FAQ - Frequently Asked Questions

General Questions

Infographic Solar Thermal Energy

What is Solar Process Heat?

Industry is responsible for around 1/3 of the total energy consumption. The largest part accrues for process heating and is today still almost completely covered by the combustion of fossil fuels. Solar Process Heat is the provision of heat for industrial processes based on solar energy. It is a major pillar for a carbon neutral industrial production. As heat is used directly, the most efficient approach is to use solar thermal collectors.

How does a solar thermal collector work?

A solar thermal collector converts solar energy into heat which can be used in different forms. The collector absorbs the incident sun rays and transfers the accruing heat to a fluid, typically water, increasing its temperature.



What is the difference between photovoltaic modules and solar thermal collectors?

Solar thermal collectors produce heat, whereas photovoltaic modules produce electricity, using incoming solar energy.



What are the different types of solar collectors?

Solar collectors can be classified into concentrating and non-concentrating technologies. Our Fresnel collector is one example of concentrating technology that uses tracking mirrors to focus the sunlight onto a pipe to generate high temperatures up to 400 ºC.

The flat plate collectors and the SunStorm air collector are examples of non-concentrating technologies, suitable for applications that need temperatures below 100 ºC. The various collector concepts differ and all have their specific advantages. Thus, the selection always needs to consider the constraints of a specific application.



How efficient are solar collectors?

The efficiency of solar collectors vary a lot, depending on several factors such as the type of collector used, the system temperature, ambient temperature and system design. Typically, we give an annual average of the efficiency considering these inputs for each specific case.

Contact us to receive a study for your case.



What are the advantages and limitations of solar thermal energy?

Solar thermal energy can be applied almost everywhere, considering that heat is a common need and can be easily stored. Besides that, solar thermal energy has these further advantages:


  + Direct savings in the utility bill;

   + Heat is generated locally using a free resource: the sun;

   + Reduction of greenhouse gas emissions as it replaces fossil fuels;

   + Can be scaled for different sizes and demands;


The main limitation of every solar technology is the availability of the solar resource. For that, we make an assessment based on your location regarding how much solar energy is available per m² of area and how much can be converted into useful heat. Another limitation is the need of a free-of-shade area suitable for the installation of the solar collectors.

Finally, solar thermal energy is typically a fuel saver in addition to another heating source. Depending on your demand, a large area may be needed, which can be evaluated in our first assessment.



 In which industrial processes can solar thermal collectors be integrated?


Solar collectors can be integrated in almost every industrial process. See some examples below:


Food Industry




Pharmaceutical Industry




Paper Industry




Textile Industry






How much does a solar thermal system cost?

The investment costs of a solar thermal system depend on various factors, including the type of technology used, the installation complexity and the size of the system.

Contact us for a personalized assessment for your case.



How much can I save on fuels if I install a solar thermal system in my company?


The savings are directly proportional to the size of your solar thermal system. For example, a solar thermal facility producing 30 % of your annual heat demand will save you 30 % on average of your utility bill.

Specific Questions about the Fresnel Technology

How does the Fresnel collector work?

The Fresnel collector is a linear concentrating solar technology composed of reflective surfaces and an absorber tube assembled in a metallic structure. The primary mirrors positioned close to the ground level track the sun in one axis throughout the day and reflect the incoming solar irradiation onto the absorber tube. The eventual sun rays that miss the tube are reflected back by the secondary reflective surface positioned above it. The metallic absorber tube, which has an evacuated glass encapsulation for reducing the heat losses, absorbs the heat and transfers it to the fluid flowing inside which is then transferred to the industrial production processes.

Check our Fresnel Collector page.

Watch an explanatory video here.



How much power can be produced using the Fresnel solar collectors?

The Fresnel collector produces 601 Watts per m² of primary mirrors under reference conditions*. The power output varies during the day depending on the solar intensity and position.

The system can be designed with power outputs from 500 kW up to 30 MW and produce temperatures up to 400 ºC.

The annual energy output for your specific location can be simulated using our state-of-the-art simulator.

Contact us today.


*reference conditions:

30°C ambient temperature

900 W/m2 direct normal radiation

160°C inflow temperature

180°C outflow temperature

Azimuth angle 90°

Zenith angle 30°



What happens if there is no or no sufficient sunshine?

The solar Fresnel system is designed with a buffer storage that can compensate for short fluctuations of the incident solar irradiation due to passing clouds. Nevertheless, solar thermal systems only work with solar irradiation available. If overcast or on rainy days, the collector will not perform and therefore a typical backup system with biomass or fuels must take place.



 Where can I install the collectors? How much area is needed?

The collector has a lightweight and modular design with very low wind resistance, being suitable for installations on rooftops or on the ground. The area must be free of shade during the day and withstand a load of around 30 kg/m².

The total area needed depends on the system size and collector strings design. A good rule of thumb is that for a system with 1 MW of power capacity, an area of around 3000 m² is needed. 

Contact us for a specific assessment.



 What type of fluids can be heated using the Fresnel collectors?

The collector can work with water, generate steam and heat thermal oil.



 What is the lifetime of the system?

The system is designed for a lifetime of + 25 years.



How complex is the maintenance of the Fresnel system?

The maintenance is very simple with only the cleaning as a short time routine, depending on the dust and pollution of the location. Other inspections and mirror alignment can be done annually. All the components are designed from industrial standards, which makes it easy to find replacement if needed.

We typically offer an initial maintenance contract so the customer has peace of mind while getting used to the system.



What is the payback time of a Fresnel system?

The payback period depends on several factors, the main ones being the available solar resource and the local cost of the fuel currently used. In some cases, it can be less than 5 years, but in others it can be more than 10 years.

Contact us for an assessment for your case.



 How does the safety control of the Fresnel system work?

As the system is designed following strict industrial standards, all the common safety features present on high temperature systems are integrated. The collectors possess safety valves, buttons, sensors and alarms, being also designed to avoid overheating by automatically defocusing mirrors. Using information from the built-in weather station, the system is capable of protecting itself from storms, strong winds and hailing via turning the mirrors into stow position.

Head Office

Industrial Solar GmbH

Basler Str. 115
D-79115  Freiburg   Germany 
Tel. +49 761 767111-0


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