Notes
Renewable vs nonrenewable
- Nonrenewable: fossil fuels (coal, oil, natural gas) and nuclear (uranium). They form far slower than we use them.
- Renewable: solar, wind, hydroelectric, geothermal, biomass, tidal. They're replenished naturally.
- Developed countries use far more energy per person. Fossil fuels supply most of the world's energy.
Fossil fuels
- Coal is cheap and abundant but releases the most $\mathrm{CO_2}$ per unit energy, plus $\mathrm{SO_2}$, mercury and particulates. Ranks: lignite, bituminous, anthracite (most carbon, most energy).
- Natural gas burns cleanest of the fossil fuels (mostly $\mathrm{CO_2}$ and water) but methane leaks are a strong greenhouse gas. Hydraulic fracturing (fracking) can contaminate groundwater.
- Oil is used for transportation. Tar sands require lots of energy and water to process.
- Cogeneration uses waste heat from electricity generation for heating, increasing efficiency.
Electricity generation
Most power plants burn fuel to boil water; steam spins a turbine attached to a generator. Typical efficiency is about 33 to 40%.
Nuclear power
Fission of uranium-235 releases heat. No $\mathrm{CO_2}$ during operation, but there's radioactive waste with long half-lives, risk of accidents (Chernobyl, Fukushima), and thermal pollution.
Renewables
- Solar: photovoltaic cells and solar thermal. Intermittent; needs storage.
- Wind: no emissions during operation, but intermittent and can kill birds and bats.
- Hydroelectric: reliable, but dams flood habitat, block fish migration and trap sediment.
- Geothermal: uses Earth's internal heat; limited to certain places.
- Biomass: wood, ethanol, biodiesel. Can be carbon-neutral if regrown, but burning releases particulates.
- Hydrogen fuel cells only release water, but making hydrogen often uses fossil fuels.
- Conservation: efficient appliances, LED lights, insulation, public transportation, and higher fuel economy.
Practice
Coal is mostly carbon.
Earth's internal heat is continuously replenished.
Fluids and gas can leak into aquifers.
$\displaystyle \frac{350}{1000} = 35\%$.
$60\text{ W} \times 10\text{ h} = 600$ Wh $= 0.6$ kWh.
Reservoirs change river ecosystems.
Fission heats water like other steam power plants.
LEDs provide the same light with less electricity.
Free response
Write your answer first, then open the scoring guide.
Free-response question
A family's home uses 900 kWh of electricity per month. Their utility charges $0.15 per kWh.
(a) Calculate the family's yearly electricity cost.
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$900 \times 12 = 10{,}800$ kWh per year. $10{,}800 \times 0.15 = 1{,}620$ dollars per year.
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(b) The family installs solar panels that produce 400 kWh per month. Calculate the yearly savings.
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$400 \times 12 \times 0.15 = 720$ dollars per year.
Check off the points you earned:
(c) Describe one environmental benefit and one drawback of solar panels.
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Benefit: no air pollution or $\mathrm{CO_2}$ while producing electricity. Drawback: panels make power only when the sun shines (intermittent), and producing them uses mining and toxic materials.
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