Keeping the Lights On

Improving how the Northwest assesses power supply adequacy

The Council is set to make improvements to the Northwest’s resource adequacy assessment this year.  John Fazio, senior power systems analyst, discussed the upcoming work to improve the annual assessment, which acts as an early warning of potential future power shortfalls, giving the region time to invest in new generating resources and in energy efficiency.   

If you need a reason why this work is important, look no further than the state of Texas. In 2021, during an intense cold snap, demand for electricity exceeded the Electric Reliability Council of Texas (ERCOT) forecast. Meanwhile, parts of the natural gas system failed, resulting in widespread blackouts that left millions of customers without electricity.  

First, some background. What is a resource adequacy assessment and how is it done? Fazio defines a resource adequacy assessment as “a measure of the ability of a power system to meet the energy requirements of its customers within acceptable limits, considering a reasonable range of uncertainty in resource availability and in demand.”

At the Council, the adequacy of the Northwest power supply is assessed annually for a single year far enough in the future so corrective actions can be made to the power system. The adequacy assessment should not be confused with the Council’s power plan, which provides a 20-year resource strategy covering a wide range of future uncertainties.

Our primary assessment tool is a computer model called GENESYS, which contains a complete representation of the Northwest power system and potential energy markets outside the region. Many different combinations of electricity demand; river flows for hydro generation; wind and solar patterns; and plant outages are modeled to determine if the existing power system can serve all demand under these varying conditions. Each combination analyzed is a simulation. Can the power system meet demand for every hour of the year? If not, there is a shortfall. The Council measures shortfalls through its Loss of Load Probability (LOLP) metric.

It must be stressed that a shortage measured by the model is not the same as a curtailment or blackout. A shortage means that the modeled system is unable to meet demand without taking emergency actions. An emergency action may prevent a shortage from turning into a blackout. The LOLP is just a measure of how often emergency actions are likely to be used.

For an example of emergency actions, lets saddle up and head back to Texas. Just a few days ago in the midst of a heat wave on May 13, ERCOT asked Texans to conserve power by setting their thermostats to 78-degrees or above and avoid using large appliances during peak hours.

The beauty of the LOLP is its simplicity – reducing results of complex modeling algorithms into a single metric. And for the Pacific Northwest, the Council deems the power supply to be adequate if the LOLP is 5 percent or less.

But is it telling enough of the story? Fazio points out that the LOLP does not measure the magnitude, duration, or frequency of potential future shortfalls. This means that the LOLP cannot distinguish between a small, one-hour shortfall and a large, long-duration shortfall.   

The upcoming work will focus on evaluating three other metrics that measure the number of shortfall events; the number of shortfall hours; and the amount of demand not served. While the GENESYS model already includes these metrics, the Council will be exploring how to set limits for each metric for future resource adequacy assessments. Over the next several months the Council will work with its advisory committees to explore options and understand implications.

Wherever the work takes us, this next resource adequacy assessment is going to be an interesting ride and we invite you to engage and follow along here.