What power sources FOR the future?


The coming years are likely to see a lot of changes in our approach to generating electricity. As the transition to cleaner energy goes ahead, the percentage of renewable energy in the power mix is set to grow, driving a switch away from the current centralised electricity generation model towards a more distributed approach involving a wider geographical spread of smaller power plants. One major issue however is that renewable energy sources (RES) are available only intermittently. The sun’s rays only strike photovoltaic installations during the day, while wind turbine blades depend on low-pressure meteorological conditions. As the proportion of our power generated from these two energy sources increases, it will become crucial to be able to store electricity during periods of high production so as to inject it into the system at times when less is being produced.

At the moment the imbalance between electricity supply and demand is evened out by cross-border power trading between the various European networks, or by ‘load management’ – i.e. levelling out demand.

Electricity storage, the term commonly used, is in fact incorrect. What you actually have to do is turn it into energy – mechanical, chemical, whatever – so that you can recover it later on.

Michael Salomon

However, many experts believe that an RES penetration rate of more than 30% of the energy mix would lead to imbalances that would be very hard to manage. A great deal of research is therefore being carried out into new storage solutions that will provide greater flexibility in power grid management. “Electricity storage, the term commonly used, is in fact incorrect,” points out Michael Salomon, CEO of Clean Horizon Consulting, explaining: “Strictly speaking, you can’t accumulate electricity. What you actually have to do is turn it into energy – mechanical, chemical, whatever – so that you can recover it later on.”

For many decades now, this task has fallen to the world’s good old traditional hydroelectric power stations, which use the ‘pumped storage’ method for load balancing. Excess electricity produced during off-peak periods is used to pump water up from a lower level into a reservoir situated at a higher altitude. Then, at peak times, the water is released to flow downwards, driving the turbines that produce electricity.

Pumped Storage Power Stations, or PSPS as engineers call them, still constitute by far the main energy reserves available. They account for some 97% of all electricity storage, totalling for example close to five gigawatts equivalent in France. However, this creates a large environmental footprint, requires investment totalling several tens of millions of euros, and meanwhile we are gradually running out of available natural sites. Huge projects of this kind are in fact no longer very fashionable, at least not in Europe. In addition, the pumped storage approach does not fit in with the decentralised model of electricity generation we are likely to see in the future. Behind the scenes, scientists and engineers are therefore working hard to find alternatives.

thE Grand'Maison Dam AT ISÈRE in the french alps  



All eyes now on lithium-ion batteries



the estimated cost price of a LITHIUM-ION BATTERy

For some years now, lithium-ion batteries have taken centre stage in these efforts. Their popularity has risen in step with improvements in performance and longer lifetimes due to the increase in the number of charge cycles, plus also recent cost reductions of around 15% a year resulting mainly from mass production for use in electric vehicles. A report from Bloomberg New Energy Finance reveals that the cost price of a battery plummeted from $1000 in 2010 to $273 in 2016, and predicts that it could fall to around $230 by 2018. This continual drop in price is actually exceeding the experts’ forecasts year after year.

As one might expect, automobile manufacturers have also now embarked on the process of using the batteries for storing electricity, thus competing with specialists LG and Samsung. Meanwhile Nissan, Mercedes and BMW have all developed their own home electricity storage offerings. Nissan has teamed up with energy management company Eaton to launch xStorage, a home energy storage system which uses new and second-hand Nissan batteries from its ‘Leaf’ cars, the world’s best-selling 100% electric car, so as to maximise the use of the batteries before they are recycled.

NISSAn home energy storage system


Eaton and Nissan have equipped the multifunctional Amsterdam Arena with a back-up electricity supply system and they also help to stabilise the Dutch electricity network when consumption peaks. According to Reuters, the Japan-based carmaker is planning to build a gigantic plant in Europe to store used batteries which, once charged up in off-peak hours, could power around 120,000 homes.

In the same vein, German auto manufacturer Mercedes-Benz is working hand-in-hand with US company Vivint Solar to produce batteries for use in the home. However, Tesla struck first on this front, launching the Powerwall in April 2015. Elon Musk’s firm actually triggered the market for home energy storage batteries, which up to that point had still been in its infancy.

Most of these automotive manufacturers also have other ventures underway and their future may well depend on their ability to develop substantial ‘vehicle to grid’ (V2G) power provision. V2G is a system whereby plug-in electric vehicles communicate with the power networks and help to maintain grid balance. Nevertheless, Rémi Gilliotte, a consultant at French company Yélé Consulting, points out the complexity of this type of solution. He agrees that “it is possible to achieve genuine synergies with grid management companies,” but stresses: “However, this approach is difficult to implement because it pre-supposes real interoperability between the various recharging infrastructures – i.e. you need agreements between the people in charge of the recharging hubs, the people managing the grid, and electric vehicle managers and users.”

Regard d'expert

Michael Salomon

Yélé Consulting

The main obstacle to deploying battery storage is the cost, which is still too high for an attractive short-term ROI

Does the boom in lithium-ion technology ensure a positive future for storing energy? This is not guaranteed. Despite the continual fall in prices, batteries are still an expensive method of storing energy. “The main obstacle to deploying battery storage is the cost, which is still too high for an attractive short-term ROI, concluded a recent report  by Yélé Consulting. “Today lithium-ion batteries are already economically competitive for peak-power operation, i.e. to stabilise or smooth out the imperfections of the electricity grid,” says Michael Salomon, warning: “but not as an additional photovoltaic solution capable of storing electricity during the day to be used at night.” Nevertheless, if the price of photovoltaic panels and batteries continue to fall, coupled with an increase in the sales price of electricity, this could well change the situation entirely within two to three years.

LITHIUM-ION BATTERIES are ALREADY economically competitive


Batteries are eclipsing alternative promising technologies

jean françois
Regard d'expert

Jean-François Le Romancer


Hydroelectric plants and compressed air storage are ‘energy’ solutions, whereas batteries serve to ensure power quality and network security

There is however another side to the coin. The popularity of batteries has rather eclipsed the alternative technologies currently under development. This is doubtless because of the tendency of the producers and promoters of battery technology to present it as the be-all-and-end-all of electricity storage. This is in fact not the case; there are as many storage solutions as there are different and complementary uses. “Hydroelectric plants and compressed air storage are ‘energy’ solutions, whereas batteries serve to ensure power quality and network security,” points out Jean-François Le Romancer, founder of French energy innovation consulting company Keynergie and ex-Director of Innovation at Belgian private electricity and gas provider Poweo.

Whatever its size, a battery provides a source of electricity that can be mobilised fast but over a shorter period of time than feasible with other energy solutions. “For example, the giant battery built in Australia by Elon Musk’s firm has a power reserve equivalent to 130 megawatt hours. By comparison, the capacity of the large PSTSs is a couple of dozen gigawatt hours (Editor’s note: the Bath County Pumped Storage Station in the US state of Virginia, the largest in the world, has 30 gigawatt hours). We’re not talking the same order of magnitude.” It is difficult to imagine, for example, that lithium-ion technology would be able to meet the future need for storage of a close to 500 megawatt wind farm situated in the the bay of Saint Brieuc (62 wind turbines of 8 megawatt capacity each), which is due to come on stream in 2020.



Rechargable flow batteries are among the promising technologies that are able to store large quantities of energy. One undeniable advantage which these accumulators have over their traditional counterparts is that battery power is independent of the storage capacity. “The power level is determined by the stack of cells where the oxidation-reduction reaction takes place, while the quantity of energy that can be stored depends on the size of the electrolyte tanks, which can be increased according to need,” explains Jean-François Le Romancer.

Companies including French firm IFP Energies nouvelles (IFP-EN) and Rennes, Brittany-based startup Kemwatt are working to perfect the development of this type of storage system. “The attractive thing about the Kemwatt solution is that it uses a biodegradable electrolyte. Prototypes of 10 kilowatt hours are now being trialled but there is still quite some development work to be done in order to reduce costs,” says Le Romancer. Using biodegradable – and therefore non-toxic – material represents enormous progress. This type of battery had not found much favour up to now as the electrolytes were based on the chemistry of vanadium chemistry and were therefore a corrosive acid medium.

clean energy is our future



Hydrogen, a much-studied means of mass energy storage

Energy firms are studying hydrogen concentrate, which can be fed into the network that was originally designed to transport natural gas 
jean françois

Jean-François Le Romancer 

Much research has been carried out into using hydrogen as another means of storing energy. For example, the ‘power to gas’ process consists of transforming electricity into hydrogen through water electrolysis and then feeding it into the gas network. The hydrogen is then either consumed directly or combined with carbon dioxide to produce synthesised methane.

Energy suppliers GRTgaz and Engie are particularly active in this field. “They’re studying hydrogen concentrate, which can be fed into the network that was originally designed to transport natural gas,” explains Jean-François Le Romancer. Engie has set in motion at Dunkirk the first French major Power to Gas hydrogen energy storage demonstration project as part of the GRHYD (Managing grids through injecting hydrogen so as to decarbonise energy) initiative. Last December GRTgaz also embarked on a similar venture with the Jupiter 1000 project, a demonstration plant that is due to be connected to the French gas transport network at Fos-sur-Mer (Bouches-du-Rhône) in the south of the country. With its 1-megawatt capacity, it will be able to power 150 homes.

Other players are looking at how hydrogen can be used to store energy in buildings. Grenoble, France-based startup Sylfen has made headlines with its development of a unique reversible storage solution for buildings such as homes running on positive energy. The company’s ‘Smart Energy Hub’ works as an electrolyser to transform into hydrogen the surplus electricity generated locally and, conversely, as a fuel cell to re-convert the hydrogen into electricity.

“The process also makes use of the heat recovered during the electrolysis, resulting in savings on the heating bill. In fact, on the basis of electricity alone, it’s very hard to be competitive using hydrogen,”

underlines Le Romancer. The approach developed by French company Powidian also uses hydrogen for energy storage purposes. However, this solution is most suited to isolated sites or those connected to poor quality power grids.

HYDROGen A promising energy SOURCE


Storing electricity in the form of hydrogen is a highly promising approach, as is lithium-ion battery technology, not least because of the available synergies between the building and transport sectors. The solution of the future will almost certainly consist of re-using the hydrogen to power vehicles running on fuel cells or else re-injecting it back into the grid, as in the testing and demonstration projects at Dunkirk and Fos-sur-Mer.

Last but not least, storing electricity via heat conversion also offers some interesting opportunities. Under this approach, you heat a refractory material capable of storing large quantities of energy in the form of heat, which can then be converted back into electricity using a turbine. A number of startups, including UK-based Isentropic and French firm Stolect, are going down this road.

By Olivier Discazeaux