Energy, sustainability and environmental impact
Energy questions test whether you can quantify energy and power and follow them through a product's life; sustainability questions test whether you can compare options on evidence rather than slogan.
Energy and power
Energy is converted, never created. Stores: kinetic, gravitational potential (mgh), elastic, chemical, thermal, nuclear. Power = energy ÷ time (W); 1 kWh = 3.6 MJ. Efficiency = useful output ÷ total input × 100%, and a Sankey diagram draws flows with widths proportional to energy. Renewables (solar, wind, hydro, biomass, geothermal, tidal) are replenished; fossil fuels and nuclear fuel are finite. Intermittent renewables need storage or backup to meet base load.
Life cycle thinking
LCA stages: extraction → manufacture → distribution → use → end of life, each with energy, water and emissions. Embodied energy is what the product carries when it leaves the factory; for kettles, fridges and cars the use phase usually dominates. Carbon footprint is expressed in kg CO₂ equivalent. Waste hierarchy: prevent > reuse > repair > recycle > recover energy > dispose. Circular economy: design out waste, keep materials in use, regenerate systems - achieved through design for disassembly, modularity, mono-material parts and reversible fasteners. Legislation: WEEE (e-waste take-back), RoHS (hazardous substances), EU energy labelling, Ecodesign requirements. Obsolescence can be functional, aesthetic or technological.
Worked example (illustrative figures)
Compare a reusable stainless bottle with single-use PET. Bottle: 15 MJ embodied energy, washed hundreds of times. PET bottle: 0.03 kg at 80 MJ/kg ≈ 2.4 MJ per bottle. A wash using 1 L of hot water plus detergent costs roughly 0.15 MJ. Saving per reuse ≈ 2.4 − 0.15 = 2.25 MJ, so break-even ≈ 15 ÷ 2.25 ≈ 7 uses, after which the reusable bottle wins. State your assumptions and units, and note that transport and the electricity mix could shift the result.
Traps
- Writing kW for energy and kWh for power.
- Assuming recycling always beats reuse; energy recovery sits below recycling in the hierarchy.
- Ignoring the use phase and transport in a comparison.
- Treating "biodegradable" as a synonym for recyclable.
- Repeating manufacturer claims such as "carbon neutral" as verified fact.
Design in society, ethics and product evaluation
Product evaluation and design-in-society questions test whether you can judge a product against evidence, law and stakeholders, and whether you can name the ethical problems a design creates.
Designing for people
User-centred design: observation, interviews, personas, task analysis, then usability trials. Inclusive and universal design means adjustability, one-handed operation, tactile and high-contrast cues, and never coding information by colour alone. Anthropometrics: design to the 5th percentile for reach, the 95th for clearance, and make the product adjustable where the user range is wide. Ergonomics: neutral wrist, lumbar support, grip diameter roughly 30–50 mm.
Law, standards, IP
CE marking is the manufacturer's declaration that the product meets the applicable EU legislation (Machinery, Toy Safety, EMC, Low Voltage, and so on); it is not a quality award and is not issued by a testing body. Harmonised standards (EN, ISO) are voluntary unless cited. In the EU, consumer goods carry a two-year legal guarantee, and producers face liability for defective products. Intellectual property: patents protect inventions (up to 20 years), registered designs protect appearance (up to 25 years in the EU), trademarks protect brand identity (10 years, renewable), and copyright arises automatically for artistic and literary work, including software.
Ethics and evaluation
Ethical issues to name: planned obsolescence, poor labour conditions and conflict minerals, e-waste exported to countries without safe recycling, data collection and privacy, dark patterns, exclusion of disabled users, and safety traded against price. Push (technology seeking a market) versus pull (market demand). Evaluation is not an opinion: test each specification criterion, record pass/fail with data, weight the criteria, and recommend changes. Formative evaluation happens during development; summative evaluation happens at the end.
Worked example
A €15 Bluetooth speaker is assessed against three criteria weighted function 0.5, durability 0.3, cost 0.2. Battery life measured 6.5 h against an 8 h requirement - partial, score 3/5; drop test passed by 4 of 5 units at 1 m, 4/5; unit cost €13.20 against a €12 target, 2/5. Weighted score = 0.5(3) + 0.3(4) + 0.2(2) = 1.5 + 1.2 + 0.4 = 3.1 out of 5. Recommendation: battery life and cost both fail the musts, so redesign the cell or renegotiate the price target before launch. The score explains why, not merely how much.
Traps
- Calling CE a quality mark or claiming it is issued by the EU.
- Confusing patents (function) with trademarks (brand) and registered designs (appearance).
- Presenting opinion as evaluation with no measurements.
- Ignoring stakeholders such as repairers, recyclers and disabled users.
- Mixing formative and summative evaluation.