissions from F fuel cells)

• Most common application is in vehicles

  • Replaces gasoline (non-renewable, GHG releasing & air polluting) with H fuel (no air pollutants released & only H2O vapor)

Creating H2 Gas

• Key challenge to H fuel cells is obtaining pure H gas (b/c it doesn’t exist by itself as a gas naturally)

  • Separating H2 gas from other molecules like H2O or CH4 is very energy intensive

    • Two main processes are steam reforming (95% of all H production) and electrolysis (less common, but more sustainable)

• Steam Reforming: burning natural gas (CH4) & using steam to separate the H gas from the methane (CH4)

  • Emits CO2 & requires NG (FF) input

• Electrolysis: electrical current is applied to water, breaking it into O2 and H2

  • No CO2 emission, but does require electricity

Hydrogen As an Energy Carrier (Pros)

• Because H2 gas can be stored in pressurized tanks, it can be transported for use creating electricity later, in a different location

  • Unlike solar, hydro, and wind where the electricity must be used as soon as it’s generated & relatively closely to the location of generation

• Can also be used as a fuel for vehicles (replacing gasoline) or to create ammonia for fertilizer, or in the chemical industry

  • As a gasoline replacement, it emits no air pollutants (NOx/PM/CO) and only H2O (tech. a GHG) no CO2

  • Manufacture of many different industrial chemicals requires H2 gas

  • Can be stored as liquid or gas, making it easy to transport

  • H fuel cells are ~80% efficient in converting chemical energy in H2 & O2 into electricity (Coal PP = 35% efficient)

Drawbacks of H Fuel Cells

• ⛰Since 95% of H2 production requires methane (CH4), H fuel cells are based on a non-renewable & CO2 releasing energy source

  • If electrolysis is used to produce H2, it’s only as sustainable as the electricity source

  • Widespread H fuel cell use would require building widespread H distribution network (similar to current system for gasoline)

  • H fuel stored in gas form in vehicles would require much larger tanks than current gasoline tanks

6.12 Wind Energy

Wind Turbine Electricity Generation

• Kinetic energy of moving air (wind) spins a turbine; generator converts mechanical energy of turbine into electricity

  • Blades of turbine are connected to gearbox by a shaft that rotates; rotating gears create mechanical energy that the generator transforms into electricity

    • Avg. turbine can power 460 homes

    • Avg. wind turbine has 15-30% capacity factor (% of total possible energy it could generate)

      • Only produces electricity in 8-55 mph winds

    • Motorized drive within shaft can turn the turbine to face wind

Wind Turbine Location

• Clustered in groups (wind projects or farms) in flat, open areas (usually rural)

  • Locating them together makes service, repair, and building transmission lines to them easier

    • Can share land with agricultural use

• Offshore wind = wind farms in oceans or lakes

  • Capitalizes on faster wind speeds

  • Does require transmission lines built across long distances to reach land though

Wind Energy Benefits and Drawbacks

• Benefits:

  • Non-depletable (isn’t decreased by its use) - even better than renewable!

  • No GHG emissions or air pollutants released when generating electricity

  • No CO2 (climate change) or NOx/SOx/PM as with burning FFs

  • Can share land uses (don’t destroy habitat or cause soil/water contamination as FFs do)

• Drawbacks:

  • Intermittency (isn’t always available) can’t replace base-load power (sources that are always available like FFs, nuclear or Geothermal)

  • Can’t replace base-load power (sources that are always available like FFs, nuclear or Geothermal)

  • Can kill birds and bats (especially larger, migratory birds)

  • Can be considered an eyesore or source of noise pollution by some

6.12 Energy Conservation

Small Scale vs. Large Scale Energy Conservation

• Small Scale:

  • Lowering thermostat to use less heat or use AC less often

  • Conserving water with native plants instead of grass, low flow shower heads, efficient toilets, dishwashers, dryers

  • Energy efficient appliances, better insulation to keep more heat in home

• Large Scale:

  • Improving fuel efficiency (fuel economy) standards

    • Ex: 20 mpg → 30 mpg

  • Subsidizing (tax credits for) electric vehicles, charging stations, and hybrids

  • Increased public transport (buses & light rails), green building design

Sustainable Home Design

• Ways to either block out or take advantages of sun’s natural heat, or keep in heating/cooling to decrease energy required

  • Deciduous shade trees for landscaping (leaves block sun in summer, but allow it in during winter)

  • Using passive solar design concepts to trap sun’s heat & decrease energy from heating system (heat absorbing walls, triple or double paned windows)

  • Well-insulated walls/attic to trap heat in winter & cool air from AC system in summer

    • This decreases electricity used by AC unit & energy used by heating system

Water Conservation

• Native plants require less watering than traditional lawns (also increase biodiversity of pollinators & require less fertilizer)

• Low-flow showers, toilets, and dishwashers do the same job with less total water (less energy to purify & pump to homes)

• Rain barrels allow rain water to be used for watering plants or washing cars

Energy Conservation - Transportation

• ~28% of total US energy use comes from transport of goods & people (2019)

  • Improving fuel economy of US fleet of vehicles conserves energy as less gasoline/diesel is needed to travel same distance

    • CAFE (Corporate Average Fuel Economy) standards are regulations set in US to require auto manufacturers to make cars that meet certain MPG standards, or pay penalties

  • Hybrids (Prius) have both a gasoline & electric engine, enabling them to have higher MPG ratings

    • Breaking system charges the electric battery, which powers electric motor

  • Electric vehicles (EVs or BEVs) like the Tesla or LEAF use no gasoline, but still require electricity (only as sustainable as elect. source)

  • Public transit & carpooling are even better energy-saving transport options

Sustainable Building Design

• Decreasing the amount of energy required to build larger buildings & heat/cool them

  • Green roof or walls can decrease runoff, and absorb sun’s heat, decreasing energy needed for cooling building & surrounding area (lessens heat island effect)

  • Sun lights on roof, or windows on sides can decrease electricity used for lighting

  • Recycled materials can reduce energy required to produce new ones (glass, wood, even fly ash from coal can be used in foundation)

Managing Peak Demand and Smart Grid Tech

• Peak demand is the time of day or year (often early night time hours or very hot weather events) that electricity demand is highest

  • If demand exceeds supply, rolling blackouts occur

  • To manage peak demand, some utilities use a variable price model for electricity

    • Users pay a higher rate during peak demand hours or events, to discourage use

    • Users pay a lower rate/kWh when using a lower amount of energy (incentivizes lower overall use)

• “Smart Grid” is just the idea of managing demand & energy sources in a more varied way

  • Ex: using smart meters for variable price models, allowing rooftop solar to direct electricity back to grid, integrating more total energy sources (especially renewable)