Regional growth, the expiration of large purchased-power contracts in coming years and the potential retirement of aging power plants are the principal drivers behind PSE's need for additional power supplies. PSE's latest Integrated Resource Plan, published in July 2009, estimates that the utility will need the equivalent of about 1,600 megawatts (MW) of new electricity supply by winter 2016-17 to meet customers' needs. Since filing its IRP, PSE has refined its resource-need analysis and concluded the resource need is higher than stated in the plan. PSE plans to file a resource-need addendum to its IRP by the end of this month, which will increase the amount of resources sought in the RFP. The new need will be presented at the proposal conference scheduled for Jan. 28, 2010.