Getting Specific About Effective Energy: The Truth About Comparing Batteries

Getting Specific About Effective Energy: The Truth About Comparing Batteries

Don't be mislead: apples-to-apples battery measurement

In the race for dominance in the energy storage market, battery manufacturers like to brag about a battery’s specific energy: how many watt-hours are delivered by each kilogram. But is it the right way to compare battery technologies? In short: no. It glosses over some critical real-world issues and results in misleading comparisons.

To use a very simple analogy, imagine you want to ship a gift to a friend. You have the choice between a selection of cheeses or a book. They both weigh the same and are about the same volume, and they should cost the same to ship, right? Wrong. While the weight and volume of the gift is the same, the effective weight and volume of the shipped package won’t be, and neither will the cost. One requires icepacks and a cooler to arrive fresh while the other can simply be put in a box. To make a meaningful comparison, you need to compare the whole package.

And it’s the same with battery systems. Comparing the innermost component of the system—a cell—does not result in an accurate comparison.

Cells make up modules which make up packs. And that’s not all; we must consider the whole battery system. For electric cars for example, the lithium-ion battery system also needs the Battery Management System (BMS), the active cooling system or Thermal Protection System (TPS), and protective armor. Each system adds weight, volume, and cost.

Why are these three measures important? The two most looked at numbers are specific energy in Wh/kg (watt-hours per kilogram) and energy cost in $/kWh (dollars per kilowatt-hour). The first tells you how much energy you can store for a given weight. The second tells you how much this energy costs you. In applications where space is limited, a third measure, energy density measured in Wh/l (watt-hours per liter) can also be essential. They are a way to compare battery chemistries and battery system designs.

Specific energy vs. effective specific energy

Typically, articles about batteries focus on the specific energy of just the cell, the innermost component of the battery system. The numbers can look good: after all, it is light without its supporting systems and relatively inexpensive. But what’s more revealing is the effective specific energy: how the whole system measures up.

It is fair for cell manufacturers to simply compare the cell, the smallest component in the battery, because they do not know how the cell will be used. But as soon as you know how a battery will be used, there’s other important information to consider. For example, the battery for an electric bike is small in capacity (Wh), does not need a sophisticated BMS, just uses air to cool it, and doesn’t need much armor to protect it.

Next time you hear an analyst predict an aggressive target price for lithium-ion batteries or an entrepreneur pitch a new battery chemistry, raise the discussion up to the whole system level.

However, a passenger electric vehicle, which weighs more than an e-bike, carries more people, and travels much faster and further. So it requires a much higher capacity battery pack, an active cooling system moving a cooling fluid through channels to cool the cells (since it gets hot moving and accelerating), a sophisticated BMS with computer, sensors, and cabling, and armor to protect the installation in case of a crash which could penetrate the pack and set the pack on fire. These three main subsystems add weight, volume, and cost.

For specific energy, increasing the weight (kg) decreases specific energy. For energy cost, increasing the dollars obviously makes it go up. And for energy density, increasing the volume lowers the energy density. In other words, while the cells still supply the same Watt hours, the battery system installed in an EV is effectively heavier, more expensive, and bulkier per unit of energy than the battery system installed in an e-bike.

When comparing different battery chemistries, the comparison should be at the system level. The discussion needs to be about the effective (or installed) specific energy, energy cost and energy density so it’s an apples-to-apples comparison.

One car, two ways to look at its battery

Let’s take a real-world example. The Chevy Bolt uses LG NMC cells with a specific energy of around 220 Wh/kg and a cell cost of $145/kWh. After all the pack level hardware and protective subsystems are accounted for the installed specific energy drops to 135Wh/kg and the installed cost rises to $225/kWh.

The numbers look even worse when the current recall of all Chevy Bolts due to fire risk is taken into account. Because every battery pack is being changed out, one could say the effective energy cost is really $370/kWh.

Changing the size and the chemistry of the battery pack can make a significant difference. For example, if the Bolt had a lower range vehicle for use in an urban setting, say 40kWh pack with a 200 mile range (after all, 95 percent of trips are under 30 miles), it could use a different type of lithium battery, lithium ferrous phosphate (LFP), or a nickel zinc (NiZn) battery. Both have a cell specific energy of 130Wh/kg and a cell cost of $100/kWh. And because they are both less prone to fires, they do not need a sophisticated BMS, no TPS and no armor.

This means that the installed specific energy would be 115 Wh/kg and a cost of $160/kWh. Why only 200 miles? That’s where energy density comes in: both of those chemistries have a lower energy density than lithium ion, so only a lower range battery pack will fit in the space in the Bolt and not change the weight significantly.

Looking beyond battery marketing

It’s popular to think that lithium-ion batteries have already won the race to dominate most energy storage markets, and much of the argument is centered on its competitive specific energy and cost. But with a true comparison of the effective or installed specific energy and cost, it’s clear that it’s not the natural winner for many use cases.

Next time you hear an analyst predict an aggressive target price for lithium-ion batteries or an entrepreneur pitch a new battery chemistry, raise the discussion up to the whole system level. How do the numbers look once you have accounted for the full system for the energy use case, whether it’s an e-bike, EV or grid storage? The first answer might not be the most relevant answer for the economics. Or for the environment which is the subject of another article.


Image: Photo by Waldemar Brandt on Unsplash 

Enzinc: ‘Zinc batteries go where lithium-ion cannot’

Enzinc: ‘Zinc batteries go where lithium-ion cannot’

By Robert Malthouse, Energy Storage Report

Could zinc batteries usurp lithium-ion’s strong market position and become the storage technology of choice?

Could zinc batteries usurp lithium-ion’s strong market position and become the storage technology of choice?

The potential certainly exists and Enzinc CEO Michael Burz is on a mission to make it happen.

Headquartered at the University of California in Berkeley’s Richmond Field Station in the San Francisco Bay area, Enzinc’s engineering team has developed a sponge-type anode technology made from zinc, and says it will be the first company offering a rechargeable zinc-based battery that can compete with lithium-ion.

Who’s backing Enzinc?

Enzinc created the anode using technology developed by the US Naval Research Laboratory. So far, Enzinc has raised north of $1.3m, mainly in the form of grants from the US Department of Energy and the California Energy Commission, as well as investments made by founders, senior advisors and angel investors.

The company recently completed 1,000 cycles of its test anode and is beginning to scale the technology into a small battery for commercial testing, which is scheduled to take place in the second quarter of next year

Battery Week: Competitors to Lithium-ion Batteries in the Grid Storage Market

Battery Week: Competitors to Lithium-ion Batteries in the Grid Storage Market

By David Roberts, Canary Media/Volts

Lithium-ion batteries probably have cars locked up, but what about grid storage?

Welcome back to Battery Week — where we use the term “week” somewhat loosely.

Up until now, we’ve been focusing on lithium-on batteries (LIBs) — why they are so importanthow they work, and the varieties of LIBs that are battling it out for the biggest battery market, electric vehicles (EVs).

It’s fairly clear from that discussion that LIBs, in some incarnation, are going to dominate EVs for a long while to come. There is no other commercial battery that can pack as much power into as small a space and lightweight a package. Plus, LIBs have built up a large manufacturing base, driving down prices with scale and industry experience. Their lock on the EV market is likely unbreakable, at least for the foreseeable future.

But there’s another battery market where some competitors hope to get a foothold: grid storage. They think there’s space in that market waiting to be claimed. 

Zinc batteries

Several companies are working on batteries that exchange zinc ions instead of lithium ions — it’s the second-most-popular metal for batteries.

Zinc has the particular advantage of being light and energy-dense like lithium, so with relatively modest adjustments, it can slipstream into the lithium-ion manufacturing process.

Zinc is plentiful, cheaper than lithium, largely benign, and makes batteries that are easier to recycle. Like other lithium alternatives, zinc sacrifices energy density, but makes some of it back up in savings on safety systems at the battery-pack level, thanks to the lack of any need for fire suppression. This puts it in the same markets as lithium iron phosphate (LFP): smaller commuter/city vehicles, robo-taxis, scooters, e-bikes — and energy storage.

Some in the zinc crew have more ambitious designs: “We think we can coexist with lithium-ion and replace lead acid,” says Michael Burz, president and CEO of EnZinc, which has developed a new zinc anode it says can come close to LIBs on energy density. Remember, lead-acid batteries are still ubiquitous. “Forklifts use them. Airplanes. Snowmobiles,” says Burz. “Data centers have huge banks of lead-acid batteries they use for switchover power.” The technology still has a $45 billion global market.

EnZinc thinks it can hit a sweet spot: close to the energy density of LIBs, close to the low cost of lead-acid, safer than either, and good enough to substitute for a big chunk of both.

Zinc anodes are “cathode-agnostic,” so Burz envisions his company becoming an anode supplier, rather than a battery manufacturer, with “Zinc Inside” labels modeled on the “Intel Inside” processor designation. Research is underway on a number of cathodes, from manganese and nickel to — just as with lithium — air. A zinc-air battery “has a system-level specific energy of anywhere between 250 to 350 watt-hours per kilogram,” says Burz, a level well above most LIBs. The trick is making it controllable and rechargeable. There are zinc-air battery companies offering commercial products that claim they’ve solved those problems, such as NantEnergy (formerly Fluidic), which is targeting its zinc-air batteries at off-grid markets in developing countries.