# Solar heat collectors: Techniques

Rooftop tubes, factory mirrors and town-sized heat pits

Source page: https://www.materialinsights.org/energy/e_solar_heat/techniques/

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 collectors**^[2](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2015/IRENA_ETSAP_Tech_Brief_E21_Solar_Heat_Industrial_2015.pdf)^[3](https://iea-shc.org/Data/Sites/1/media/events/webinars/2025-06-24/m.spork-dur--solar-market-trends-in-a-nutshell.pdf)^[4](https://52.iea-shc.org/Data/Sites/1/publications/Press-Article-SHWW-Edition-2025.pdf)^[5](https://www.aee-intec.at/wp-content/uploads/2025/04/dateien1794.pdf)^[6](https://task9.iea-shc.org/Data/Sites/1/documents/statistics/Technical_Note-New_Solar_Thermal_Statistics_Conversion.pdf) | 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 ponds**^[2](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2015/IRENA_ETSAP_Tech_Brief_E21_Solar_Heat_Industrial_2015.pdf)^[5](https://www.aee-intec.at/wp-content/uploads/2025/04/dateien1794.pdf) | 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 concentrators**^[2](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2015/IRENA_ETSAP_Tech_Brief_E21_Solar_Heat_Industrial_2015.pdf)^[3](https://iea-shc.org/Data/Sites/1/media/events/webinars/2025-06-24/m.spork-dur--solar-market-trends-in-a-nutshell.pdf)^[4](https://52.iea-shc.org/Data/Sites/1/publications/Press-Article-SHWW-Edition-2025.pdf) | 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 heating**^[3](https://iea-shc.org/Data/Sites/1/media/events/webinars/2025-06-24/m.spork-dur--solar-market-trends-in-a-nutshell.pdf)^[4](https://52.iea-shc.org/Data/Sites/1/publications/Press-Article-SHWW-Edition-2025.pdf) | 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 pans**^[7](https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-salt.pdf) | 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 collectors**

A selectively coated absorber sits under glass in an insulated box or inside a vacuum tube. Water or antifreeze carries heat to a storage tank.^[2](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2015/IRENA_ETSAP_Tech_Brief_E21_Solar_Heat_Industrial_2015.pdf)^[3](https://iea-shc.org/Data/Sites/1/media/events/webinars/2025-06-24/m.spork-dur--solar-market-trends-in-a-nutshell.pdf)^[4](https://52.iea-shc.org/Data/Sites/1/publications/Press-Article-SHWW-Edition-2025.pdf)^[5](https://www.aee-intec.at/wp-content/uploads/2025/04/dateien1794.pdf)^[6](https://task9.iea-shc.org/Data/Sites/1/documents/statistics/Technical_Note-New_Solar_Thermal_Statistics_Conversion.pdf)
**Solar air heaters, cookers, dryers, stills and ponds**

Air 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.^[2](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2015/IRENA_ETSAP_Tech_Brief_E21_Solar_Heat_Industrial_2015.pdf)^[5](https://www.aee-intec.at/wp-content/uploads/2025/04/dateien1794.pdf)
**Industrial process heat from concentrators**

Troughs, Fresnel mirrors or tubes with reflectors heat water, steam or oil up to about 400 C for factory boilers.^[2](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2015/IRENA_ETSAP_Tech_Brief_E21_Solar_Heat_Industrial_2015.pdf)^[3](https://iea-shc.org/Data/Sites/1/media/events/webinars/2025-06-24/m.spork-dur--solar-market-trends-in-a-nutshell.pdf)^[4](https://52.iea-shc.org/Data/Sites/1/publications/Press-Article-SHWW-Edition-2025.pdf)
**Solar district heating**

Collector fields heat water piped to towns; pits or tanks store summer heat for winter.^[3](https://iea-shc.org/Data/Sites/1/media/events/webinars/2025-06-24/m.spork-dur--solar-market-trends-in-a-nutshell.pdf)^[4](https://52.iea-shc.org/Data/Sites/1/publications/Press-Article-SHWW-Edition-2025.pdf)
**Solar salt pans**

Brine evaporates in shallow ponds until salt crystallises.^[7](https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-salt.pdf)

#### Sources

1. [Solar Heat for Industrial Processes: Technology Brief E21](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2015/IRENA_ETSAP_Tech_Brief_E21_Solar_Heat_Industrial_2015.pdf) IRENA and IEA-ETSAP, 2015
2. [Solar market trends in a nutshell (Solar Heat Worldwide 2025 webinar, M. Spork-Dur, 24 June 2025)](https://iea-shc.org/Data/Sites/1/media/events/webinars/2025-06-24/m.spork-dur--solar-market-trends-in-a-nutshell.pdf) IEA Solar Heating and Cooling Programme / AEE INTEC, 2025
3. [Press article: Solar Heat Worldwide, Edition 2025](https://52.iea-shc.org/Data/Sites/1/publications/Press-Article-SHWW-Edition-2025.pdf) IEA Solar Heating and Cooling Programme, 2025
4. [Solar Heat Worldwide 2023 edition: Global Market Development and Trends 2022, Detailed Market Figures 2021 (Weiss and Spork-Dur)](https://www.aee-intec.at/wp-content/uploads/2025/04/dateien1794.pdf) IEA Solar Heating and Cooling Programme / AEE INTEC, 2023
5. [Technical Note: New Solar Thermal Statistics Conversion (reference collector parameters, 0.7 kWth per m2)](https://task9.iea-shc.org/Data/Sites/1/documents/statistics/Technical_Note-New_Solar_Thermal_Statistics_Conversion.pdf) IEA Solar Heating and Cooling Programme, 2004
6. [Mineral Commodity Summaries 2026: Salt](https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-salt.pdf) US Geological Survey, 2026

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_solar_heat/index.md)
- [Overview](https://www.materialinsights.org/energy/e_solar_heat/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_solar_heat/correlation/index.md)
- [Efficiency](https://www.materialinsights.org/energy/e_solar_heat/efficiency/index.md)
- [Resources and labour](https://www.materialinsights.org/energy/e_solar_heat/resources/index.md)
- [Impact on the biosphere](https://www.materialinsights.org/energy/e_solar_heat/biosphere/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_solar_heat/links/index.md)