In Japan, progress has been made in developing more scenarios of solar power generation. The Nippon Road and others have developed solar panels embedded in parking lots and sidewalks. Expectantly, if solar panels are laid on all roads in Japan, the power generation capacity is equivalent to more than 300 nuclear power plant units. Since there are limited places suitable for solar power generation in Japan, roads, windows and agricultural greenhouses are expected to be used for generating green power, and solar power is likely to become the energy for local consumption.
“It won’t move a bit when a 15-ton truck passed by,” the head of the Production Technology Department of Nippon Road was pretty proud of their work cooperated with a solar cell start-up, F-WAVE Company Limited, to bury solar panels in the road.
Road is taken as the first choice for solar power generation site, because nothing will be affected with such design, and people and vehicles can pass as usual.
More than 90% of the solar panels in circulation on the market are made of silicon and are installed on roofs, hillsides, open spaces, etc. In order to increase the setting place, the packaging technology using materials that are easy to transmit light is being developed in the solar panel industry recently, and the light wavelength used for power generation is also changed according to the purpose.
Solar panels such as those placed on the road in Japan are made of silicon, and the outer frame is made of solid hard plastic. Generally, roads are repaired in 10 years, and solar panels are considered to have such a long life. The solar panel ensures the safety of vehicles and pedestrians through anti-skid processing. Even if the road expands and contracts with the change of temperature or bends due to the passage of large vehicles, the panel can also bear.
The energy conversion efficiency of solar panels is about 8%, and that of high-efficiency products is about 20%. Although the conversion efficiency is relatively low, the goal is to lay a large number of panels for use in local facilities such as the pavement and parking lots. In August 2022, the construction was carried out with the battery in the facilities in Tsukuba.
BASF in Germany and Solar Earth Technologies in Canada are also developing integrated solar panels on the road. The energy conversion efficiency has reached 12.7%. From April to June 2023, empirical experiments were carried out in Beijing and Shanghai of China, North America, Asia, Africa and Europe.
Some enterprises are also promoting practicality. Colas, a large French road construction enterprise, made solar panels laid in parking lots and other places practical in 2019. It has also been introduced by Canada, the United Arab Emirates (UAE) and other countries.
There is also great potential to use windows of residential buildings to generate electricity. Although some solar panels can be set on the windows before, the panels are colored to absorb light, and due to the design, the space for setting is limited.
Solar panels that can be used as transparent windows have attracted much attention. Ubiquitous Energy, an American start-up funded by ENEOS Holdings (HD), has developed solar panels that can be used as windows. This is a transparent organic thin-film solar panel, which absorbs ultraviolet and infrared rays invisible to the naked eye for power generation and can penetrate visible light. At present, the highest level of energy conversion efficiency laboratory is 10%. The product can be exported stably and will be listed in the United States as early as 2025.
The trend of using farmland for solar power generation is also expanding. Previously, solar panels were only installed on fallow land, but now they are planned to be installed on agricultural greenhouses.
Swiss start-up Voltiris has developed solar panels installed on the ceiling of agricultural greenhouses. Its working principle is to gather the light through the ceiling to generate electricity. The sunlight contains light of multiple wavelengths, and the company’s solar panels only use green light and near-infrared light to generate electricity. It is said that vegetables such as tomatoes and sweet peppers grow by absorbing light of other wavelengths, so this kind of panel will not hinder the growth of vegetables and can give full play to the power generation capacity, which is planned to be commercialized within 2023.
To promote this application, technicians need to solve the issue of energy conversion efficiency and cost. For example, when it is used for highway, if the traffic volume is large, the power generation efficiency will decline, resulting in the reduction of the advantages of introducing solar power generation. The Nippon Road said that if the road with solar panels is built, the cost will be several times more than that of ordinary roads.
There may also be a need to modify the road law. The current law of Japan does not envisage embedding solar panels into the road. Relevant people in charge of the company said, “If the country clearly proposes the required specifications and standards of solar panels through the implementation of empirical experiments in the future, it may put forward the requirements for the revision of laws through industry groups, etc.”.
The Japanese government supports the introduction of solar power generation in various regions. At the review meeting held in November 2022, Japan’s Ministry of Land and Transport stated that it would publicly solicit highway solar power generation technology, and implement outdoor performance confirmation testing and subject review. The French and Dutch governments are also providing support for the installation of road integrated solar panels. Due to the devaluation of the yen and the energy crisis that followed Russia-Ukraine conflict, Japan’s electricity bills continue to rise.
The problem of massive solar panels being discarded has also raised concerns. According to SolarPower Europe, the world has installed 170 million kilowatts in 2021. Compared with wind and geothermal power generation, solar has a shorter period before being put into operation and can be easily introduced. However, with the increase of installation, the waste problem is becoming more and more serious.
According to the estimated data of Japan’s New Energy and Industrial Technology Development Organization (NEDO), the amount of solar panel waste in Japan will reach a peak around 2035 to 2037, about 170,000 to 280,000 tons per year, equivalent to 1.7% to 2.7% of the final disposal of industrial waste. At present, most of the panels are treated by landfill.
Countermeasures in this regard are becoming business opportunities. Mitsubishi Chemical’s subsidiary completed a factory in February that can process 90,000 solar panels and about 1,500 tons of solar panels per year. It is said that more than 99% of the resources can be reused, and it is expected to reduce 2,000 tons of carbon dioxide.
Europe has also strengthened restrictions on waste solar panels and managed the resource recovery rate through legal provisions. Japan also launched a discussion on the need for recycling under the leadership of the Ministry of Environment. The introduction of energy needs to consider the life cycle from cost, energy consumption, waste and other aspects.
