The battery, with its ultra-competitive costs and maturity, is currently winning the ongoing battle for electricity storage. Despite uncertainties about the sources of raw material supply, batteries are expected to remain competitive for some time to come. Huge investments are being made in research and industrialization. Not to mention communication budgets.
Batteries are mainly used for short-term storage needs (less than 24 or 48 hours) and are very versatile. Indeed, hydrogen does not appear to be the ideal competitor, as it is more likely to be used for mass storage or other applications such as mobility. For stationary storage, the battery has a discreet but particularly formidable competitor: the flywheel.
Doesn’t that sound familiar? New technology from years of research? Not really.
We have all seen them and we use them every day: we have all played the spinning top or, just yesterday, the hand spinner. In the industrial sector, they are sometimes used as a backup system for emergency power supply for computer servers or for certain applications requiring energy storage for a short period of time. As some car racing enthusiasts know, this technology has been used to recover energy during braking and to reuse it later. McLaren and Ferrari successfully used it during the 2008 to 2010 Formula 1 seasons, and more recently Audi and Porsche on their LMP1 prototypes which shared many recent wins at the Le Mans 24 Hours.
The principle is simple: a mass and an electric motor are placed on the same axis. When we produce too much energy (for example, solar cells in the middle of the day), we can convert it into kinetic energy by accelerating our top with the electric motor. And when we need to recover the energy, we reverse the process, the electric motor becomes a generator, thus returning the stored energy to the grid. You can find more information on the general principle here.
What does it take to make a good flywheel? A homogeneous mass, a shaft with very efficient bearings to limit losses, an electric motor and a solid housing! The latter plays a very important role for the safety of the whole. Indeed, if a mechanical problem, such as a bearing failure, compromises the integrity of the steering wheel, which rotates at very high speed, could cause significant damage around it. Imagine a large spinning top in a porcelain shop… The housing is there to protect as much as possible the consequences of a mechanical failure on the steering wheel itself. That said, the technology is very old, known, and safe. In fact, we hear more often about burning electric cars that firefighters have had trouble putting out than about porcelain broken by a mad spinning top. But security is fundamental. And precisely, when we discuss the subject with our guest of the day, he doesn’t kick in the door, quite the contrary.
It is time for me to introduce André Gennesseaux, the founder of Energiestro, a French start-up that is on the way to revolutionizing the flywheel market. A concrete case. When you listen to him, you instantly perceive his pragmatism and analytical sense. He knows the subject at the fingertips and he is loquacious. A very interesting project that we like very much. André, the floor is yours:
I am delighted to introduce you to Energiestro. The project was founded a few years ago. We are developing a concrete flywheel to store energy in kinetic form. The steering wheel is coupled to an electric motor that allows charging or discharging. Today, the steering wheel market remains a niche market because prices are very high. Concrete makes it possible to offer a solution at a very attractive cost.
Your main competitors have developed steering wheels made of steel or composite materials. The storage capacity increases in proportion to the mass of the steering wheel but to the square of the speed. It is therefore possible to store more energy if the steering wheel rotates faster. This is one of the main arguments put forward by designers of composite steering wheels.
You’re right, you’re right. Composite flywheels have a much higher mass density than we do. They also have significant constraints. Due to their high speed, they require magnetic bearings to limit friction losses and a higher vacuum in the housing. This makes the product more complex and above all more expensive. However, the problem is the cost per kWh (of energy) stored. With a concrete flywheel, it is possible to make manufacturing cheaper and use technologies that are simpler, easier to maintain and also more durable. Our objective is to achieve the same initial investment cost as Lithium-Ion batteries, but with unlimited use and possible recycling of materials. The return on investment is therefore much higher than that of Lithium-Ion batteries.
It is assumed that the balancing of the mass on the axis of rotation is a crucial problem for the proper functioning of the steering wheel. What about concrete, which seems less homogeneous than steel, for example?
This is a question we are often asked, but it is not a problem. Concrete is heterogeneous at the microscopic level but, on average, it remains homogeneous. The moulding process also facilitates homogeneity around the vertical axis.
We talked about security. This is a subject that is particularly important to you.
Flywheels are safe equipment but there is no such thing as zero risk. Given the amount of energy stored, it is necessary to know and anticipate mechanical failure modes. On the one hand, our numerical models show that, in extreme cases, concrete breaks down by centrifugation and that a large part of the energy is dissipated by crushing. On the other hand, we have chosen to bury 90% of our flywheels to guarantee absolute safety. It is certainly our greatest strength compared to the competition. We are currently working on the industrialization of the prototype, to make each component safe, durable and easy to maintain. We are in the final stages of development, which will reassure us that we will achieve our very ambitious objectives.
Precisely what are the next steps in your development? We imagine you’re generating interest.
Indeed, we receive recurring requests to buy our flywheels. We are working on the reliability of the product and the next step is the construction of a pilot plant in France to validate the production phase. The flywheels will be simple to produce to easily duplicate the process elsewhere. The components must also be robust and accessible because the lifetime of the flywheel is almost unlimited. Wherever the plants could be located, we simply need high performance concrete for manufacturing.
What are you looking for today?
We have started the process of seeking funding for the pilot plant. We need about ten million euros to complete this phase. The markets we are targeting are non-interconnected areas, and the needs are huge, and countries have already shown an interest in our technology. Our flywheels can be used as storage for solar power plants to increase their potential tenfold at all latitudes.
You do have a little anecdote to share with us?
Oh, yes! At the beginning of the project, we received requests from knowledgeable individuals who wanted to buy our steering wheel. When they were told that the product was not available for sale, some replied: “We’ll invest, so it’ll be faster!” And that’s how some became shareholders.
The dream for every entrepreneur! We look forward to hearing about the rest of Energiestro’s adventure, but I am sure we will have the opportunity to talk about it again. Thank you André Gennesseaux for sharing some of your time with us!