Generators and alternators: Engineering methods
Synchronous giants, wind machines and humble dynamos
What this tab covers The engineering methods that can do this conversion, compared on efficiency, scale, economics, limitations and reliability.All generators use electromagnetic induction; they differ in how the field is made (electromagnet or permanent magnet), whether output is AC or DC, and how they are cooled.
Comparison
| Method | Efficiency | Scale | Economics | Limitations | Reliability |
|---|---|---|---|---|---|
| Synchronous turbo-generators and alternators127 | up to 98.9-99% | tens of kVA (gensets) to 2,250 MVA | Bundled with the turbine; priced inside the turbine-generator package | Must run at fixed speed; largest units need hydrogen and water cooling. | Designs in service for over 50 years; stainless steel water boxes reduce clogging of hollow copper bars. |
| Wind and variable-speed generators315 | high, but depends on converter losses (not quantified in cited sources) | 0.25-10 MW per machine | Rare-earth magnets add material cost and supply risk: JRC puts wind turbine needs at about 51-180 kg of neodymium, 4-35 kg praseodymium, 6-17 kg dysprosium and 1-7 kg terbium per MW, depending on design. | Need converters; depend on rare-earth magnet supply. | Siemens Energy reports more than 40,000 wind generators in service. |
| Dynamos | lower than alternators because of brush and commutator losses | small (bicycle lamps, educational and legacy DC uses) | Niche | Brush wear and sparking. | Brushes need regular replacement. |
| Electromagnetic induction (the principle) | not a device; sets no thermodynamic limit | from microwatt energy harvesters to gigawatt generators | Not applicable | Losses only from resistance, magnetic hysteresis and eddy currents. | Not applicable |
Synchronous turbo-generators dominate grid supply: coal and gas alone made about 55% of world electricity in 2025 (calculated from IEA shares of 34% and 21%), all through such machines, plus nuclear and hydro. They reach 99% efficiency and last decades, with cooling as the main design constraint. Variable-speed wind generators trade a little efficiency in converters for the ability to capture energy at any wind speed. Dynamos survive only in niches. Solar PV and batteries are the main sources of grid power that do not use a rotating generator.
How each method works
Synchronous turbo-generators and alternatorsA DC-excited rotor spins at a speed locked to grid frequency inside a three-phase stator. Used in every coal, gas, nuclear and most hydro plants, and in gensets.
Wind and variable-speed generatorsPermanent-magnet or induction generators run at varying speed; power electronics convert their output to grid frequency.
DynamosA rotating armature with a commutator (segmented switch) produces DC. Historically the first practical generators; now largely replaced by alternators plus rectifiers.
Electromagnetic induction (the principle)Any changing magnetic flux through a coil induces a voltage; the same law runs transformers, induction cooktops and wireless chargers.
Sources
- GIGATOP generators Arabelle Solutions, 2025
- Air-cooled generators (GEN-A) GE Vernova, 2025
- Generators for power generation (product overview and references) Siemens Energy, 2025
- Global Energy Review 2026: Electricity supply IEA, 2026
- The role of rare earth elements in wind energy and electric mobility (Alves Dias, Bobba, Carrara, Plazzotta), EUR 30488 EN European Commission Joint Research Centre, 2020