Keywords

1 Introduction

Since 1995 Design for Sustainability (DfS) is part of the curriculum of our bachelor and master studies at Industrial Design Engineering of the Delft University of Technology. Within the educational program the faculty hosts a minor on Sustainable Design Engineering since 2008. An academic minor is a university student’s secondary field of study or specialization during their undergraduate studies. The minor has been highly useful as a platform to pilot new ways of teaching engineering for sustainable development.

Instead of having students make Life Cycle Assessments (LCA) and introduce them to straightforward checklists to improve their product designs, we wanted to challenge our students to develop a critical understanding of sustainability and use multidimensional assessments to back up their findings. Sustainability is not just about environmental benefit but also about useful products and added value. This paper describes our educational approach in one of the courses within the minor of Sustainable Design Engineering, the photovoltaics practicum. Our objective in this paper is to illustrate how such a multidimensional assessment works in practice and how it has helped students develop a more critical, systemic perspective on sustainability.

In Sect. 2 the pedagogical structure of the practicum is given illustrated by examples of student work. In Sect. 3 a review of the students’ evaluations is presented and the paper ends with a discussion, conclusions and recommendations.

2 PhotoVoltaics Practicum

The solar energy industry is currently one the fastest growing industries in the world. With declining prices and increasing efficiencies, solar cells may become promising energy harvesters in consumer products. In this practicum our students are asked to disassemble and study a product powered by solar cells. The objective is to learn (hands-on) how these products are constructed, and to assess the practical, technical and environmental feasibility.

2.1 Approach

Students work in teams of 4–5 people. At the end of the ten week course the teams have to deliver a report and poster presentation. Together these two deliverables constitute the final grade.

During the Photovoltaics (PV) practicum we ask the teams to assess a product with integrated PV cells e.g. a solar powered lamp, see Fig. 1. The assessment is based on three sustainability factors:

Fig. 1
figure 1

Examples of solar products used in the practicum: the Solio solar powered charger (Solio 2015), the IKEA Sunnan solar lamp (IKEA 2014) and the ETON Rugged rukus Bluetooth speaker (Eton 2014)

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  1. 1.

    Usability, does the PV technology offer any added value and how does this reflect on the product’s usability?

  2. 2.

    Technological feasibility, does the product function as it should under the intended circumstances?

  3. 3.

    Environmental impact, is there a positive energy return on energy invested?

The overall learning goal is to make the students aware that when a PV product fails on one of these three factors it cannot be regarded a sustainable product. E.g. if the PV cell in its use context is too small to comply with the power consumption of the products’ main function, the product will be discredited and become a gadget. When a product is difficult in use, or is multi-interpretable it will probably end up in a drawer or in the garbage. When the environmental impact of the product is higher than the environmental gain during its life, the product will not contribute to a sustainable future.

2.2 Usability Assessment

In the first two weeks of the course students have to actively use and test the product in their own environment, the so-called “field trial”. The students take turns in testing the product and have to record their findings in a diary or log, in which they describe memorable interaction moments and take pictures. Figure 2 shows such part of a diary of one of the student teams.

Fig. 2
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Diary of one of the teams, who were assigned a PV-powered phone charger

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The students should write down their expectations of the product beforehand. During the field trial they should make note of the pattern and frequency of use (which have to be clocked), the ease of use and general functioning of the product, and their frustrations and feelings of satisfaction while using the product. Finally, they have to compare their preliminary expectations with their experience after use. An important realisation from the field trial is the context-dependency of PV products. In a predominantly cloudy Netherlands (the practicum takes place in early autumn) the students quickly learn that there’s often not enough solar power available to make the PV products function as they should. Some excerpts from students diaries:

…sunlight from 10:00 am to 07:30 pm. Even after 7,5 h of charging the lamp did not work

And:

Day 1, 09.30 am. “Oh shit, I have to put that solar thing outside, or it won’t charge.”

Day 1, 11.03 pm. “It doesn’t work yet. Better luck tomorrow.”

There were also positive experiences:

17 September 07.30 “the sun came up. The solar panel on the lamp could charge the batteries.”

17 September 20:00 “I turned the lamp on. Bright light.”

17 September 02:00 “I turned the lamp off. I was still able to read.”

2.3 Technological Assessment

In weeks 3–5 of the practicum, the task is to determine the use context and energy balance of the PV-powered product. The students have to draw up a realistic use-scenario based on their field trial and other data at hand, e.g. from the product packaging, manual or the internet. Next, they have to calculate the Energy Balance (EBR) to find out if the harvested energy matches with the used energy over a realistic time-period. The EBR is calculated by taking the ratio of the yielded energy per day/week (E in ) over the energy demand of the product per day/week (E out ). This ratio shows if the harvested energy matches with the energy use of the product, giving the students a sense of direction on the technological feasibility of the product, see Table 1.

Table 1 The technological feasibility of the product-PV combination by calculating the EBR
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Students are given lectures on calculating the EBR, but also about irradiance basics, where the difference between potential harvestable light-power in indoor situations versus outdoor are explained, which varies between 0.1 and 1000 W/m2 for respectively indoor situations and bright outdoor sunlight. They have to do their own tests and measure the PV-cell in question in out- and inside situations, and also in laboratory test-cabinets (Fig. 3).

Fig. 3
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PV test outside, and the laboratory test using closed PV-test cabinets

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To assess if the potential harvestable power and the power production of the PV cells matches a realistic use scenario, the students are given the task to disassemble the product, measure the solar cell characteristics and determine the power and energy consumption of the product’s function. Furthermore the students have to identify all components and draw up an electronic schematic (Brain 2012) which shows the interlinked connection between the power consumer (the product’s main function), the intermediate accumulator (battery) and the power producer (PV cells), Fig. 4.

Fig. 4
figure 4

Measuring the power production of the PV cells and the power consumption, and an overview of components of the Eton Rugged Rukus speaker

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When the students are finished with the lab sessions they have to test the technological feasibility by means of Energy Balance Matching (Kan 2006; Kan & Strijk, 2006), questioning if the harvestable energy over a certain period matches with the power consumption of the product in the same time period.

2.4 Environmental Assessment

Weeks 5–7 are used to do the environmental assessment, where students are asked to generate a Fast-track Life Cycle Assessment (LCA) of the product (Vogtlander 2012; Goedkoop et al. 2013; ISO 2006) and calculate the Energy PayBack Time (EPBT) of the product (U.S. DoE 2004; Peng et al. 2013; Sullivan and Gaines 2012).

During the disassembly workshop the product is torn down to single-material parts and, mostly electronic, components. All materials and components are documented in a Bill of Materials and Processes (BoMP), which includes the material type, weight, probable production process and origin of production; i.e. the Life Cycle Inventory (LCI). After inventorizing the students have to evaluate the potential environment impact of the product system over the total life cycle of the product. Students are asked to use the Cumulative Embodied Energy Demand indicator in MegaJoules and the Global Warming Potential in kgCO2-equivalent as their main environmental impact indicator. The first indicator can also be used to calculate the EPBT. The second indicator is the mainstream indicator for companies to show their products’ environmental burden. With the LCA students should determine the main contributors on the environmental impact of the product and make a comparison with a similar product which is powered by the grid or a low-voltage charger only, and that does not make use of PV cells.

The Energy PayBack Time (EPBT) is defined as “the amount of years it will take before a PV-system produces as much energy as could be produced by the current grid-mix, using the same amount of primary energy”, based on (Fthenakis and Kim 2011; Raugei 2013):

$$EPBT = \frac{{E_{PP} }}{{E_{OUT} }}$$

where E PP is the primary energy input of the total PV system (module + components) during its whole life cycle [MJp] and E OUT is the net annual primary energy savings (from the grid) due to electricity generation of the PV systems [MJp/yr].

2.5 Reporting

After the three assessments the student teams have to interpret all the acquired knowledge and bring this back to a scientific poster and report. Based on the findings from the field trial, lab work and the analyses they have to suggest options to improve the products’ PV system, clearly argumented with facts and figures.

3 Review 2011–2014

In the past three runs of the minor (2011–2014) 150 students have followed the same approach. This has given us a large database of multidimensional assessments on different PV powered products, and allows us to draw conclusions on the validity of our approach.

The objective was to give the student the ability to make a critical assessment on an initially perceived sustainable product by giving them tools to assess not only the environmental impact of the product but also on technology matching and usability. To give an impression on the results of the different teams over the years, an overview of quotes and calculations are given in Table 2 for four products from cohort 2011 to 2014 after performing the multidimensional sustainability assessment.

Table 2 Multidimensional-assessment results of some of the products evaluated in 2011–2014
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4 Discussion and Conclusions

Because this course was limited in time spent (2 ECTS, equalling 56 h per team member) there was, unfortunately, no time for very detailed analysis and proper redesign. Students had to use already acquired skills to assess the products properly. Amongst others the environmental impact is assessed by using an LCA, which was taught in one of the parallel courses of the minor.

The student teams consisted of different disciplines ranging from industrial design, mechanical and aerospace engineers to students with an art background. The structured approach in this course contributed to good teamwork and high-value results, which was well appreciated by most of the students attending the course.

Our findings show that many of the currently available products with integrated PV systems (lamps, chargers, household appliances, etc.) are initially perceived as “green” and sustainable. After the multidimensional assessment students however invariably reach a more nuanced perspective, with some products failing to pass the test and others, to some surprise, passing the test. From reflections in the final reports and our evaluation sessions with the students, the students indicated how the multidimensional assessment has made them a “better” engineer, more equipped to see through the “greenwash”, and give a balanced assessment of the real value of solar cells integrated in products. The course was successful in reaching our goal to teach our students critical thinking and design by assessing a product from multiple dimensions instead of only one.