Pursuant to the commission’s rulemaking authority, public utilities supplying electric or natural gas service to customers shall periodically file an integrated resource plan with the commission. Utility integrated resource plans shall evaluate renewable energy, energy efficiency, load management, distributed generation and conventional supply- side resources on a consistent and comparable basis and take into consideration risk and uncertainty of fuel supply, price volatility and costs of anticipated environmental regulations in order to identify the most cost-effective portfolio of resources to supply the energy needs of customers. The preparation of resource plans shall incorporate a public advisory process. Nothing in this section shall prohibit public utilities from implementing cost-effective energy efficiency and load management programs and the commission from approving public utility expenditures on energy efficiency programs and load management programs prior to the commission establishing rules and guidelines for integrated resource planning. The commission may exempt public utilities with fewer than five thousand customers and distribution-only public utilities from the requirements of this section. The commission shall take into account a public utility’s resource planning requirements in other states and shall authorize utilities that operate in multiple states to implement plans that coordinate the applicable state resource planning requirements. The requirements of this section shall take effect one year following the commission’s adoption of rules implementing the provisions of this section.