The Sacramento Municipal Utility District's withdrawal this week from a major Northern California power-transmission project complicates its transition to renewable energy.

SMUD planners foresaw using the new high-voltage lines to carry power to Sacramento from new wind, solar and geothermal energy projects envisioned for Lassen County and northwestern Nevada. SMUD cited financial uncertainties for the pullout.

Together, the projects could have provided nearly all of the new renewable energy SMUD needs to line up over the next decade to meet state and district mandates, said Jim Shetler, the utility's assistant general manager.

"We've got a lot of hole to fill," he said Thursday.

SMUD is on pace to get one-fifth of its electricity from renewable sources this year. By 2020, the figure must hit 33 percent - an increase of about 1.7 billion kilowatt-hours of renewable energy a year.

It would take around 700 megawatts of new solar or wind capacity to hit that target. That's equivalent to around 200,000 typical residential rooftop solar-power systems.

SMUD already must go far afield for its low-carbon power. This year, about half will be generated outside California. The utility buys electricity from wind farms in Oregon and a biomass plant in Washington. It pays a landfill operator in Texas to pump methane into the natural gas pipeline network to offset some of the gas burned in SMUD's Cosumnes power plant.

Without access to Lassen-area renewables, SMUD will look to maximize local resources, Shetler said. It is expanding wind farms on its 6,000 acres of property in Solano County. The same land might support tens or even hundreds of megawatts of solar power. Local efforts to turn garbage and plant waste into energy might chip in as much as 100 megawatts. Small hydroelectric projects could add a few dozen megawatts.

SMUD is developing a plan - due by the end of the year - that will formalize its renewable-energy strategy through 2020, Shetler said.

Weighing investments in renewable power is particularly difficult now because the electricity sector is changing so rapidly.

Many clean-energy technologies haven't been widely deployed yet, adding uncertainty to cost comparisons.

Rules governing the power grid are evolving, making it difficult to predict the feasibility of buying electricity from distant sources in the future.

In addition, as renewable-power mandates take hold elsewhere in the country, SMUD and other California utilities are likely to face more competition - and higher prices - when they bid for out-of-state energy.

It's possible that SMUD could still get some power from renewable-energy projects in the Lassen County area. If another investor steps in and the transmission lines are built, SMUD might be able to purchase any excess capacity.