Electricity Basics: Watts, Volts, Amps, Kilowatt-Hours
The Central Distinction
The single most important distinction in energy literacy:
Power (watts) the rate of energy flow right now
Energy (watt-hours) the total amount of energy over time
Confusing these is the most common mistake in infrastructure coverage. "The solar farm produces 100 megawatts" and "the solar farm produces 100 megawatt-hours" mean very different things.
A 100 megawatt-peak solar farm can, at full sun, produce 100 megawatts of power, instantaneously. Over a year, it will produce maybe 200,000 megawatt-hours of energy (because it doesn't run at full power 24/7).
A useful analogy: power is like speed; energy is like distance. A car going 100 km/h for 1 hour covers 100 km. A car going 50 km/h for 2 hours also covers 100 km. Power (the speed) differs; energy (the distance) is the same.
The Unit Ladder
Power units (rate):
W watt basic unit; 1 joule per second
kW kilowatt 1,000 W
MW megawatt 1,000,000 W (a million watts)
GW gigawatt 1,000,000,000 W (a billion watts)
TW terawatt a trillion watts (planetary scale)
Energy units (quantity):
Wh watt-hour 1 W for 1 hour
kWh kilowatt-hour the standard unit on your electricity bill
MWh megawatt-hour 1,000 kWh
GWh gigawatt-hour 1,000,000 kWh
TWh terawatt-hour 1 billion kWh
The relationship: energy = power × time. A 1 kW heater running for 2 hours uses 2 kWh of energy.
Your electricity bill is in kWh. The utility is tracking energy, not power, though the peak power you draw can also matter (separate demand charges).
Scale
The numbers become intuitive once you anchor them to familiar things.
Household appliances (power)
LED lightbulb 10 W
Phone charger 5 W
Laptop 30-60 W
Desktop computer 100-500 W
Fridge 100-300 W (running; less on average)
Toaster 800-1500 W
Hair dryer 1500 W
Microwave 1000-1500 W
Electric kettle 2000 W (2 kW)
Electric oven 2000-3000 W
Electric car charger 7-11 kW (home); up to 350 kW (fast charger)
Household energy (over time)
US average home, annual ~10,000 kWh (or 10 MWh)
UK average home, annual ~4,000 kWh (gas is separate for heating)
One day of an average home ~30 kWh (US) or ~10 kWh (UK)
A laptop running 8 hours ~0.4 kWh
An air conditioner on a hot day 5-20 kWh
Generation (power capacity)
Rooftop solar array 3-10 kW
Large wind turbine 3-10 MW each
Utility solar farm 10 MW to several GW
Natural gas plant 100 MW to 2 GW
Nuclear reactor ~1 GW (large), ~300 MW (small modular, if built)
Large hydro dam Up to 22 GW (Three Gorges)
Aggregates
A small country peak demand ~1 GW
A large city peak demand 5-50 GW
California peak demand ~50 GW
US continental peak demand ~700 GW
Global electricity use ~30,000 TWh per year
Global primary energy ~180,000 TWh per year (all energy, not just electricity)
Knowing these to an order of magnitude makes infrastructure news immediately more readable.
Voltage and Current, Briefly
Two more units worth knowing, though they matter less for day-to-day literacy:
Volt (V) electrical pressure; higher voltage pushes more current
Amp (A) rate of electron flow; 1 coulomb per second
Watt = V × A power equals voltage times current
Your home outlets are at 120 V (US) or 230 V (most of the rest of the world) at low current. High-voltage transmission lines run at 100,000 V to 1,000,000 V to move large amounts of power with low losses.
High voltage matters because power losses in transmission are proportional to the square of current. For the same power, higher voltage means lower current means much lower losses. This is why transmission lines are high voltage and household wiring isn't.
AC and DC
Alternating Current (AC): the current direction reverses many times per second (50 or 60 times, depending on country). Used by most of the grid and household power.
Direct Current (DC): current flows one direction, like from a battery. Used inside most electronic devices, in solar panels, and in some long-distance transmission.
AC vs DC matters because:
- AC is easy to step up and down in voltage (with transformers). DC requires electronics
- Solar panels produce DC; they need inverters to feed the AC grid
- Electric vehicles use DC for motors and batteries; they charge from AC grid via onboard converters
- Long-distance undersea or cross-continent transmission sometimes uses HVDC (high-voltage DC) because AC has more losses at very long distances
For literacy: know that this distinction exists; you don't need the engineering details.
Frequency
The grid's AC runs at 50 Hz (Europe, Africa, most of Asia) or 60 Hz (US, Canada, parts of Latin America). This frequency is the heartbeat of the grid.
If generation exceeds demand, frequency rises slightly. If demand exceeds generation, frequency falls slightly. Grid operators balance supply and demand second by second to keep frequency stable.
The grid falling off its frequency (say, 59 Hz on a 60 Hz system) is a serious emergency; it can trip protective systems and cascade into blackouts. Chapter 04 covers the grid in detail.
Reading Your Bill
Your electricity bill typically shows:
- Total kWh used in the billing period
- Rate per kWh (possibly varying by time of day or season)
- Fixed charges (hook-up, meter, network fees)
- Taxes and surcharges
Compare: if you paid $0.15 per kWh and used 500 kWh, the usage portion is $75. Your actual bill is often more because of fixed charges and taxes.
The typical US household at 10,000 kWh/year at $0.15/kWh pays $1,500/year or $125/month in energy, plus fixed charges.
Many places have time-of-use pricing: higher rates during peak hours, lower at night. Some have fixed monthly capacity charges separate from usage. Details vary.
Primary Energy vs Final Energy
A subtle distinction, important for climate discussions:
- Primary energy: the energy content of fuels and natural resources (oil, coal, gas, uranium, sunlight, wind)
- Final energy: the energy delivered to the user (electricity, gasoline at the pump)
A gas power plant might be 50% efficient: 100 units of primary energy (gas) become 50 units of final energy (electricity). The rest is lost as heat.
This matters because:
- Electric cars use primary energy more efficiently than gas cars (even counting generation losses) because electric motors are more efficient than internal combustion engines
- Energy-transition statistics can look different depending on whether you count primary or final energy
- Renewables have no comparable "conversion loss" on the input side (sunlight and wind are free); this changes how totals compare across sources
Common Confusions
"My solar panels produce X watts"
At peak sun, for a few hours. Not on average. Not at night. A 5 kW peak rooftop system produces more like 20 kWh/day on average in sunny places, less elsewhere.
"The new plant is X megawatts"
That's capacity. Capacity factor tells you how much energy it actually produces. Solar at ~20-25% capacity factor; wind at ~30-45%; gas at variable; nuclear at ~90%. Chapter 08 explains capacity factor.
"We need more generation"
Sometimes. Often you need more transmission, or more demand flexibility, or more storage. "Generation" is one variable among several. Chapter 04 and 09 go deeper.
"Kilowatt-hours per hour"
This is just kilowatts. Someone who says "kilowatt-hours per hour" has confused the units. Gently correct them (internally) and proceed.
Common Pitfalls
"It's just units; who cares." Units are the first layer of literacy. You can't read any energy argument without them
"MW and MWh are the same." They're not, and the mistake often flips conclusions. Check every number for which kind
"I'll just memorise a few numbers." Memorise orders of magnitude. The specific numbers change; the orders don't. An LED is not 1 W or 100 W; it's about 10 W, and you should know that
"The bill is too confusing." It is, by design. Read the kWh used, the rate, and the total; ignore the administrative noise unless you're optimising
"We're running out of electrons." We're not. Electrons are conserved. We're running out of the capacity to produce and deliver enough power at the right moments. Power, not electrons, is the scarce quantity
Next Steps
Continue to 03-generation.md for how electricity actually gets made.