A clean grid requires firm power. Here’s what that means for energy storage

The Biden administration’s infrastructure plan, released last Wednesday, has accelerated an already lively discussion about the changes that will be necessary to decarbonize the U.S. power grid.

In the week leading up to the release of the American Jobs Plan, three studies were published analyzing how various regions in the U.S. can meet their electricity needs with low or zero carbon sources.

The most geographically focused of these, the LA100 study, conducted by the National Renewable Energy Laboratory explored several pathways for the Los Angeles Department of Water and Power (LADWP) to meet its electricity needs with reliable, up to 100% renewable power by 2045 or earlier. A second study (Long et al.), from leaders in academia, consulting, and nonprofits, focuses on California, while a third study (Sepulveda et al.), from MIT and Princeton academics, explores regions like Texas and the Northeast.

The three studies echo a common conclusion in the growing literature on net zero carbon power grids: while solar, wind, and lithium-ion batteries will meet the majority of future electricity demand, clean, firm resources provide significant cost savings and reliability benefits over a renewables and lithium-ion only approach.

At Form Energy, we live and breathe energy storage, so we’re naturally interested in what these new studies mean for batteries and beyond. What follows is our summary of the implications of these studies for the energy storage industry, complemented by our original analysis.

 

Spoiler Alert: Cost and Duration Matter. A lot.

While the various studies take different approaches to modeling storage, they all conclude that ultra-low cost storage can decrease the costs of zero carbon grids substantially and that the capability to generate over multiple days of adverse weather is critical for reliable, low carbon power.

Sepulveda et al. conclude that storage technologies with energy capacity capex costs less than $20 per kilowatt-hour can save billions in electricity costs relative to systems with only renewables, lithium-ion, and carbon capture, nuclear, or hydrogen. Furthermore, and relatedly, they also conclude in an analysis of Texas and the Northeast that storage technologies “exceeding 100 hours” in duration play the biggest role in reducing power system costs.

LA100 finds that renewably-produced hydrogen paired with onsite storage and converted to electricity in a combustion turbine or fuel cell (the only ‘long duration’ technologies modeled) could be a key pillar to an early, 100% decarbonization strategy. This is true, even at the high costs that LA100 modeled — $3,200 per kilowatt to $5,300 per kilowatt depending on year and technology, or three to five times the cost of today’s combined cycle power plants. As for duration, the LA100 study doesn’t explicitly define the duration of the hydrogen storage technologies modeled (although we can imply $/kWh costs from duration assumptions). Rather, it states that the technologies have “many days of capacity” and finds that grid reliability is maintained by discharging for “extended periods over multiple sequential days [to] ensure load balancing on consecutive days or weeks with low wind and solar resource availability.” This value is especially apparent in constrained grid areas like the Los Angeles basin in California.

While Long et al. don’t explicitly model long duration storage in their core cases, they do model “zero carbon fuels” that include hydrogen, at costs ranging from $15 per MMBtu to $50 per MMBtu (or roughly 5 to 17 times today’s natural gas prices, implying LCOEs ranging from roughly $0.12 per kilowatt-hour to $0.40 per kilowatt-hour). The models all implicitly assume that the infrastructure required to store and deliver this fuel is embodied in the fuel prices. In turn, they similarly find that these fuels are cost effective to maintain reliability “when the sun doesn’t shine for many days.”

It is also important to note that while all of these exercises point to the value of storage that can power grids for multiple days, all studies also point to the fact that a technology inclusive, portfolio approach delivers the least cost decarbonized electric system, a finding we have confirmed many times over in our own modeling.

 

Can storage be “firm”?

While these studies and others point to the value of firm zero carbon technologies, few provide a clear definition of “firm.” The inclusion of hydrogen as a “firm” option in these studies adds further confusion, as any hydrogen strategy (whether blue or green) would require storage and other supporting infrastructure and would be subject to weather vagaries. Aligning on this definition can help provide clarity to policy makers, regulators, utilities, and entrepreneurs.

In practice, all resources are subject to availability conditions. As we learned from the February 2021 storms in Texas that brought down roughly one-third of the state’s “firm” thermal generation, no technology class is perfect. Ultimately, firmness is defined by the relevant regional weather and demand conditions, and firm resources must be able to consistently meet a given demand under a wide variety of weather conditions.

To understand what those conditions could look like in one of the focus regions of these recent studies, we analyzed 35 years of intermittent generator profiles from the solar and wind generation datasets used in the California Public Utilities Commission’s (CPUC) Integrated Resource Plan to determine what types of resources might be necessary to provide clean firm power in California.

Our findings show that periods of low intermittent generation1 lasting between 50 and 100 hours occur fairly often (roughly once every two years) and that periods lasting from 100 to 150 hours occur roughly once every ten years. In one of the most severe of these events, which occurred in December 2010 and is shown in Figure 1 below, renewable output was well below expected levels for six days.

Figure 1: December 2010 low-renewables event in California
Note: figure shows expected output under the proposed 2030 intermittent generation mix generated in the CPUC’s IRP proceeding

 

Even under more moderate definitions of low generation (where “moderate” means extended generation shortfalls that are within the Planning Reserve Margin of 15%), we did not find a single event lasting longer than 150 hours. In other words, in California, storage systems that can discharge at full power for at least 100 hours could provide clean firm power in all but a 1-in-10 year weather event, during which 150-hour systems would be sufficient.

This echoes findings from a February 2021 study of the Northeast U.S. from ISO-NE and DNV GL, which found that wind lulls lasting three days occur annually, while five day lulls are less common. While our analysis focuses on California, the underlying method is broadly applicable and can be applied for regionally-specific, data-driven definitions of firm, zero carbon power.

In summary, these recent papers and an examination of renewable availability in California point to the need for a new class of storage — multi-day storage — that can firm power grids across multiple consecutive days of low renewable energy output.

 

Scaling firm, multi-day storage

Researchers are increasingly aligned on the need for firm zero carbon technologies. Recent work has clarified that, for storage to be truly firm, it will need to reach dramatically lower costs and longer durations than today’s commercial technologies. Data-driven and model-based analyses point to the need to provide dispatchable energy for more than 100 hours to be truly firm, and at a price point which enables that, which starts at <$20/kWh. While no commercial technology today can meet this challenge, the benefits to society of doing so would be enormous.

To decarbonize the grid, renewables will need to be built out at a record pace; transmission will need to be upgraded; carbon dioxide and hydrogen pipeline networks will need to be retrofit or built from scratch (if carbon capture and hydrogen are to be a large part of the strategy); and low cost storage capable of providing multiple days of firm power will need to be commercialized and scaled.

While ambitious to be sure, the Biden administration’s recent American Jobs Plan shows that there has never been a better time for visionary infrastructure, innovation, or decarbonization plans to meet the challenge of climate change.

1 We defined low intermittent generation as having a 3-day moving average hourly output that was at least 25% below average. This amount is roughly consistent with two standard deviations below average.