Service life tests for storage batteries used in islanded power systems with renewable energy sources

Abstract

We investigated the service life of storage batteries to provide recommendations on the design of energy storage systems used in islanded energy systems based on renewable power sources. The service life of maintenance-free, sealed lead-acid batteries produced by absorbed glass mat (AGM) technology was determined by endurance tests carried out by repeated charge/discharge cycles according to specified load profiles, implemented at a specialized Chroma Test System station. Three battery load profiles were simulated: one for the standard DC charge/discharge mode, and two for the charge/discharge modes from renewable energy sources. To this end, the actual data obtained from monitoring the operating modes of a wind power plant were used. It was found that the battery service life depends on the intensity of stress factors. Among them, the throughput factor has the most pronounced influence on the battery lifespan. To extend the service life of storage batteries, it is proposed to separate the charge/discharge modes in time. For batteries operated on renewable energy profiles, this approach decreases time intervals between full charges and at low battery levels, which increases the battery service life by 14%. A solution to designing an energy storage system for microgrids was proposed, which consists in the use of a combined double-circuit energy storage unit. An experimental prototype of such a unit with a power of 15 kW was developed. The use of a combined energy storage unit in the microgrid system: increases the battery service life by 20–30% compared to analogues; improves the static and dynamic stability of the local energy system with a response time of no more than 50 ms towards power change; allows a fuel replacement level of at least 25%; reduces the electricity cost by 25–30%.

Review of Battery Energy Storage Systems Modeling in Microgrids with Renewables Considering Battery Degradation

“…They are the impact of the battery capacity fading as it depends on stochastic charging in microgrids with a large penetration of renewable energy as well as on stochastic discharge (in the case of connecting an active consumer or an increase in the load from electric vehicles), regulation of the energy market using BESS, etc. It is necessary to identify the main stress factors affecting the degree of degradation of the batteries thata re used in the microgrid, which is significantly different from their operating conditions in DC power systems [53]. The next section, based on existing studies, indicates the most important stress factors that influence the power losses of batteries in microgrids.…”

“…The wide range of values of generated and consumed power determines the presence of ripple in the charging and discharging currents of the battery storage. Pulsed currents cause rapid degradation and shortening of battery storage life [53]. The effect of the depth of discharge on battery degradation at the grid scale has not been sufficiently studied.…”