San Antonio, Texas
June 10, 2012
June 10, 2012
June 13, 2012
25.1167.1 - 25.1167.21
Solar Power System Design to Promote Critical Thinking in Freshman Engineering StudentsApproximately 70 first-year students enrolled in an introduction to engineering course designed asolar power electric system for a hypothetical highway rest stop. The educational approachutilized followed the EFFECTs (Environments For Fostering Effective Critical Thinking)methodology: to ask students an over-arching ‘driving question’ (i.e., “How much will it cost toinstall a solar power system at the renovated rest-stop?”), staged ‘guiding questions’ to help studentsindependently discover relevant design constraints, the use of active learning modules to teachfundamental principles relevant to the design, and journal entries where students were asked to reflect onlessons learned and demonstrate critical thinking.Students were initially shown the components of a solar power electric system, including a photovoltaicsolar panel and charge controller, deep cycle battery, inverter, sample appliances, and measurementinstrumentation. After a brief demonstration of how the system worked, students received a decisionworksheet containing the driving question. Students then considered supporting questions, such as, “Whatfactors will determine the sizing of a solar power system at this location?”, “What information would youneed to gather in order to provide a reasonably good estimate of the cost?”, and “What are some methodsthat you can use to gather the required information?” Through individually considering these questions,then pairing with classmates to compare and discuss responses, and subsequent classroom discussion, thestudents themselves uncovered many of the relevant design parameters that must be considered in order todesign the system in question and more accurately answer the driving question. Thus, while an instructor-provided question was used to initiate discussion the design problem, students independently identifiedpotential design constraints (e.g., number of people using the hypothetical rest stop, intensity of sunlightat the project location, efficiency of the inverter in converting 12 Volt direct current to 120 Voltalternating current, etc.), considered what information would be needed in design, and outlined potentialmethods for obtaining that information.Hands-on learning modules allowed students to characterize system components, learn fundamentalrelationships that govern system behavior, and work in teams to apply these lessons to system componentsizing. In Module 1 students estimated electrical demands by measuring the power required for severalelectrical devices (e.g., hair dryer, pump, computer, fan, etc.). Students calculated demands in terms ofrunning loads, peak start-up loads, and daily energy requirements (i.e., kWh used per day). Working inteams students prepared tabular estimates of electrical demands, and following an in-class discussionwere given an opportunity to revise their estimates to account for demands that might have beenoverlooked or improved understanding of how to perform relevant calculations.In Module 2 students characterized inverter efficiency by running an appliance and comparing the powerdrawn from the battery to the power drawn from the inverter. Applying this understanding of componentefficiency enabled students to link electrical demand estimates to inverter, battery, and solar panel sizing.Module 3 asked students to size the system’s battery and investigate the principles of energy density bytiming how long a deep-cycle battery of known mass could power an appliance. Students determined thebattery requirements for the project site by relating the experimentally-derived energy density relationship(i.e., kWh / kg of battery) and previously calculated electrical demands. Module 4 was an exploration ofsolar panels, where students took readings of how much power was generated by the demonstrationsystem relative to measurements of solar radiation intensity. After experimentally developing an‘efficiency factor’ for the solar panels (i.e., W/m2 of panel per W·hr/m2 of solar radiation), studentsdetermined the required size and number of solar panels by considering solar radiation data near theproject site. Following the four active learning modules, students were asked to prepare a final systemdesign, including interpolated cost estimates.Assessment of student learning was two-fold: (1) scoring of work submitted according to traditionalmeasures of quality (e.g., logical organization, reasonable assumptions, correctness of calculations,neatness of solutions, etc.), and (2) evaluation of reflective journal entries according to a rubric developedto assess and promote critical thinking. Journal entries were categorized as “Reflective” (Student usesmultiple observations to draw a conclusion. Majority of reasoning must be valid. Student makes newconnections among topics within the course.), “Novice” (Student uses at least one observation to draw aconclusion. Reasoning may be vague or contain some faults. The student makes connections frommaterial directly out of class. Repetition of what was said in class.), or “Unreflective” (Journal entrysubmitted, but no evidence of critical thinking.) Journal entry scores were tracked over time, and post-activity surveys were used to evaluate student impressions of learning modules, the journal writingprocess, and perception of whether an effective critical thinking environment was established. Figure 1 – Demonstration system utilized by students in experimentation and characterization of system components.
Wait, I. W. (2012, June), Solar Power System Design to Promote Critical Thinking in Freshman Engineering Students Paper presented at 2012 ASEE Annual Conference & Exposition, San Antonio, Texas. https://peer.asee.org/21924
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