critical raw materials used for these kinds of batteries, including cobalt, vanadium and phosphorus. One strategy, which some companies have chosen to manage this risk, is to engage in mining activities closer to consumer markets. According to a recent Financial Times article, Infinity Lithium is seeking a permit for a lithium mine in Spain, while Savannah Resources wants to develop an opencast mine in Portugal. Other examples include the German start-up Vulcan Energy Resources, looking to extract lithium from geothermal waters, or Tesla, which wants to start mining lithium in Nevada, US. All these planned mining activities will improve the security of lithium supply but will take time and require significant investments. Another way to avoid possible supply chain constraints and related negative socio-environmental impacts is to shift from Li-ion batteries to alternative battery systems, where the main components do not consist of critical raw materials.
The company has developed a long duration energy storage solution, called TES.POD, which is able to store thermal energy and dispatch it as electricity and low temperature heat for 13 hours or more, depending on demand. The concept of the TES.POD is based on two main components. The first one is a thermal energy storage using a non-critical raw material – recycled aluminium silicate – as a phase changing storage medium, which is heated up to 600˚C by electricity (charging cycle). A Stirling engine is the other main component and converts the stored heat back to electricity and supply of low temperature heat at 55 - 65˚C on demand (discharging cycle). The TES.POD has interesting advantages compared to incumbent battery systems. One is the high constant charging power that enables the TES.POD to be fully charged in 6 hours. This characteristic is very important for operating in a real environment when using solar or wind power as the main charging source. Take, for instance, the production profile of a fix-tilt PV plant presented in Moving away from critical raw materials Figure 1. It is evident that there are only 6 - 8 hours per Azelio, a Swedish SME high-tech company, chose to go day during which a PV plant generates power at a higher down this route where the main components of battery level. The power produced during the morning and early storage systems do not rely on critical raw materials. evening hours is very low and is not enough to charge a long duration battery system. Li-ion batteries used for long duration storage – for example with 13 hours of constant discharge power – would need considerably more time than these available 6 - 8 hours to charge the battery. It is an inherent technical attribute of Li-ion batteries and it will be the case for the time being. This means that Li-ion batteries cannot provide the required 13 hours, as requested, of power under these conditions. The only solution to this problem is to significantly oversize the PV field and, most important and of greatest cost, to oversize the Li-ion battery capacity. A further advantage of Azelio’s storage system is its ability to switch modes directly from charging to discharging mode, and achieving this whilst with full operating discharging power. Figure 1. Typical daily power demand curve and power production of a photovoltaic Li-ion batteries cannot achieve this without (PV) installation. losing performance. Trying to discharge a Li-ion battery directly after charging it with full power is possible but results in an accelerated internal energy consumption. As a result, the Li-ion battery cannot supply full power for the required discharging time of, for instance, 13 hours. Additionally, unlike Li-ion batteries, Azelio’s TES.POD is designed to offer 100% depth of discharge and is able to charge and discharge at standard operational capacity, regardless of the state of charge of the system. Normally, the depth of charge of Li-ion batteries is in the region of 80% and they cannot charge or discharge with constant operational power. The input power of a Li-ion battery must be reduced as the battery is approaching the upper limit of its state of Figure 2. Largest supplier countries of critical raw materials to the EU. charge. The same happens for its output power,
22 ENERGY GLOBAL SPRING 2021