The potential of solar heat for industrial processes in Germany

Abstract

Industry represents a very promising application area for solar thermal technology, since it accounts for 27% of the total final energy consumption in Germany and uses 74% of its energy consumption as thermal energy. In order to develop this application area, it is necessary to know which industrial sectors have the highest potential and which processes within these sectors are most suitable for the integration of solar heat. For this paper the industrial heat consumption in Germany was analyzed, which leads to the selection of the most promising sectors within industry. Furthermore, the quantitative potential for Germany in total and for 11 selected sectors, that were identified to be most promising for the use of solar heat, was calculated. These are Chemicals, Food and beverages, Motor vehicles, Paper, Fabricated metal, Machinery and equipment, Rubber and plastic, Electrical equipment, Textiles, Printing and Wood. These sectors are analyzed to identify suitable processes for the integration of solar heat. In total the theoretical potential of solar heat for industrial processes below 300 °C in Germany accounts for 134 TWh per year, the technical potential being 16 TWh per year or 3.4% of the overall industrial heat demand. This is the highest share of the European potential of 72 TWh per year. The results of this study facilitate the prioritized application of solar thermal energy in industrial sectors and processes for Germany and other countries.

Full text

Potential for Solar Process Heat in Germany -
Suitable Industrial Sectors and Processes
Christoph Lauterbach*, Bastian Schmitt, Ulrike Jordan and Klaus Vajen
Kassel University, Institute of Thermal Engineering, 34109 Kassel, Germany
* Corresponding Author, solar@uni-kassel.de
Abstract
The industrial sector represents a very promising application area for the further widespread of
solar thermal technology, since it accounts for 30 % of the total final energy consumption in
Germany and uses 75 % of its useful energy consumption as thermal energy. A review of existing
potential studies in the field of solar process heat in combination with an analysis of the German
industrial energy consumption leads to the selection of promising sectors and processes within
industry. These are thoroughly analyzed regarding their potential for integration of solar thermal
energy. Furthermore, a potential for the application of solar process heat in Germany is calculated.
The results of this study facilitate the application of solar thermal energy in prioritized industrial
sectors and processes.
1. Introduction
The final energy consumption in Germany accounted for 2,450 TWh in 2007 and the industry sector’s
share was 737 TWh, representing 30 %. The high importance of the industrial heat demand is proven
by the fact that it accounts for 75 % of the industrial useful energy consumption, as shown in Figure 1.
In the following chapters, the figures regarding the industrial heat demand are provided in terms of
useful energy.
Fig. 1. Final energy consumption in Germany and
useful energy consumption of the industrial sector in 2007 [1]

Both, the quantified potential for solar process heat in Germany and a qualitative analysis of the most
promising industry sectors and processes is necessary to classify the feasibility for a further
implementation of solar heating systems in industrial companies. Because no comprehensive potential
study exists for Germany so far, the industry was analyzed in consideration of the results of previous
studies. The results of these previous studies and the German energy statistics of the year 2007 were
used to select the most promising industrial sectors and processes for the use of solar process heat.
2. Previous Potential Studies and its Results
Potential studies, which have been performed in the past for different countries or regions, identified
several industrial sectors and processes as suitable for the application of solar heating systems. A
subtask of IEA Task 33/IV summarized the main outcomes of the potential studies performed in
different countries all over the world [2]. The existing studies differ significantly in the approach to
quantify the potential for solar process heat. For example, some use the number of employees for the
calculation, others determined available roof areas. One of the most comprehensive potential studies is
the Austrian study PROMISE [3]. For this study the potential was calculated by a top-down approach
using Austrian energy statistics. Questionnaires were used for the identification of promising sectors
and processes. To gather more information about the energy demand and processes of industrial
companies, 650 questionnaires were spread and 56 were returned. Because many of these
questionnaires suffered by a lack of essential data only 32 questionnaires could finally be used. The
following industry sectors were identified to be most promising for the application of solar thermal:
• Food products and beverages
• Textiles
• Rubber and plastic products
• Articles of concrete, cement and plaster
As mentioned by the authors of the study, only single answers were received for the sectors of paper
and paper products as well as metal processing. These sectors were not identified to be promising for
the application of solar process heat. Due to the lack of information about these sectors, this exclusion
can be doubted. In the following, some of the main differences of other previous potential studies will
be described. Only additional sectors to those identified in PROMISE will be mentioned in this paper.
For the study “POSHIP – The Potential for Solar Heat for Industrial Processes” [4], which investigated
the potential for solar process heat in Spain and Portugal, a bottom-up approach was used. This was
done by a case by case analysis and an extrapolation to the whole sector. The following additional
sectors were identified as promising:
• Tobacco products
• Leather and leather products
• Paper and paper products
• Chemicals and chemical products
• Motor vehicles and trailers
Further potential studies for Australia (state of Victoria only) [5], Italy [2], the Netherlands [6],
Sweden [7], and Cyprus [8] partly supported the identified sectors, but only the sector of machinery
and equipment was identified additionally. Within the project Procesol I and II [9], a potential study
for Greece and Wallonia was conducted and the German industry sectors of food products and

Industry sectors Austria Iberian
Peninsula Italy Netherlands Greece Germany Wallonia
(Belgium) Victoria
(Australia)
Food products and
beverages xxx x xx x x
Tobacco products xx x x
Textiles xxx x xx x x
Leather and leather
products xx x
Paper and paper
products xx x xx x x
Chemicals and
chemical products xx x x x
Rubber and plastic
products x
Articles of concrete,
cement and plaster x
Machinery and
equipment x
Motor vehicles and
trailers xxx x
beverages, paper and paper products and textiles were analyzed regarding their potential for solar
process heat. The key sectors, which were identified by previous potential studies, are summarized in
Table 1. The table indicates that some sectors like food products and beverages where identified as
promising in nearly all executed potential studies, whereas others are only mentioned in a few studies.
Table 1. Results of previous potential studies adapted to German Classification of Economic Activities [10]
A quantitative potential for solar process heat was estimated only in some of the studies described
above. The results are displayed in Figure 2.
Figure 2. Solar process heat potential in selected European countries [2]
The figure shows that the calculated potentials are in a range between 3 and 4.5 % of the industrial
heat demand in the particular region and is in the range of 60 PJ respectively 16.7 TWh for Austria,
Spain, Portugal, Italy and the Netherlands.

Sum Share*
< 100°C 100°C..500°C 500°C..1000°C >1000°C Sum PH
Food products and
beverages 9.4 11.6 0.0 0.0 21.1 7.3 28.3 5.1%
Textiles 2.9 0.0 0.0 0.0 2.9 2.1 5.0 0.9%
Wood and wood
products 1.3 0.3 0.0 0.0 1.6 0.3 1.9 0.3%
Paper and paper
products 3.0 11.1 0.0 0.0 14.1 2.9 17.0 3.1%
Chemicals and
chemical products 15.4 24.0 51.2 12.6 103.2 8.3 111.5 20.2%
Rubber and plastic
products 1.0 3.8 0.0 0.0 4.8 1.9 6.7 1.2%
Fabricated metal
products 2.0 1.6 0.9 2.1 6.5 6.5 13.1 2.4%
Machinery and
equipment 1.7 1.3 0.6 1.7 5.3 5.6 10.9 2.0%
Motor vehicles 3.0 2.3 1.1 3.1 9.5 9.9 19.4 3.5%
Sum: 39.8 55.9 53.8 19.5 168.9 44.8 213.8
Share of industrial
heat demand: 7.2% 10.1% 9.7% 3.5% 30.6% 8.1% 38.7%
Industry sector Process Heat HW &
SH
3. The Potential for Solar Process Heat in Germany
Prior to the calculation of the potential for solar process heat in Germany, a decision is necessary
which industry sectors should be considered. This decision is mainly based on the results of previous
studies. In addition, the total amount and distribution of the heat demand of the mentioned sectors by
temperature level is analyzed to determine their relevance. Of the sectors mentioned in Table 1,
tobacco products and leather and leather products are excluded because of a very low relevance in
Germany. Articles of concrete, cement and plaster is not considered due to the (very high) heat
demand at high temperatures. One can assume that the small amount of low temperature heat used in
this sector can be covered by heat recovery. The only industry sectors considered for this study which
are not already mentioned in the chapter above are wood and wood products and fabricated metal
products. This is due to the fact that these sectors have a reasonable heat demand at low temperatures
and only little at high temperatures. Furthermore, some solar heating systems are already in operation
at electroplating companies, which are part of fabricated metal products. This demonstrates the general
feasibility of this sector for the application of solar process heat plants. Table 2 shows the selected
sectors and a breakdown of their heat demand.
Table 2. Breakdown of heat demand for selected industry sectors [11]
*of the industrial heat demand; all numbers without units in TWh; HW: hot water; SH: space heating
The table indicates that the sectors identified as promising for the application of solar process heat
represent a substantial share of the industrial heat demand. In total, theses sectors consume nearly
40 % of the industrial heat demand in Germany including hot water and space heating. The heat
demand for industrial processes as well as hot water generation and space heating are considered for
this potential study as it is often not even possible to determine them separately in a certain industry. In
many cases one heat distribution network provides the energy for the production process and the hot

water and space heating consumers. The sectors of chemicals and chemical products and food products
and beverages have the highest shares of the low temperature heat demand. For the evaluation of the
heat demand structure regarding the quantified potential for solar process heat, the temperature range
of 100 °C to 500 °C has to be subdivided. Table 3 shows a breakdown of the temperature level up to
500 °C for chemicals and chemical products and food products and beverages and the entity of sectors.
As this table is also based on another source, the numbers differ slightly from the ones in Table 2.
Table 3. Breakdown of the industrial heat demand without hot water/space heating up to 500°C [11/12]
To calculate the potential of solar heat for industry in Germany, the technical potential shall be
determined in a first step by considering the process heat demand up to 250 °C as well as the demand
for hot water and space heating. For food products and beverages and chemicals and chemical products
the distribution of Table 3 was applied to the data of Table 2 to determine their heat demand up to
250 °C. For paper and paper products and wood and wood products the total heat demand for the range
100 °C to 500 °C was considered, since there is no heat demand above 200 °C within these sectors
[13]. For rubber and plastic products, fabricated metal products, machinery and equipment and motor
vehicles a share of about 17 % of the heat demand between 100 °C to 500 °C was considered. This is
based on the figures for all industry sectors of Table 3. With these shares of the heat demand between
100 °C to 500 °C and the heat demand below 100 °C as well as the demand for hot water and space
heating, a technical potential for solar heat for industry can be calculated to about 115 TWh/a. Further,
the numbers in Table 3 indicate, that the most important temperature range for the application of solar
process heat in Germany is below 150 °C. The share of the industrial heat demand in the temperature
range of 150 °C to 250 °C is not negligible, but much smaller. Of course, the calculated technical
potential cannot be covered with solar energy completely, but is further restricted. First of all, the
process heat demand as well as the hot water and space heating demand can be reduced by energy
efficiency measures like heat recovery. Furthermore, a fraction of the required heat has to be supplied
by electricity for different reasons, and in many cases sufficient space is not available for the
installation of solar heating systems.
Following [3], a share of 60 % of the technical potential for low and medium temperature processes
cannot be used due to the restrictions mentioned above. Furthermore, an average solar fraction of 40 %
is proposed. Applying these numbers to the technical potential of 115 TWh, the potential for solar heat
in industry in Germany is about 18 TWh or 3.3 % of the total industrial heat demand. Although
additional industry sectors were considered for the calculation of the potential, it is below the average
of the results of previous studies which estimated potentials in a range of 3 to 4.5 %. This is based on
the fact, that German industry has more high temperature processes than industry in countries like
Austria and Spain due to a higher share of heavy industries like steel production. Nevertheless, the
absolute number of 18 TWh represents in absolute figures by far the highest potential for solar process
heat in European countries.
<100°C 100-150°C 150-200°C 200-250°C 250-300°C 300-500°C Other
All sectors 12.7% 11.3% 4.1% 1.2% 0.8% 8.1% 61.9%
Food products and
bevera
g
es 42.9% 40.7% 16.4% 0.0% 0.0% 0.0% 0.0%
Chemicals and
chemical
p
roducts 22.5% 9.2% 7.0% 6.1% 3.0% 8.0% 44.3%

4. Promising Sectors for Solar Applications in Germany
In addition to the analysis of the heat demand of different sectors, the investigation of industrial
processes in general can identify suitable points for integration of solar thermal energy. [2] and [3]
identified industrial processes including cleaning, drying, evaporation and distillation, blanching,
pasteurization, sterilization, cooking, melting, painting, and surface treatment as suitable areas of
application. However, these processes are often not comparable for different industrial sectors, as some
boundary conditions can vary in a wide range. For example, temperature and required time of washing
processes depend very strongly on the treated product. Although these promising processes occur in
nearly all industrial sectors, significant differences exist regarding the integration of solar heating
systems. Although the mentioned processes are promising for solar heating application, a closer
investigation of the promising industry sectors is necessary. The first results of this investigation are
presented in the following.
4.1 Food Products and Beverages
The sector of food products and beverages was identified as promising in all previous potential studies.
As mentioned in the last chapter, this sector has a large heat demand in the temperature range up to
150 °C. Common processes are pasteurization of liquid goods at 65 to 100 °C, cooking at 100 °C in
meat processing, blanching of vegetables or meat at 65 to 95 °C, drying and evaporation at 40 to
130 °C in fruit and vegetable processing or cleaning of products and production facilities at 60 to
90 °C. Taking into account its big share of the industrial heat demand at low temperatures, the results
of the previous studies and the variety of suitable processes, the food industry has a great potential for
the use of solar thermal energy.
4.2 Textiles
As already shown, the heat demand of the textiles sector is limited to temperatures below 100 °C.
Within the textile industry washing at 40 to 90 °C, drying and a large number of finishing processes
like dyeing and bleaching at 70 to 100 °C or desizing at 80 to 90 °C are the main consumers of process
heat. As a first guess, up to 25 to 50% [3] of heat needed in the textiles sector could be covered by
solar thermal energy. This represents a large potential, although the share of the low temperature heat
demand of the overall energy consumption of the German industry is quite low.
4.3 Paper and Paper Products
Within the pulp and paper industry, about two-thirds of the heat demand is needed at temperatures
higher than 100 °C, which is unfavourable for solar heating systems containing standard components,
but could in principle be provided with more advanced collector technologies. On the other hand, one-
third is still consumed at advantageous temperatures below 100 °C for process heat, hot water and
space heating. The preheating of boiler feed water represents a promising application for solar thermal
energy in this industry sector, as steam is needed for drying of paper products. Furthermore, the share
of energy cost is about 11 % of total manufacturing costs [14], which indicates the high importance of
energy efficiency and the utilization of renewable energy in this sector.

4.4 Chemicals and Chemical Products
The chemical industry is one of the most important sectors of the German economy. The processes
within the sector are very demanding regarding energy and resources. Energy costs are about 4 to 5 %
of the total manufacturing costs. The German chemical industry accounts for 20 % of the final energy
demand of German industry [15]. The heat demand plays a major role within this energy demand, and
although a large amount is needed at high temperatures, there is still a considerable heat demand at low
and medium temperatures as shown in Table 2 and 3. Potential processes for solar heat are especially
bio-chemical processes with temperature levels about 37 °C as well as preheating and polymerisation
processes [16].
4.5 Rubber and Plastic Products
According to [17], the German plastics processing industry has had an energy demand of 15.2 TWh in
2000. In [18] it is stated that about 40 % of the energy consumed is used for process heat applications.
Table 2 shows that at least a reasonable share of this heat demand is needed at low and medium
temperatures. Still many processes in the plastics industry require temperatures over 150 °C. Besides
the supply of hot water and space heating, drying of plastic pellets is a potential process for solar
thermal energy. The pellets are air-dried at temperatures from 50 to 150 °C to ensure quality during
moulding.
4.6 Fabricated Metal Products
According to [19], the share of energy is only 0.3 to 1.6 % of the total manufacturing costs within the
sector of fabricated metal products. Here, the heat demand plays a major role for the overall energy
demand. [18] states a share of 45 % for the heat demand with respect to the total energy demand. Table
2 shows that a reasonable share is required at low and medium temperatures and the demand for hot
water and space heating is quite high. The required heat is needed at low temperatures, especially for
coating processes. For example, surfaces are etched in about 70 °C warm solutions and air-drying is an
often used process that requires hot air with about 120 °C.
5. Conclusion
The heat demand plays a major role for the industrial energy demand as it accounts for 75 % of its
useful energy consumption. This heat is needed in several industry sectors at low and medium
temperatures, which is the major requirement for the utilisation of solar thermal energy. Some industry
sectors like food products and beverages and textiles offer various options for the integration of solar
process heat, whereas in others the utilization will be limited to a few processes. The major constraints
for the application of solar heating systems in industry are the huge potential of energy efficiency
measures, operational reasons and an absence of suitable roof area. Furthermore, guidelines for
planning, installation and operation of large solar heating systems in industrial companies are not
available today. If at least some of these constraints can be eliminated, a share of about 3.3 %
respectively 18 TWh of the German industries heat demand could be covered by solar thermal energy.

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The authors gratefully acknowledge the financial support provided by the Reiner-Lemoine-Stiftung and the
German Federal Ministry forthe Environment, Nature Conservation and Nuclear Safety, contract No. 0329601T.
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research project.