Demand: When Do We Use Energy?

Power usage changes from moment to moment as devices are turned on and off. The power needed each moment is called demand. For example, if every home in Stehekin turns on an electric space-heater at the same time, the community as a whole would have very high demand in that moment. If all the space-heaters are turned off the next minute, the demand drops.

The demand in any given moment drives how much power must be generated. Stehekin has limited power generation, so its demand is also limited.

The Problem: Demand Peaks

Most of the time, Stehekin’s demand is within the amount of power the hydro plant can generate. As an example, the power demand of a single day in Stehekin is shown below. For most of the day, demand is not a problem (shown in green), and the hydro plant can generate enough power to meet the community power needs.

The problem occurs when the demand goes above what the hydro plant can generate. This happens 7 times in the below example (shown in yellow). Each time, the D2 diesel generator was turned on.

If the peak demand is greater than what the hydro and D2 can generate together, power outages occur. As demand in Stehekin continues to grow, these demand peaks could occur more often and for longer.

Graph showing generator output at Stehekin Power Plant on August 8, 2019.

Demand in the Future

The peak demand in Stehekin can already reach the limit of what the existing hydro plant and D2 generate, and we project that demand will continue to grow in the future. Applications for new electrical service in the Stehekin Valley are expected to greatly increase peak demand, and the existing hydro and D2 generators cannot meet the expected demand.

It’s difficult to predict the moments of high demand. Based on historical data, peak demand issues typically happen when the average annual demand is above 150 kW. We expect this limit to be reached sometime between 2021 and 2027, as shown below.

A graph of past and projected future load growth in Stehekin.