Is solar+storage eligible for net metering in Massachusetts? Tesla and others want to know
A key emerging use for energy storage is pairing it with solar power, but, as is often the case, technology and business strategies are ahead of regulations.
Massachusetts could be the first state to provide comprehensive guidance focused solely on pairing energy storage with solar panels.
An inquiry underway at Massachusetts’ Department of Public Utilities merges several cases into a single docket (17-146). The inquiry takes up two separate but related issues: the eligibility of energy storage systems to net meter and the application of the net metering rules regarding participation of net-metered facilities in the Forward Capacity Market run by ISO-New England.
It may seem obscure now, but “the issue is going to come up in every jurisdiction,” Todd Griset, a partner with Preti Flaherty’s energy and telecommunications practice, told Utility Dive.
Net metering alternative
Energy storage has often been seen as an alternative to net metering. In states where net metering benefits have been reduced or even eliminated entirely, such as Hawaii, energy storage can enable solar owners to store solar power when it is abundant and withdraw the stored energy when electricity rates are higher, saving solar owners money and making up for some of the lost net metering revenue. But combining net metering and storage complicates matters, as seen in the Massachusetts case.
In some respects, net metering and energy storage are at odds. Net metering can be seen as providing a giant battery (in the form of the grid) to solar customers, obviating the need for storage. That conflict was brought under the same roof when automaker and battery manufacturer Tesla bought out SolarCity in November 2016. There is some irony in the fact that one of the companies spearheading the use of both batteries and net metering is Tesla.
In May, Tesla filed a petition with the Massachusetts DPU seeking emergency declaratory relief or an advisory ruling on the eligibility of solar-powered generation systems paired with battery storage for net metering.
At the heart of Tesla’s petition was an email from National Grid stating that it “does not believe that battery storage is eligible for net metering, and does not intend to provide net metering services to a solar facility that includes battery storage.” The email went on to recommend that a solar-plus-storage system could “apply for treatment as a Qualifying Facility” under the Public Utility Regulatory Policies Act.
National Grid is “supportive” of the DPU’s review of the net metering issues, spokesman Robert Kievra said in an email. “There are a number of policy and other considerations that need to be evaluated” such as legal requirements, eligibility criteria and enforcement, he said.
The DPU issued an advisory ruling Sept. 12 finding that the solar-plus-storage system, as presented by Tesla, is eligible for net metering. But the DPU noted in its order that its ruling was limited and that it applied to Tesla only, which appears to be contradicted by a footnote in its advisory opinion.
The DPU “does not adopt any new rule” and that the general eligibility of solar-plus-storage systems “requires further investigation.”
In a footnote, the DPU noted that its advisory opinion “is generally applicable to all solar net metering facilities paired with battery storage” that meet certain criteria. But the DPU also put all net metering stakeholders “on notice” that the outcome of its current inquiry could “alter or expand” its view of solar-plus-storage systems.
The DPU also acknowledged National Grid’s concerns about the potential for gaming with solar-plus-storage systems and said that would be taken up in the inquiry.
One way a paired solar-plus-storage facility could be used to game the net metering system would be if a battery were charged when rates are low and discharged later to receive net metering revenues.
Tesla makes clear in its petition that gaming is not in its intentions. The company stipulates three criteria for net metering eligibility, which DPU cites in its order. They are 1) the solar net metering facility must have a nameplate capacity of 60 kW (AC) or less, 2) the battery will be charged only from the solar net metering facility and 3) the battery storage component will not export power to the grid.
The last criterion would seem anomalous, given that net metering is designed to compensate energy shipped back to the grid from a distributed energy resource. But Tesla’s meaning is made clear in a similar filing for declaratory relief (Docket #4743) it filed in September in Rhode Island. In that filing, the company explains that the default factory setting for the solar inverter on its Powerwall H6 “disables battery charging from the grid and allows charging to occur only when there is power available from the solar panels.” The Rhode Island case is still pending.
The issues raised by Tesla comprise only one part of the ongoing inquiry in Massachusetts….