The National Electricity Supply System

Electricity as a national system

In Grade 8 you learnt how electricity travels from a power station to your home. In Grade 9 we zoom out further: electricity is not just a local pipeline, it is a national system that must constantly balance how much electricity is being generated against how much is being used (demanded) by homes, businesses, factories, hospitals and schools right across the country, at every moment of the day.

Generation: where South Africa's electricity comes from

Most of South Africa's electricity is generated by Eskom, the state-owned power utility, using a mix of sources:

Transmission: moving electricity across the country

Power stations are often far from cities. Electricity is stepped up to very high voltages (hundreds of thousands of volts) using transformers, then carried over long distances along the national grid — a network of pylons and transmission lines criss-crossing the country. High voltage is used because it reduces energy losses over long distances.

Distribution: getting power to the end user

Near towns and cities, transformers step the voltage back down at substations. Municipalities then distribute this lower-voltage electricity through local networks to homes, schools, farms, and businesses. This is the "last mile" of the system.

Supply and demand: a constant balancing act

Electricity is difficult and expensive to store in large quantities, so it must be generated at almost the exact same moment it is used. This means the amount of electricity flowing onto the grid (supply) must be carefully matched to the amount being drawn off it (demand) at every instant.

• Demand rises and falls throughout the day — for example, it is usually higher in the early morning and evening (people cooking, heating, using appliances) and lower late at night.
• Demand also varies by season — winter evenings in South Africa typically see the highest demand of the year, due to heating and earlier darkness.
• If supply is greater than or equal to demand, the system runs normally.
• If demand exceeds the electricity available to supply it, the grid becomes unstable and could fail completely (a total blackout) unless action is taken.

Load shedding: a real example of supply-demand mismatch

Load shedding is the controlled, planned switching off of electricity to particular areas, on a rotating schedule, when the total demand on the national grid is greater than the electricity available to supply it. It is used as a last resort to protect the whole grid from an uncontrolled collapse.

• Why it happens: South Africa's generation capacity (largely ageing coal power stations requiring maintenance and breakdowns) has, at various times, not been able to keep up with national demand.
• How it works: Eskom and municipalities divide the country into groups ("stages"). As the shortfall between supply and demand grows, higher load shedding stages are declared, and more areas are switched off for scheduled periods to reduce total demand back to a level the available supply can handle.
• Why not just make more? Building new large power stations or maintaining old ones takes years and enormous investment — supply cannot be increased overnight to match a sudden shortfall.

Diversifying supply for the future

To secure a more reliable electricity supply, South Africa is working to diversify its energy sources — relying on a wider mix of generation methods rather than coal alone:

• Solar power: South Africa has some of the highest levels of sunshine in the world, making solar photovoltaic and solar-thermal power stations highly effective, especially in provinces like the Northern Cape.
• Wind power: Coastal and inland wind farms (e.g. in the Eastern and Western Cape) are being built to add electricity to the grid.
• Independent power producers (IPPs): Private companies are increasingly licensed to generate electricity (often renewable) and feed it into the national grid alongside Eskom's supply.
• Household and business solar: More homes, farms and businesses are installing their own solar panels and battery storage, reducing the demand they place on the national grid.