Solar heat collectors: Techniques
Rooftop tubes, factory mirrors and town-sized heat pits
What this tab covers The methods used to capture this energy: how each works, and how they compare on efficiency, cost, life-cycle emissions, maturity and scale.Most solar heat comes from rooftop water heaters, mainly evacuated tubes in China; concentrators and collector fields are starting to serve factories and towns.
Comparison
| Method | Efficiency | Cost | Life-cycle emissions | Maturity | Scale |
|---|---|---|---|---|---|
| Flat-plate and evacuated-tube collectors23456 | About 67-72% at rating conditions; fleet capacity factor about 9% (calculated) | Systems EUR 180-500 per m2 (EUR 450-1,100 per kWth, 2015) | No harmonised life-cycle figure | mature | 544 GWth delivering 443 TWh (2024); 17.8 GWth added in 2024; evacuated tubes about 69% of capacity (2021, calculated) |
| Solar air heaters, cookers, dryers, stills and ponds25 | No consistent figures in the sources used | Active air heating EUR 300-450 per m2 | No harmonised figure | mature (most); pilot (solar ponds) | Air collectors about 1 GWth worldwide (2021); no global data for the others |
| Industrial process heat from concentrators234 | 50-56% rated (calculated); capacity factors 4-29% | Troughs USD 600-2,000 per kWth; heat 6-9 euro cents per kWh (2015) | No harmonised figure | early commercial | 1,315 systems (2024), 106 added (120 MWth) |
| Solar district heating34 | Bracht, Germany: 75-80% solar share of heat from 11,637 m2 of collectors and a 26,600 m3 pit store | No figure in the sources used | No figure | early commercial | 346 towns and cities; 10 new systems (74 MW) in 2024 |
| Solar salt pans7 | No figure in the sources used | No figure | Very low: no fuel for evaporation | mature | Solar salt is 9% of US salt sold or used (2025); world salt output about 270 Mt |
Rooftop water heaters are the cheapest solar heat, as little as EUR 20-50 per MWh where simple and sunny, but heat cannot travel far, so systems must match local demand. About half of industrial heat is needed below 400 C, with a technical solar potential put at about 15 EJ by 2030, yet only about 1,300 industrial systems exist.
How each method works
Flat-plate and evacuated-tube collectorsA selectively coated absorber sits under glass in an insulated box or inside a vacuum tube. Water or antifreeze carries heat to a storage tank.23456
Solar air heaters, cookers, dryers, stills and pondsAir heaters warm air for rooms or crop drying; cookers focus sunlight on a pot; stills evaporate salty water that condenses clean; ponds trap heat in a salty bottom layer.25
Industrial process heat from concentratorsTroughs, Fresnel mirrors or tubes with reflectors heat water, steam or oil up to about 400 C for factory boilers.234
Solar district heatingCollector fields heat water piped to towns; pits or tanks store summer heat for winter.34
Solar salt pansBrine evaporates in shallow ponds until salt crystallises.7
Sources
- Solar Heat for Industrial Processes: Technology Brief E21 IRENA and IEA-ETSAP, 2015
- Solar market trends in a nutshell (Solar Heat Worldwide 2025 webinar, M. Spork-Dur, 24 June 2025) IEA Solar Heating and Cooling Programme / AEE INTEC, 2025
- Press article: Solar Heat Worldwide, Edition 2025 IEA Solar Heating and Cooling Programme, 2025
- Solar Heat Worldwide 2023 edition: Global Market Development and Trends 2022, Detailed Market Figures 2021 (Weiss and Spork-Dur) IEA Solar Heating and Cooling Programme / AEE INTEC, 2023
- Technical Note: New Solar Thermal Statistics Conversion (reference collector parameters, 0.7 kWth per m2) IEA Solar Heating and Cooling Programme, 2004
- Mineral Commodity Summaries 2026: Salt US Geological Survey, 2026