High-Level Concept of the Hybrid Energy Storage

HYBRIS’ basis is the optimisation of advanced hybrid systems as high-performant, cost-effective and environmentally-friendly solutions in microgrid applications. HYBRIS is an industrially driven project that wants to validate viability and cost effectiveness of the use of novel Hybrid Energy Storage System (HESS) and its integration coupled with innovative microgrid systems. This flexible hybrid system will be optimized in 3 use case (Energy services in island grids, Energy services in private grids & EV charging stations in e-mobility) and validated by using 3 demonstration sites.  

Hybridization of energy storage system in HYBRIS project stays for the combination of two different electrochemical storing technologies with different nature; one meant for peak power management and the other one for large storage of energy. The high-power efficiency and fast response battery, is based on a Lithium ion Battery (LiB), a TOSHIBA-SCiB technology. While the use of the large energy capacity is based on Aqueous Organic Redox Flow Battery (AORFB). The smart combination of these two batteries will allow to work in the maximum efficiency working points making profitable the investment made in this hybrid system and making it more sustainable.  

In following, a brief description of both systems will be presented: basic concepts of the different chemistries involved (LiB and AORFB).  

Figure 1 Scheme of a ) Lithium ion battery (LiB) and b) Redox flow battery (RFB) 


SCiB technology is a rechargeable battery released by Toshiba that shows some important features, this is due to extremely power densities and efficiency offered by this lithium chemistry over the other ones. LTO anode chemistry is based on lithium titanium oxide anode, that on one hand, provides superior performance especially in avoiding thermal runway events and on the other hand extends battery lifespan. The operative temperature range of this battery goes from -30°C to 55°C and safety is enhanced with a very low risk of fire or explosion. 

From the point of view of power, the proposed modules based on these LTO cells, have the module capacity to work with current peaks several times bigger equivalent as minimum to 3C (135A). These higher rates are feasible but imply a redesign of the battery cooling system in order to prevent temperature rise beyond 55ºC (maximum safe working temperature of LTO batteries). The chosen dimensions of the TOSHIBA LiB system for HYBRIS will be a 50kW/15kWh SCiB-battery that will consist of a battery stack made up of 12 modules SCiB Type 3-23 in series connected. The 12 Modules will deliver a nominal voltage of 330V and the maximum DC current will be limited to 200A (4,5C rate) for the case scenario. 

Figure 2 Each module is constituted by 24 units of SCiB-23Ah cells (left top element on the picture).  


The second component of the hybrid system is based on a AORFB technology addressed to increase the energy capacity of the system. The main requirement is to bring a big amount of stored energy at low cost. Even accepting low energy density values (7,8 Wh/l) much lower than the energy density for the chosen lithium ion based battery option, 134 Wh/l, but also much less expensive, be able to supply the required energy capacity. Although the most mature technology of this alternative is based in the use of Vanadium based Redox Flow Battery, here for avoiding the use of vanadium with the environment associated problems and its price fluctuation, it has been proposed the deployment of this HESS component based on the use of aqueous organic electrolyte, AORFB.  

One of the most relevant and unique feature of this type of technology is the ability of independently separating power and energy capabilities, thus allowing flexible design. It becomes essential also as component in a HESS system in order to be combined with a lithium ion based battery taking care of the power management whereas the AORFB becomes responsible of the energy supply. The energy capacity is determined by the amount of electrolyte stored in the external tanks, while the power depends on the active area of cells and the number of them.  

The energy buffer component of the hybrid system proposed by Kemiwatt system is based on a greened and cheaper technology thanks to the use of organic molecules and easily recyclable materials. The Kemiwatt battery uses non-flammable aqueous organic electrolyte and operates well in a temperature range coming from 10°C to 45°C. Advantages offered are no-thermal runaway and a greater safety compared to other battery technologies. The ability of releasing energy at constant power for times of more than several hours makes RFB technology suitable for a wide range of energy services.   

The AORFB provided by KEMIWATT, will be a 5kW/15kWh system and consists of an electrochemical reactor constituted by a stack of 55 cells, each of this single cells deliver almost 1V and stuck in series can provide a nominal voltage of 55V. This system can work at a maximum current of 165A and the whole AORFB system will weight around 10 tones. 

Figure 3 example of AORFB containerization1)Stack, 2)electrolyte tanks, 3)electrolyte pump, 4)pump power input, 5)electrolyte pump, 6)Structure support of stack.  

Written by Elías Martínez, from IREC