By Etienne Letournel (Newheat)
Large solar thermal fields (up to several tens of thousands of m2) of flat plate collectors (FPC) can produce heat under 100°C at high efficiency. This level of temperature is sufficient to address miscellaneous applications in the district heating networks and industry sectors, to lower their CO2 emissions related to energy production. This article provides examples of possible applications.
Developed especially in Denmark since the 70’s, solar thermal production for district heating is becoming the standard for existent network extension or new networks in Europe.
The solar heat can replace the gas part of energy during the summer and part of the midseason. With daily heat storage in above ground tanks, the coverage is around 20% of the annual heat consumption of the network. But with pit heat storage (inter seasonal storage), it could be increased up to 70 or 80%. This fact highlights the key role of energy storage for an intermittent energy such as solar heat.
Several industries need low temperature for their processes, and the following paragraphs give examples for some of them.
The drying process for malt production requires big quantities of heat, all around the year. A well-designed solar thermal plant can preheat drying air flow and cover between 40 to 50% of the total annual heat needs of the malthouse. In some cases, the solar plant can be coupled with heat pumps or pit heat storages, to increase the renewable part above 80%.
To dry bricks before cooking them in furnaces, industrial plants use big volumes of hot air, usually produced by gas burners. Solar heat can be used to preheat the air flow up to 60°C, before the gas burners (see the diagram below). The part of solar heat can represent 50 to 60% of the addressable needs.
Production of European whey powder is increasing each year, because of the needs of food industry. Usually, in the production site, heat is produced thanks to gas boilers. The need for drying air is important all year long and represents big part of the total heat consumption of the site. Like for bricks factories, it is possible to preheat drying air thanks to solar heat, up to 60 or 65°C, before finalizing the heating with gas, thus decreasing CO2 emissions of the site.
In the mining, metallic and non-metallic exploitation industry, thermal energy plays a key role in low-temperature separation and refining processes such as leaching, drying, electrowinning, as well as in high-temperature processes like pyrometallurgy and foundries. Particularly in low temperature processes, it is already demonstrated that solar thermal technologies can supply 100% of the energy needs to the process at very competitive prices. On top of that, in Remine Water project, new ways of solar heat use are explored through the recycling of water within the site of MATSA.
