The heat wave moving through large portions of the U.S. this week is not just uncomfortable. For commercial energy users, it may be quietly setting the cost of their electricity bills for the next year or more. That is because of something called capacity tags.
Capacity tags, sometimes called capacity obligations or peak tags, are charges that show up on commercial electricity bills separate from the energy itself. They represent what you pay for the right to draw power from the grid, not the power you actually use.
Here is how it works: regional grid operators, like PJM (the Pennsylvania-New Jersey-Maryland Interconnection, which manages the grid across 13 states in the Mid-Atlantic and Midwest), or ERCOT (the grid operator for most of Texas), need to ensure that enough power generation exists to meet peak demand. To fund that capacity, they assign each large energy user a share of the cost based on how much electricity that user drew from the grid during the highest-stress hours of the prior year.
That share is your capacity tag. And it follows you into the next contract period, often for 12 months or more.
Grid stress peaks when demand peaks. Demand peaks when millions of buildings and facilities crank up air conditioning at the same time during extreme heat.
This week's heat wave is affecting areas like the Southeast, Mid-Atlantic, Texas and the Midwest, which sit inside PJM, ERCOT and other major grid regions. When temperatures spike across those regions simultaneously, grid operators record their highest demand hours of the year.
Those hours are the measurement window that determines capacity tags. If your building is consuming heavily during those peak hours your capacity tag goes up. That higher tag then gets priced into your electricity supply contract and delivered as a line item on your bills.
The cost difference between a high capacity tag and a low one can be significant for large commercial users.
Transmission tags, also called transmission charges or network service charges, cover the cost of moving electricity from where it is generated to where it is used. Like capacity tags, they are typically calculated based on your usage during a set of peak demand hours.
The measurement windows for transmission tags vary by grid region and utility, but the core dynamic is the same: the more electricity you pull from the grid during high-stress moments, the higher your transmission obligation. Heat waves create exactly the kind of high-stress moments that move these numbers.
Together, capacity and transmission charges can represent a meaningful portion of a commercial energy bill, often 25-30%, and they are almost entirely invisible to buyers who only look at their supply rate.
The short answer: reduce consumption during peak demand hours, specifically during extreme heat events.
For most commercial buildings, that means shifting non-essential load away from afternoon hours on the hottest days, pre-cooling a building before peak hours, adjusting thermostat set points slightly, or curtailing equipment that does not need to run during a demand spike. This is sometimes called load curtailment or demand response.
The challenge is that peak hours are not always predictable in advance, and grid operators do not always announce them publicly with enough lead time to act. Businesses that actively track grid conditions, or work with an advisor who does, are in a much better position to respond than those who only see the consequences on their next bill.
For businesses operating in deregulated energy markets, capacity and transmission tags are a key reason why choosing an energy supplier based on supply rate alone can be misleading. A supplier quoting a low per-kilowatt-hour rate may still expose a buyer to significant tag-related costs that were never factored into the comparison. Understanding the full cost structure of an energy contract, not just the commodity rate, is what separates a defensible energy procurement strategy from a guess.
Capacity and transmission tags are charges assigned to commercial energy users based on how much electricity they consume during peak demand hours, and extreme heat waves are when those hours happen. If your building runs hard during a heat event, you may carry a higher cost obligation into your next contract period. Reducing consumption during the hottest peak hours is the most direct way to limit that exposure.