Abstract
Meeting rapidly growing global energy demand—without producing greenhouse gases or further diminishing the availability of non-renewable resources—requires the development of affordable low-emission renewable energy systems. Here, we develop a hybrid renewable energy system (HRES) for automotive applications—specifically, a roof-installed photovoltaic (PV) array combined with a PEM fuel cell/NiCd battery bus currently operating shuttle routes on the University of Delaware campus. The system’s overall operating objectives—meeting the total power demand of the bus and maintaining the desired state of charge (SOC) of the NiCd battery—are achieved with appropriately designed controllers: a logic-based “algebraic controller” and a standard PI controller. The design, implementation, and performance of the hybrid system are demonstrated via simulation of real shuttle runs under various operating conditions. The results show that both control strategies perform equally well in enabling the HRES to meet its objectives under typical operating conditions, and under sudden cloud cover conditions; however, at consistently high bus speeds, battery SOC maintenance is better, and the system consumes less hydrogen, with PI control. An economic analysis of the PV investment necessary to realize the HRES design objectives indicates a return on investment of approximately 30% (a slight, but nonetheless positive, ~$550 profit over the bus lifetime) in Newark, DE, establishing the economic viability of the proposed addition of a PV array to the existing University of Delaware fuel cell/battery bus.
Highlights
The use of internal combustion engines (ICEs) to power vehicles has become so widely recognized as unsustainable and environmentally hazardous as to spur the development of cost-effective and reliable alternatives, including renewable energy systems for automotive applications
We evaluated the performance under algebraic and PI control via simulation of bus operation under various conditions: typical summer and winter conditions; sudden changes in cloud cover; and intermittent periods of sustained increase in bus speed
We showed that under typical operating conditions during summer and winter, the PV/fuel cell/battery hybrid renewable energy system (HRES) is able to meet bus power demands, and maintain the battery state of charge (SOC) at 65%, with either control strategy
Summary
The use of internal combustion engines (ICEs) to power vehicles has become so widely recognized as unsustainable and environmentally hazardous as to spur the development of cost-effective and reliable alternatives, including renewable energy systems for automotive applications. The consequences of not handling these challenges adequately are (1) overuse or underuse of the battery in meeting the power demand; and (2) deep battery discharge (80% SOC) [7], the latter condition being undesirable because it initiates oxygen-producing side reactions in the battery, which can reduce the battery’s operating lifetime [8] Because these challenges may be met with appropriately designed control systems, one of our goals is to design and evaluate control strategies that will enable the PV/fuel cell/battery HRES to satisfy the bus’s power demand while maintaining the battery SOC at. Rule-based methods use a set of pre-defined logical statements to control the vehicle given current operating conditions and desired set points Because they are simple, such methods are computationally efficient and relatively cheap to implement, but have been shown to provide adequate power demand and battery SOC control while reducing hydrogen consumption [9,10,11,12,13,14].
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