Abstract
The paper describes the results of different types of ageing tests performed by Terna (the Italian Transmission System Operator) applied to several electrochemical technologies, namely lithium-based and sodium-nickel chloride-based technologies. In particular, the tested lithium-based technologies exploit a graphite-based anode and the following cathode electrochemistries: lithium iron phosphate, lithium nickel cobalt aluminium, lithium nickel cobalt manganese, and lithium titanate. These tests have been performed in the storage labs located in Sardinia (Codrongianos) and Sicily (Ciminna). The aim of the storage labs is intended to give the electrical grid ancillary services, for example, primary frequency regulation, secondary frequency regulation, voltage regulation, synthetic rotational inertia provision, and many more. For the primary frequency regulation service, the ageing of the batteries is difficult to foresee as the ageing tests are not standardized. The authors proposed some novel cycle types, which showed that, in several cases, the frequency regulation cycle ages the batteries much more than the standard cycle. The standard cycle definition has been adopted in the paper to identify a battery cycle test that was carried out to uniformly compare and rank the different technologies. Moreover, sodium-nickel chloride batteries are unaffected by the types of cycle and have a negligible ageing. In addition, lithium manganese oxide and lithium titanate batteries show very good behaviour with a slight degradation of the dischargeable energy, irrespectively of the type of cycle. Inversely, lithium nickel cobalt aluminium technology shows a considerable ageing and a strong dependence on the cycle types. Even if the theoretical explanations of such aging behaviours need time to be understood and expounded, the authors are convinced that the scientific community should become aware of these experimental results.
Highlights
Terna, the Italian Transmission System Operator, has undertaken a wide experimentation and employment of large-scale stationary electrochemical energy storage [1,2]
During the testing process, it became clear that some technologies were not able to withstand a continuous cycling without experiencing temperatures higher than the nominal ones; it was necessary to introduce a rest time of one or more hours between the consecutive cycles, in order to allow for a safe battery operation
Thisisisanan important result; is difficult to foresee as the frequency regulation cycle is less stressful from a thermal and energetic it is difficult to foresee as the frequency regulation cycle is less stressful from standpoint
Summary
Terna has chosen these two energy storage strategies in the high-voltage network; in the former, the electrochemical energy storage systems (EESSs) are conceived to release the renewable generation from electric loads and to avoid overload conditions in the existing overhead lines This operating mode requires a high energy/power ratio, of about 8 h, so that those EESSs are called ‘energy intensive’ installations [3,4,5]. Three installation sites are located in the Apennines in the south of Italy (near Benevento), accounting for an overall installed power of 34.8 MW Na–S storage In the latter, the energy storage systems have the important role of supporting the electrical network during the frequency regulation processes [3].
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