Energy systems and markets
Every time you switch on a light, cook or charge your phone, you are drawing on an enormous system: hundreds of thousands of miles of power lines, thousands of power plants and a market that sets the price hour by hour. Think of your family's electric bill: Why does it change from month to month, and why might your utility charge more at 6 p.m. than at 2 a.m.? Understanding that system — which sources feed it, how what you consume is measured and why the price changes throughout the day — is the first step toward making sensible technical and economic decisions. We'll come back to that bill at the end of this page.
Primary energy sources
What reaches your home, and how it is billed
A home usually receives several supplies, and each has its own meter and billing unit. Electricity is measured by the electric meter in kilowatt-hours (kWh). Natural gas is measured by the gas meter in therms or in hundreds of cubic feet (ccf). Water is measured by the water meter in gallons or in hundreds of cubic feet. Gasoline or heating oil, if used, is bought by the gallon.
A bill usually has two parts: a fixed charge (a monthly fee for being connected to the grid, no matter how much you use) and a usage charge (the rate per kWh times the kWh you used). Sales tax or other fees may be added.
List the common energy supplies that reach a home (electricity, natural gas, etc.) and explain which meter measures the consumption of each and in which unit it is…
List the common energy supplies that reach a home (electricity, natural gas, etc.) and explain which meter measures the consumption of each and in which unit it is billed.
An electricity bill usually includes a fixed charge (for the agreed power capacity, even if not used) and an energy usage charge (for the $\text{kW} \times \text{h}$…
An electricity bill usually includes a fixed charge (for the agreed power capacity, even if not used) and an energy usage charge (for the $\text{kW} \times \text{h}$ consumed). Explain what each term pays for and analyze what would happen to the bill of a home that contracts a high power capacity but uses very little energy.
Classify these energy sources as renewable or non-renewable, briefly justifying each case: (a) solar, (b) coal, (c) wind, (d) natural gas, (e) hydroelectric, and (f)…
Classify these energy sources as renewable or non-renewable, briefly justifying each case: (a) solar, (b) coal, (c) wind, (d) natural gas, (e) hydroelectric, and (f) nuclear.
Explain the difference between primary energy (the source as obtained: sun, gas, uranium) and final energy (the energy you use: electricity at the outlet, gasoline at…
Explain the difference between primary energy (the source as obtained: sun, gas, uranium) and final energy (the energy you use: electricity at the outlet, gasoline at the pump), with an example of converting one into the other.
Name three renewable energy sources and write which natural phenomenon each one uses (solar radiation, wind, dammed or flowing water).
Name three renewable energy sources and write which natural phenomenon each one uses (solar radiation, wind, dammed or flowing water).
Power and energy: the unit that gets billed
Explain with a household example the difference between power (measured in $\text{kW}$) and energy (measured in $\text{kW} \times \text{h}$): use the example of a…
Explain with a household example the difference between power (measured in $\text{kW}$) and energy (measured in $\text{kW} \times \text{h}$): use the example of a $2000\ \text{W}$ oven turned on for half an hour to illustrate both quantities.
The electric bill charges for $\text{kW} \times \text{h}$. Explain what $1\ \text{kW} \times \text{h}$ represents using an example (a $1000\ \text{W}$ appliance running…
The electric bill charges for $\text{kW} \times \text{h}$. Explain what $1\ \text{kW} \times \text{h}$ represents using an example (a $1000\ \text{W}$ appliance running for one hour) and why it is a unit of energy and not of power.
Service capacity (the amperage rating of your home's electrical service) is the maximum power you can use at the same time at home. Explain what happens if you plug in…
Service capacity (the amperage rating of your home's electrical service) is the maximum power you can use at the same time at home. Explain what happens if you plug in appliances that exceed it (the circuit breaker trips and power is cut) and how the situation is resolved.
A house has a contracted power capacity of $4.4\ \text{kW}$. Calculate whether the oven ($2\ \text{kW}$), washing machine ($2\ \text{kW}$), and electric cooktop (…
A house has a contracted power capacity of $4.4\ \text{kW}$. Calculate whether the oven ($2\ \text{kW}$), washing machine ($2\ \text{kW}$), and electric cooktop ($1\ \text{kW}$) can operate at the same time by adding their power ratings, and explain two practical choices that would prevent exceeding the limit without changing rate plan.
From the power plant to the home: the power grid
The smart electricity meter measures and communicates consumption. Explain what it measures exactly, how often it sends data to the utility company, and one advantage it…
The smart electricity meter measures and communicates consumption. Explain what it measures exactly, how often it sends data to the utility company, and one advantage it has over the traditional meter.
The figure shows the chain that carries electricity from where it is generated to a house, but one of the stages is covered with a question mark, as shown in the figure.…
The figure shows the chain that carries electricity from where it is generated to a house, but one of the stages is covered with a question mark, as shown in the figure.
Indicate which stage is missing from the chain, explain what happens during it, and explain why that stage is carried out at very high voltages instead of directly at $220\ \text{V}$.
Between the power plant and your home there are several transformers. Explain what a transformer does, why voltage is stepped up for transmission and stepped down for…
Between the power plant and your home there are several transformers. Explain what a transformer does, why voltage is stepped up for transmission and stepped down for consumption (in relation to line losses), and where you have seen transformers in your town or city (substations, pad-mounted transformers, utility poles).
The electricity market: price, mix and time of day
A country's 'energy mix' is the breakdown of sources used to generate its electricity. Analyze why this distribution matters so much in three areas: dependence on other…
A country's 'energy mix' is the breakdown of sources used to generate its electricity. Analyze why this distribution matters so much in three areas: dependence on other countries, price stability, and greenhouse gas emissions, giving an example of a source in each argument.
Time-of-use rates divide the day into periods with different prices. Explain how this works, which household appliances should be scheduled during off-peak hours…
Time-of-use rates divide the day into periods with different prices. Explain how this works, which household appliances should be scheduled during off-peak hours (electric water heater, washing machine, dishwasher), and why these appliances can wait while others cannot.
Rooftop solar and managing intermittency
Solar energy is cheap but intermittent; natural gas is expensive but available on demand. Explain what renewable intermittency is and three ways to manage it in the…
Solar energy is cheap but intermittent; natural gas is expensive but available on demand. Explain what renewable intermittency is and three ways to manage it in the electrical system (pumped-storage reservoirs, batteries, interstate transmission lines).
A bill has a fixed monthly charge of $\$10$ and a usage of $250\ \text{kW} \times \text{h}$ at $0{,}\$18$ per $\text{kW} \times \text{h}$. (a) Calculate the total amount…
A bill has a fixed monthly charge of $\$10$ and a usage of $250\ \text{kW} \times \text{h}$ at $0{,}\$18$ per $\text{kW} \times \text{h}$. (a) Calculate the total amount excluding tax. (b) Calculate what percentage of the total corresponds to usage and what percentage to the fixed charge. (c) Reason who is affected more by a high fixed charge: someone who uses a lot or someone who uses very little.