PJM on Sept. 9 added Marginal Emission Rates to the public information available on its Data Miner tool.
The new feed will be published in real time, every five minutes, and will reflect the Marginal Emission Rates of carbon dioxide, nitrogen oxides and sulfur dioxide for individual load nodes on the wholesale grid.
To create the new feed, PJM is applying the data used in its annual emission rates report, which features both average and marginal emission rates from electric generators in the PJM footprint. (See Emission Rates in PJM Continue Multi-Year Decline.)
PJM does not receive live emission data from plants.
The 5-minute Marginal Emission Rates will not represent specific rates based on the exact output level of a generator at any given moment in time – for example, differing emission rates that might apply when a generator is first starting up compared with when it is at maximum output.
As explained in the Marginal Emission Rates Primer on the Data Miner page, the emission rates data will correspond with the marginal unit or units representing the locational marginal price of energy.
Marginal units are those that would increase or decrease output in response to an increase or decrease in demand. In some situations, the marginal units, and hence the marginal emission rates, can provide an indication of what would happen based on a change in consumer behavior.
However, the PJM system is vast and dynamic, with millions of values changing from one moment to the next.
This means the marginal units – and their emission rates – in one five-minute interval might be completely different from those in the following interval.
“It’s important to understand that marginal units do not provide a prediction of what would happen. They only show what has just happened,” the primer notes.
PJM stakeholders have identified potential uses for Marginal Emission Rates to determine the times each day when electricity use can have the least impact on the environment by drawing on lower-emitting resources.
PJM looks forward to collaborating with industry partners to see how this data may be put to use and potentially further refined in the future.