Energy, Sustainability and Technological Projects: Sources, Efficiency, Impact and Methodology
The energy and project block rewards clean unit handling and a structured answer. Expect a consumption, cost or CO₂ calculation, a comparison of energy sources, and questions on the phases, tools and documents of a technological project.
Energy concepts and units
- Energy is measured in joules; power in watts. 1 kWh = 3.6×10⁶ J; 1 tep ≈ 41.87 GJ.
- Primary energy is the resource as extracted; final energy is what reaches the user; the difference is conversion and transport losses.
- Efficiency η = useful output / input, always below 1 for real devices.
- Renewable sources (solar, wind, hydro, biomass, geothermal, tidal) are replenished naturally; fossil and nuclear fuels are finite, though nuclear generation itself is low-carbon.
Environmental impact
- The CO₂ emission factor converts electricity into emissions, typically around 0.15–0.30 kg CO₂ per kWh on the Spanish grid, and falling as renewables grow.
- Impacts to mention by source: combustion emissions and particulates, nuclear waste, land use and visual impact of wind farms, habitat flooding by reservoirs, and the manufacturing footprint of photovoltaic panels.
- Life-cycle assessment covers extraction, manufacture, use and end-of-life; circular economy aims to keep materials in use through reuse, repair and recycling.
Projects
- Phases: identify the need, feasibility study, specifications, design, planning, construction or prototyping, testing, and documentation.
- Tools: Gantt charts schedule tasks in time; PERT networks show dependencies and the critical path, and the critical path fixes the minimum project duration.
- Documents: technical report, budget, drawings, specifications and operating manual. Standards and patents protect and normalise the result.
Worked example
A 100 W lamp runs 5 h per day for 30 days. Energy = 0.1 kW × 5 h × 30 = 15 kWh. At 0.15 €/kWh the cost is 2.25 €. With an emission factor of 0.25 kg CO₂/kWh the emissions are 3.75 kg CO₂. Replacing it with a 12 W LED over the same hours uses 1.8 kWh, saving 13.2 kWh, 1.98 € and 3.3 kg CO₂ over the month.
Traps that cost marks
- Quoting kW where kWh is required, or omitting the time factor.
- Converting kWh to joules with 10³ instead of 3.6×10⁶.
- Confusing a Gantt chart (time schedule) with a PERT network (dependencies and critical path).
- Stating 'renewables have no impact', which ignores manufacturing and land use.