Dust

The Gulf region and Arabian Peninsula is an ideal region for solar power. There is plenty of sunshine, lots of unused land, high local energy demand and available capital. However, dust both in the air and settled, spoils this picture.

Regardless of the question whether thermal or photo voltaic (PV) will make the race, dust has to be taken into account.

For thermal solar power, both dust in the air and dust on reflectors have a relevant negative effect. Light is scattered and lost. Consequently reflectors rely on impeccably cleaned surfaces. In contrast, PV is much more tolerant to defused sunlight. However, once enough dust is deposited on PV panels it will start to shade off sunlight and ultimately decreases the performance.

On the Arabian Peninsula dust is omnipresent. Summer and winter sand storms (Shamal) disperse vast amounts of mineral dust particles into the air almost throughout the year. The occasional cold-front sand storm (Habub) can dump high amounts of dust in a matter of minutes. The Gulf region is in fact a very dusty place.

Cleaning large PV arrays

Dust on PV panels is generally easy to clean off. PV surfaces do not have to be cleaned perfectly. But how do you clean 130 soccer fields (900'000 m²) of solar surface? Just like any surface, but very much faster.

A 100 MW PV power plant is composed of about 900'000² m of solar surface. Think of 130 soccer fields or 3600 tennis courts of glass surface. You may hire 150 people, give them a broom and lots of water to drink. They might do the job, despite the unpleasant heat. They possibly finish the whole surface after 2 weeks and then start anew.

Another way is to send one mobile robotic cleaning machine and let it clean the entire surface in less than 10 days, no human error, no human live support, no water consumption. This is exactly what the Swiss company Robonaut GmbH has in mind.

The fully automated robotic system

As mentioned before, high speed and constant quality are some of the key factors. It is clear in my opinion, that cleaning very large PV parks by sending an armada of people around with a broom might not be the most efficient method. You may agree, that a machine of some sort would be a necessity.

A manually operated machine bears the risk that operators make mistakes. The monotonous work and the required high operating speed increase this risk significantly. Now, how do you build this machine so that operators cannot make mistakes and do not damage the Installation. Simple, the machine must do all the critical manipulations autonomously, with no operator involved.

A sensor guided mobile robotic system does exactly that. It eliminates human factor or worse human error. It does the same job much faster and more reliably than a manually operated machine. In fact it can operate 24/7 with unchanged quality and reliability in contrast to a manually operated system.

At this point I would like to remind you, that damage on the PV arrays caused by human error is very costly and not predictable.

All that is needed is a reasonably built array of PV modules and a wide enough passage in between the arrays.

In very large PV parks, one task is to do the cleaning, another is to drive intelligently through the PV arrays, minimizing the unproductive time like having to drive to a service point. Changing from the end of a panel array to the beginning of another must be optimal and very fast.

A structure to support and guide the cleaning head is generally a very good idea. However, this must be planned and integrated by the company who builds the panel arrays. Besides the added cost, it is difficult to motivate the numerous manufacturers to add such a feature.

The solution by robonaut

The off-road mobile robot system with the brand name Xpedous cruises alongside the PV panel array using a redundant navigation system and many sensors. It caries all the cleaning machinery on-board and is powered by a suitable energy source. The sensor guided cleaning arm floats over the panel array. It does not require any support on the panels or the array structure. On reaching the end of an array the cleaning arm is lifted off and put down at the next array. Dust is collected automatically into a container. As mentioned before there is no water used for the cleaning process.