SMUD, Among Other Utilities, Uses Cloud Seeding To Increase Hydropower

Cloud seeding could become increasingly prevalent in California as utilities there face the twin challenges of drought and reaching the state’s net zero emission goals intended to combat global warming.

The Sacramento Municipal Utility District (SMUD), one of several California utilities with a cloud seeding program, provides an example of how a public power utility uses the technology to augment its hydroelectric resources.

SMUD uses cloud seeding to increase snowfall on the Upper American River Basin where the utility has a series of hydroelectric dams. Increased snowfall leads to more snowpack. When the snow melts and runs off, it increases the amount of water in the utility’s reservoirs, providing greater potential for hydropower generation during high electric demand summer months.

SMUD has been using cloud seeding since 1969 and has found that “on average cloud seeding increases snowpack by roughly three to 10 percent,” Kaitlyn Bednar, SMUD’s hydrographer, said.

“So, for example, in an average year if we get 50 inches of snow water equivalent, cloud seeding can increase that value to 55 inches, translating to a large increase in runoff and power generation,” Bednar said.

“That extra five inches more than pays for itself and provides carbon free power,” Bednar said, noting that the equivalent generation from a natural gas-fired plant would produce “six thousand times as much carbon dioxide as our seeding program.”

SMUD’s current budget for its cloud seeding program is $1.5 million over five years, but the allocations vary from year to year depending on the hydrological conditions and the number of suitable storms.

SMUD’s program focuses on glaciogenic seeding, which laces clouds with microscopic silver iodide particles. Those particles have a similar crystal structure to ice that allows moisture to attach to them and grow heavy enough to precipitate in the form of snow.

SMUD’s seeding season runs from Mid-November through mid-April. In addition, certain criteria are needed for a successful seeding. The clouds need to have a suitable water content, and the temperature has to be cold enough, at least negative 4 degrees Celsius, for moisture to crystalize on the silver iodide particles and then precipitate as snow. “We rarely have a season we don’t cloud seed,” Bednar said. This season, SMUD had 10 seedable events. The goal is to have the utility’s reservoirs completely full by the end of the winter months. “We’ll take all the moisture we can get,” she said.

A third party, RHS Consulting, does the actual seeding for SMUD by flying in or above clouds and setting off silver iodide flares mounted either on the plane’s wing or belly. Each seeding event uses a handful of flares with each flare emitting anywhere between 20 to 200 grams of silver iodide.

The amount of silver iodide released during cloud seeding is not harmful to the environment, Bednar said. It is low in toxicity, insoluble in water, and has low bioavailability. SMUD also tests the areas seeded every five years and to date has found no adverse effects. The utility uses two control areas outside of the project area where cloud seeding does not occur to compare with its seeded area.

Other California public power and investor-owned entities, such as the Northern California Power Agency and Pacific Gas and Electric, also have been engaged in cloud seeding operations for years. And the California Energy Commission (CEC) with the state Department of Water Resources in November hosted a workshop on Cloud Seeding for Precipitation Enhancement.

The CEC, in fact, “may consider future research related to cloud seeding, as described by the proposed EPIC 4 investment plan,” Michael Ward, CEC’s media officer, said via email.

If approved by the state’s Public Utilities Commission, that initiative could support efforts to, “advance strategies for managing California’s hydropower resources for optimal contribution to grid operations and foster development of cost-effective, robust approaches for meeting anticipated needs for zero-carbon, fast-ramping resources,” the CEC said.

Those efforts could include “field research to measure, and ultimately improve, the cost-effectiveness and efficacy of precipitation enhancement through seeding clouds with tiny particles intended to increase the amount of atmospheric water vapor that condenses and falls to the ground as snow or rain,” The CEC said.

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