The severe soiling of reflectors deployed in arid and semi arid locations decreases their reflectance and drives down the yield of the concentrating solar power (CSP) plants. To alleviate this issue, various sets of methods are available. The operation and maintenance (O&M) staff should opt for sustainable cleaning methods that are safe and environmentally friendly. To restore high reflectance, the cleaning vehicles of CSP plants must adapt to the constraints of each technology and to the layout of reflectors in the solar field. Water based methods are currently the most commonly used in CSP plants but they are not sustainable due to water scarcity and high soiling rates. The recovery and reuse of washing water can compensate for these methods and make them a more reasonable option for mediterranean and desert environments. Dry methods, on the other hand, are gaining more attraction as they are more suitable for desert regions. Some of these methods rely on ultrasonic wave or vibration for detaching the dust bonding from the reflectors surface, while other methods, known as preventive methods, focus on reducing the soiling by modifying the reflectors surface and incorporating self cleaning features using special coatings. Since the CSP plants operators aim to achieve the highest profit by minimizing the cost of cleaning while maintaining a high reflectance, optimizing the cleaning parameters and strategies is of great interest. This work presents the conventional water-based methods that are currently used in CSP plants in addition to sustainable alternative methods for dust removal and soiling prevention. Also, the cleaning effectiveness, the environmental impacts and the economic aspects of each technology are discussed.

This paper describes the accelerated ageing of commercially available silvered polymer film by contact cleaning using brushes and water in the presence of soiling created by dust and sand particles. These conditions represent cleaning regimes in real concentrating solar power (CSP) solar fields in arid environments, where contact cleaning using brushes and water is often required to clean the reflecting surfaces. Whilst suitable for glass reflectors, this paper discusses the effects of these established cleaning processes on the optical and visual characteristics of polymer film surfaces, and then describes the development of a more benign but effective contact cleaning process for cleaning polymer reflectors. The effects of a range of cleaning brushes are discussed, with and without the presence of water, in the presence of sand and dust particles from selected representative locations. The experiments were repeated using different experimental equipment at Plataforma Solar de Almería (PSA) in Spain and Cranfield University in the UK. The results highlight differences that are attributable to the experimental methods used. Reflectance measurements and visual inspection show that a soft cleaning brush with a small amount of water, used in a cleaning head with both linear and rotational motion, can clean polymer film reflecting surfaces without inflicting surface damage or reducing specular reflectance.

Reflectors for concentrated solar thermal technologies need to withstand 20 or even 30 years of outdoor exposure without significant loss of solar specular reflectance. In order to test the durability of innovative reflectors within a shorter period of time, an accelerated aging methodology is required. The problem with accelerated testing is that poor correlation between laboratory and field test results has been achieved in the past. This is mainly because unrealistic degradation mechanisms are accelerated in the weathering chambers. In order to define a realistic testing procedure, a high number of accelerated aging tests have been performed on differently coated aluminum reflectors. The degradation mechanisms of the accelerated tests have been classified and systematically compared to samples that have been exposed at nine different exposure sites outdoors. Besides the standardized aging tests, innovative aging procedures have been developed in such way that the agreement to the degradation pattern observed outdoors is increased. Although degradation depends on materials and location, five generic degradation mechanisms were detected. Standardized tests only reproduced one or two of the five mechanisms detected outdoors. Additionally, several degradation effects that were not observed outdoors appeared. The innovative accelerated aging tests of artificially soiled samples were able to reproduce three of the five mechanisms observed outdoors, presenting a much more realistic overall degradation pattern.

Concentrating solar thermal technologies have experienced an important boost in the last few years. Besides the production of electricity, they are particularly useful for the supply of industrial process heat. The industrial atmospheres affecting these solar plants typically contain gaseous pollutants that are likely to promote corrosion on the components of the solar facility, specifically solar reflectors, thereby compromising their optimal performance and the overall system efficiency. Seven accelerated aging tests were designed to study the effects of three air pollutants (H₂S, SO₂ and NO₂) on the durability of two commercially available reflector types (silvered-glass and aluminum), both in single-gas tests and in multicomponent gas mixtures. Additionally, the same material types were exposed outdoors at five representative polluted sites, including industrial, urban and coastal environments. Reflectance and optical microscope monitoring corroborated which degree of corrosion was developed on a specific type of reflector in the different tests with gaseous pollutants, as well as the synergistic effects of gas combinations. For example, tests with sulfur were harmful for silvered-glass reflectors (up to a total of 16 corrosion spots), whereas aluminum was particularly affected by tests with NO₂ (numerous micro spots of around 50 μm size). Moreover, comparisons of the corrosion patterns found in accelerated-aging and outdoor exposures revealed which laboratory test reproduced the different real polluted atmospheres in the most realistic way, which is the main goal of this work. For instance, the degradation found at Site 2 was reproduced by Test NO₂+SO₂, with an acceleration factor of 27.

Renewable energy today is no longer just an affordable alternative, but a requirement for mitigating global environmental problems such as climate change. Among renewable energies, the use of solar energy is one of the most widespread. Concentrating Solar Power (CSP) systems, however, is not yet fully widespread despite having demonstrated great efficiency, mainly thanks to parabolic-trough collector (PTC) technology, both on a large scale and on a small scale for heating water in industry. One of the main drawbacks to this energy solution is the large size of the facilities. For this purpose, several models have been developed to avoid shadowing between the PTC lines as much as possible. In this study, the classic shadowing models between the PTC rows are reviewed. One of the major challenges is that they are studied geometrically as a fixed installation, while they are moving facilities, as they have a tracking movement of the sun. In this work, a new model is proposed to avoid shadowing by taking into account the movement of the facilities depending on their latitude. Secondly, the model is tested to an existing facility as a real case study located in southern Spain. The model is applied to the main existing installations in the northern hemisphere, thus showing the usefulness of the model for any PTC installation in the world. The shadow projected by a standard, the PTC (S) has been obtained by means of a polynomial approximation as a function of the latitude (Lat) given by S = 0.001 − Lat² + 0.0121 − Lat + 10.9 with R² of 99.8%. Finally, the model has been simplified to obtain in the standard case the shadows in the running time of a PTC facility.