California is working to add renewables and make its power mix as clean as possible. But an excess of solar during the middle of the day means the state's efforts are not uniform — some hours are cleaner than others.

In order to wring all possible emissions out of the state's generation, the California Public Utilities Commission has pushed out new accounting methodology that was designed to provide insights into the emissions associated with the resources necessary to match load profiles, which will press utilities to focus on granular hourly data.

An Administrative Law Judge (ALJ) last month issued a ruling finalizing the methodology for greenhouse gas (GHG) emissions accounting in the integrated resource plan filings utilities are required to file by Aug. 1. The Clean Net Short (CNS) methodology will apportion GHG emissions to each load-serving entity (LSE) based on projected hourly electricity demand.

But while the new methodology has support from several groups — including investor-owned utilities, commission staff, The Utility Reform Network and the Natural Resources Defense Council — stakeholders say improvements can be made.

"California right now is producing more solar than it needs at certain parts of the day, and that isn't necessarily taken into account if you use the annual methodology," Deborah Behles, counsel for the California Environmental Justice Alliance, told Utility Dive. The CNS methodology, she said, is an attempt to more granularly capture actual emissions. 

California has moved to finalize the new methodology and the ruling notes that it is "unique in that it is an hourly methodology, whereas many others are based on annual averaging."

The CNS methodology apportions GHG emissions to each LSE "based on its projected hourly electricity demand," as opposed to "many GHG accounting frameworks that are source-based, accounting for emissions directly from power plants, regardless of the load they serve."

The Clean Net Short methodology "isn't perfect," Katherine Ramsey, staff attorney for Sierra Club, told Utility Dive in an email. There are many suggested improvements, but it represents real progress, according to her.

Along with the California Environmental Justice Alliance, Sierra Club told the commission in filed comments that while "there are benefits to using the GHG calculator's hourly methodology, we also recommend improving its accuracy."

Among the improvements the groups would like to see made to the CNS methodology:

• Include consideration of air quality impacts, contractual agreements and GHG emissions from behind-the-meter combined heat and power resources
• Incorporate lifecycle emissions into assumptions, including the system GHG emissions intensity
• Incorporate more granular emissions information for owned or contracted GHG-emitting resources

"That said, an hourly accounting methodology is absolutely better than an annual accounting, because we need to ensure that California's load-serving entities are responsible for all of the greenhouse gas emissions that they actually generate in serving their customers," Ramsey told Utility Dive.

The Clean Coalition in its comments said it supported the methodology, but with "additional recommendations." The non-profit is concerned that load reductions from "more aggressive" demand response, energy efficiency programs and behind-the-meter solar PV "would not properly be credited for avoiding GHG-emissions but would instead be left in the CNS and thus be attributed with the hourly GHG emissions associated with system power."

While the methodology includes baseline load profiles with some generic behind-the-meter resources factored in, the group said "we anticipate that some LSEs may find that DR or EE programs to be cost effective and develop programs to exceed the amount included in load projections."

While there are many suggestions to improve the methodology, even from supporters, most say it remains an improvement.

"California has done an incredible job of cleaning up its emissions during the solar-producing hours," Ramsey said. "But to take the greenhouse gas reductions further, we need utilities to be thinking about every hour of their customers' demands, thinking critically about what resources run when, and working to figure out how to limit the greenhouse gas emissions even during the later hours of peak demand."