Student Project: Instrumentation and Control of Solar-Powered Algae Bioreactor

Energy harvesting biofuel systems use a constant amount of energy to monitor and control biofuel production. It is important to produce biofuels efficiently as these systems become much larger and sophisticated. Renewable energy resources improve environmental impact and sustainability. Improving solar cell efficiency through various measurement techniques expands the need for an independent energy harvesting system. Solar cells used to control microcontrollers and numerous system devices must be optimized to run an efficient system. The students developed a 3D printed circuit control board with a solar-powered algae bioreactor to monitor growth. The solar cells were common polycrystalline wafers that are available to consumers from online sources. The cells were then tested within an algal continuous flow system to determine effectiveness and efficiency as an energy resource. Examining such methods with an integrated solar bioreactor provides insight to students of practices towards improving solar cell efficiency through various fluid substances, transparent, and opaque material. In the process, students learn to use equipment for rapid prototyping. The project gives students knowledge and literacy in bio-fuel technology manufacturing as it has become an increasing area of interest. Introduction and Overview The student project was aimed to utilize solar energy through production of biomass and photovoltaics. Obtaining energy from biomass is through a system known as a photobioreactor (PBR). There has been considerable interest in PBRs. This is due to algae’s high rate of growth with the production of lipids, which can be easily processed into bio-fuel [1]. The availability of sunlight limits productivity, so it is important to use it efficiently. During the summer season and in locations that gain more solar exposure, solar intensity is high and prepared for exploitation. Although solar intensity is high in specific locations, algae cannot absorb all of the solar spectrum, which is transferred into heat. Due to this inefficiency of solar energy usage, the algae culture overheats, and productivity becomes low [2]. For this reason, Wakayama et al. (2000) studied the effect of an oscillating light cycle from hours to seconds because several researchers have suggested the cycle arrangement to enhance the light conversion efficiency. They also proposed to combine the photobioreactor with solar cells that could utilize the light that was blocked for intermittent periods. The highest light conversion efficiency reported is 8%, while the theoretical maximum is 10 % [3]. Light intensity on the algae throughout the growing medium is a key parameter affecting algae growth. Algae generally need light intensities between 30 W/m2 and 100 W/m2 which is around 1/10 of the light intensity of direct sunlight. If light intensity levels are too high, there is poor additional growth and even a phenomenon known as photo inhibition. Photosynthesis is proportional to the number of suitable photons, not energy (as in e.g. silicon solar cells). Given this, for example, blue photons are no more “useful” in terms of photosynthetic output than red photons. Photosynthesis only uses a specific window of the solar spectrum photons between 400 and 700 nm (visible light) and this absorption spectrum is not uniform but has peaks at 450nm and 680nm [2]. The combination these two technologies improve algae growth and prevent photobleaching. The modulated light effect is meant to be achieved by placing black cardboards in a planar array onto a photobioreactor while moving the algae inside the photobioreactor in a linear flow. Thus, as the algae travel through the reactor, and they are exposed to light when they are in a region between the cardboards, then to dark when they are underneath them. The project gives students an innovative technology that is produced on a large scale within industry. Using energy harvesting techniques and rapid prototyping devices, the students gain valuable experience in producing and enhancing the efficiency of a system with modern methods of manufacturing. The project is multidisciplinary and encompasses areas of bio, electrical, and mechanical engineering. It seeks to give students knowledge and improve literacy in bio-fuel manufacturing and production by investigating photosynthesis, respiration, and control board electronics for aquatic environment needs [5]. Technical Description The project was a capstone project that extended for 3 consecutive terms. The tasks are shown in Figure 1’s Gannt chart. Students worked with Chlorella due to its high oil retention, which is approximately 30% of its entire mass [4]. Algal cultures in photobioreactors have high optical density, which results in the surface-cells absorbing most of the light, leaving only the residual part of the radiation for the cells on the bottom and limiting their growth. External layers are exposed to excess light and dissipate more than 50% of their photons to avoid radiation damage. Following this idea, alternation of light/dark cycle can be beneficial to the growth of the algae, as it will make the photosynthesis more efficient. The students sought to optimize algae output while effectively reducing the area of exposure Figure 2. FIGURE 2 LIGHT CYCLE EXPOSURE TO ALGAE FIGURE 1 GANNT CHART Different experiments were carried out to test how the adjusted light and dark cycles to optimize photosynthetic efficiency in algae growth in the photobioreactor. The different tests were completed by varying the spaces between the shadings and the flow rate to determine productivity in algae growth changes and compare it with a fully exposed system. With the use of CAD modeling, the students were able to perform fluid flow simulations with their designed bioreactors (Figure 3). Acrylic was chosen for the bioreactor because of its optical transparency. Sheets were ordered and cut using a CO2 laser cutter. The support frame was modeled then assembled with industrial polymer adhesives (Figure 4). Students became engaged as contact with mechanical, electrical, chemistry, and biology departments applied a diverse background of knowledge towards the project. An optical cell counter was used from the department of biology to determine concentration of algae for experimentation. The handheld device was used to correlate concentration with wavelength (Figure 5). Absorbance of wavelength was used with a miniaturized spectrophotometer (Figure 6). The data collected from the cell counter and the spectrophotometer was used to calibrate solar intensity and algal density with an Arduino control board. The information was used to determine the overall exposure through the acrylic material and the algae to the photovoltaics. The exposure determined the efficiency and required power to run the control board to operate the system. Students investigated various available photovoltaics available to the market to integrate into the system. After cost and power requirements were analyzed, they then continued to pursue 3D printing a control board circuit. The 3D-PCB printer is called Squink. A manual for using the device was created for rapid prototyping. The 3D printing device prints conductive ink onto a substrate from a GRBL file. DipTrace was used to create the circuit board and its layers. The circuit was then converted to a PCB file using auto-router. The file was then 3D modeled to determine its size with the given components. DipTrace has a high-quality shape-based autorouter and the Grid Router suitable for simple PCBs and FIGURE 3 CAD DESIGN (USED FOR FLUID SIMULATION) FIGURE 4 ASSEMBLED BIO‐REACTOR WITH PRE‐ PLACEMENT OF PVS FIGURE 5 HANDHELD CELL COUNTER DEVICE FIGURE 6 SPECTROPHOTOMETER AND WAVELENGTH ABSORBANCE single-layer boards with jumper Designing a PCB 39. Single-layer boards usually have longer traces but give many other benefits for prototyping. DipTrace has several verification options on different levels of PCB design (Figure 7). For example, Design Rule Check (DRC). It verifies object sizes, length/phase parameters of high-speed nets, and clearances between different objects according to user-defined rules. The DRC results in the error-report list. Violations are marked with red and magenta circles directly on the design area. Design Rule Check in DipTrace operates in regular (offline) and Real-Time modes. Manual routing can also be done by students to edit specific traces and to specify the width of the traces independently (Figure 8). Design rules can be defined by net classes, class-toclass rules, and detailed settings by object types for each class or layer. DipTrace features a design process with real-time DRC, which reports errors before making them. Students are then able to determine errors with their design to save costs on error prints, which reduces project time and material waste. The board can be previewed in 3D and exported for mechanical CAD modeling (Figure 9). Design Rule Check (DRC) with in-depth detailing, net connectivity verification, and comparing to source schematic ensure maximum quality of the final design. DipTrace automatically places a 3D model to fit the pattern's drawing. Students entered appropriate values into the corresponding fields on the 3D Model Properties section (shift, angle, and scale for each axis). In this case, the resistor needed to rotate 90 degrees and shift it up a bit. Specify 90-degree Z Angle and 0.03 inch Z Shift to complete this circuit. FIGURE 9 3D MODEL OF CONTROL BOARD Modeled PCB layering was self-learned as students became familiar with the intricate process of component layout and layered printing. The program gave them optimization of board layout to fit the parameters of their reactor without sacrificing quality. An instructional table was created by FIGURE 7 DESIGNED PCB CIRCUIT FIGURE 8 ROUTING TRACE (CONTROL BOARD) student of the project to help others seeking to 3D print a PCB (Table 10). The