Upgrades to existing natural gas and hydroelectric generation plants, adding new renewable resources, and enhanced energy efficiency measures are the highlights of the 2011 electric integrated resource plan (IRP) that Avista submitted Thursday to Washington and Idaho state regulators.

The plan details projected growth in demand for energy and the new resources needed to serve customers over the next 20 years.

In the 2011-2031 IRP timeframe, Avista anticipates adding almost 100,000 retail customers with a 1.6 percent annual growth in electric demand.

The utility plans to meet this growth with a mix of new renewable and natural gas generation resources, efficiency upgrades at existing generation facilities and various energy efficiency measures.

Avista Utilities President Dennis Vermillion said, "The IRP describes strategies to meet projected energy demand and renewable portfolio standards through energy efficiency and a careful mix of new renewable and traditional energy resources."

This plan helps us balance meeting customers' needs for safe, reliable energy with satisfying renewable portfolio standards, both in the near and long term, he said.

The plan calls for Avista to continue system upgrades and improvements to deliver energy to our customers more efficiently and reliably, he said.

It calls for Avista to obtain new resources in a responsible and environmentally sound manner and at a reasonable cost to our customers, Vermillion said.

"Energy efficiency is one of the lowest-cost new sources of energy," he said. "Together with our customers we can make wise use of all our energy resources."

Each IRP is a thoroughly researched and data-driven document to guide responsible resource planning for the utility. The IRP is updated every two years and looks 20 years into the future.

"The IRP was developed with the help of a technical advisory committee made up of customers, utility commission staff, consumer advocates, academics, utility peers, government agency staff and Avista's energy analysts," said Clint Kalich, manager of resource planning for Avista.