By Philip Reed
Editor's note: The following report summarizes data from WAPA's Hydropower Conditions webpage for straight power purchase costs, which are based solely upon hydrology, actual hydropower generation and related generation shortages. Readers may review all data by visiting wapa.gov, Power Marketing, Hydropower Conditions
One of the biggest challenges for hydropower is water variability due to intermittent drought and flooding. By definition, hydropower needs water to generate electricity. Without it, WAPA must buy power on the open market from other sources to meet contractual obligations to its customers. This is referred to as purchased power.
In an ideal year, snowpack around the West is average or above average, yielding snowmelt runoff to recharge reservoirs behind the dams and powerplants that provide the power WAPA markets. Federal dam owners such as the Bureau of Reclamation, the Army Corps of Engineers and the International Boundary and Water Commission move water to federal hydroelectric powerplants.
WAPA markets the subsequent power generated to around 700 preference customers. Its customers, in turn, sell that power to more than 40 million Americans.
Water around WAPA in 2021
WAPA's actual generation was 80% of average in water year 2021, for a total generation of 21,916 gigawatt-hours. For the same period, total purchased power was 3,976 GWh with actual purchase power expenses of $250,236,417 equating to $62.93 per megawatt-hour.
The Colorado River Storage Project Management Center projected most probable purchase power expenses for water year 2021 to be $57,140,561. Actual purchase power expenses were a bit lower, at $50,722,378. The cost per MWh was $41.07.
Lake Powell ended the water year with an elevation of about 3,545 feet, or 155 feet from maximum reservoir level and 55 feet from the minimum generation level. The storage volume for Lake Powell was 7.3 million acre-feet at the end of September, or about 30% of capacity.
Extreme drought throughout the Colorado River Basin has resulted in about 181,000 acre-feet of additional water being released from Upper Colorado River Basin reservoirs to try to maintain Lake Powell elevation above 3,525 feet. However, even with additional releases from upstream reservoirs, Lake Powell is expected to drop below 3,525 feet. Consequently, additional releases from these reservoirs are being considered.
Desert Southwest's hydrology is mostly dependent on the Colorado River Basin snowpack and precipitation above Lake Powell. The region's most probable projected purchase power expenses were $31,965,259. Actual purchase power expenses were lower, at $25,518,630, with a cost per MWh of $100.43.
Lake Mead elevation at the end of September was around 1,068 feet, or about 117.8 feet above the minimum generation elevation for Hoover Dam. The total side inflow into Lake Mead for water year 2021 was 593,000 acre-feet, which represents a 31% decrease from the previous year and 46% of the normal annual side inflow.
Aggregate system storage for the Lower Colorado River Basin, or Lakes Mead, Mohave and Havasu, was 11.2 million acre-feet at the end of September, or 39% of the Lower Basin capacity.
In Rocky Mountain, at the end of September, reservoir inflows were 67% of average and reservoir storage was 99% of average. The most probable projected purchase power expenses were $13,382,848, but actual purchase power expenses were notably higher at $23,247,676. The cost per MWh was $39.26.
Sierra Nevada ended the water year with 54% of the 15-year average reservoir storage for Trinity, 47% for Shasta, 53% for Folsom and 66% for New Melones. Accumulated inflow for the same date was 32% of the 15-year average for Trinity, 52% for Shasta, 35% for Folsom and 36% for New Melones. The region began water year 2021 with a most probable projection of purchase power of $6,009,783 but ended with a significantly higher actual expense of $18,846,261. The cost per MWh was $31.48.
In Upper Great Plains, extreme drought conditions are occurring in most of North Dakota, northwest South Dakota and northeastern Montana, with some exceptional drought conditions in northcentral Montana and North Dakota. Severe and moderate drought as well as abnormally dry conditions are present in much of the lower half of South Dakota.
The yearly runoff forecast for the Missouri River basin as of Nov. 1 was 15.4 million acre-feet, or 58% of average. Runoff above Sioux City for October was .92 MAF, or 75% of average. System storage as of Nov. 23 was 43.4 MAF. The region's most probable projection for purchase power was $23,562,864. Actual purchase power expenses were $131,901,472. The cost per MWh was $101.75.
Average purchase power amounts and prices for the year were skewed by the extreme pricing and increased purchasing during the polar vortex on Feb. 15-16, with UGP significantly exceeding its purchase power estimates for the year in only February.
Anticipating water year 2022
The Seasonal Drought Outlook provided by the National Weather Service's Climate Prediction Center in November 2021 predicted persistent drought throughout the western United States. Additional significant drought development is also predicted in states such as Arizona, Colorado, Kansas, New Mexico, Oklahoma and Texas.
The predictions show drought conditions improving in the northwest, such as in Idaho, Oregon, Washington and Wyoming.
The NWS emphasized that its predictions are made in accordance with large-scale trends, which are based on “subjectively derived probabilities guided by short- and long-range statistical and dynamical forecasts." They emphasize caution and regular checking of updated drought predictions.
Note: The author is a public affairs specialist.