The grid is changing rapidly. Not only is the U.S. power supply shifting from coal to gas and increasingly renewable energy, but the rise of behind-the-meter resources are creating a new electricity paradigm.
The evolution in thinking is slower, with many clinging to concepts such as baseload power. A new report by energy software expert Dick Brooks and his firm, Reliable Energy Analytics, looks at how other ways of looking at and talking about electricity demand could be updated to serve the needs of electricity supply today and in the future.
Comparing ISO Load Forecasting Methodology takes as its starting points the methodologies used by ISO New England and New York ISO to factor in the effects of behind-the-meter PV in load forecasting.
From there, the report calls for an “industry-wide standard methodology” for forecasting behind-the-meter resources, including “agreed semantics and business practices”.
Peak and PPGR
In particular, Brooks notes that looking at “peak demand” – the total end demand from consumers – gets more complicated on systems with a high portion of behind-the-meter solar.
“But what does it really mean when an ISO publishes a load forecast with a ‘Peak Demand’ (a.k.a Peak Load) number in this era of Distributed Energy Resources (DER)?” asks the report’s executive summary. “Does this number represent the maximum consumption of electric power by consumers within a load area or service territory at a given moment in time?”
To deal with this inherent confusion, Brooks recommends the use of a new term: “peak power from grid resources” (PPGR), which clearly refers to the demand that must be met by front-of-the-meter resources.
Ramping and EPRR
Adjusting estimates of daily peak demand is not the only change that is needed in the new electricity paradigm. In particular, grids with very high proportions of solar – whether behind or in front of the meter – must grapple with the large amounts of power that come on and off during the course of the day.
As such, grid operators must not only have resources on hand that can handle demand, but that can ramp rapidly to adjust to changes in output. As a means to address this technical challenge, Brooks has proposed a new metric, “estimated peak ramp rate” (EPRR), and has proposed that this be calculated over a defined period, such as five minutes.