Environmental Science / Unit 8: Energy Resources
8.1 Energy Basics and Sources
Notes
Energy is the ability to do work. Humans use energy for electricity, transportation, heating, and industry.
- Nonrenewable sources: coal, oil, natural gas (fossil fuels), and uranium. Renewable sources: solar, wind, hydro, geothermal, biomass, tidal.
- Fossil fuels supply about 80% of the world's energy today.
- Electrical energy is measured in kilowatt-hours (kWh): $\text{energy (kWh)} = \text{power (kW)} \times \text{time (h)}$.
- Energy efficiency $\displaystyle = \frac{\text{useful energy output}}{\text{total energy input}} \times 100\%$. Most energy conversions waste energy as heat (second law of thermodynamics).
- Example: a 2 kW heater running for 5 hours uses $2 \times 5 = 10$ kWh. At $0.15 per kWh the cost is $1.50.
Practice
A 1.5 kW space heater runs for 4 hours. How much energy does it use?
$1.5 \times 4 = 6$ kWh.
A 100-watt (0.1 kW) bulb runs for 10 hours. Electricity costs $0.20 per kWh. What is the cost?
$0.1 \times 10 = 1$ kWh, and $1 \times $0.20 = $0.20$.
A power plant takes in 100 units of fuel energy and delivers 35 units of electricity. Its efficiency is:
$\displaystyle \frac{35}{100} \times 100\% = 35\%$. The remainder is lost as waste heat.
Ready for more? Take the Unit 8 test.