An Interview with Tim Hennessy of Imergy Power Systems

Redox flow battery technology is the most cost-effective and reliable energy storage solution available anywhere in the world today. Based on a proprietary vanadium electrolyte formulation with a catalyst and additives, Imergy Power Systems has developed an energy storage system that is not only robust and efficient but can also be charged and discharged completely, thousands of times a year, without impact on its lifespan. This in turn will enable substantial cost reductions, grid stabilization and the ability to fully unlock the potential of large scale renewable energy, thereby putting an end to all the worries about intermittency and unreliability.   REM talked to Imergy President Tim Hennessy to find out more.
An Interview with Tim Hennessy of Imergy Power Systems

Tell me a bit more about Imergy and what it does?

Imergy designs and manufactures vanadium flow battery systems. The simplicity of the design creates a robust, cost-effective and efficient system that can be charged and discharged completely, and cycled thousands of times a year without impact on its lifespan. Integrated power electronics manage the charging and discharging processes, and the architecture allows the system to be scaled up in size by simply increasing the electrolyte volumes.

Imergy’s Energy Storage Platform (ESP) includes all the peripheral items for a plug-and-play device. Most battery companies will quote a price for the battery that does not include electronics, controls, battery management system, etc. But Imergy’s ESP has everything included as part of a package.

The key difference between a flow battery and a lithium ion (Li-ion) battery is that the Li-ion battery is built around a cell. The kilowatts (power) and kilowatt hours (duration) are combined in each cell, you can’t separate the two, so if you want more kilowatts (power) you have to buy another battery, and you get more kilowatt hours. Flow batteries allow you to separate the power and the energy, so if you want more power, you just add more stacks. If you want more energy, you just add more liquid into the tank, a bit like adding petrol to a fuel tank in a car in a sense.

What is vanadium, how is it sourced and how much of it is available?

Vanadium is a metal, No23 on the Periodic Table and the only element to have four different states. It’s normally used to turn iron into steel, making it flexible, so it’s a common and well-known material.

What are the main drawbacks with lithium ion (Li-ion) batteries? Why are vanadium flow batteries superior to Li-ion?

Battery performance should be based on cycle life, service life, charge rate, discharge capacity, round-trip efficiency, and performance under broad temperature ranges. Imergy’s Vanadium flow battery has a proven lifespan with no cycling limitations and an electrolyte chemistry that does not degrade over time. The energy storage system operates in ambient temperature conditions from -20° Celsius to +55° degrees Celsius. The ESP provides flexible charging operation with no impact on life or system efficiency - from 0 to 100% depth of discharge - and operates with a round-trip efficiency of 70%.

Unlike a vanadium flow battery, which uses only vanadium in the electrolyte, the nature of a Li-ion battery involves the mixing of lithium and some element, such as iron, or phosphate for example, in the battery. So the more you use the battery, the quicker it will wear out. That is not the case with a vanadium flow battery.

With large scale renewable energy projects, you need to have long duration capability for energy storage to act as a buffer to absorb excess energy and smooth out the deficits. That’s where vanadium flow batteries come in. You also want to be able to do thousands and thousands of cycles or partial cycles. The maximum number of partial cycles you can get from a lead acid battery today is about 2000 cycles. The maximum from a lithium battery is about 3600 partial cycles. So they have a limited capability when you try to integrate them with renewable energy sources. Utilities will use this as an argument against implementing renewables, suggesting that you can’t trust these short-duration renewables to be there when you need them.  But with vanadium flow batteries you can put in 5-10 hours of energy storage and use it all the way through a power outage, deep cycling 100% through the night hours.  And that’s exactly where it fits into the renewable integration plans.

If you look at Germany at the moment, it has a huge number of wind farms and solar arrays and so there is a lot of energy it can’t use. So it either exports energy to other parts of Europe or it turns off the systems, which is a waste of the generated energy, and very expensive as a tremendous amount of money has been invested in putting the generation equipment in the field. If you could combine those wind and solar resources with vanadium-based energy storage systems you could match the number of hours with the number of ride-through hours that you need and you get a firm supply, and again the argument that the Utilities makes about “we can’t trust the wind or the sun” is eliminated.

What are the financials of using vanadium, what kind of savings can it generate compared to Li-ion?

With regard to cost, PV energy is currently about 10 cents per kilowatt hour in the US while in India it is 6-7 cents per kilowatt hour. If you combine that energy with a flow battery you get a smooth supply at a cost that’s lower than or equal to the grid, and a lot lower than running a diesel engine.  It can match the life of the wind farm and PV and therefore is a real alternative to diesel or other expensive fossil fuel.

We’ve made three platforms that provide long durations of energy that match the load you require:

ESP5 – a small system delivering 30 kilowatt hours which can be used for a house or for mobile communications.

ESP30 – is a flexible and scalable system providing about 200 kilowatt hours for commercial and industrial on and off-grid deployment

ESP250 – providing 1 Megawatt hour, suitable for utilities, renewables integration and other large operations. It is optimised to provide cost savings.

How fast is the energy storage sector growing?

Forty percent of the world’s electrical energy is derived from heavy fuel oil or diesel. It’s expensive, dirty, and difficult to ship across long distances. With PV and energy storage, you can drastically reduce the amount of diesel that’s used. This means that diesel-based markets such as Africa, Indonesia and the island communities are all growing very fast. And the “diesel plus PV plus storage” market as a whole is rapidly growing across the globe. 

Many parts of India suffer from 4-6 hours of outage daily, so every building has a diesel generator outside. That is a tremendous amount of expensive diesel. The best way to address this is with battery storage. Store the energy when the grid is available, and when the grid disappears, instead of consuming diesel, you just discharge the battery.

In the US and the UK, there is a central grid, but energy policy that is quite complicated. There’s a mix of generation sources on the grid like coal fired, nuclear, and pumped hydro, and the question is how do you efficiently add renewables to create the right mix of generation in order to help meet the needs of a growing economy without adding more generation capability. The answer is the addition of batteries distributed around the grid to provide leveling of the variability in the renewable energy, and that total mix can help eliminate the need to build more central generation.  And this is where there is a very large opportunity, but slow moving market in the U.S., U.K., and the rest of the developed world.

What kind of technologies can these batteries be used for?

In terms of Li-ion, Tesla, Samsung, Sony, Panasonic, Mercedes Benz and so on are all using it. With Tesla, it’s for cars, with the others it’s more for mobiles, laptops etc, but they are looking for other applications.

Li-ion is generally expensive and there is a limited amount of cheap lithium. This means the costs are around $1500 per kilowatt hour in Japan, $500 per kWh in China, some I’ve even heard numbers as low as $200 per kWh. However, you also have to add the balance of plant, cooling, a battery management system and more, so you end up with an average of $600-$700 per kilowatt hour. It’s really expensive, and that is not economically attractive to utilities.

We’re always going to need multiple technologies for different applications, so a flow battery won’t be suitable for a car, it’s too big.  Li-ion is suitable for cars and for mobile communications, but it’s not suitable for a wind farm because it can’t do frequent deep cycles economically. 

Success will be defined by delivering what is technologically needed in the most cost-efficient manner. A battery should be evaluated in terms of the Levelised Cost of Energy (LCOE). It takes into account all of the factors that you need to make the battery work over time – maintenance cost, replacement cost, etc., and it asks what does that cost over 10 to 20 years.

A conventional lead acid or lithium battery needs to be replaced within three years. Vanadium electrolyte never wear out. So with vanadium you immediately get a much lower LCOE. You do not need to replace close to 80 percent of the system cost over its 20 year life using a vanadium battery. Efficiency is good, operating costs are low.

I’ve heard that Li-ion batteries can explode – how common is this and under what circumstances?

There are several different types of Li-ion. Some of them are more likely than others to experience runaway fires like the buses in China and those that have impacted the airline industry. Most of these have been designed with fire safety in mind, but the issue is that when they do catch fire, they’re almost impossible to put out.

A much larger limitation is when you put them together, so for example you might put 8,000 cells in a car battery, so you’ll need a very sophisticated cooling system, management system and so on to make sure they’re in balance and you don’t overcharge one. Because if you overcharge one, it will get hot and then it can catch fire. So do you want to put 50,000 of them in a wind farm? Probably not a smart idea.

Flow batteries are much simpler. They contain an aqueous-based electrolyte, they can’t get hot, they can’t catch fire, and they are intrinsically safe. They can operate at much lower cost, so flow batteries are the way to go for large renewable energy plants. The batteries can also be made by small companies as we use mostly commercial materials like plastic pipes and tanks.

What is the expected life of a vanadium battery and how can it be disposed of sustainably when that life is over?

With regard to disposal, you have to dispose of conventional lead acid and Li-ion batteries in a very careful manner. Li-Ion can be explosive, and both are toxic and so recycling is a very onerous and a very polluting process. The same is true with Li-ion and that means the costs are increased both on a societal and a first-cost basis. With vanadium flow batteries there is no disposal problem because you keep on using it. The vanadium is benign because you can even reuse it for other purposes, such as in making steel.

At Imergy we recover vanadium from waste products, such as the fly ash dumps at coal plants, from mining and industry and so on. An example is the tar sands in Canada which create massive dumps, in which there is lots of vanadium.

How many companies are starting to switch to vanadium away from Li-ion?

Vanadium systems are already below the costs for Li-ion systems, so the economics are already competitive. They can be used in the utilities sector for frequency regulation and utilities are already starting to look at switching. We had an enquiry from an independent power producer (IPP) who commented that our costs were 25 percent to 30 percent lower than Li-ion over the life of the system.

How long will it be before they are in general use, replacing Li-ion?

Imergy is already below the projected cost of lithium in a substantial manner, So the economics are very compelling for us.  In the “switching” market, where lithium has had a foothold for frequency regulation, vanadium is now being considered as an alternative because the technology is more cost effective over a 20-year period. 

But as I mentioned earlier, each application will have a technology that best addresses the need.  Imergy will have about 200 systems in India at the end of this year, including those storing solar-generated electricity for rural electrification and solar powered minigrid projects.  We’ll have a similar number in Africa, mostly in hot rural areas. Conventional batteries in hot regions begin to fail quickly. These installations, among others in the U.S., Europe, Asia, Africa, and the Caribbean represent a need for long-duration energy storage that is extremely cost effective, delivers unlimited cycles, operates safely in extreme temperatures, is environmentally safe and sustainably designed.  Lithium cannot do that. Vanadium Can.

For additional information:

Imergy Power Systems

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I admire the work of this man. Fantastic.
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