Rocky Mountain Institute

How much does energy storage really cost?

energy battery storage
ShutterstockClaudio Divizia
With a new generation of batteries on the horizon, calculating costs will be key.

Energy storage is often hailed as a game changer for renewable energy reliability. But what will it take to ensure that storage is an economic solution?

In November, financial advisory firm Lazard released its inaugural Levelized Cost of Storage Analysis (LCOS). Well known for its Levelized Cost of Energy Analysis (LCOE) analysis — now out in version 9.0 — Lazard's publishing an analysis of storage is a major sign that it considers battery energy storage a critical technology that’s here to stay.

But a closer look at Lazard’s LCOS shows something RMI’s October Economics of Battery Energy Storage report noted: battery economics are usually evaluated on the basis of single-use cases; stacking multiple uses greatly can enhance battery economics; and evaluating those economics gets difficult quickly.

The use cases and stacked value streams — in addition to per-kWh cell cost declines — offer tremendous opportunity. 

RMI’s report primarily looked at the value, not cost, of a basket of multiple, stacked uses for customer-sited storage systems. Lazard focused on the costs of several physical storage technologies (including the lithium-ion studied in RMI’s report) and not "alternative" storage options such as building-as-storage, water heater-based storage and other demand flexibility options.

It evaluated those storage technologies on the basis of a variety of single-use cases such as frequency regulation and peak shaving/demand charge reduction. Lazard compared those costs to conventional, fossil-fuel alternatives. 

Jesse Morris, a manager at RMI and co-author of RMI’s battery report, said, "We did not make this comparison in our Economics of Battery Storage report for a number of reasons, but Lazard’s analysis is a great first step. It adds to a strong foundation from which the industry can better understand multiple-use cases.

"In the end, this is the comparison that we need to be able to make if we're going to convince regulators that a distributed energy resource-focused future is a lower-cost alternative."

Batteries are tricky to evaluate in part because they aren’t strictly a demand- or supply-side solution. They’re an arbiter of supply and demand, serving as either generation or load depending on whether they’re discharging or charging. So the favorable finances of storage can use all the clarity and all the study they can get.

Shifting from single- to multi-use cases

The LCOS examined single-use cases, which is how most batteries are deployed today. But single uses are not how RMI proposes (or how Lazard expects) they be deployed in the future. Batteries today are used for a minority of their useful lifetimes.

They can do much more than sit idle most of the time, and increasing their use rate greatly can enhance the value they provide to customers and the grid. 

"In point of fact, it will be possible to use batteries for more than one thing, which means their value is higher than is being captured in our study," said Jonathan Mir, managing director and head of North American Power and Utilities at Lazard. "I think we’re going to have to do the same thing around the stacked use cases."

Storage costs are dropping

Both reports find that the age of the battery is here, largely because costs have dropped so far, so fast. Mir said, "This reminds us very much of where utility-scale renewables were seven or eight years ago," when Lazard began covering renewable costs in its LCOE series.

"To us, this seems like an inflection point where you can see external factors causing demand to really take off and then you wind up with price declines as manufacturing scales up," he said.

Lazard’s analysis also predicted significant cost declines over the next five years, based on a survey of industry experts. For example, the median expected five-year price decline for lithium-ion storage is 47 percent below today’s costs.

The LCOS calculated the costs of eight energy storage technologies for 10 single-use cases, half behind the meter (including augmenting residential solar PV) and half in front (including transmission-upgrade deferral). It compared these to the costs of conventional alternatives such as natural-gas peaker plants or diesel generators.

The study found that the costs of storage are within "striking distance" of conventional alternatives for many single-use cases, including lithium-ion batteries used for frequency regulation and flow batteries used to defer adding a new peaker plant.

The challenge of multi-use accounting

What the LCOS analysis didn’t do is estimate the cost of energy storage when it is used for multiple, stacked services, a key to realizing the value of storage to customers and the grid. 

Most of storage’s costs are fixed, capital costs. But variable costs — as well as battery lifetime, potentially capacity loss over time and ultimately replacement — depend on the use or uses to which a battery is put over its lifetime, especially how often it is charged and discharged. This makes it difficult to state the cost of a given storage technology for a variety of multiple, stacked services.

"That is our ambition," said Lazard’s Mir. "It’s important to capture, because we think our study is likely underestimating the value and potential of storage because storage would be used in more sophisticated ways than are being illustrated, but the quantitative analysis and framework to illustrate that is still being developed. It is another indicium of how immature the industry is."

Evaluating battery energy storage economics is hard, and RMI sees opportunities to build on Lazard’s commendable start. The basic problem is finding a levelized cost that can be added in as services are stacked in different combinations.

Garrett Fitzgerald, a senior associate at RMI and co-author of the Economics of Battery Energy Storage report, explained, "By combining fixed costs and variable costs that are determined by what services and how often they are being provided, you end up with a total lifetime cost of providing just a single service. It is not possible to then determine the incremental cost of stacking other services on."

For example: “It would be incorrect to simply add the LCOS of frequency regulation and the LCOS of peaker replacement as an estimate of the LCOS of a system providing both," said Fitzgerald.

The importance of value stacking

Establishing a framework to measure the value (and cost) of stacked use cases for storage should be possible. Mir said, "To us, that is a natural evolution of the study."

But, he noted, "We have not seen a good solution in the public domain for how to demonstrate this idea, so we will come up with a framework. We understood it as a very important qualification to the work we were doing, which is why we tried to be so clear about it."

Indeed, the third page of the LCOS is devoted to explaining exactly how the energy storage value proposition depends on the stacking of multiple uses and adding together the value streams they create. RMI’s Morris said, "Their description is very clear and an excellent way to think about the comparison between stacking values and comparing different stacks of value to a given cost."

The current state of play

Lazard considered only unsubsidized costs and disregarded the additional value created by such things as avoiding the toxic or climate-changing emissions of conventional fossil-fueled technologies. Nor does Lazard take into account state incentives, such as California’s SGIP and mandatory battery storage legislation.

"Their comparison of all chemistries performing all use cases against a gas peaker plant or a reciprocating diesel engine (depending on the application) is extremely helpful," said Morris. Should subsidies for storage be introduced at the national level, Lazard will factor them in the same way it does for LCOE. 

So what did Lazard find? Of all the permutations analyzed, only one — lithium-ion batteries providing frequency regulation to the grid — was cost effective when performing a single, unstacked service today. The study also predicts that seven combinations (all with batteries) will be cost effective within five years.

These include two use cases — peaker replacement and industrial peak shaving/demand charge avoidance — for which multiple battery chemistries will be cost-competitive with their diesel and natural-gas alternatives. 

The LCOS does contain this encouraging caveat, however: "A number of [technology and use case] combinations are within ‘striking distance’ and, when paired with certain streams of value, may currently be economic for certain system owners in some scenarios."

These combined value streams that come with stacked uses need to be accurately and easily accounted for.

The road ahead

"Costs will come down naturally with scale; they always do," said RMI’s Fitzgerald, but he cautioned, "Storage won’t be mainstream until there are more channels for developers or storage owners to find revenue." As examples of the new channels being opened up for storage, he cited "things like aggregated wholesale market participation in California or distributed system platform providers as described in New York’s REV proceeding." 

Fitzgerald said, "Storage can do a lot for the grid, and it can do most when behind-the-meter. Regulation is changing that will allow distributed storage to collect revenue for these services."

In consequence, he said, "most of the industry is focused on opening up new revenue streams and moving toward customer-sited and customer-focused services, such as demand charge management or solar-plus-storage solutions." Lazard’s Mir added, "We see that demand increasing pretty rapidly."

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