Unit 6 Beta

Energy Resources and Consumption: the one-page sheet

6.1 Renewable and Nonrenewable Resources

Energy resources are sorted by how fast nature replaces them. Nonrenewable sources (coal, oil, natural gas, nuclear fuel) form over millions of years, so their supply is fixed. Renewable sources are replenished on a human timescale: sunlight and wind are nondepletable, while wood and other biomass are depletable and stay renewable only if they are harvested no faster than they regrow.

Nonrenewable resources exist in a fixed amount and form far more slowly than we use them: coal, oil, natural gas and the mined ore used as nuclear fuel.
Renewable resources are replenished naturally at or near the rate we use them: sunlight, wind, moving water, Earth's internal heat and biomass.
Some renewables are nondepletable (sunlight, wind): use does not reduce the supply. Others, like wood, are depletable: renewable only if harvest does not outpace regrowth.
Renewable is about the rate of replacement, not about pollution: a source can be low carbon and still nonrenewable, and wood smoke pollutes even though wood is renewable.

every unit burned today is gone for any human timescale, so the supply is fixed and nonrenewable using it does not lower tomorrow's supply, so it is renewable and nondepletable the stock shrinks year after year, so a renewable resource is depleted the stock stays steady and the resource stays renewable in practice

renewable resource: An energy source or resource that is replenished naturally at or near the rate people use it, such as sunlight, wind, moving water, Earth's internal heat and biomass.
nonrenewable resource: A resource that exists in a fixed amount and forms far more slowly than people use it, such as coal, oil, natural gas and nuclear fuel.
depletable resource: A renewable resource that can run down if it is used faster than it is replaced, such as wood cut faster than the forest regrows.

6.2 Global Energy Consumption

The world runs mostly on fossil fuels, about 80 percent of its energy. Energy use per person is far higher in developed countries, while total use is growing fastest in developing countries as their populations and incomes rise. Reading energy data means comparing totals and per-person values with numbers, and percent change is (new - old) / old × 100.

Fossil fuels supply about 80 percent of the world's energy. Oil is the largest single source, used mostly for transportation; coal is the largest single source of electricity worldwide.
Energy consumption per person is highest in developed countries. The United States has about 4 percent of the world's people and uses roughly one sixth of its energy.
Use is rising fastest in developing countries as they industrialize. About 2.1 billion people lack clean cooking fuels and burn mostly wood, charcoal, crop waste or dung.
Total use = population × use per person. Read graphs for both the total and the per-person value, and compare with numbers.

factories, vehicles, appliances and heating or cooling spread energy use per person rises, often more than tenfold world use of coal, oil and natural gas keeps growing world energy use rises as developing countries grow in both

energy consumption: The amount of energy a person, country or the world uses in a period, given as a total (such as exajoules per year) or per person (such as gigajoules per person per year).

6.3 Fuel Types and Uses

The main fuels differ in energy per kilogram, carbon dioxide per unit of energy and use. Coal ranks from lignite to bituminous to anthracite as heat and pressure raise its carbon and energy content. Crude oil is refined into transportation fuels; natural gas, mostly methane, releases about half the carbon dioxide of coal for the same energy but is not zero emissions. Cogeneration puts waste heat to use.

Coal ranks by energy content: peat (not yet coal), lignite, bituminous, anthracite. Coal is used mainly for electricity and steel making.
Petroleum (crude oil) is refined by boiling point into gasoline, diesel, jet fuel, heating oil and asphalt. Tar sands hold bitumen, a heavy oil that takes much energy and water to extract.
Natural gas is mostly methane. It releases about half the carbon dioxide of coal per unit of energy: cleaner, but not zero emissions.
Wood and charcoal are the main fuels for many poorer households. Cogeneration captures waste heat from making electricity and uses it to heat buildings or water.

they do not fully decay and form peat it becomes lignite, then bituminous coal, then anthracite energy per kilogram rises, so less fuel is needed for the same energy it releases less carbon dioxide per unit of energy, though not zero

coal: A solid fossil fuel formed from plants buried in swamps and changed by heat and pressure over millions of years; it ranks from lignite to bituminous to anthracite as its carbon and energy content rise.
peat: Partly decayed plant material from waterlogged bogs; the first stage in coal formation, with high moisture and low energy per kilogram.
natural gas: A fossil fuel that is mostly methane; it releases about half as much carbon dioxide per unit of energy as coal, but it is not zero emissions.
petroleum: Crude oil: a liquid fossil fuel formed from buried sea organisms and refined by boiling point into gasoline, diesel, jet fuel, heating oil and asphalt.
cogeneration: Combined heat and power: using the waste heat from making electricity to heat buildings or water, so more of the fuel's energy is put to use.
tar sands: Deposits of sand, clay, water and bitumen (a thick, heavy oil); the bitumen is mined or melted out with steam, using much energy and water, and upgraded to crude oil.

6.4 Distribution of Natural Energy Resources

Energy resources are spread unevenly because they depend on geology and climate. Fossil fuels sit in sedimentary basins where ancient organisms were buried; Earth's internal heat is near the surface at plate boundaries; sunlight, wind and falling water vary with latitude, clouds and terrain. A country without the resources it uses must import energy. Proven reserves count what can be recovered profitably now, and reserve ÷ yearly production estimates how long they last.

Fossil fuels lie where ancient swamps and seas buried organic matter: a few regions hold most of the world's oil and gas, and a few countries most of the coal.
A proven reserve is the part of a deposit that is known and can be recovered profitably with today's technology; it rises with higher prices or new techniques, not only new discoveries.
Renewables depend on place too: sunlight is strongest in dry, clear, lower-latitude regions; wind on coasts, plains and offshore; falling water on steep rivers with steady flow; Earth's internal heat at plate boundaries.
Years a reserve lasts = reserve ÷ production per year, if production stays the same.

coal, oil and natural gas are concentrated in those sedimentary rocks heat from underground is practical in places like Iceland, but not everywhere renewable resources also vary from place to place it must import energy, so its supply and prices depend on other countries

proven reserve: The part of a fuel deposit that is known to exist and can be recovered profitably at current prices with current technology; it changes with prices, technology and production.

6.5 Fossil Fuels

A fossil fuel power plant burns fuel to make steam, which spins a turbine and generator. Each step loses energy as heat, so only about a third of the fuel's energy becomes electricity; overall efficiency is the product of the step efficiencies. Fossil fuels are dense and reliable but release carbon dioxide and pollutants. Fracking has unlocked shale gas and oil, with risks to groundwater and air.

A power plant converts energy in steps: chemical (fuel) to heat (steam) to motion (turbine) to electricity (generator). Each step loses some energy as heat.
Overall efficiency is the product of the step efficiencies: $0.88 \times 0.37 \times 0.98 \times 0.94$ $\approx 0.30$ , about 30 percent. To find the input needed, divide the output by the efficiency.
Hydraulic fracturing cracks shale with high-pressure water, sand and chemicals to free natural gas and oil; it can contaminate groundwater and release volatile chemicals and methane.
Fossil fuels are energy-dense, storable and reliable, but they release carbon dioxide and air pollutants, their extraction damages land and water, and their supply is fixed.

its chemical energy heats water into high-pressure steam the turbine spins a shaft connected to the generator electricity flows out to the power lines about two thirds of the fuel's energy is lost as waste heat, and burning releases carbon dioxide

power plant: A facility that makes electricity; in a thermal power plant, fuel heats water into steam that spins a turbine, which turns a generator.
hydraulic fracturing: Hydraulic fracturing: pumping water, sand and chemicals under high pressure into shale rock to crack it and free natural gas or oil.

6.6 Nuclear Power

Nuclear power plants split uranium-235 nuclei in a controlled chain reaction; the heat makes steam that spins a turbine, with no carbon dioxide released while running. Radioactive isotopes decay with a fixed half-life, so amount left = start × 0.5^(time ÷ half-life). The costs are a nonrenewable mined fuel, waste that must be stored for thousands of years, warm water released to rivers, and the rare but severe risk of a meltdown.

The fuel is uranium enriched to about 3 to 5 percent uranium-235. Nuclear fission splits its nuclei, releasing heat and neutrons in a chain reaction; control rods absorb neutrons to control it.
Radioactive decay: unstable nuclei give off radiation and change into other elements. The half-life is the time for half of the radioactive atoms to decay. Amount left = start × 0.5^(time ÷ half-life).
Nuclear waste (spent fuel) stays dangerous for thousands of years; it is kept in cooling pools and then dry casks, and the United States has no permanent storage site.
No air pollution or carbon dioxide while running, but uranium is nonrenewable, mining it disturbs land, plants release warm water, and a meltdown (Three Mile Island 1979, Chernobyl 1986, Fukushima 2011) can spread radioactive material.

the nucleus splits (fission), releasing heat and 2 or 3 more neutrons a steady chain reaction makes a steady supply of heat steam spins a turbine and generator, with no carbon dioxide released spent fuel must be cooled and stored for thousands of years, and loss of cooling can cause a meltdown

uranium: The radioactive metal used as nuclear fuel; reactor fuel is enriched to about 3 to 5 percent uranium-235, the isotope that splits easily.
nuclear fission: The splitting of a heavy nucleus, such as uranium-235, when struck by a neutron, releasing a large amount of heat and more neutrons that can continue a chain reaction.
radioactive decay: The process in which an unstable nucleus gives off radiation and changes into a different element or isotope.
half-life: The time it takes for half of the radioactive atoms in a sample to decay; amount left = starting amount × 0.5^(time ÷ half-life).
nuclear waste: Radioactive material left from nuclear power, mainly spent fuel rods, which stays dangerous for thousands of years and must be stored away from people and water.
meltdown: Severe overheating of a reactor core after loss of cooling, so the fuel melts and radioactive material may escape, as at Three Mile Island, Chernobyl and Fukushima.

6.7 Energy from Biomass

Biomass energy releases the sunlight stored in wood, crops and waste, either by burning or by making biofuels such as ethanol and biodiesel. It is renewable when harvest matches regrowth, and regrowth reabsorbs the carbon dioxide released. But burning biomass pollutes the air, especially indoors, and fuel crops use land, water and fossil energy; clearing forest for them can release more carbon than the fuel saves.

Biomass energy comes from wood, charcoal, crop waste, dung and plants grown for fuel. It is renewable but depletable.
Biofuels: ethanol is fermented from crop sugars (corn, sugarcane) and blended into gasoline; biodiesel is made from plant oils or animal fats.
Burning biomass releases carbon dioxide, soot and particles. Indoor smoke from cooking fires harms the lungs, a major cause of illness in poorer countries.
Biomass is near carbon neutral only if regrowth keeps pace. Corn ethanol takes much fossil energy to make; clearing forest for fuel crops releases more carbon than the fuel saves.

energy and carbon are stored in wood, crops and waste its energy is released, along with carbon dioxide, soot and other pollutants they take the carbon back up, so the cycle is close to carbon neutral carbon dioxide rises, habitat is destroyed and soil erodes

biofuel: A liquid or gas fuel made from biomass, such as ethanol fermented from corn or sugarcane, biodiesel from plant oils or animal fats, and biogas from manure or waste.

6.8 Solar Energy

Solar energy can be turned into electricity by photovoltaic cells or by mirrors that make steam, or used as heat through active collectors or passive building design. It releases no emissions while running and never runs out, but it is intermittent, so it needs storage or backup, and large solar farms use land and can disturb habitat. Savings are kWh times the price per kWh.

Photovoltaic cells turn sunlight directly into electricity. Active solar systems use collectors with pumps or fans to move heat, and concentrated solar plants use mirrors to make steam. Passive solar design uses windows, overhangs and thermal mass.
In the Northern Hemisphere, sun-facing windows and panels face south; in the Southern Hemisphere, north.
Solar releases no air pollution or carbon dioxide while running, but its intermittency (night, clouds, winter) means it needs storage or backup.
Drawbacks: large land area for big farms, habitat disturbance in deserts, and mining and manufacturing for panels. Savings = kWh × price per kWh.

it knocks electrons loose and makes an electric current, with no fuel and no emissions the heat warms water or buildings, or drives a turbine a building warms itself in winter with no pumps or fans output falls, so solar needs storage, a grid or backup

photovoltaic cell: A photovoltaic (PV) cell turns sunlight directly into electricity, with no moving parts; many cells make a solar panel.
passive solar: Heating and lighting a building with the sun through its design alone: sun-facing windows, overhangs and thick walls or floors that store heat, with no pumps or fans.
active solar: Solar systems that use equipment such as pumps, fans or mirrors to collect and move the sun's heat, including rooftop water heaters and concentrated solar power plants.
intermittency: The property of an energy source that is not available all the time, such as solar at night or wind on calm days; it means storage or backup is needed.

6.9 Hydroelectric Power

Hydroelectric power turns the energy of falling water into electricity with a turbine and generator. It is renewable, emits nothing while running and can be adjusted quickly, which makes it the world's largest renewable source of electricity. But dams flood valleys, displace people, block fish migration, trap sediment and change rivers downstream. Run-of-the-river and tidal systems avoid large reservoirs but have their own limits.

Hydroelectric power: falling water spins a turbine and generator. Output depends on how much water flows and how far it falls.
Types: large dams with reservoirs (storage, flexible output), run-of-the-river systems (little or no reservoir, less flooding, output follows the river) and tidal energy (tides driven by the moon).
Advantages: renewable, no emissions while running, reliable, quick to adjust, reservoirs store energy and help control floods.
Disadvantages: flooded land and displaced people, blocked fish migration, trapped sediment, altered river flow and temperature, methane from decaying plants in reservoirs, and reduced output in droughts.

the water stores energy because of its height it spins a turbine that turns a generator, making electricity with no fuel burned land and homes are lost, sediment settles behind the dam, and decaying plants release methane fish migration is cut off and the river below gets less sediment and changed flow and temperature

hydroelectric power: Electricity made by water falling through a turbine that turns a generator, usually at a dam that holds water in a reservoir.
run-of-the-river: A hydroelectric system that runs part of a river's natural flow through turbines with little or no reservoir, so it floods little land but its output follows the river.
tidal energy: Electricity made by turbines that catch the flow of ocean tides, which are caused by the moon's gravity, as they move in and out of a bay or channel.

6.10 Geothermal Energy

Geothermal energy is heat from Earth's interior. Where hot rock is near the surface, at plate boundaries and hot spots, wells bring up steam to spin turbines day and night, and cooled water is reinjected so the resource lasts. Ground source heat pumps move heat between buildings and the steady-temperature shallow ground almost anywhere. Limits are few good power plant sites, drilling costs, some released gases and the risk of depleting a field.

Geothermal energy is heat from Earth's interior, from radioactive decay and heat left from Earth's formation. It is renewable when managed.
Power plants need very hot water or steam near the surface, found near plate boundaries and hot spots (Iceland, New Zealand, California). They run day and night.
A ground source heat pump uses electricity to move heat between a building and shallow ground, which stays at a steady temperature, so it works almost anywhere.
Drawbacks: few suitable sites for power plants, high drilling costs, release of hydrogen sulfide and dissolved minerals, and depletion if water is withdrawn faster than it is replaced.

heat flows outward and is close to the surface near plate boundaries and volcanoes the steam spins a turbine and generator, day and night, with no fuel burned the reservoir is refilled so the heat source is not depleted a ground source heat pump can heat a building in winter and cool it in summer almost anywhere

geothermal energy: Heat from Earth's interior, from radioactive decay and heat left from Earth's formation, used to make electricity where hot rock is near the surface or to heat buildings.
ground source heat pump: A ground source heat pump uses electricity to move heat between a building and the ground a few meters down, which stays at a steady temperature, heating in winter and cooling in summer.

6.11 Hydrogen Fuel Cell

A hydrogen fuel cell turns the chemical energy of hydrogen and oxygen into electricity without burning, and its only exhaust is water. But hydrogen is an energy carrier that must be made, mostly from natural gas today, so emissions move to where it is produced. Fuel cells refuel quickly and suit buses and trucks, but hydrogen is hard to store, fueling stations are scarce, and the chain from electricity to wheels is far less efficient than a battery.

A hydrogen fuel cell combines hydrogen and oxygen to make electricity, with water as the only exhaust. No combustion, no carbon dioxide from the cell.
Hydrogen is an energy carrier: it must be made. Most comes from natural gas (releasing carbon dioxide at the plant); electrolysis with renewable electricity is very low carbon but costs more.
Fuel cell drawbacks: few fueling stations, hydrogen is hard to store (high pressure, flammable, low density), costly catalysts, and energy lost making and moving hydrogen.
Do not confuse with battery cars: long recharging times and large mined lithium batteries are battery-car drawbacks. Fuel cell vehicles refuel in minutes and have long range.

hydrogen stores that energy as a fuel (an energy carrier) ions cross the membrane while electrons flow through the outside circuit as electric current water forms as the only exhaust; nothing is burned the whole chain is less efficient than charging a battery directly

hydrogen fuel cell: A hydrogen fuel cell combines hydrogen and oxygen chemically, without burning, to make electricity; its only exhaust is water, but the hydrogen must first be made using energy.

6.12 Wind Energy

Wind turbines turn the kinetic energy of moving air into electricity with blades, a gearbox and a generator. Wind is renewable, needs no fuel, releases no carbon dioxide while running and shares land with farming, so it has some of the lowest life-cycle emissions of any source. Its drawbacks are intermittency, which calls for storage or backup, harm to birds and bats, noise and views, and the need for new power lines.

A wind turbine turns the kinetic energy of moving air into electricity. A wind farm is a group of turbines, on land or offshore.
Taller towers and offshore sites reach faster, steadier wind; output rises steeply with wind speed (about eight times for double the speed).
Advantages: no fuel, no emissions while running, very low life-cycle carbon dioxide, land shared with farming, income for landowners.
Drawbacks: intermittency, bird and bat deaths, noise and changed views, and new transmission lines from remote windy areas.

wind carries kinetic energy across plains, coasts and seas the rotor turns a shaft, a gearbox speeds it up and a generator makes electricity there is no air pollution or carbon dioxide while running, and land below can still be farmed output falls, so a grid with much wind needs storage, a wide network or backup

wind turbine: A machine whose blades are spun by the wind, turning a generator to make electricity; a group of them is a wind farm, on land or offshore.

6.13 Energy Conservation

Energy conservation means using less energy; energy efficiency means using less for the same service. Savings are calculated by chains whose units cancel: the change in watts times hours, converted to kWh, then times the price for dollars and times the emission factor for carbon dioxide. At home, insulation, thermostats, LEDs and efficient appliances save energy; at large scale, fuel economy standards, hybrid and electric vehicles, public transportation and green building design do.

Energy conservation is using less energy (turning things off, lowering the thermostat, driving less). Energy efficiency is getting the same service with less energy (LEDs, insulation, efficient appliances).
Energy (kWh) = power (kW) × time (h). Set up chains so units cancel: W × h/day × day/yr × 1 kWh/1,000 Wh.
Then convert: cost = kWh × price per kWh; carbon dioxide = kWh × kg per kWh; payback = extra cost ÷ yearly savings.
At home: insulation, programmable thermostats, LEDs, efficient appliances, shade trees and windbreaks. Large scale: fuel economy standards, hybrid vehicles and electric vehicles, public transportation, green building design.

the home uses fewer kWh of electricity and less fuel for the same comfort and light power plants burn less fuel to meet demand less carbon dioxide and other pollution is released, and the family pays less savings are multiplied across millions of homes and vehicles

energy conservation: Using less energy, usually by changing behavior, such as turning off lights, lowering the thermostat or driving less.
energy efficiency: Getting the same service with less energy, such as LED bulbs, insulation or appliances and cars that use less energy for the same work.
hybrid vehicle: A vehicle that pairs a gasoline engine with an electric motor and battery, recapturing braking energy to use less fuel; an electric vehicle runs on a battery alone.