IN DEPTH: Solar under Sakurajima
As the sun sets behind Sakurajima, children collect the porous, volcanic rocks that float across Kagoshima Bay from the mountain’s base, while fishermen cast their lines for one last try before the pink hue of the late-afternoon sky gives way to the inky darkness of night.
Sakurajima, Japan’s most active volcano, is part of life in this region of Kyushu, Japan’s laid-back sun-dappled southern island. With almost constant eruptions since 1955, locals are used to the ash, which often falls from the sky like a fine snow and settles where it lands.
The ash is one of a series of unique challenges faced by Japan’s two biggest PV plants (both on Kyushu), mainly due to their siting on reclaimed land, in what is an extremely earthquake-prone country.
Yet these challenges — which, bizarrely, include attacks from aggressive crows — have given the developers and O&M teams opportunities to experiment with new construction, maintenance and monitoring methods that could open up important new revenue streams in the future.
Marubeni’s 82MW (DC) Oita plant sits on a 105-hectare plot of reclaimed land in a half-industrial, half-suburban neighbourhood of Oita city, surrounded by leafy nature trails and shallow, muddy channels where locals dig for razor clams. Its location, jutting into the steel-grey waters of Beppu Bay, is perfect for a solar plant. There is high insolation, a shadow-free environment and it is right next door to Kyushu Electric Power’s LNG-fired 2.3GW Shin-Oita power plant, meaning that all the infrastructure needed was already there.
“The transmission line was available from the beginning,” says Yoichi Fujimoto, director of Oita Solar Power, the Marubeni subsidiary leading the project, while pointing to a pylon 50 metres away. “It was a very nice location for the grid connection.”
When Japan introduced its generous feed-in tariff scheme in July 2012, Marubeni sensed an opportunity, promptly investing more than $200m to build the plant — Japan’s largest. And according to Fujimoto, the gamble is already paying off.
“Yesterday, we sold about ¥20m [$200,000] of electricity,” he gushes. “It’s a very nice plant, even on weekends.”
But building on land reclaimed from the sea has brought its fair share of potential problems. There is the threat of corrosion from the salty sea air; the risk of a direct strike from a tsunami; and the fact that reclaimed ground is notoriously unstable during earthquakes.
When the Great East Japan Earthquake struck on 11 March 2011, causing the tsunami that devastated the Fukushima-Daiichi nuclear plant, the ground in reclaimed areas such as Tokyo’s Toyosu district cracked open and water started bubbling up, forcing the evacuation of residents and the temporary closure of nearby Tokyo Disneyland.
So Hitachi designed the racks and foundations of the solar panels to not only withstand a quake of up to level six on Japan’s seven-point seismic scale, but also not to sink into the ground if “liquefaction” occurs, because the concrete foundations are not drilled into the ground.
“Our foundations will stay level if they sink, so the panels won’t be damaged,” says Fujimoto.
The foundations were constructed using slip-forming — in which concrete is poured continuously into prefabricated frames.
“This is one of the main reasons we could shorten the construction period by as much as 50 days. It’s very quick and requires fewer people,” Fujimoto says. “And this is the first use of slip-forming for solar.”
He explains that salt corrosion is not the big issue it could have been at Oita. Under Japanese law, standard 20-year warranties used to safeguard against corrosion are only applicable for solar panels installed at least 500 metres from the sea. Yet the project’s module supplier, South Korea’s Hanwha Q Cells, agreed to offer Marubeni a two-decade guarantee on its panels, a move not followed by any of its Japanese counterparts.
“They’re ready to bear the cost over the long term,” Fujimoto says. “The panels can be damaged by salt, but Hanwha Q Cells is ready to replace them.”
A tsunami is also not a particularly large concern — not because the relatively sheltered Beppu Bay is protected from a giant wave (it is, after all, close to the seismically active Nankai trough that runs along much of Japan’s eastern coast) — but because the 6.8-metre-tall wall around the plant is deemed to be sufficient protection.
The biggest tsunami that could strike the site would be no more than 2.3 metres high, says Fujimoto. “And we covered the maximum probable loss with insurance.”
Fujimoto seems more concerned about a problem that, like the ash at Kyocera’s 70MW Nanatsujima plant, falls from the sky.
“Crows have been one of the biggest problems so far,” he says.
The birds — notoriously aggressive in Japan — have taken a dislike to the massive, shiny plant, and damaged numerous panels by dropping stones on them from the air.
It became such a problem that Marubeni asked its EPC contractor, Hitachi, to develop a way of identifying which of the 340,000 panels had been affected.
“Of course, the best way would be to mount sensors on each panel,” Fujimoto says. “But that would be problematic because we’d have to ensure the technological reliability of all those sensors — the headache would become double.”
Instead, Hitachi developed a remote string-monitoring system, which allows Marubeni to isolate the problematic panels.
“But we still didn’t know what to do with that data,” Fujimoto says. “So Hitachi developed a method. And now we want to standardise that.”
Fujimoto also developed a system to scan barcodes on the panels with a smartphone. “We want to standardise this for other PV projects. It reduces paperwork and we can track records for 20 years.”
Fujimoto hopes to use these new ideas as the basis for eventually offering solar EPC services in other markets.
“We have a lot of experience and data now,” he says.
“So in the future, maybe we can convince overseas operators about our technology, while providing EPC and remote monitoring systems.”
“With our string monitoring system, the costs are a bit high, but the system can save money for PV plant owners. It can help operators in other countries avoid headaches.”
On the southern side of the island, roughly 300km away, lies Kyocera’s 70MW Nanatsujima plant, which briefly became Japan’s largest PV plant when it was switched on last November.
Here, across the water from Sakurajima — which forms a spectacular backdrop to the facility on clear days — the ash has been less of a problem than expected.
“The panels have been covered by ash before, but the rain and wind has washed it away,” says a young maintenance worker for Fukuoka-based electrical-equipment specialist (and Kyocera partner) Kyudenko, as he drives between the arrays that cover most of the 35-year-old plot of reclaimed land that never ended up fulfilling its original purpose as a shipyard. “So we haven’t yet had to wash the panels yet. But the ash is worst in July and August.”
The 29,000 Kyocera modules at the Kagoshima city site are installed at a 20-degree tilt — an ideal compromise between maximising sunlight exposure and an incline that allows the ash to slough off.
“We budgeted for ash maintenance,” says Nobuo Kitamura, president of Kyocera’s Kagoshima Mega Solar Power unit. “But so far, there hasn’t been a need.”
And experiments have already shown that even when covered by ash, the panels have been able to generate up to 70% of their designed capacity. But the jury is still out, as a major eruption has not occurred since the plant came on line last November.
Salt corrosion is also not a big issue, mainly because Kyocera — which leads the consortium that owns the project — provides the panels itself, and has always looked at Nanatsujima as a kind of R&D facility, a way to establish itself as a total-solutions provider.
The consortium has taken a different approach to Oita in terms of guarding against potential liquefaction of the reclaimed land it is situated on. “We used longer bolts than usual for the concrete bases that the arrays are mounted on,” says Ichiro Ikeda, Kyocera’s general manager of solar marketing. “The bolts are 16cm longer, so if liquefaction occurs, the rack will stay mounted to the frame.”
And now Kyocera is applying the lessons it has learned at Nanatsujima to build a massive 430MW solar plant in Nagasaki prefecture, also on Kyushu.
It has already received approval for the project, which it hopes to start building with four partners in the 2016 financial year.
“These are the kinds of things we’re now learning,” says Ikeda. “We’re trying to collect data now and look at how we can manage the business.”