My honors thesis took the form of a creative project. My final deliverables are my research presentation (pdf attachment) and solar powered electric scooter (image attachment). The goal of my project was to fix a second-hand electric scooter and create a solar-powered charger for its battery. The research portion of my creative project focused on exploring the circuit elements in a solar charging schematic and their relationships to power output. First, I explored methods of maximizing power output of the basic solar charging schematic. To find the maximum power output based on different settings of photocurrent (sunlight), I wrote a MATLAB code to calculate maximum power based on its derivative with respect to voltage set equal to zero. Finding this maximum power point in MATLAB allowed me to find its corresponding current and voltage output to produce that exact power. With these max current and voltage values, I was able to solve for an ideal resistor value to set in series with the solar panel in order to achieve these values. In doing so, I designed a maximum power point tracker (MPPT). This became an essential component in my charger’s final design. Next, I explored the microcircuit level of a solar panel schematic. In order to do so, I had to break my single diode model into several diodes in series, resulting in the overall solar panel voltage drop (aka the voltage rating of the solar panel) being divided N times. To find what this N value for a given solar panel is, I performed a lab experiment using a small solar panel and a floodlight to gather the panel’s turn on current and open circuit voltage. These two values helped me find the solar panel’s N value after linearizing the lab data. Now, with a much deeper understanding of solar charging circuitry, I was able to move forward with the design and implementation phase. The design and implementation portion of my creative project included the physical assembly of the solar-powered scooter. First, I analyzed the efficiency differences between having an AC coupled vs. DC coupled system. Due to the added complexity of AC conversions, I deemed it unnecessary to use an inverter in the charger. The charging schematic I designed only called for a charge controller and MPPT, both parts that could easily DC couple the system. Keeping the system in DC from solar panel to battery was definitely the most efficient method, so DC coupling was my final selection. Next, I calculated the required current and voltage output of my charger to meet the specs of the battery and the requirements I set for my project. Finally, I designed a solar array based on these ratings. The final design includes one 30 W panel in parallel with two series-connected 5W panels. The two series panels are affixed on the scooter neck for a built in charge design so that the scooter can be charged anywhere (outside while not in use). The big panel can be connected using a parallel branch in the charging cord that I spliced for added current if charging is set up in a stationary setting (by a window at home). The final design serves the need for sustainable micro mobility in a daily 50% depletion use case kept above 20% charged at all times.

In this thesis report, I aim to explain the realities of humanitarian efforts to implement solar panel systems in rural communities, the challenges they face, and why they fail. I will also compare case studies of both unsuccessful and successful projects, which will lead to a proposed solar panel system design for a single home completed in collaboration with Arizona State University's Engineering Projects in Community Service (EPICS) Program for the Shonto Solar project.

Much of Nepal lacks access to clean drinking water, and many water sources are contaminated with arsenic at concentrations above both World Health Organization and local Nepalese guidelines. While many water treatment technologies exist, it is necessary to identify those that are easily implementable in developing areas. One simple treatment that has gained popularity is biochar—a porous, carbon-based substance produced through pyrolysis of biomass in an oxygen-free environment. Arizona State University’s Engineering Projects in Community Service (EPICS) has partnered with communities in Nepal in an attempt to increase biochar production in the area, as it has several valuable applications including water treatment. Biochar’s arsenic adsorption capability will be investigated in this project with the goal of using the biochar that Nepalese communities produce to remove water contaminants. It has been found in scientific literature that biochar is effective in removing heavy metal contaminants from water with the addition of iron through surface activation. Thus, the specific goal of this research was to compare the arsenic adsorption disparity between raw biochar and iron-impregnated biochar. It was hypothesized that after numerous bed volumes pass through a water treatment column, iron from the source water will accumulate on the surface of raw biochar, mimicking the intentionally iron-impregnated biochar and further increasing contaminant uptake. It is thus an additional goal of this project to compare biochar loaded with iron through an iron-spiked water column and biochar impregnated with iron through surface oxidation. For this investigation, the biochar was crushed and sieved to a size between 90 and 100 micrometers. Two samples were prepared: raw biochar and oxidized biochar. The oxidized biochar was impregnated with iron through surface oxidation with potassium permanganate and iron loading. Then, X-ray fluorescence was used to compare the composition of the oxidized biochar with its raw counterpart, indicating approximately 0.5% iron in the raw and 1% iron in the oxidized biochar. The biochar samples were then added to batches of arsenic-spiked water at iron to arsenic concentration ratios of 20 mg/L:1 mg/L and 50 mg/L:1 mg/L to determine adsorption efficiency. Inductively coupled plasma mass spectrometry (ICP-MS) analysis indicated an 86% removal of arsenic using a 50:1 ratio of iron to arsenic (1.25 g biochar required in 40 mL solution), and 75% removal with a 20:1 ratio (0.5 g biochar required in 40 mL solution). Additional samples were then inserted into a column process apparatus for further adsorption analysis. Again, ICP-MS analysis was performed and the results showed that while both raw and treated biochars were capable of adsorbing arsenic, they were exhausted after less than 70 bed volumes (234 mL), with raw biochar lasting 60 bed volumes (201 mL) and oxidized about 70 bed volumes (234 mL). Further research should be conducted to investigate more affordable and less laboratory-intensive processes to prepare biochar for water treatment.