ASTEP – Application of Solar Thermal Energy to Processes

Solar Heat for Industrial Processes (SHIP) is becoming increasingly relevant as one of the ways to meet the high thermal energy demand required for industry. This involves a double benefit: firstly, by using a renewable energy source, fossil fuel consumption is reduced and therefore the emission of pollution and greenhouse gases into the atmosphere; secondly, heat for industrial processes becomes a new market niche for solar technology, which can lead to a decrease in the cost of solar collectors through economies of scale in manufacturing and learning-curve advances in deployment.

The comparably higher capital expenditure, lack of compact thermal storage and absence of suitable incentives have resulted in a considerable gap between the utilization potential and presently installed capacity of Solar Heat Industrial Process (SHIP) systems. The ASTEP project tackles these barriers by improving the feasibility of solar thermal systems thanks to two features. The proposed system, namely SunDial is based on the Linear Fresnel Reflector (LFR) technology, which is considered as the most promising one for reducing the CAPEX. However, the system has a rotary structure instead of a linear one. Therefore, the first feature is the modularity of the SunDial, which can make the system more easily installed in the industry, as well as contribute to cost reduction. The second feature is the possibility of introducing a two-axis tracking system without a large increase in the cost, which allows a performance improvement that should lead to higher operating temperatures or increase the feasibility in regions with high latitude, characteristic in most of the EU countries.

Nowadays, Fresnel technology seems to have great potential to reduce the Levelized Cost of Energy (LCOE) in CSP. This is due to the fact that lineal Fresnel collectors have obvious economic advantages when compared to other technologies: (1) Only one receiver is used for the whole array of mirrors, and it is fixed. As a result, no rotating joints or flexible hoses are required, and therefore no environmental or health issues due to hot oil leakages must be prevented. In addition, thanks to this configuration the tracked structure is lighter and thus the rotating mechanism is simpler. (2) There is no need for glass-metal welds, which often cause receiver ruptures due to dilatation coefficient differences. Therefore, the receiver is more robust. (3) Mirrors are less expensive and easier to clean thanks to their low curvature.

Although most of the comparative studies between Parabolic Troughs and Fresnel are focused on electricity production (not relevant in ASTEP), there is another application for which Fresnel collectors are particularly attractive, which is to generate thermal energy for industrial processes, in the temperature range 150ºC-400ºC. For industrial applications, the Rotary Fresnel Collector is even more attractive, as the investment cost is reduced in regards to a conventional Fresnel, and the operation and maintenance are simple and reliable.

A latent thermal energy storage system will be installed, in order to accommodate the delay between solar energy supply and heat demand. Different phase change materials (PCM) will be considered for the temperature levels of the End Users' requirements. The development of a storage system based on hybrid active-passive heat transfer techniques will be developed in the frame of the ASTEP project. This enables its manageability in relatively small sizes, as required by industrial sites.

The use of honeycomb inserts, as energy storage concept for this proposal, is intended for increasing the surface-to-volume ratio in the storage system. At the same time, the mechanical integrity of the honeycomb, compared to other inserts like metallic foams, will ensure the full impact of thermal cycling on the long-term effectiveness of the system.

The hybrid nature of the thermal storage system to be implemented accounts for an active control of the power release, based on the regulation of the mass flow distribution across the multi-tube arrangement. This is of special interest for designing a LTES system with separated thermal capacity and power.

These systems must be integrated in a global control system, which includes not only the collector and the storage, but also the heat exchanger and absorption chillers in the case of refrigeration requirements. Specific tailored designs and control strategies addressing individual user demand profiles, location data, max and min thermal demand, and operational times. Compactness in design, all the equipment can be located outdoors on the building roof or a free lot, thus sparring valuable plant or industry floor.

In this project, two applications have been selected:

• Pasteurization process in the food industry in Greece (37.93 N) with a temperature demand of 170 ºC. (the provision of solar-driven chilling, typically requiring a heat source of at ~140 ºC) will also be included at this site).

• Preheating process in a fabricated metal industry in Romania (latitude 47.1 N), with a temperature demand above 220 ºC.

The proposed solar concept will be adapted to the different processes of the two industries, at different temperatures and located at different latitudes. This is one of the main advantages of ASTEP: its versatility to provide heat at very different conditions and thermal loads even within the same industry, thanks to reliable solar heat production and suitable management of the energy thanks to the thermal storage system.

In addition, the modularity of the proposed concentrator may lead to a fast application of the concepts to different industries and different sizes. Multiple concentrator modules can be installed in parallel with common storage within an integrated ASTEP system. This will aid in the standardization of the system, which will be done during the project in order to allow ease of replication.

In addition, ASTEP will use Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD) to provide structural, thermal and fluid analysis to optimise the solar collector and the STE system which is also an innovation into SHIP systems.

The main activities of the ASTEP project will bring the technology from the first laboratory test completed (TRL 3) to a large-scale prototype tested in intended environments (TRL 5).

The consortium is made of 16 partners, from which 6 are RTOs and Academia, 6 engineering and equipment SME, 2 process industries and 2 bridging the gap companies/RTO.