The development of an adequate resource strategy requires an assessment of the needs of the regional power system over time. The needs are assessed for the baseline and different policy scenarios, and a way to identify the capabilities of resources within a strategy to meet those needs are calculated.

The load-resource balance[1] of the power supply can provide a general indication of future resource needs. However, better and more accurate methods of assessing those needs are available. Load-resource balance is a deterministic assessment of resource gaps and is calculated by simply comparing expected future demand with expected resource availability. For planning purposes, a reserve margin is commonly added to the demand forecast, to account for future uncertainties, such as river flows, temperature, generator forced outages and renewable resource generation. The objective is to ensure that generating capability equals the expected demand plus reserves. However, this approach does not guarantee an adequate supply because reserves may fail to cover all possible combinations of undesirable future conditions. Furthermore, load-resource balance does not provide any indication of the likelihood, the magnitude or the duration of potential shortfall events, which are key parameters for system planners. A better approach toward assessing resource needs is to use probabilistic methods, which more accurately quantify the amount of generating capability needed to ensure that the likelihood of shortfall events does not exceed customer’s tolerance (i.e., the Council’s adequacy standard).

The Council’s adequacy assessment is used as a check on resource development. It assesses whether the regional power supply has sufficient resources to limit the LOLP to no more than 5 percent, assuming only existing resources and the targeted level of energy efficiency savings. The Council’s needs assessment differs from an adequacy assessment in that it does not include targeted energy efficiency savings and generally spans a longer period (20 years vs. 5 years). The needs assessment determines the expected magnitude of energy and capacity shortfall gaps during key years over the study horizon. The gaps are assessed by estimating how much new generating capability is needed to ensure that the power supply’s LOLP does not exceed the Council’s five percent adequacy standard.

[1] The load-resource balance for the regional power supply is reported annually in the Bonneville Power Administration White Book and in the PNUCC Northwest Regional Forecast of Loads and Resources.