A recent Arizona State University report has found that estimated reserve margins across the Western states will be far lower than previous estimates suggest. Reserve margins are a measure of available generation capacity over and above the capacity needed to meet normal peak demand levels. Regulatory bodies usually require producers and transmission facilities to maintain a constant reserve margin of 10% to 20% of normal capacity as insurance against breakdowns across the system or sudden increases in energy demand.
The study, which looks at power delivery over the next 50 years for the 14 Western states served by the Western Electricity Coordinating Council (WECC), found that extreme heat events and drought are occurring with greater frequency and duration, putting a significant strain on installed and planned generation capacity. According to estimates published in the study, power providers may be overestimating planning reserve margins by as much as 20% to 25%.
For a system designed to deliver safe, affordable, and reliable power, this is a problem. Power providers do not currently account for climate change impacts in their operations, which could leave utilities and grid operators more exposed to unforeseen weather events than previously thought.
According to the study, forecasts about the impact on specific generation sources vary. Baseload nuclear and coal power plant capacity would be most impacted by reduced cooling water during the hottest days. Reduced stream flow would is also expected to reduce hydroelectric capacity in drier regions, but increased precipitation, particularly in the Pacific Northwest, could temper these losses. Although, combustion turbines – fueled by natural gas or renewable natural gas (RNG) in some cases – and solar PV lose output as air temperate rises, the impact on solar PV capacity is expected to be negligible. The researchers also concluded that potential changes in wind speed and air density would not have a major impact on wind generation capacity.
The study points to increased momentum behind the power grid becoming more distributed and dynamic. Not only are solar PV, energy efficiency, and other distributed energy resources (DER) a powerful tool for reducing greenhouse gas emissions across the grid, with the emergence of the energy cloud, they will help utilities and grid operators deliver on their obligation to provide safe, affordable, and reliable power.
A Way Forward
Increased penetration of DER also reduces the impact of line loss, a key issue across the West. As bulk high-voltage power cable shoulders the burden of moving capacity from remote areas to population centers dispersed across the expansive Western region, aging high-voltage power cables are prone to expansion and sagging, causing more resistance across the system and requiring increasing levels of generation. Severe heat events could exacerbate the situation further, eventually posing a threat to public safety.
Although the Arizona State University study is worrisome, many of the innovations and tools necessary to mitigate the impact of climate change on the grid are available today. Efforts by the U.S. Environmental Protection Agency to regulate carbon emissions in the power sector through the Clean Power Plan (CPP) are expected to force utilities and regulators to shift the generation mix away from heavily polluting generation sources, which would help insulate the WECC region from the impact of severe heat and drought.