Energy for the layperson

The plain version

Power is the rate at which energy is delivered, measured in watts (W). Energy is the total amount delivered over time, measured in watt-hours (Wh).

A 100 MW power plant running flat out for 24 hours produces 2,400 MWh of energy. The plant's size is power; what it actually delivered is energy.

• Kilowatt (kW) = 1,000 W — a household kettle or a small solar roof
• Megawatt (MW) = 1 million W — a small to medium power plant
• Gigawatt (GW) = 1 billion W — a national fleet (Eskom is ~46 GW)
• Terawatt (TW) = 1 trillion W — continental and global scale

Why it matters on your bill

Utilities bill you for energy (kWh), but they must build for power (kW) — enough capacity to meet the highest moment of demand. That is why peak demand, not total consumption, drives the cost of new plants.

Definition

Capacity factor is the ratio of the energy a plant actually produces to what it would produce running at full output all year.

A solar farm typically lands at 20–25% because of night and cloud. A geothermal plant in Kenya's Rift Valley can exceed 90%, which is why it serves as baseload.

• Solar PV: 20–25%
• Onshore wind: 25–40%
• Hydro: 30–60% (rainfall dependent)
• Geothermal: 85–95%
• Coal / CCGT: 50–85% depending on maintenance and fuel supply

Electromagnetic induction

Hydro, wind, coal, gas, geothermal and nuclear all end in the same place: something spins a coil inside a magnetic field and induces a current. Only the force doing the spinning changes.

Thermal cycles

Coal and steam plants use the Rankine cycle: burn fuel, boil water, expand steam through a turbine, condense, repeat. Efficiency sits at 30–40%.

Gas turbines use the Brayton cycle: compress air, burn gas, let hot gas drive the turbine directly. Combining both cycles (CCGT) recycles exhaust heat and pushes efficiency past 60%.

The photovoltaic effect

Solar PV skips the heat entirely. Photons knock electrons loose in silicon and produce current directly — no moving parts, which suits remote and harsh sites across the continent.

Three segments

Generation converts a primary source into electricity. Transmission moves it long distances at high voltage to limit losses. Distribution steps it down and delivers it to homes and businesses.

Losses and quality

Transmission and distribution losses exceed 20% in several Sub-Saharan countries, split between technical losses (heat in the wires) and non-technical losses (theft and billing errors). Cutting losses by five points can free more power than a new mid-sized plant.

Grids must also hold frequency near 50 Hz and voltage in a narrow band. When demand outruns generation the frequency falls, equipment trips, and the grid can collapse.