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As renewable energy sources, such as solar systems, are becoming more popular, the focus is moving into more effective utilization of these energy sources and harvesting more energy for intermittency reduction in this renewable source. This is opening up a market for methods of energy storage and increasing interest in batteries, as they are, as it stands, the foremost energy storage device available to suit a wide range of requirements. This interest has brought to light the downfalls of batteries and resultantly made room for the investigation of ultra-capacitors as a solution to these downfalls. One of these downfalls is related to the decrease in capacity, and temperamentality thereof, of a battery when not used precisely as stated by the supplier. The usable capacity is reliant on the complete discharge/charge cycles the battery can undergo before a 20% degradation in its specified capacity is observed. This article aims to investigate what causes this degradation, what aggravates it and how the degradation affects the usage of the battery. This investigation will lead to the identification of a gap in which this degradation can be decreased, prolonging the usage and increasing the feasibility of the energy storage devices.

One of the greatest challenges associated with efficient energy use in unmanned aerial vehicles (drones) is that of the energy storage systems – more specifically it's weight and capacity. Current hydrogen fuel cell drones have very promising flight durations, but have a low power density thus performing poorly at peak power demands. Supercapacitors are known to have high power densities and respond significantly well to peak power demands. For this research it is desired to evaluate how supercapacitors can affect the operation of an existing hydrogen fuel cell system, when combined. This study will include the evaluation of the viability of a DC-DC converter used to reduce the size (and subsequently, weight) of a supercapacitor bank. It also evaluates whether specified switching of the sources has an effect. Using data generated from the experiment it was determined that the DC-DC converter (with efficiency >94%) reduced the efficiency (by 0.5%) and duration (by 3.8%) of the supercapacitor bank whilst increasing the weight (by 16.7%). It was also seen that the method of selective switching offered no benefit over that of a self-selecting system, where the former obtained 223 s of usability and the latter 365 s. However, comparing all the results it was observed that the addition of a supercapacitor bank allowed for an improvement in energy- and power density, of the hydrogen fuel cell system, from 0.65 Wh/kg to 1.19 Wh/kg and from 69.7 W/kg to 125.7 W/kg, respectively.

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Energy storage devices are fast becoming a necessity when considering a renewable energy harvesting system. This improves the intermittency of the source as well as significantly increasing the harvesting capacity of the system. However, most energy storage devices have a large limitation with regards to their usable life—this aspect is especially relevant to batteries. The degradation of batteries (and energy storage devices) plays a large role in determining their feasibility and the degradation is determined through capacity estimations—due to the inability/difficulty of directly measuring instantaneous capacity. This article aims to research the various methods used to estimate the capacity as well as the applications of these measurements aimed at reducing the degradation of the energy storage device. Through this research, the advantages and disadvantages of the measurements and their applications will be revealed, which will then highlight an area in which these estimations or their applications can be improved. The novelty of this paper lies in the graphical representation of the capacity measurement techniques, and how they relate to each other, as well as the relations and differences between their applications, highlighting the limitations in how the measurements are used.