Photovoltaic and solar thermal collectors are widely employed and tested in the urban sector; however, application in the industrial sector is still scarce. Implementation of solar energy in industrial processes is constrained by several obstacles such as the identification of the best point of integration (process-specific thermodynamic and physical requirements) and the storage sizing to allow operation in the absence of solar radiation. This demonstrates the need for a comprehensive methodology that captures the main losses at reasonable resolution time, optimizing the complete system and therewith the related economics.
One important point that is often neglected is that integration of more efficient or less emitting heating sources (such as solar thermal) should always be compared to other process optimization measures. Process integration is an indispensable step in capitalizing the maximum heat recovery potential together with retrofitting of the heat exchanger network. Beyond this, further measures should be considered such as mechanical vapor re-compression (MVR), and integration of heat pumps.
Method and Results
A comprehensive methodology was developed (and implemented into the computational framework OSMOSE, used in the IPESE group) that allows simultaneous optimization of the process’ refrigeration and renewable utility system (See Figure1).
The proposed methodology was illustrated on the basis of a Swiss dairy plant where different solar components were compared and evaluated based on the total cost and the CO2-equivalent emissions. The methodology includes derivation of a cost-optimal solar field, heat pump, and thermal storage tank sizing as well as optimal operation of the system during all operating periods.
The main conclusions are summarized below (from Figure 1):
- Mechanical vapour recompression and heat pumping reduce the boiler consumption, emissions (60%) and total cost (33%) of the system, implicitly improving the efficiency of resource utilization.
- Solar-only integration without consideration of heat pumping will lead to emission reductions (70%) though reducing costs by a smaller degree (25%) and an oversizing of the solar system.
- The best results were achieved in terms of cost and emissions for a combination of solar technologies and heat pumping with emission reductions between 70-85%, and cost reductions between 33 and 50%.