TOKYO --  Solar panels have sprung up across Japan in the past few years, after the government introduced a "feed-in tariff" in July 2012 that guarantees prices for electricity generated from renewable energy. When these panels reach the end of their working lives in 20-30 years, they will create a mountain of waste.

By 2020, Japan's Environment Ministry forecasts the country's solar-panel waste will exceed 10,000 tons. After that, the pile really starts growing: reaching 100,000 tons in 2031 and topping 300,000 tons in 2033, the 20th anniversary of the feed-in tariff. Between 2034 and 2040 the amount of waste produced is expected to hover around 700,000-800,000 tons annually. The projected peak of 810,000 tons is equivalent to 40.5 million panels. To dispose of that amount in a year would mean getting rid of 110,000 panels per day.

Cuts like a knife

To help clear away the mountain of spent solar panels, the Environment Ministry has been studying how to recycle since fiscal 2013. It released guidelines on the subject in April this year.

A solar panel is composed of five layers. The first, which is directly exposed to the sun, is made of glass. Next comes a layer of ethylene-vinyl acetate copolymer, or EVA, a sealant made from resin. The third layer is the cell that produces the electricity. The fourth is again EVA. The final layer is a backing sheet.

To fuse them, the layers are heated in a vacuum, a process that melts the EVA and, when pressure is applied, causes the cell and the glass to stick together. The panel is completed by attaching an aluminum frame and a junction box -- a bundle of wires -- to both ends of the panel.

Because the glass and the cells are firmly attached to the EVA, it is difficult to separate them by smashing them to pieces and sorting them out. This led the Environment Ministry and the state-backed New Energy and Industrial Technology Development Organization, or NEDO, together with private companies, to begin working on new technologies to pry the sandwich apart in 2014. 

One such company is NPC, which makes solar panel manufacturing equipment. NPC has developed a process called the hot knife method, which can separate the cells of a panel from the glass in about 40 seconds. The panel is placed between two rollers, which move it along and hold it steady until it runs into a "hot knife" -- a 1 meter-long, 1 centimeter-thick steel blade that is heated to 180-200 C and slices the cell and the glass apart.

The thickness of the glass and the materials used in the EVA differ, depending on the manufacturer. "Technology to fine-tune the angle of the blade, temperature and other factors is required," said Masafumi Ito, NPC's president.

In August, the company made a serious push into the solar panel recycling business by setting up PV Techno Cycle, a 50-50 joint venture with Hamada, an Osaka-based industrial waste disposal company. It set a goal of processing 50,000-100,000 panels within three years, with 80% to be recycled and the rest to be reused. It aims to generate 500 million yen ($4.8 million) in sales.

Toshiba Environmental Solutions, based in Yokohama, southwest of Tokyo, also has technology that can separate solar cells from glass. It has recycled about 30,000 solar panels so far and can handle about 3,500 panels per month, or about 44 tons by weight.

Its technology separates the cell from the panel by scouring it off with a fast-spinning steel brush. What is left is a sheet of glass, the same end product as NPC's method. The difference is that Toshiba Environmental Solutions' method grinds the cells into a fine powder, whereas NPC's leaves behind a sheet of cells.

"The powdered cells have a high silver content and smelting companies buy it at high prices," said Shinji Takeda, vice president of Toshiba Environmental Solutions. "Because it is a dry process, and the technology uses neither solvents nor heat, the environmental burden is also low."

Making it pay

Glass makes up 80% of a solar panel's weight. Solar panels require high transparency and therefore glass that is much higher in purity than that used in construction. Scrap glass sells for 0.5-1 yen per kilogram in Japan. At that price, the 10-15kg of glass in a solar panel is worth about 15 yen at most.

NEDO aims to foster low-cost technologies to process solar panel waste. It wants to bring down the cost to less than 5 yen per watt by the end of fiscal 2018. That translates to 1,000 yen for a 200-watt panel, excluding transportation cost. 

Low demand for scrap and the high cost of employing workers to disassemble the aluminum frames and other components will make it difficult to create a profitable business unless recycling companies can charge several times more than the target set by NEDO, according to Toshiba Environmental Solutions. The company plans to develop recycled sheet glass that is worth more than glass scrap.

It is also important to promote reuse. The generating capacity of solar panels declines over time, dropping by about 2-4% every five years. Thus, after 20 years, a solar panel operates at 80% efficiency. That is high enough for places like Africa, where electricity grids are underdeveloped. A solar panel operating at 50% of capacity is sufficient to power a few household appliances.

One of the challenges with reuse is that it is impossible to predict the rate at which a panel will deteriorate. This makes it hard to set a price for used solar panels or determine whether installing them is worth the cost. Toshiba Environmental Solutions has been developing technology that enables it to evaluate the decline in solar panels' output over time using a solar simulator.

Another challenge is to improve testing efficiency. It is time-consuming to determine whether old panels can be reused because they cannot be tested individually. NPC has developed a way to conduct a simplified test on panels currently in use. The technology uses infrared rays to peer inside the panels and determine whether they can be reused, based on where wires have been severed and how badly damaged a certain part of a cell is.

More panels may need to be disposed of quickly in response to natural disasters, such as earthquakes and typhoons, and future upgrades. Industry leader Toshiba Environmental Solutions can currently handle 44 tons of solar-panel waste a month. It would take 19 years for the company to process even the 10,000 tons of waste expected in 2020. New technologies and a nationwide network of recycling facilities will be needed to deal with the coming wave of old solar panels.