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