Solar Heat for Industrial Processes
The use of solar heat for industrial processes (SHIP) is an extremely promising segment, though still representing a small part of the sales in the solar heat sector in Europe and worldwide.
When considering industrial needs for heat, usually the first image that comes to mind is that of metallurgy. While some industrial processes require very high temperatures, most of the energy needed for industrial processes requires low or medium-temperature heat. Industrial processes can use low temperature for washing or dyeing textiles. The dairy sector uses heat for washing and pasteurization. Other industries, such as mining, can use it for leaching. Therefore, the use of low temperature heat in industrial processes can be widely diverse. The biggest potential is seen in the food and beverage industry but also in the metal and mining sector.
Solar thermal systems are well suited for generating low temperature heat up to 150°C. This can already be supplied by commercially available solar thermal collectors. Most solar applications for industrial processes are on a relatively small scale and still largely of an experimental nature. There is potentially a wide range of solar thermal applications. There are already well known applications of solar thermal heat in breweries, mining, agriculture (crop drying) or textile sector. In 2015 about 150 large-scale SHIP systems are documented worldwide ranging from 0.35 MWth to 100 MWth.
A system providing solar heat for industrial processes includes a large or very large solar collector field, through which a working fluid circulates. This fluid can be water, a combination of water and glycol or other. By means of a heat exchanger, the heat is transferred from the primary circuit to the process heat circuit in the form of hot water, air flow or steam, depending on the requirements of the industrial process. The system may incorporate a heat storage unit. This unit can be used to increase the period of the day when heat is supplied to compensate for variations of the solar resource, but also to even out the fluctuating heat demand at batch processes. In such systems, an adequate function and yield control is essential for the regulation of the solar system and to identify potential breakdowns of the systems or loss of performance. A system is considered very large when it is over 350 kWth (500 m²), although such systems can have a wide range of sizes.
The benefits of solar thermal systems, in particular for such large systems, cover environmental, political and economic aspects.
Environmental benefits stem from the capacity to reduce harmful emissions. The reduction of CO2 emissions depends on the quantity of fossil fuels replaced directly or indirectly, i.e. when the system replaces the use of carbon-based electricity used for water heating. Depending on the location, a 1.4 MWth (2000 m²) system could generate the equivalent of 1.1 MWhth /year, a saving of around 175 Mt of CO2 (1).
Political and economic benefits are associated with the potential savings in energy costs and the possibility of improving energy security by reducing energy imports, while creating local jobs related to the manufacturing, commercialization, installation and maintenance of solar thermal systems.
Regarding energy costs, and potential savings, there are three main aspects to consider that have a bigger impact on the comparable costs of the energy produced by a solar thermal system. These are the initial cost of the system, the lifetime of the system and the system performance. These factors depend on the location (affecting climate, insulation, taxes, cost of living, etc.) and quality of the system (affecting performance, lifetime and cost). This can vary significantly from country to country. Therefore, average investment costs for solar thermal systems can vary greatly from country to country and between different systems. According to the IEA, for large systems in Europe, the investment costs can go from 315 to 936 EUR/kWth. In terms of energy costs, it can range from 20 to 70 USD/ MWhth (18 to 63 EUR/MWhth) in Southern United States and between 36 and 135 EUR/MWhth in Europe.