June 10, 2019 1

A recent fire at a utility-owned energy storage facility near Phoenix, Arizona has implications for everyone who is standardizing around lithium-ion batteries to design storage systems. Since lithium represents about 95 percent of the market, this is a topic of near-universal interest.

Especially for me. My experience with lithium-ion batteries goes beyond the storage system engineering and design work we do here at SepiSolar. Ten years ago, not long after founding SepiSolar, I helped launch Green Charge Networks, an early leader in lithium battery deployments. That’s where I saw technology, product configuration, permitting, performance, and operational risks associated with lithium batteries begin to materialize.

The industry is moving fast to push lithium battery deployment to new heights, but we still cannot easily quantify risks. Nor the costs.

We at SepiSolar are technology agnostic. Our commitment is to openly consider the costs and benefits of all commercially viable design options. Given how many projects appear to be treating lithium as the only commercially viable technology, I encourage developers to reevaluate lithium—particularly after the recent fire in Arizona—and consider flow batteries as an alternative that can be deployed at lower cost, greater speed, and superior safety.

Arizona storage system fire

Reported facts about the fire at the McMicken Energy Storage facility are limited. Based on local media reports, we know that firefighters responded to an incident on April 19. While inspecting the 2 MW / 2 MWh battery system, eight firefighters suffered injuries in an explosion. The cause is unknown. All of the firefighters with the most serious injuries were in stable condition in the days following the blast.

The system owner, Arizona Public Service, switched off other energy storage projects in the aftermath of the fire but, as Greentech Media has reported, APS is not wavering on plans to deploy 850 MW of battery storage by 2025.

The entire industry will be paying close attention when investigators reveal their findings about the root cause of the fire and the ensuing sequence of events. Even now, however, developers can size up the inherent risks that all projects using lithium-ion batteries should address.

Lithium battery risks

Eight years ago, when the US Department of Energy awarded Green Charge Networks a $12 million grant to deploy lithium battery storage systems, I was bullish on the technology. If anyone was a believer in lithium, it was me. Then, one by one, the following risks came to light.


Every time you cycle a battery, capacity and efficiency drops bit by bit. Performance on day 30 will not be the same as on day 1. How well does your financial model sold to your client calculate degradation along the performance line?

Thermal runaway

It’s critical to make sure that a battery operates according to its specification. This means when you integrate lithium batteries at a facility, the function of the HVAC system expands from comfort to safety. Now, when an HVAC system requires a little maintenance, it’s not just an O&M concern, but a safety risk. A battery that begins to operate outside of its normal temperature range can experience thermal runaway.

Hazardous materials

Lithium-ion batteries use materials that can introduce safety and environmental hazards if not properly contained. The storage industry needs an effective process for salvaging lithium, nickel, cobalt, or manganese. There’s no need to reinvent the wheel. We can borrow best practices from the solar industry, which has recycling for silicon-based solar modules and collection and recycling of cadmium-telluride thin film modules at the end of their operating lifetime.

Warranty claims

Lithium battery vendors have not yet established a track record showing the warranty claims rate. Or the frequency of warranty claims, which reflects the long-term failure rate for systems operating in the field. Early adopters carry the risk that failures may exceed expectations, straining the supplier’s ability to make good on all claims. In fact, engineers at one large lithium battery supplier have published a peer-reviewed scientific paper saying that lithium batteries are degrading faster than expected and proposing a patent to resolve the issue, suggesting that the risks should be taken seriously.

Human rights

Three years ago, the Washington Post published an expose on cobalt mining practices in Congo, where children help populate the workforce that uses hand tools to dig in underground mines, exposing themselves to health and safety hazards. Cobalt is an ingredient in lithium batteries. The Post has also traced the lithium supply chain from parts of Chile, where indigenous communities have struggled to protect the environment and win local economic benefits from the extraction and sale of the lucrative mineral.

Downstream costs

The low upfront cost of lithium batteries is only part of the total cost of ownership, one that excludes downstream costs associated with operations and maintenance of the batteries, the fire detection / suppression system, or the HVAC system that keeps the batteries within their specified temperature range. A failure to perform proactive operations and maintenance could not only increase long-term costs but void the manufacturer’s warranty.

Parasitic load

As industry analysts have gained a deeper understanding of how much storage capacity is needed to keep storage-integrated HVAC systems running, it appears that round-trip efficiency for lithium battery systems may be lower than originally thought. Citing Lazard’s ongoing levelized cost of storage analysis, Greentech Media has reported that parasitic loads could knock down system efficiency by 17 percent or more.

Advantages of flow batteries

In recent years, I have had many opportunities to compare lithium batteries and vanadium flow batteries side by side, while designing storage systems at SepiSolar and performing battery tests in partnership with Nextracker. The battery test, ongoing since 2017, consists of over two dozen battery types, including 5 lithium batteries, 6 flow batteries and 2 flywheels, plus an ultracapacitor, an advanced lead-acid battery, a copper-zinc battery, and a nickel-iron battery.

Through firsthand experience, one key observation at this point is that the market currently has two leaders in the race to achieve lowest total cost of ownership: lithium batteries and vanadium flow batteries. Vanadium flow batteries have earned a place on the leaderboard based on advantages in cost, performance, installation speed, safety, and design simplicity.


Please note, first of all, that battery costs vary based on storage system design and use case. The battery cost for a commercial system used principally for demand-charge reduction will be different than the battery cost for a grid-scale storage project designed for transmission and distribution deferral.

That said, Nextracker has shown that vanadium flow batteries can yield a lower total cost of ownership than lithium batteries due to significantly lower O&M costs over 20 years.


Nextracker has also demonstrated a competitive installation process with vanadium flow batteries. Installation of Nextracker’s NX Flow, a solar-plus-storage solution using Avalon Battery’s vanadium flow battery, requires less installation time and fewer materials than a central storage system due to being shipped “wet.” This means it’s full of electrolyte from the factory. It’s the first battery in the world to demonstrate this feature.

The battery is pre-commissioned and integrated with a 3-port string inverter at the factory. All battery-to-inverter wiring is complete on arrival. Before installation, the construction crew drives piles and installs cross rails to set up a mounting platform. Then the crew places the battery with a forklift and bolts the battery to the platform. Finally, the crew connects DC and AC wiring from the solar array to the inverter. Here is a 3-minute demonstration.


All plated batteries, including lithium batteries, have inherent safety risks. If you take the positive and negative sides and create a short circuit, the wire can get so hot that it explodes. Firefighters have reported on fires in electric vehicles that get damaged in a car crash, get towed, and catch fire days later.

Vanadium flow batteries have three key safety advantages. First, you can turn a vanadium flow battery off, preventing the device from charging or discharging altogether, and with zero voltage on both the positive and negative terminals. Second, the temperature rise in a flow battery is limited. Even if you short the battery on the chemical side or the fluid side, the temperature rises briefly and then drops, and the battery can be placed back into service immediately with no downtime to speak of. It’s the most boring test you’ll ever see. Finally, there are no flammable, toxic, nor hazardous materials or components. Check out this white paper on energy storage system safety from retired San Jose Fire Captain Matthew Paiss to learn more.

Battery design

Flow batteries are simple by design. They consist of two chemical solutions, one with positively charged ions, another with negatively charged ions. When connected to a generator (actually, a reversible fuel cell) the battery charges by pulling ions from the positive solution and pushing them into the negative solution. When you switch the battery to discharge, the ion flow goes in reverse and generates an electric current. The “secret sauce” of vanadium flow batteries is that the entire electro-chemical reaction happens in a purely aqueous state, which translates to “no degradation,” which translates to “lowest LCOS.”

Trust and visionary thinking

As a licensed engineering firm, SepiSolar’s first obligation is to follow national and jurisdictional codes and standards. The value of our design work depends on our ability to optimize the best products and technologies for the right applications that maximize benefits and minimize costs, all while providing structural and electrical engineering stamps in all 50 states. Beyond that, SepiSolar follows a set of core values that promotes trust and integrity, and encourages visionary thinking.

When customers approach us to design lithium batteries for residential and commercial applications, we do it. When customers ask us to advise them on the tradeoffs between battery technologies, we do that as well, covering all the topics raised here.

Our commitment to promoting trust and visionary thinking compels us to discuss openly the risks (and, therefore, costs) of lithium batteries, especially in the aftermath of the Arizona storage system fire. While we hope the industry can mitigate all the risks, many have not yet been fully addressed. Meanwhile, we owe it to the Arizona firefighters who suffered injury to engage in an open discussion about lithium batteries.

Our customers are remarkably entrepreneurial. We expect that contractors will quickly adapt to market changes by delivering storage solutions that balance cost, speed, and safety.

Please contact us if you want to learn more about engineering and design for storage systems using flow batteries.

CA Small Business Enterprise

Certification ID:

Bidder/Supplier ID:

NAICS Codes:
541330 – Engineering services
541340 – Drafting services
541490 – Other specialized design services
541618 – Other management consulting services
541690 – Other scientific and technical consulting services
541990 – All other professional, scientific, and technical services

D-U-N-S number:

811024, 81101701, 81101516, 81101604, 43232614, 81101505

Subscribe to the SepiSolar newsletter:

Subscribe Now