Why Electricity Prices Move Hour To Hour

Wholesale electricity prices change every few minutes and can swing enormously within a day. The mechanism is a direct consequence of the fact that power cannot easily be stored.

Supply and demand must match continuously

Electricity consumed at any instant must be generated at that instant. There is no inventory to draw down and no backlog to work through later.

System operators therefore run markets that clear repeatedly through the day, matching offers to generate against forecast demand for each short interval.

Because the balancing is continuous, prices are recalculated continuously, which is unusual among commodities and is the root of the volatility.

The marginal generator sets the price

Generators are dispatched in order of cost, cheapest first, until demand is met. The price paid is set by the last unit required.

Every generator receives that price regardless of its own cost, which gives cheaper plants their margin and keeps the incentive to reduce costs intact.

This is why adding low-cost generation lowers prices broadly. It pushes more expensive plants out of the dispatch order, changing which unit sits at the margin.

Demand follows predictable daily patterns

Consumption rises in the morning as activity begins, dips in the middle of the day in some systems, and peaks in the evening.

Weather shifts the whole curve, since heating and cooling loads are large and respond quickly to temperature. Forecasting error therefore translates directly into price movement.

Because the shape is broadly known in advance, most of the volatility comes from deviations rather than from the underlying pattern.

Fuel costs move the whole curve

Where gas plants frequently set the marginal price, the gas market propagates into electricity prices with little delay.

A sustained change in fuel cost shifts price levels across all hours, distinct from the hour-to-hour variation caused by demand and renewable output.

This is why electricity and gas prices often appear to move together even in systems where gas provides a modest share of total generation.

Scarcity produces extreme values

When available capacity barely exceeds demand, prices can rise to levels far above normal, because the market must attract every remaining resource.

These intervals are rare but account for a disproportionate share of annual revenue for plants that run only occasionally, which is how such plants remain viable.

Most markets impose a cap on how high prices may go, which limits exposure but also weakens the signal that would otherwise attract new capacity.