Forms of Energy
Energy exists in many forms: kinetic (motion), potential (stored position), thermal (heat), chemical (stored in bonds), electrical, nuclear, radiant (light), and sound. Engineers design systems to convert energy from one form to another for useful work.
Conservation of Energy
Energy cannot be created or destroyed — it can only change form (First Law of Thermodynamics). However, every real energy conversion loses some energy as waste heat (Second Law). A perfectly efficient engine is impossible.
Efficiency
Efficiency = (Useful output energy / Total input energy) × 100%. A coal power plant is roughly 35% efficient — 65% of coal's chemical energy becomes waste heat. Modern combined-cycle gas plants reach ~60%. Solar PV panels are ~20% efficient at converting sunlight to electricity.
Renewable vs. Non-Renewable
Non-renewable sources (coal, oil, natural gas, nuclear) have finite supplies or produce long-lived waste. Renewable sources (solar, wind, hydro, geothermal, biomass) are continuously replenished. Renewables now produce over 30% of global electricity and the share is growing rapidly.
Energy in Systems
Engineers trace energy through systems using Sankey diagrams — diagrams where the width of flow arrows represents energy quantity. This reveals where the biggest efficiency losses occur and where engineering improvements would have the greatest impact.