This teaching course aims at providing insight on the thermal processes involved in the conversion of solar radiation into useful thermal energy in order to characterize the efficiency of solar thermal collectors and assess the performance of solar thermal systems.

The main subjects covered are: estimation of solar radiation availability, optical and thermal characteristics of solar collectors, systems and applications of solar thermal energy, solar thermal systems design and thermo-economic optimization methods.

The student:

• knows the fundamentals of heat transfer and solar radiation, and understands the processes involved in the conversion of solar radiation into useful heat;
• knows the principles of sorption cooling, and is able to describe in both mathematical and graphical terms the operation of sorption cooling cycles;
• knows the hydraulic layout of various solar thermal systems, and understands their operating principles;
• knows the design methods that are used for the thermo-economic optimization of solar thermal systems.

The student is able to apply the acquired knowledge to:

• develop the thermal efficiency model of different solar thermal collector types;
• define the specifications of the different system components involved in solar thermal plants, including thermal storages, heat exchangers, safety devices, and heating and cooling appliances;
• design solar thermal systems and verify their correct functioning with the help of a computer modelling and simulation tool;
• assess the energy and economic performances of solar thermal systems.

After passing the exam, the student is able to:

• approach the design of thermal systems complemented by different renewable energy technologies;
• make design decisions independently;
• critically evaluate the impact of design decisions on system performances and costs;
• use technical standards and norms for the energy performance evaluation of solar thermal plants.

FUNDAMENTALS

1. Solar radiation

Characteristics of extra-terrestrial solar radiation and solar radiation at ground level, solar geometry, sky models, instruments and methods for solar radiation measurement. Availability and utilizability of solar radiation.

2. Transmission and absorption of solar radiation

Selected heat transfer topics. Optical properties of covers and mirrors. Transmittance-absorptance product: directional and spectral dependence. Absorbed solar radiation.

3. Flat plate collectors

Energy balance equations for a simple flat-plate collector. Overall heat loss coefficient. Temperature distribution on the collector plate. Fin efficiency, collector efficiency and collector heat removal factors. Liquid and air collectors.

4. Concentrating solar collectors

Energy balance equations for the concentrating collector: concentration ratio. Concentrating systems: fixed, single axis tracking, double axis. Direct normal irradiance (DNI); Intercept factor; Global thermal efficiency; Optical and thermal performances. Characteristics of Sun tracking systems.

5. Performance of solar collectors

Definition of efficiency curve. Test methods for solar collectors: American and European standards.

6. Thermal energy storage

Requirements of thermal energy storage in solar thermal systems. Water storage: thermal stratification. Solid-liquid phase change storage. Seasonal thermal storage. Dimensioning of the storage system: calculation of energy performance and financial aspects. High temperature storages: technologies (molten salts, phase change material, thermocline, concrete), challenges and costs.

SYSTEMS AND APPLICATIONS

7. Active solar thermal systems

Solar water heaters for sanitary hot water production: small-scale systems and multi-family house systems. Solar combi-systems: space heating and domestic hot water production. Solar thermal systems for space cooling. Industrial applications of solar thermal heat: process heat.

8. Solar thermal systems design

The solar loop: low-flow and high-flow systems. Collector fields: hydraulic balancing, orientation, series and parallel connection, shadowing. Modified collector efficiency; piping heat losses. Heating loads calculation. Solar fraction.

9. Financial evaluation of solar thermal projects

Key performance indicators in financial evaluations: boundary conditions and uncertainty. Thermo-economic optimization.

10. Simplified design method: F-Chart

Origin of the F-Chart methods. The F-Chart methods for solar water heaters and combi systems.  

11. Modelling and simulation tools

Transient simulation of solar thermal systems for hot water production with MATLAB. Worked-out examples of solar system simulations: dimensioning, control strategy implementation, operation optimization.

12. Solar cooling and refrigeration

Thermally driven cooling technologies: absorption and adsorption chillers, desiccant evaporative cooling systems. Solar driven cooling and refrigeration systems.

13. Medium and High temperature applications

Applications of medium and high temperature collectors: process heat, concentrating solar power.

Basic knowledge of thermodynamics and heat transfer.

The examination consists of a written exam covering the theoretical aspects, and an oral exam covering the system design aspects.

The written exam consists of two to three problems and aims at verifying: i) the knowledge of the fundamentals of solar radiation, optics and heat transfer mechanisms involved in solar thermal energy conversion; ii) the ability to approach the efficiency model of different solar collector types; iii) the knowledge of the operating principles of sorption cooling processes. Clarity of exposition and precision in mathematical formulations are of key importance.

The oral exam consists in the discussion of a project assignment and aims at verifying: i) the knowledge of the operating principles of solar thermal collectors; ii) the knowledge of the methods used in the dimensioning of solar thermal plants; iii) the ability to make suitable design decisions based on specific system boundary conditions and/or operational requirements; iv) the critical evaluation of the project results.

Students carry out the project assignment, independently or in group of two, and submit the project report before the date of the written exam.