Design and simulation of photovoltaic system for reduced demand from electric bus charging
Date
2023
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Publisher
University of Delaware
Abstract
As more electric vehicles (EVs) hit the road, there comes the necessity of charging all of those vehicles. This presents certain challenges, the most important being managing the large power demand. At their headquarters in Wilmington, the Delaware Authority for Regional Transit (DART) has a fleet of eight electric buses. Because of the current practice of simultaneously charging many buses, they face high demand charges on their electric bill. To reduce this charge, DART tasked our research team at the University of Delaware with designing a photovoltaic (PV) system with the option of adding backup storage in hopes of reducing the demand. DART recently implemented a charge management system to better control the charging of the buses and shift more of the demand to off-peak hours. ☐ Measurements of the parking lot space at the main DART facilities in Wilmington using satellite images allowed an estimate of usable space for solar carports which was converted to monthly electric power and energy using the National Renewable Energy Laboratory’s (NREL) PVWatts calculator. Utilizing this information, along with historical electrical usage data from DART’s charge management system, an estimated annual load profile was modeled. Simulations were then run using System Advisor Model (SAM) software, developed by NREL, to determine the most applicable renewable energy system. Billed demand was incorrectly calculated in SAM, so the benefits of adding a PV + battery system are less apparent in the results. Ultimately, it was shown that a PV system at 100% capacity relative to the estimated load, plus one hour of backup storage, or 75kWh, would provide the highest Net Present Value (NPV) for DART at $261,333, with a simple payback period of 10.1 years and a discounted payback of 23.2 years. The analysis of economic data allowed our team to select said system as our recommendation for DART’s future renewable energy microgrid. An improved ability to incorporate the actual tariffs and demand charges would give more accurate results and likely predict even faster payback and a higher NPV than reported here.
Description
Keywords
Battery, Microgrid, Photovoltaic system, Renewable energy, Solar carports