Table of Contents
Introduction
Solar thermal for industrial processes uses heat from the sun to supply the hot water, steam, or high temperature heat that factories and other industrial facilities need. Instead of using fossil fuels like natural gas or oil to raise temperatures, these systems use solar collectors that concentrate or capture sunlight and turn it into usable heat. This approach fits into broader solar thermal technologies, but it is specifically designed to match the continuous, high demand for heat in industry.
Solar heat can be used in many branches of industry, from food and beverage to textiles, chemicals, mining, and manufacturing. Since a large share of global industrial energy consumption is for heat rather than electricity, using solar thermal here is an important opportunity to reduce fuel use and emissions.
Types of Industrial Heat Demand
Industries use heat in different ways and at different temperatures, so not every process is suitable for every solar thermal technology. At the low end, there are processes that need warm water, such as washing, cleaning, or preheating, usually below about $100^\circ \text{C}$. At medium temperatures, often between about $100^\circ \text{C}$ and $250^\circ \text{C}$, industries need hot water or low pressure steam for cooking, pasteurization, textile processing, or drying. At higher temperatures, above about $250^\circ \text{C}$ and reaching up to several hundred degrees Celsius or more, many processes need high pressure steam or direct heat for applications such as chemical reactors, metal treatment, or some kinds of drying and concentration.
Solar thermal systems for industry are often discussed in terms of supplying process heat in the range called solar heat for industrial processes, or SHIP. Most current SHIP projects focus on low and medium temperature heat because these are technically easier and cheaper to achieve with today’s collectors. High temperature industrial heat is more challenging and is sometimes linked to more advanced solar thermal and concentrating systems.
Solar Collector Technologies for Industry
Industrial applications need collectors that can deliver heat at the right temperature and do so reliably during many hours of sunshine each year. For low temperature needs, flat plate collectors and evacuated tube collectors can often be used. These are similar to those used for domestic solar water heating, but in industry they are typically deployed in much larger fields and integrated with existing boilers and heat networks.
For medium temperature ranges, evacuated tube collectors or improved flat plate collectors with better insulation and selective coatings are common. These can reach temperatures in the range required for processes like pasteurization or low pressure steam generation, although efficiency drops as temperatures rise.
For higher temperatures, concentrating solar collectors become important. These include parabolic troughs, linear Fresnel systems, and in some cases small central receiver systems. They use reflective surfaces to focus sunlight onto a receiver tube or point, which raises the temperature of a heat transfer fluid, often to $300^\circ \text{C}$ or more. This hot fluid can then generate steam or deliver direct heat to industrial equipment. These concentrating systems are more complex and need direct sunlight, so they are best suited to regions with high levels of clear sky solar radiation.
Integrating Solar Heat into Industrial Systems
Industrial sites usually already have boilers, heat exchangers, storage tanks, and internal networks that distribute steam or hot water. Solar thermal needs to fit into this existing structure without disrupting sensitive processes. There are several main ways to integrate solar heat.
In direct integration, solar heated fluid is fed straight into the industrial process at the point where heat is needed. This approach is simple but requires careful matching of temperature and flow, because industrial processes often demand stable conditions.
In indirect integration, solar heat is used to preheat feedwater for boilers or to raise the temperature of a separate thermal fluid that then transfers heat to the process through a heat exchanger. This is a common method for retrofitting solar onto existing plants, because it allows the conventional boiler or heater to remain in place and provide backup when solar is insufficient.
Some systems use solar heat to supply low temperature stages of a process, such as preheating, washing, or drying, while higher temperature stages still rely on fossil fuels. This partial substitution can still save a significant share of fuel, especially in processes where the largest share of energy is at lower temperatures.
Role of Thermal Energy Storage
Industrial operations typically run longer hours and require steadier heat than the sun can provide. For this reason, thermal energy storage is often an essential part of solar industrial heat systems. Storage allows collected heat to be used later in the day or even across days, reducing the mismatch between solar availability and process demand.
Simple storage solutions use insulated hot water tanks. For medium temperature systems, pressurized water tanks or specialized thermal oils can store heat at higher temperatures. In some concentrating systems, molten salt or solid materials such as concrete or packed beds of stones can be used as storage media. The principle is that thermal energy $Q$ stored in a material can be approximated by:
$$Q = m \, c_p \, \Delta T$$
where $m$ is the mass of the storage material, $c_p$ is its specific heat capacity, and $\Delta T$ is the change in temperature.
Thermal energy storage design must ensure that the storage capacity $Q$ is large enough to cover periods without sun while maintaining the required process temperature, otherwise industrial operations can be interrupted.
Well designed storage smooths out short term fluctuations in solar input and can allow the solar fraction, the share of heat supplied by solar energy, to become higher without compromising process reliability.
Matching Solar Supply and Industrial Demand
A central design question for solar thermal in industry is how to match variable solar supply with relatively inflexible industrial heat demand. Industries often operate in shifts, sometimes 24 hours per day, while solar input is limited to daylight and varies with weather and seasons. To handle this, designers analyze load profiles, which show how much heat is used over time, and solar resource profiles, which show expected solar radiation.
Once these profiles are understood, the solar system can be sized to supply a chosen share of the average heat demand. The result is often described by the solar fraction. Very high solar fractions require big collector fields and storage systems, which increases cost. Moderate solar fractions can be more economical and still deliver notable fuel savings. In almost all cases, there remains a backup heat source, often the existing boiler, that can make up any shortfall.
Because many industrial processes cannot be easily stopped and restarted, reliability is critical. Any solar integration strategy must guarantee that when solar output drops, the conventional system automatically compensates so that process temperatures and steam pressures remain within specified ranges.
Industrial Sectors and Use Cases
Solar thermal is already being applied in several sectors where the processes are heat intensive and temperatures are in a favorable range. In food and beverage industries, solar heat can supply hot water for cleaning equipment, process water for brewing or dairy processing, and low pressure steam for cooking and pasteurization. These uses typically fall in low to medium temperature ranges and can often be served by non concentrating collectors.
In the textile and leather industries, a lot of energy is needed for washing, dyeing, and drying. Many of these steps operate at temperatures between about $60^\circ \text{C}$ and $180^\circ \text{C}$, which is suitable for evacuated tube or concentrating collectors, depending on the specific requirement.
Mining and mineral processing sometimes require low to medium temperature heat for solution heating and drying, especially in regions with strong solar resources. In some chemical and pharmaceutical applications, process heat in the medium temperature range is also suitable for solar integration.
There is growing interest in applying higher temperature solar thermal to more demanding processes, such as some types of chemical synthesis or metal processing, but these are at an earlier stage of deployment and require more advanced collector and storage systems.
Advantages and Practical Challenges
Using solar thermal for industrial processes offers several advantages. It can significantly reduce the consumption of fossil fuels and therefore cut greenhouse gas emissions and local air pollutants at the plant level. Over the life of a system, solar heat can reduce exposure to volatile fuel prices, because sunlight is free once the system has been installed. For industries located in regions with high solar radiation and rising fuel costs, this can become an important part of their energy strategy.
Solar thermal systems can often be installed on unused land near factories or on large roof areas, which allows existing infrastructure to support new clean energy without major changes to product lines or core processes. In some cases, solar heat can also reduce the load on cooling systems by freeing them from heat rejection tasks that were associated with less efficient boilers.
At the same time, several practical challenges exist. Many industrial sites do not have detailed data on their heat demand at different times of day and across seasons, which makes optimal design harder. Space for collectors and storage might be limited, especially in dense industrial zones. Integrating solar into complex process chains can be technically demanding and may require redesign of some steps. Additionally, industries often expect very short payback periods for investments, while solar thermal systems pay back over longer time frames, even if they are profitable in the long run.
The variability of solar radiation and the need for reliable continuous operation also pose challenges. Engineers must design control systems that coordinate solar fields, storage, and backup boilers so that the transition between solar and conventional heat happens automatically and without affecting product quality.
Future Prospects and Innovation
Research and innovation are expanding what solar thermal can do for industrial processes. New collector designs aim to reach higher temperatures with lower cost and improved durability. For example, advanced linear Fresnel and parabolic trough collectors with better selective coatings and improved tracking systems are being developed to reduce heat losses and increase efficiency.
There is also progress in high temperature receiver materials that can withstand thousands of heating and cooling cycles, which is important for industrial reliability. In parallel, new thermal storage concepts, such as solid particle systems and phase change materials, are being explored to store heat at higher temperatures and higher density.
Digital control systems and better sensors are helping integrate solar thermal more smoothly into industrial automation. With better data, plants can adjust process schedules to align some operations with sunny periods, or at least make better use of stored heat. Hybrid systems that combine solar thermal with other renewables, such as biomass or heat pumps, are being tested to deliver more continuous and flexible low carbon industrial heat.
As policies evolve to support decarbonization in industry, solar thermal for industrial processes is expected to play a larger role, especially where solar resources are strong and heat demand falls into suitable temperature ranges.