Abstract:As microgrids grow in popularity, the cost of energy storage becomes a more and more pressing issue for the industry to solve. One potential solution to this problem is the development of second-life battery-based energy storage systems (ESSs). This paper discusses the design, construction, and operation of a commercial-scale microgrid consisting of 164.5 kW of solar photovoltaics (PV), 262 kWh of energy storage, 2 buildings with a total area of 1550 m2, and an average power demand of 85 kW. The ESS was built using second-life Nissan Leaf battery modules to demonstrate the performance potential of retired electric vehicle (EV) batteries for stationary energy storage. Prior to assembling the ESS, each Nissan Leaf module was tested to characterize its state of health (SoH). The average SoH of the modules before use was 71%, however evidence gathered suggested this is near the upper limit of initial second-life battery health. This challenges the conventional wisdom in the literature that EV batteries are retired soon after they reach 80% SoH. Data from the first year of microgrid operation were presented, demonstrating that the second-life batteries performed as designed. Analysis revealed that the microgrid achieved an average reduction in maximum peak-time demand of 60% and peak-time energy use of 39%. Results support the case that second-life batteries are well-suited for commercial-scale energy storage.

Key words: Energy storage, second life, microgrid, lithium ion, battery, reuse