20 July 2023 |

Battery vs. Oppenheimer


Batteries are the hottest energy storage technology in town. And not just for EVs.

Battery energy storage systems are the fastest growing energy resource (not just energy storage resource) in California right now. And whether you look at China or the U.S., as far as utility-scale energy storage is concerned, batteries are growing faster than any other technology.

The growth of battery-energy storage systems has looked like in CAISO, charted.

That makes batteries the Barbie on today’s Barbie vs. Oppenheimer climate tech continuum.

They’re hot. They’re en vogue. They’re relatively inoffensive and unlikely to spark significant debate (though everything under the sun in climate tech can spark some debate).

So which technology or technologies is the Oppenheimer in this metaphor? To answer that question, we’ll first need to take a survey of the other energy storage options.

Rotten tomatoes: Energy storage edition

Rather than merely introduce other viable energy storage technologies, we’re going to rank them. To this end, here’s a quick 101 on the criteria we’ll use:

  1. Cost: What is the all-in cost of developing and deploying this technology?
  2. Duration: Does the tech lend itself to longer-duration (8+ hours) storage (batteries don’t)?
  3. Round-trip energy efficiency: How much energy do you lose In one round of charging and discharging (~5% for batteries)?
  4. Scalability: How easily can the tech be scaled, both in size and across geographies
  5. Readiness: What’s the level of tech ‘proven-ness’ here? Is this tech in the lab stage or already operating at utility-scale?

There are innumerable other criteria that one could analyze, including power (is the tech capable of rapid discharge [batteries are]), response rate (is the tech capable of ‘coming online’ rapidly? [batteries are]), and portability (can you / how easily can you move the stored energy?), but to get this newsletter out on time, we’ll stay relatively focused on the above.

Next up, here are the five tech categories we’ll look at today. These aren’t exhaustive, but cover the majority of options folks are seriously working on:

  1. Hydrogen: Swinging for the fences
  2. Pumped hydro: The old goat
  3. Compression and liquefaction: The dark horse
  4. Geothermal energy storage: Underground punk
  5. Thermal systems: More than hot air?

Hydrogen: Swinging for the fences

Hydrogen is primarily seen as an essential agent of industrial decarbonization: From steelmaking to fertilizer, many industrial processes require hydrogen. And 99%+ of hydrogen used globally today comes from fossil-fuel sources. 

As a result, energy storage isn’t necessarily the first thing folks consider when they propose producing green hydrogen. That said, in the same way clean electricity can be used to produce ‘green; hydrogen for industrial applications, hydrogen can be used to store energy chemically.

  1. Use electricity to split hydrogen out of water (or another substance) in electrolysis
  2. This process can be reversed via a hydrogen fuel cell to discharge energy again

Theoretically, this is a scalable, portable (you can liquefy and ship hydrogen or pipe it), and highly long-duration storage option. Challenges crop up in commercialization, cost, and round-trip energy efficiency. Hydrogen conversion has a ’round-trip’ loss rate closer to 50% (batteries’ loss rate is closer to 5%). Scaled storage of hydrogen is another challenge. Massive underground caverns, e.g., ones that previously housed natural gas, aren’t in infinite supply.

Why did I choose “swinging for the fences” as the ‘persona’ name I used for hydrogen? One could imagine a global economy where hydrogen is readily used in a) transportation b) industrial decarbonization c) co-firing with natural gas d) energy storage (and further applications). It could be a massive winner, though folks have talked about that for decades without making serious headway (and applications like hydrogen-powered consumer cars have stalled out). 

Still, both the EU and the U.S. are seriously considering how to stimulate more investment and development of ‘hydrogen hubs’ and hydrogen technologies, so let’s not write it off.

Side note: Some folks are also still exploring other power-to-gas applications (e.g., synthetic natural gas) for energy storage; I won’t spend time on that right now as the principles are similar.

Charting the potential storage capacity and duration of different technologies (source here)

Pumped hydro: The old goat

I feel like I’ve written about pumped hydro a lot at this point in introducing other energy storage topics. Pumped hydro is the heavyweight (literally) incumbent; it constitutes the lion’s share of grid-connected and utility-scale energy storage in both the U.S. and China and other markets.

While it occasionally gets a newfangled re-brand (e.g., “water battery”) in media coverage, make no mistake, this is an age-old approach to energy storage. Pumped hydro uses excess energy to move water up a hill and lets the water run downhill later to spin a turbine.

You can build big, relatively long-duration energy storage projects this way. And developers do. But expanding capacity is constrained by siting, the systems aren’t particularly flexible, and building big infrastructure is notoriously cumbersome, especially in the U.S.

Compression and liquefaction: The dark horse 

Compressing air or other gasses is a form of mechanical energy storage. Approaches in this category typically leverage excess electricity for the compression phase and then discharge energy later by allowing compressed air or liquified gasses to expand again, spinning turbines.

For example, a high-flying climate tech company called Energy Dome aims to commercialize a CO2-gasification energy storage system. This week, the Milan-based company announced an additional €17M in Series B funding. Its CO2 battery uses electricity to move CO2 gas through a compressor, condensing it into a liquid. To discharge energy later, the CO2 is gasified again; as it expands, it turns a turbine that generates electricity. 

These systems offer moderately longer duration than batteries, but, like pumped hydro, are sizable infrastructure projects for which costs can be hard to control.

Geothermal energy storage: Underground punk

In the same way that geothermal is generating some excitement as a form of consistent and clean power, there are geothermal energy storage applications. 

Geothermal energy storage systems can store energy in various ways by leveraging differences in water temperatures and pressure in twin wells. For more on the technical specifics of how this might work, I will tap in MIT Technology Review and Fervo Energy here

For our purposes today, suffice to say that while these aren’t commercially ready technologies (they’re still a bit underground), they potentially offer significant duration and high round-trip energy efficiency. Plus, if geothermal as a clean energy technology scales in coming decades, it stands to reason many plants could also offer this type of flexibility and storage.

A concentrated molten salt storage system with solar power in Fuentes de Andalucia, Spain (Shutterstock)

Thermal systems: More than hot air?

Thermal energy storage systems comprise a wide range of approaches that ‘boil’ (sorry) down to similar underlying processes. These systems use electricity to heat or cool a substance and then reverse the order of operations to rerelease energy. Molten salt systems, for instance, store solar-generated heat.

Although several active projects are worldwide and the technologies here are technically ‘ready,’ these systems are rare. Storage duration is also typically lower than other technologies explored above, and scalability isn’t necessarily competitive either. Specific applications, like molten salt (see above), can feature high RTE and duration though and will likely continue to crop up globally in specific sites.

The net-net

To close off our comparisons today, here are my not-super-scientific conclusions and scorings on these five energy storage technology categories. Please do write in with your vehement disagreements!

If it were up to me, I’d continue to invest in hydrogen (even if it didn’t work out in cars) & hydro

With the heavy lifting of this newsletter over, we now get to return to the question we opened with: Who is the Oppenheimer on the Barbie to Oppenheimer energy storage spectrum? 

Let me drop a bomb on you. It’s nuclear energy. Some analysts maintain none of this would matter if nuclear power were the staple of the power grid. If that were the case, we wouldn’t need muchenergy storage to balance intermittent renewable energy. My entire focus on energy storage would be unfounded. 

Is that a take I put stock in? Theoretically, sure. But considering new nuclear power projects are few and far between in the West, and reactors (even if small) take at least five years to build, I still feel pretty good about positioning myself closer to team battery, er, Barbie, for now.