Although the non-residential segment represents 57 percent of the existing installed capacity, it represents 96 percent of the reserved capacity. The fast-growing non-residential PV capacity makes Japan one of the hot markets for PV Operations and Maintenance (OM) services.

Fuji Keizai Co., a research and consulting company, forecasted that the 2013 non-residential PV OM market in Japan will almost quadruple by 2020. The research firm specifically projected that the maintenance market will grow from ¥1.5 billion in 2013 to ¥8.2 billion in 2020 and the operations market will grow from ¥16.3 billion to ¥60.4 billion. 

To meet the growing OM demand cost effectively and efficiently, Japan is turning to high-tech gadgets. 

Sohgo Security Services Co, known as ALSOK, is a leading security services provider in Japan. The company currently has the largest market share in PV security monitoring for large-scaled, ground mount PV systems. “We install infrared or thermal camera systems around perimeter fence lines and provide 24/7 surveillance monitoring services from central monitoring centers located throughout the nation. We monitor and detect module or copper wire thefts, which occur during construction and also wild animals that damage wiring systems during operation,” said Hiroshi Fujisawa at ALSOK.

ALSOK’s solar customers approached the company and asked whether it could provide module inspection services as well. Having developed security robots, the company expanded its expertise into “flying” robots — unmanned aerial vehicles (UAV), otherwise known as drones — to conduct panel inspections from the air.

Drone inspecting solar modules. Credit: ALSOK

Drones equipped with high-definition and thermal imaging cameras can detect malfunctioning modules, specifically hot-spots, which can reduce electricity production. The company also takes aerial photos for site surveys and to monitor construction progress using an autonomously operated drone. Currently in the US, San Francisco-based Skycatch offers very similar services for SolarCity and First Solar. 

ALSOK launched the testing service with drones in October for its existing customers who subscribe to its PV security monitoring services. Using a drone is a cost competitive alternative to taking aerial photography from a helicopter or using manual labor to conduct inspections in –large, remote fields.

“It takes 15 minutes (for a drone) to fly over a 2-MW system to collect necessary data for inspection while it will take about three hours to check 2 MW worth of modules by hands,” said Fujisawa. With a fully charged battery, a drone can fly for about 25 minutes and the company currently charges ¥200,000 – 300,000 for one fly.  The company will make this service available to any customer, including wind projects, starting April 2015.

There is another type of robot working for the growing solar PV OM market in Japan.  Sinfonia Technology Co. developed iRobot’s Roomba-like cleaning robots called “Resola” that autonomously scrubs the module surface with water.

Resola, the module cleaning robot. Credit: Sinfonia Technology Co.

Even in Japan where there is a reasonable amount of rainfall, solar modules still gather dust, dirt, and other debris that can block sunlight and reduce electricity generation. “Dragonflies lay eggs on PV modules, seeing blue PV modules as water,” said one PV project developer in Japan. This misdirected instinct can cost PV owners unless modules get cleaned up in a timely manner to ensure maximum productivity. 

Bird droppings also pose a serious risk. “During cold seasons, waterfowls land on PV modules to warm up themselves and leave some droppings. When it doesn’t rain, droppings get dried out and stay on modules,” complained another project developer. 

Sinfonia Technology has over 100 years experience in developing electric machinery, from printers to aerospace power generation systems, and has applied its mechanical expertise to develop the autonomous cleaning robot with water, which cleans not only loose dirt and debris, but also stuck-on messes like bird droppings.

Resola is approximately 26 inches (670 mm) in width, 21 inches (545 mm) in depth, and 6.8 inches (173 mm) in height. “It weighs less than 44 pounds (20 kg) so that one person can carry it easily,” said Koichi Dakimoto at Sinfonia. It runs on a rechargeable lithium-ion battery and a full charge equals about five hours of operation time.

The robot cleaner is currently targeted for ground mount systems at tilt angles of 5-20 degrees and applicable only for mono- and poly-silicon solar modules. Like Roomba, it has a self-navigation system. Resola’s infrared sensors allow it to climb up the slope from the bottom of the system, detect edges (or cliffs), and continue moving horizontally and then down the surface of the system, without falling.

Resola module cleaning path (figure re-created with translation from Japanese to English). Credit: Sinfonia Technology Co

Furthermore, to prevent Resola from slipping from the sloped, wet module surface, its wheels are covered with non-slip rubber like shoe soles.

Resola cleans solar modules with a spinning brush and squeegee, which moves like a windshield wiper blade. It moves from the top to the bottom of the slope so that debris and dirty water are gathered at the bottom.  A tank holds up to 2.7 liters of water, which can cover about 246 square-feet or 45 modules on average. “The cleaner comes with three settings: Under the hard-scrub setting, the tank lasts for about 30 minutes while 90 minutes under the gentle-scrub setting,” said Dakimoto.

When the battery power level or water level become low, for safety, Resola is programmed to move down to the bottom of the slope and waits for the battery to be exchanged or for the water tank to be filled. The company is currently marketing Resola exclusively for the domestic market.                             

As the number of PV installations has significantly increased in such a short period of time, project developers have come to realize that PV is not maintenance free and it can cost a considerable amount of money to keep the system shipshape and operating at the maximum level.  In the growing Japanese PV market, cost-effective and efficient OM tools and services will have a significant role in minimizing OM costs while maximizing production revenues.