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Standorte für solare Prozesswärme müssen über günstige Einstrahlbedingungen und genügend Fläche zur Kollektoraufstellung verfügen.
© Ritter XL Solar GmbH
Supporting industrial and commercial processes with solar thermal energy
Themeninfo II/2017

Industrial heat demand according to temperature level
© Universität Kassel
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Solar process heat

Around three-quarters of the final energy consumption in the industrial sector in Germany is caused by process and space heating. Solar heat can be used in many different ways in the low-temperature operations in particular, as well as in the commercial, trade and services sectors. International studies confirm the global potential for this technology.

Most users are familiar with solar heating plants above all for space heating or supply of domestic hot water in residential buildings. Rightly so: around 90% of all systems are installed in single- and two-family homes (as of 2015). However, there are other areas in which it can make sense to use solar thermal energy. These include for example the integration of solar thermal energy into local and district heating networks, solar air conditioning and solar process heat for industrial and commercial use. For companies who want to save on energy costs in the long term and improve their own CO2 balance, integrating solar thermal energy into their processes can be an interesting option. The extent to which costs can be saved with a solar heating plant depends on many factors: the scale of the measures, the technology selected and not least the future development of energy prices. One thing is certain, however, and that is that a solar heating plant contributes towards reducing CO2 output.

Since heat cannot be transported over long distances at low loss, only those sites are suitable for using solar process heat which offer both favourable irradiation conditions and sufficient space to set up collectors. During periods of low solar irradiation, conventional systems have to cover the full energy requirement. The integration of solar heating plants is an interesting option for companies that operate only during the day and with processes for which a comparatively low temperature is required. Here, the food industry has suitable areas of use, for example.

Unlike space heating and domestic hot water, solar process heat is used in operations for the production, further processing or finishing of products, or for the provision of a service that requires process heat. The use of renewable energy sources for the provision of heating and cooling is supported by the market incentive programme for the promotion of renewable energy sources on the heating market (MAP) funded by the German Federal Ministry for Economic Affairs and Energy. Here, there are also funding opportunities for process heat generated in solar heating plants.

The system concepts for industry and commerce vary much more widely than domestic applications. Planners must adapt the solar heating plants to the individual requirements of each company. This publication introduces special technical features and typical areas of use, and provides guidelines and funding opportunities for the use of solar process heat.

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The potential for solar thermal energy

In order to reduce CO2 emissions in industry and commerce in the long term, heat requirements must be reduced and the use of renewable energy sources must increase. In order to achieve this, companies must first check whether measures for increasing efficiency or heat recovery make sense. For example, in production halls and workshops, exhaust heat is frequently generated which can be re-used for processes such as heating or drying. In many cases, industrial processes can be supported with renewable energy sources. Here, solar process heat offers a wide range of options for reducing the need for fossil energy sources. Solar process heat can be used particularly efficiently when temperatures below 100 °C are required, no exhaust heat can be used for the purpose, and there is a consistent need for heat, at least during the radiation-rich months of April to September.

The theoretical potential for the use of solar thermal energy can be estimated from the heat requirements of the individual sectors. The leading player here is industry, which uses 73% of final energy for heat. It is followed by the trade, commerce and services sector (TCS) with 55%. However, it is not enough simply to consider the process and space heating needs in order to identify potential uses for solar process heat. A key selection criterion is the temperature level needed. According to calculations made by the University of Kassel, for the maximum temperature range of 300 °C which can be technologically realised, solar process heat can cover around 3.5% of the industrial heat demand. This corresponds to around 16 TWh p.a. With an average system yield of 400 kWh/(m2 p.a.), this is the equivalent of around 40 million m2 of collector area, in other words, around 5,600 football fields. Due to the low level of direct radiation in Germany, here, the focus is on the temperature range below 150 °C, however.

In the TCS sector, there are almost no processes that require the high temperature range. This means that a far larger share of the heat requirement could theoretically be covered by solar thermal heat. With a collector area of around 100 million m2 (as a comparative value: in Germany, a collector area of around 20 million m2 is currently installed), solar thermal energy could, according to the estimates made by the University of Kassel, provide 40 TWh p.a. of heat in this sector. Unlike in the industrial sector, the heat requirement here is affected to a far greater extent by the seasons, since the share of space heating needed is greater. During the summer, the need for space heating decreases.

Processes below 100 °C are particularly well suited for integrating solar heat. This temperature level is needed for many processes in industry, commerce, trade and services. They include heating of feed water or make-up water for boilers, with which industrial processes are heated, as well as washing, cleaning or drying. A significant portion of the low temperature heat demand is caused by air handling units. These are used in many fields in order to create production conditions that are defined by specified air humidity and temperature levels. The temperatures needed for a process can vary strongly, depending on the field of use and the product to be produced, processed or finished.

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Authors

Dr. Bastian Schmitt and M.Sc. Dominik Ritter
University of Kassel, Institute of Thermal Engineering

Dr. Federico Giovannetti
Institute for Solar Energy Research in Hamelin (ISFH)

Links

www.solare-prozesswärme.info
Website with general information on solar process heat (in German)

Fraunhofer ISE
Fraunhofer Institute for Solar Energy Systems

www.aee-intec.at
AEE - Institute for Sustainable Technologies

Institute of Solar Research
from the German Aerospace Center (DLR e.V.)

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