The solar market has been dependent on traditional cleaning systems for decades. Recently, however, there has been a noticeable shift from traditional to semi-automatic and automatic cleaning. Historically, traditional methods have been used since the beginning of solar power development in the country. Semi-automatic cleaning appeared around 2010. For the purposes of this article, “semi-automatic” may be defined as a combination of automatic rotary brush systems on the modules or between rows, and manual cleaning; while automatic systems require minimal manpower. The article is based on InSolare’s experience in the solar industry since 2009. InSolare is a technology leader (>250 MW completed and >300 MW in the pipeline) and has a team of over 200 employees who are led by a PhD holder with around 50 patents. The key methods for cleaning solar plants can be divided into three types.
Traditional wet cleaning: Here, a water pipe network is constructed across the solar plant, with nozzles built at predefined intervals/locations for the cleaning team to plug in the hose pipes as required. A brush/mop/cloth may be used by the cleaning team after spraying water on modules. This facilitates the most effective cleaning, but is slow, expensive and uses a lot of water, which may not be available at remote sites. Water spray systems, using nozzles, sprinklers or other means, have attracted attention. However, these are deployed mainly in areas where access is a challenge, such as commercial/industrial superstructures, car parks or residential areas.
Semi-automatic: This involves a combination of automatic rotary brushes/other means of cleaning with the water pipe networks used in traditional systems. This method reduces the overall cost with respect to manpower and water usage.
Automatic: This method involves a set of robotic equipment along with accessories, and requires minimum manual intervention. The robotic system can be powered via an auxiliary power system or the solar power generated by the module itself, if a battery system with sufficient capacity is provided within. As per our experience, this method requires detailed planning to account for the lay of the land as well as the typical execution/integration nuances. Automatic systems have far-reaching effects across the entire life of a plant, helping achieve higher generation through optimal utilisation of the installed systems.
Other methods include chemical cleaning with/without special coatings on modules. The table compares traditional, semi-automatic and automatic cleaning based on different parameters.
Automatic systems have recently attracted attention, having been deployed at many projects. Semi-automatic and automatic methods are still at early stages of evaluation with respect to life cycle advantages. More innovative approaches are needed to arrive at a stage where such systems become technically and commercially acceptable for all applications. Automatic systems may be more viable in areas where the manpower cost is high and/or water usage is a concern. Innovations can be made with respect to minimising deficiencies, as described in the table.
Contrary to wet cleaning systems, dry cleaning systems may require further studies with respect to their soiling factor, as most dry cleaning systems blow dust particles into the air. These airborne particles may settle on neighbouring modules, which may counteract the benefits of regular cleaning. As a result, the soiling factor could rise, and commercial viability may be further reduced. These studies should take area, wind speed, wind direction, cleaning speed, seasonal effects, morning dew and other such parameters into consideration.
Hybrid solutions are also being evaluated in the form of various combinations of cleaning methods. For larger projects, a hybrid approach may be a more viable solution to the challenges of manpower, water systems and geography.
Currently, most project owners and asset management teams are inclined towards automatic solutions. But it is indeed the time to evaluate the life cycle considerations of automatic solutions against hybrid solutions. This is especially important when comparing battery disposal and the energy used for charging to the water and manpower required for traditional cleaning.
InSolare is working on developing analytical models to find suitable solutions to challenges on a case-by-case basis.