دانلود رایگان ترجمه مقاله بررسی متدهای مختلف تمیزکاری بازتابنده های خورشیدی در کارخانه های CSP – الزویر ۲۰۱۴

مطالعه روش های مختلف تمیزکاری بازتابنده های خورشیدی مورد استفاده در کارخانه های CSP

Study of different cleaning methods for solar reflectors used in CSP plants

Abstract

Soiling and dust accumulation in reflectors for concentrating solar plants (CSP) plants decrease their reflectance and, as a consequence, the solar field efficiency. Minimizing the cost of the cleanliness is a key issue for the solar-plant feasibility. This work is focused on optimizing the cleaning method of solar reflectors for CSP applications under real outdoor conditions in a semi-desert climate. The testing consisted on outdoor exposing of solar reflectors and applying different cleaning methods. According to results obtained, the most effective cleaning method is the one based on demineralized water and a brush, with an average efficiency of 98.8% in rainy periods and 97.2% in dry seasons. The innovative cleaning method based on a steam device with a soft tissue was inefficient (efficiency of 97.3% in a rainy period). If the number of passes applied with the high- pressure demineralized water method is highly enough, this method is as effective as the one based on brushing and the addition of a detergent does not increase its effectiveness.

۱ Introduction

 Power generation with CSP plants is a current practice increasingly booming in order to contribute to an energy production sustainable with the environment, using the solar resource. Although different technologies are available, the most commonly used are solar towers and parabolic-though collectors. They are basically composed of a power block and a solar field, which concentrates solar energy through solar reflectors. These CSP plants can only use the incoming direct solar radiation, called beam radiation or direct normal irradiance (DNI). Appropriate site locations for CSP plants are normally in arid to semi-arid regions, where the DNI resource is very high, because acceptable production costs of commercial CSP plants are typically where DNI exceeds between 1700 and 2000 kWh/m2 year [1]. In addition, the vegetation or other elements like buildings, does not shade the area and therefore the whole surface is receiving the incoming solar radiation. The fact that CSP plants are installed on arid and semi-arid regions involves the existence of important amount of dust and sand in the ambient. Soiling and dust accumulation in solar reflectors of CSP plants causes absorption and scattering of direct solar beams, decreasing mirrors reflectance, and solar field performance and power sales as a result [2]. To guarantee that all solar beams reach the receiver, that is, to keep a suitable average mirror reflectance and a good solar-plant efficiency level, a proper cleaning method has to be frequently applied. As example, around 500,000 m2 of parabolic-trough reflectors are installed in a typical 50-MWe commercial CSP plant in South Spain, with a 7.5-hours molten-salt storage system [3]. Hence, collector cleanliness represents one of the most costly expenses of the solar-plant operation and maintenance (O&M), and minimizing this cost is an important issue for the solar-plant economic feasibility [2]. Main action in CSP plants to remove the soiling is based on water, washing the reflecting surface with pressurized water, but depending on the plant location this natural resource can be limited, i.e., on arid or semi-arid regions. Therefore, the necessity of optimizing the cleaning method in every single CSP plant, becomes a very relevant issue. Although some authors have made a research effort in optimizing the cleaning procedure [4-8], some important technical aspects have not been studied in detail yet. For that reason, this paper focuses on optimizing the cleaning method of solar reflectors under real outdoor conditions, trying to find out the best cost-effective combination. The test consisted on outdoor exposing and cleaning of several solar reflector samples at the outdoor test area that the Optical Aging Characterization Laboratory (OPAC) has to this purpose at the Plataforma Solar de Almería (PSA), in South Spain. OPAC laboratory is a collaborative research project between Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT) and Deutsches Zentrum für Luft- und Raumfahrt (DLR). PSA is located in Tabernas Desert (South Spain), that is, it has a semi-desert climate.