AC 2012-3377: SOLAR POWER SYSTEM DESIGN TO PROMOTE CRIT-ICAL THINKING IN FRESHMAN ENGINEERING STUDENTS

Dr. Isaac W. Wait, Marshall University

Isaac W. Wait is an Associate Professor of engineering in the College of Information Technology andEngineering at Marshall University in Huntington, W.V. Wait conducts research and teaches courses inwater resources and environmental engineering, and is a registered Professional Engineer in the states ofOhio and West Virginia.

c©American Society for Engineering Education, 2012

Solar Power System Design to Promote Critical Thinking in Freshman Engineering Students

Abstract

Approximately 70 first-year students enrolled in an introduction to engineering course designed a solar power electric system for a hypothetical highway rest stop. The educational approach 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 to install a solar power system at the renovated rest-stop?”), staged ‘guiding questions’ to help students independently discover relevant design constraints, the use of active learning modules to teach fundamental principles relevant to the design, and journal entries where students were asked to reflect on lessons learned and demonstrate critical thinking and where instructors assessed student responses using a critical thinking rubric.

The purpose of this paper is to describe a recently developed and implemented application of the EFFECTs methodology, explaining key aspects of the pedagogical rationale with specific learning activities and student outcomes. The materials that were provided to students are provided in this paper, along with descriptions and discussion of observed benefits and challenges associated with implementing an EFFECTs-oriented design project in a first year introductory engineering course, so that engineering educators can evaluate the suitability of implementing EFFECTs in their own courses.

Introduction

Big class sizes, students with misunderstandings about the nature of engineering, sometimes uncertain course objectives and outcomes, and students who have not yet developed rigorous study habits or the ability to apply deep reasoning are among the many challenges faced by instructors who teach introductory courses in engineering to freshman students1. Yet, in spite of these challenges, engineering educators who work with freshman students must find ways to engage students’ enthusiasm and develop the engineering mindset and habits of attention to detail that are required for subsequent success. One of the key tools that has been used to achieve these important goals is to implement design activities in first-year engineering courses.

The purpose of this paper is to explain a first-year design activity that has been developed, and outline the pedagogical benefits that can arise in an environment that promotes critical thinking by employing a sequence of staged questioning, student reflection, and instruction of fundamental concepts in the context of practical hands-on activities.

The benefits of exposing freshman engineering students to design are important and varied. Improvements in the understanding of fundamental concepts2, specific skills and body of knowledge3 and increased attainment of the program outcomes associated with accreditation4 are

associated with freshman design project implementation. In the eyes of new students who are entering a new field of study with high hopes and broad aspirations, the chance to immediately receive the hands-on learning opportunities associated with design projects as been reported to lead to increased levels of enthusiasm for engineering2, stimulation of curiosity and creativity and an enhanced motivation for applying correct principles of technical writing5, and an appreciation of the opportunities to meet new people, work in teams, and use real engineering tools that are inherent in a design project environment6. These individual benefits combine to yield an advantage that is important to both students and institutions alike: elevated levels of student retention in engineering7.

In spite of the accepted potential benefits of incorporating design projects into freshman-level engineering courses, there are concerns and challenges that often limit instructors: the perception that course schedules are already too full and that there isn’t time for additional topics, difficulties in accommodating large number of students with limited equipment resources, and attachment to the mindset that an instructor’s role is solely to “lecture” rather than to create an environment where learning occurs. Likewise, students can develop concerns with active learning exercises and design projects, including complaints about projects that are overly simplistic relative to the complex fundamental topics that are being taught5, the perception that design simply should not be taught to students as new to engineering as freshman are1, and the complexity of managing personalities and workloads that can arise in a group work environment.

One method for overcoming these limitations and concerns, and helping to promote the capture of benefits associated with design at the freshman level, is the methodology known as “Environments for Fostering Effective Critical Thinking” or EFFECTs8. This approach seeks to facilitate critical thinking in students by asking students to use estimation to answer a specific “driving question” related to principles of engineering (e.g., “How many tons of soil do you need to build a 100-ft long section of levee?”), and then through several supporting questions nudge students to themselves identify which unknowns must be specified, what forces or phenomenon might be used to estimate behavior, and which information sources could be used to assemble the tools that would allow for a more informed and accurate answer to the driving question. Following the introduction of the driving question and supporting questions in the “Decision Worksheet”, students are asked to respond to questions in a “Journal Entry” with the dual purpose of reinforcing the student’s critical thinking from the earlier exercise and giving the opportunity to evaluate the strength of the student response relative to an established critical thinking rubric. Past implementations of the EFFECTs methodology have been studied for the inter- and intra-rater reliability of assessment of critical thinking on student journal entries, and have found a high level of reliability9.

Following the Decision Worksheet and first Journal Entry, “Active Learning Modules” are sequenced to introduce skill items, fundamental principles, and key concepts that students can use to further improve their response to the Driving Question that was introduced in the Decision Worksheet (see Figure 1). In the case of the driving question, “How many tons of soil do you need to build a 100-ft long section of levee?”, active learning modules could include demonstrations or experiments that teach students principles of material density, soil composition, and compaction. The series of Active Learning Modules, coupled with Journal

Entries and instructor evaluation and feedback on the critical thinking demonstrated in answering questions that prompt student journal entries, culminates in a final student design or report that utilizes all of the experimental resources, body of knowledge items, and engineering judgment that has been cultivated during the EFFECTs process.

Figure 1 – EFFECTs framework.

The outcome of the application of the EFFECTs methodology, as illustrated in Figure 2, is that students have received core knowledge in the context of a hands-on learning activity that is authentic, which leads to the development of fundamental technical skills that can be applied to solve design problems and analytical questions9. During this process students develop “Engineering Judgment” – the capacity to apply critical thinking to assess the rationality, practicality, reasonableness, and correctness of possible solutions to problems. In this way, the EFFECTs methodology provides a route for instructors to move beyond the mindset that engineering programs need only provide core knowledge and technical skills, and that students can be left to themselves synthesize that capacity to think critically.

Figure 2 – Relationship between the design and analysis process, critical thinking, and engineering judgment.

Solar Power EFFECT Approach

Based on the experiences of the author, some characteristics that can promote a topic’s utilization in the EFFECTs methodology include: (a) a basic familiarity of the topic by students, (b) topics and concepts for which hands-on learning activities can be developed, (c) the existence of fundamental principles, equations, or laws that can be taught to students such that they can apply this information to refine their estimate of the answer to the driving question, and (d) a topic that is somehow interesting, immediate, or relevant to students such that it will capture their attention and enthusiasm. In this regard, Solar Power was selected for the development of the materials, resources, and activities that support the EFFECTs methodology. The handouts supplied to students, including the driving and supporting questions, journal entry questions, and active learning modules are provided in the Appendix.

During the first day of this sequence of activities, students were initially shown the components of a solar power electric system, including a photovoltaic solar panel and charge controller, deep cycle battery, inverter, sample appliances, and measurement instrumentation. After a brief demonstration of how the system worked, students received the decision worksheet containing the driving question:

“How much will it cost to install a solar power system at the renovated rest-stop?”.

Students then considered supporting questions, such as,

“What factors will determine the sizing of a solar power system at this location?”,

“What information would you need to gather in order to provide a reasonably good estimate of the cost?”, and

“What are some methods that 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, the students themselves uncovered many of the relevant design parameters that must be considered in order to design 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 identified potential design constraints (e.g., number of people using the hypothetical rest stop, intensity of sunlight at the project location, efficiency of the inverter in converting 12 Volt direct current to 120 Volt alternating current, etc.), considered what information would be needed in design, and outlined potential methods for obtaining that information.

The hands-on learning modules that were developed allowed students to characterize system components, learn fundamental relationships that govern system behavior, and work in teams to apply these lessons to system component sizing.

In Module 1 (Demand Estimation) students estimated electrical demands by measuring the power required for several electrical devices (e.g., hair dryer, pump, computer, fan, etc.). Students calculated demands in terms of running loads, peak start-up loads, and daily energy requirements (i.e., kWh used per day). Working in teams students prepared tabular estimates of electrical demands, and following an in-class discussion were given an opportunity to revise their estimates to account for demands that might have been overlooked or improved understanding of how to perform relevant calculations.

In Module 2 (Inverter Efficiency Characterization) students characterized inverter efficiency by running an appliance and comparing the power drawn from the battery (the inverter itself, Whistler Pro-2500W, provides a measure of the watts being consumed) to the power drawn from the inverter, measured by connecting a power-measuring device (Kill A Watt, model P4460) to the 115 Volt side of the inverter. Applying this understanding of component efficiency enabled students to link electrical demand estimates to inverter, battery, and solar panel sizing.

Module 3 (Battery Weight, Capacity, and Modeling)asked students to size the system’s battery and investigate the principles of energy density by timing how long a deep-cycle battery (two of Universal Battery model UB12220 wired in parallel) of known mass could power a hair dryer that was consuming a known amount of power. By comparing the actual run-time of the battery-powered hair dryer to a regression-derived estimate of projected run time – based on battery mass and capacity data that students found online – students were exposed to the principles of numerical and physical modeling. Students determined the battery requirements for the project site by relating the experimentally-derived energy density relationship (i.e., kWh / kg of battery) and previously calculated electrical demands from Module 1.

Module 4 (Solar Panel Characterization)was an exploration of solar panels (Epcom 50 Watt solar panel), where students took readings of how much power was generated by the demonstration system 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), students determined the required size and number of solar panels by considering solar radiation

data near the project site. Following the four active learning modules, students were asked to prepare a final system design, including interpolated cost estimates.

Assessment of the student learning during the modules was two-fold: (1) scoring of work submitted according to traditional measures 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 developed to assess and promote critical thinking. Journal entries were assessed using a rubric modified from the original EFFECTS Critical Thinking Rubric9; student responses were classified as summarized in Table 1.

Table 1 – Journal entry evaluation rubric.

Classification Points Characteristics

Reflective 5 Student uses multiple observations to draw a conclusion. Majority of reasoning must be valid. Student makes new connections among topics within the course.

Novice 3

Student uses at least one observation to draw a conclusion. Reasoning may be vague or contain some faults. The student makes connections from material directly out of class. Repetition of what was said in class.

Unreflective 2 Journal entry submitted, 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 writing process, and perception of whether an effective critical thinking environment was established. Over the course of the EFFECT’s administration, the average journal entry critical thinking assessment score increased from 3.7 (standard deviation = 0.7) to 4.1 (standard deviation = 1.3), indicating an improvement in student’s ability to demonstrate evidence of critical thinking in response to an open-ended question.

Conclusions

The EFFECTs methodology was utilized to develop and administer a hands-on, active learning solar power design project for freshman engineering students. Students initially estimated the anticipated cost of providing a solar power system for a hypothetical highway rest stop without any supporting information and resources, such that they were forced to consider what information sources were missing and what phenomenon needed to be better understood (e.g., the relationship between the size and number of deep-cycle batteries and the amount of power that can be supplied during a 24 hour cycle). Following this initial exercise, supporting learning activities related to Demand Estimation, Inverter and Efficiency Characterization, Battery

Capacity and Numerical Modeling, and Solar Panel Characterization were conducted prior to students performing a final design based on the application of all of the activities and principles.

Since principles of solar power were not taught in this course prior to the semester that the EFFECTs methodology as also implemented, it is not possible to directly assess the relative impact that this solar power EFFECT had upon student learning of the underlying fundamental principles. However, it is the perception of the author that there were direct improvements in student engagement and interest that arose out of the active learning exercises, and the EFFECTs framework of a sequence of guided questioning, student reflection, and instruction of fundamental concepts in the context of practical hands-on activities. Since students approached the driving question from their own personal perspective, it seemed that there was a sense of ‘buy-in’ among many students while completing the project. Likewise, calculations and estimations that might have seemed abstract in the absence of a hands-on learning activity were instead easily understood, and the ‘reasonableness’ of student calculations could be judged relative to their prior physical observations of in-class models.

The following observations were made during the development and administration of this new EFFECT:

Equipment limitations. Only having one of some equipment items made it difficult for each student to have adequate hands-on time. Providing this equipment in an open lab environment and making some aspect of the activity and out-of-class assignment, whereby each student can have as much hands-on time as they wish, is a potential solution to this issue that will be utilized in the future.

Assessment of Journal Entries. For a course with 70 students, it was a challenge for the instructor to assess student responses to journal entries and provide meaningful feedback to students. In view of this, it may be preferable to either limit application of EFFECTs in smaller courses or train and utilize graduate students to review and assess student journal entries for critical thinking.

Time between modules. Since several class periods were between each of the active learning modules, some students misplaced handouts or otherwise seemed to lose track of the key ideas associated with this project. In view of this, it might be preferable, when possible, to stage active learning exercises in successive class meetings. Alternately, it could be helpful to require students to assemble a project portfolio containing all of the project-related materials and content.

Acknowledgements

The author acknowledges the National Science Foundation for financial support (Division of Undergraduate Education, Award Number 1022661).

References

[1] Orwin, E.J. and Bennett, R. J. “Trials and Tribulations of a Freshman Design Course.” Proceedings of the 2002 ASEE Annual Conference and Exposition, Montreal, Quebec, Canada, June 16-19, 2002.

[2] Comolli, N., Kelly, W, and Wu, Q. “The Artificial Kidney: Investigating Current Dialysis Methods as a Freshman Design Project.” Proceedings of the 2010 ASEE Annual Conference and Exposition, Louisville, KY, June 20-23, 2010.

[3] Dong, J. and Warter-Perez, N. “Collaborative Project-Based Learning to Enhance Freshman Design Experience in Digital Engineering.” Proceedings of the 2009 ASEE Annual Conference and Exposition, Austin, TX, June 14-17, 2009.

[4] Shaw, D. and Tanyel, M. “Lessons Learned from a Multi-Faceted Freshman Design Project: Software Development, Electronics, Mechanical Construction, Software-Hardware Interface and Economics.” Proceedings of the 2008 ASEE Annual Conference and Exposition, Pittsburgh, PA, June 22-25, 2008.

[5] Soysal, O. A. “Freshman Design Experience: Solar Power Irrigation System for a Remote Farm.” Proceedings of the 2000 ASEE Annual Conference and Exposition, St. Louis, MO, June 18-21, 2000.

[6] Veltman, T., Rosehart, W., Eggermont, M., and Onen, D. “Evaluation and Analysis of Freshman Design Courses in Engineering.” Proceedings of the 2011 ASEE Annual Conference and Exposition, Vancouver, British Columbia, Canada, June 26 – 29, 2011.

[7] Milano, G. B., Parker, R., and Pincus, G. “A Freshman Design Experience: Retention and Motivation.” Proceedings of the 1996 ASEE Annual Conference, Washington, DC, June 23-26, 1996.

[8] Caicedo, J. M., Flora, J., Pierce, C., Nichols, A., Graf, W., and Timmerman, B. "Environments For Fostering Effective Critical Thinking (EFFECTs)."Proceedings of the 2008 ASEE Annual Conference and Exposition, Pittsburgh, PA, June 22-25, 2008.

[9] Caicedo, J. M., Flora, J., Pierce, C., Nichols, A., Graf, W. and Timmerman, B., Ray, T. "Assessment of environments for fostering effective critical thinking (EFFECTS) on a first-year civil engineering course", Proceedings of the 2009 ASEE Annual Conference and Exposition, Austin, TX June 14-17, 2009.

Appendix – Handouts provided to students (Fall 2011 semester. Updated materials may be developed over time. To receive copies of the latest versions of these materials, please contact the author.)

Name: ______________________      Partner Name: _________________________ 

    Solar Power EFFECT – Day 1   (Decision Worksheet and Driving Question) 

A highway rest‐stop between Battle Mountain, NV and Winnemucca, NV is being upgraded to include 

restroom facilities and vending machines.  Because of its remote location, electricity is not available 

from ‘the grid’, and solar power is being explored as an alternative.  

 

Driving Question: 

•  How much will it cost to install a solar power system at the renovated rest‐stop? 

It will cost $______________ to install a solar power system at the renovated rest stop. 

 Supporting Questions 

What factors will determine the sizing of a solar power system at this location?                

  

What information would you need to gather in order to provide a reasonably good estimate of the cost?  

           

What are some methods that you can use to gather the required information?    

              

Identify some things that your partner thought of that you initially did not, and briefly explain why they are important.  

 

 

 

Name: ___________________     Partner Name: _______________ 

      Solar Power EFFECT – Day 2   (Demand Estimation) 

A highway rest‐stop between Battle Mountain, NV and Winnemucca, NV is being upgraded to include 

restroom facilities and vending machines.  Because of its remote location, electricity is not available 

from ‘the grid’, and solar power is being explored as an alternative.  How much will it cost to install a 

solar power system at the renovated rest‐stop? 

Today you will develop an estimate of the electric demands of the system. 

You have received the following additional information from the project planners: 

On average, it is anticipated that 1500 people per day will utilize the rest stop. 

There will be three candy and three soda vending machines. 

Water will be provided using a 1.5 hp pump. 

The building footprint is anticipated to be approximately 30 ft x 60 ft.  

Information not specifically provided should be reasonably estimated. 

 

Activity Questions 

1. Fill in the table below.  

Device  Volts  Amps  Watts 

Fan       

Computer       

Hair Dryer           

Air Pump       

  What is the relationship between Volts, Amps, and Watts?  

2. What fraction of the hair dryer's power requirements are for the fan vs. for the heating elements?     3. If the computer idled 24 hours per day for 1 year, how many kWh would be consumed?     4. How long could the hair dryer run on 'high' if 100 Amp‐hours of 12‐Volt power was available? (Note: 

assume 100% efficiency in converting DC to AC.)     5. Make a list of devices in the rest stop that will consume power, and  how long you anticipate they 

will run during the day.  

Item  Starting Watts 

Running Watts 

Running Hours per Day 

       

       

       

       

       

       

       

       

       

       

       

       

       

       

 

We estimate the peak electrical requirements for the rest stop to be ____________ Watts. 

We estimate that the rest stop will consume ____________ kWh per day.

Name: ___________________          

Solar Power EFFECT Day 3 –InverterEfficiency Characterization  

   

Fan Setting  Heat Setting 

Kill‐A‐Watt Measurement (watts) 

Inverter Measurement (watts) 

Efficiency 

Low  Cool       

Low  Low       

Low  Medium       

Low  High       

High  Cool       

High  Low       

High  Medium       

High  High       

 Average Efficiency:  

___________ %  Activity 3 Questions:  

1. At high‐fan, high‐heat, how many volts, amps, and watts was the hair dryer drawing from the inverter? 

         

2. At high‐fan, high‐heat, how many volts, amps, and watts was the inverter drawing from the battery?  

      

3. If you were going to run the hair‐dryer on high‐fan, high‐heat for 30 minutes: o How many kWh is required?  o How many Amp‐Hours will the hair‐dryer consume?  o How many Amp‐Hours will the inverter consume?  

               The ampere is a measure of the amount of electric charge passing a point in an electric circuit per unit time with 6.241 × 1018 electrons, or one coulomb per second constituting one ampere.  The volt is defined as the value of the potential difference (voltage) across a conductor when a current of one ampere dissipates one watt of power in the conductor.  One watt is the rate at which work is done when one ampere (A) of current flows through an electrical potential difference of one volt (V).  (1 W = 1 J/s = 1 N∙m/s)   Journal Entry Question:  In class this week we characterized the efficiency of the inverter.  Explain how knowing the inverter efficiency will affect your design of other system components, such as (1) the batteries, and (2) the solar panels.   

Name: _____________________________           

Solar Power EFFECT Day4 –Battery Weight, Capacity, and Modeling  

  

Run Time Experiment             

Weight of battery (lb): ___________  Load Applied1 (W): __________  Actual run time (min): ____________  Power used (kWh): _______________  1Note: Be sure to account for inverter efficiency 

  Part A) Go online, and find six different deep‐cycle batteries where the weight and capacity specifications are quoted. Try to get a wide range of data points. Fill the table provided below.    

Battery Model  Website  Weight (lb)  Capacity (Amp‐Hr)  Capacity (kWh)2 

         

         

         

         

         

         

2 Note: kWh = (Amp‐hr) x (battery voltage) / (1000 W/kW)  Part B) In Microsoft Excel, perform a linear regression to determine an equation that relates battery capacity (kWh) and weight (lb). 

Previously determined demand (kWh required) for 

the highway rest stop: _______________ 

Previously determined inverter efficiency (%): 

_______________ 

Create a plot of the data (Select the data, then go to Insert, Scatter…) 

Right‐click on one of the data points, and choose “Add Trendline” 

Check “Display Equation” and “Display R‐squared”   Part C) Based on the weight of the battery tested in‐class: 

What should the capacity (kWh) be according to the equation developed in Part B? 

What is the “Percent Error” between the actual capacity and predicted capacity?  

100%

Actual

EstimatedActualError  

    

 

 

 

 

 

 

Part D) Based on your previously determined demand for the highway rest stop, what is the weight of 

batteries that will be required? 

Name: ________________________________           

Solar Power EFFECT Day 5 –Solar Panel Characterization  

  

Panel Characteristics 

Length (cm) _______________  Width (cm) __________  Quoted Capacity (W): ____________      Measured Capacity (W): ________________   Identify the factors that will influence how much solar panel area is required to supply the electrical 

demands that you have previously estimated. 

 

 

 

 

 

 

 

 

 

 

Based on the demonstration and measurements performed today, what data sources could you use to 

calculate the solar panel surface area that would be required? 

 

 

 

 

 

 

 

 

 

 

 

What panel area would be required to collect 176.6 kWh per day?  Make assumptions and estimate 

parameters as needed, and identify them clearly as you perform this calculation. 

Name: ________________________________          

Solar Power EFFECT– Final Design of Electrical System 

Due Friday, November 11th 

Fill in the blanks and submit calculations that address the following sections: 

1. Demand Estimation 

Based on the devices that you believe will be used in the rest stop, revise your Demand Estimation 

calculations in order to take into account the principles that have been illustrated in the active learning 

exercises, and the corrections that you previously identified as necessary. Attach calculations and a 

summary of your demand estimation, and fill in the blanks below. 

Estimated peak electrical requirements for the rest stop: _____________ Watts 

Estimated power demand for the rest stop: _____________ kWh per day               

2. Inverter 

Based on the peak electrical requirements identified above, go to the following website and select an 

inverter to be used at the rest stop.http://www.solarelectricsupply.com/inverters.htmlFill in the blanks 

below, attach a printout of the specifications of the inverter that you have selected, and attach a 

printout of your numerical model of cost (explained below). 

Inverter selected –   Size / Capacity: ___________________ 

Manufacturer: _______________________  Model #: ______________________ 

Efficiency: _________________     

Estimate the cost of this inverter by creating a linear‐regression model in Excel with the following 

inverter price data: 

Watts  Cost ($)  Manufacturer

5000  4100  SMA 

2000  1680  Magnum 

8000  4676  Radian 

2000  1277  Exceltech 

3000  1188  Samlex 

300  241  Morningstar 

 

  Estimated Cost of Inverter: ___________________________ 

   

3. Batteries 

Based on the power demand identified in Part 1, the efficiency of the inverter, the batteries available on 

this website (http://www.solar‐electric.com/batteries.html) and any other factors that you deem 

important (e.g., extra power storage for cloudy days), fill in the following: 

  Total battery capacity required (Amp‐Hr  @ 12 Volts): ________________________ 

  Battery manufacturer & model selected: _______________________________________ 

  Number of Batteries Required: ____________________________ 

  Total Cost of Batteries: _________________________________ 

Note: attach your calculations for this section. 

4. Solar Panels 

Based on the estimated power demand for the rest stop (i.e., kWh required per day), the assumption of 

15% efficiency for solar panels, and the solar irradiance data provided below, determine the total 

surface area of solar panels required for the highway rest stop. 

Time Irradiance (W/m2) 

7:00  0.0 

8:00  14.6 

9:00  86.1 

10:00  137.1 

11:00  182.7 

12:00  201.1 

13:00  255.9 

14:00  293.7 

15:00  302.7 

16:00  203.7 

17:00  0.0 

 

  Total surface area of solar panels required (m2): ____________________ 

  Assuming $375 per m2, total cost of solar panels: ___________________ 

Note: attach your calculations for this section. 

 

Summary: How much will it cost to install a solar power system at this rest stop? __________________