Pulse: how the price moves across the day

Why an average day has this shape

The shape comes from two daily rhythms laid on top of each other. Demand rises in the morning as people wake and businesses open, stays high through the working day and peaks again in the early evening, when homes light up and cook. Solar output rises with the sun, peaks around midday and is gone by evening. Where there is plenty of solar, the midday hours become the cheapest of the day even though demand is high.

After sunset, solar drops away within a couple of hours while demand is still near its peak. Gas plants, imports, pumped storage and batteries that can start quickly fill the gap. They are the dearest plants in the queue, and the last one needed sets the price for everyone selling in that hour. Residual Load shows that evening gap directly, and Marginal Fuel models which kind of plant is setting the price.

The chart averages every weekday in the window onto one axis. A windy winter day can be cheap from morning to night and a still, cloudy one dear all day, and neither looks much like the average. The Spread shows how far apart the prices were on each single day.

The seasons move the curve as well. The midday dip is deep in summer, when the sun is up for longer and higher in the sky. In winter it all but disappears, and the cheapest hours fall at night. A household on a flat tariff pays the same for every hour, so the swing reaches its bill only through a dynamic tariff, which Flexibility explores.