【New Energy Applications】Comprehensive Overview of Solar Highway Construction

II. The meaning of solar highways
1. Definition
A solar highway refers to a system in which solar photovoltaic power generation is achieved by utilizing the highway’s pavement, facilities along it, and the surrounding environment; this power is then used to supply electricity to both the highway infrastructure itself and the residents living along it. 2. Theoretical concept: The theoretical concept of a solar highway involves embedding solar cell arrays within the road surface of highways, and seeking new types of optical materials for use in constructing such road surfaces. This new type of pavement material (such as transparent ceramics and concentrating lenses) must not only meet the requirements for highway traffic, but also facilitate the transmission and focusing of sunlight, so that the solar photovoltaic arrays laid beneath it can receive solar radiation. In other words, the combined effect of the intermediate layer and the topmost layer should meet the design standards for highways, thereby ensuring traffic safety on them. III. A brief introduction to China’s solar energy resources. As is well known, solar energy is a green resource that is inexhaustible and unlimited in supply. It is estimated that the energy of solar radiation reaching the Earth’s surface per second amounts to 8.0×1013 kW, which is equivalent to the energy produced by the combustion of 5.5 million tons of standard coal. The solar energy received by China’s land surface each year is equivalent to 170 billion tons of standard coal. China is rich in solar energy resources; in over two-thirds of the country, the annual sunshine duration exceeds 2,000 hours. However, because solar energy is highly dispersed and the energy flux density is low, only about 1000 W of solar energy reaches the ground per square meter.

IV. International Development Trends 1. United States The United States was the first country to conduct research on solar highways. In 2006, a scientist couple from Idaho, USA, Scott Brushaw and Julie, first proposed the idea of using solar panels to replace traditional asphalt in order to build so-called “solar roads,” and they received research funding support from the U.S. Federal Highway Administration. In 2009, they received the first **grant** for building a prototype road with solar panels. In the spring of 2013, the Bruso couple launched a pilot project to build an outdoor parking lot using solar panels in Sandpoint, Idaho. Scott believes that the parking lot is an excellent testing ground for experimenting with LED lighting and power generation systems. The direction arrows and parking lines can be reconfigured to cope with peak parking times, and the electricity generated can supply power to nearby businesses. To this end, the local authorities **rewarded them with $750,000. At present, the biggest obstacle to promoting this type of solar road is the high level of investment required and the excessive costs involved. The U.S. Energy Department has allocated funds to companies working on the development of solar roads, with the aim of significantly reducing production costs and making solar highways a reality so that they can be put into use as soon as possible. 2. Italy: As the first country in the world to build highways, Italy is set to make another new innovation. The Catania-Syracuse A18 highway (a 30-kilometer section added to Sicily’s 600-kilometer highway network) will be a highway powered entirely by solar energy, and it will be the world’s first solar-powered highway. 3. Netherlands: The Netherlands is trying to install solar panels on ordinary roads. The Dutch Academy of Applied Sciences established a project team for the “Solar Road” initiative, and developed a new type of solar cell system that uses a focusing device to concentrate the sunlight absorbed by the road surface on a small, high-efficiency solar cell. Their solar-powered devices are set to be used for experimental road paving in a small town near Armstrong. According to researchers’ estimates, the solar roads they have installed can generate around 50 kilowatt-hours of electricity per square meter per year, while each household in the Netherlands consumes 3,500 kilowatt-hours of electricity per year. 4. United Kingdom: The world’s first national network of highway electric vehicle charging stations was put into use in the UK in September 2011. Such **solar charging stations have already been installed at 12 highway service areas, and free charging stations will be put into use at another 18 service areas. This move means that electric vehicles will be able to travel to anywhere in the UK for the first time. The charging station network was built by Ecotricity, an environmental energy company. The company’s founder said, “Statistics show that electric vehicles do not need to be charged while traveling in towns; it is on the intercity highways that charging is actually necessary.” ” 5. As reported in Germany on November 16, 2010, solar panels were installed on the A4 motorway in Aschaffenburg, Germany, making effective use of unused space; this is Germany’s most important solar power project. 16,000 solar panels have been installed in a highway tunnel in Germany, which will generate 2.8 megawatts of electricity. This project requires an investment of 11 million euros, and it will take 16 years to recoup that investment. 6. Switzerland: In 1989, Switzerland built the first solar-powered sound barrier system, which not only effectively reduces noise but also generates electricity from solar energy. Now, countries such as Germany, the UK, France, and Italy **have begun to trial solar sound barriers. 7. Belgium: The European company Enfinity installed a solar photovoltaic power generation system that is 2.1 miles (approximately 3.6 kilometers) long in an underground railway tunnel located alongside Highway 4 (HSL4) in Belgium. The system uses 16,000 solar panels, covering a total area of 50,000 square meters (about the size of 8 football fields), with a total cost of $21 million. The electricity generated by solar power is used for some railway infrastructure, including lighting and heating, as well as to supply half of the electricity needs of the nearby Antwerp Central Station. The annual power generation amounts to 3,300 megawatt-hours, sufficient to supply about 1,000 households, and it can reduce carbon dioxide emissions by 2,400 tons per year. 8. Australia: The Australian sustainable energy company GoingSolar integrates solar panels into the soundproof walls of highways. GoingSolar’s first highway project was carried out on the Tullamarine Calder Highway, where a solar panel sound barrier measuring 500 meters in length was installed. 9. Japan: In 2013, Saga Prefecture in Japan planned to issue permits to operators engaged in power generation using solar panels, allowing them to use free of charge the slopes of high-standard roads managed by the prefecture. The site for the power generation facility is the southern slope of the Ariake Sea Coast Road, spanning approximately 2 kilometers from near the Kubota interchange to the Fukushoegawa Bridge.

V. Domestic Overview In some areas of our country, solar power is already being used to supply electricity to certain outdoor devices in surveillance systems on highways. The devices that were powered up at first were only those with low power consumption, such as cameras and microwave detectors in the comprehensive monitoring system. Since last year, on the newly built section of the Shian District portion of the Beijing-Hong Kong-Macao Expressway expansion project – the Handan Southeast Ring Road (38 kilometers long) – all outdoor mechanical and electrical equipment is powered by solar energy, thereby achieving a cable-free design for this road section. This approach helps to realize the innovative goals set by the national and provincial transportation authorities, namely to create a technology demonstration road that is leading in China and among the best in the world. Currently, the construction of this project is in progress, and it is expected to be completed by May. Overall, no domestic department or organization has yet put forward any ideas or plans for creating solar highways, let alone conduct any research, exploration, or pilot projects. Nevertheless, some highway sections have already installed solar photovoltaic power generation systems using facilities along the route such as service areas, toll stations, tunnels, and sound barriers, to supply power for lighting and heating within these facilities, achieving significant economic benefits as well as energy-saving and environmental protection outcomes. The examples below are just a few of them. 1. Henan Province: In September 2011, a 60-watt-peak (Wp) solar photovoltaic power plant was built at the Anyang service area along the Beijing-Hong Kong-Macau Expressway; it is now connected to the grid for power generation. This power plant is the first solar photovoltaic power plant in the country. It generates 85,850 kilowatt-hours of electricity per year, which helps to save 780 tons of standard coal. It is expected to operate steadily for 25 years. 2. In January 2014, in Shaanxi Province, the 110-kilowatt photovoltaic power plant project located on the Chaitiaoling section of the \"Shi Tian Expressway\" in Xixiang County was completed and passed the grid connection acceptance tests. This project adopts a user-side grid-connected power generation approach, with an estimated annual power generation of 150,400 kWh. The electricity generated is primarily used for lighting and power supply in the Chatiaoling Tunnel, serving as an important part of the tunnel’s power infrastructure; it helps to save 150,000 yuan in costs each year. Over 25 years of operation, the power plant can save 1,466 tons of standard coal, reduce carbon dioxide emissions by 3,749 tons, and reduce sulfur dioxide emissions by 113 tons. 3. In Fujian Province, the Jinjiling Tunnel solar power generation system and the Minyue main highway station solar power generation system were built on the first phase of the Yongwu Expressway. 4. Sichuan Province: According to reports from May 2012, the first highway service station gas station powered by photovoltaic energy was built in Yanbian, Sichuan Province. This was the first highway service station gas station in that region to utilize solar photovoltaic systems for power generation. The project is located within the Panzhihua Service Area near the Xinjiu section of the Panxi Expressway. It consists of 164 solar photovoltaic panels that form a 30-kilowatt photovoltaic power generation system. The project mainly consists of a 20-kilowatt fixed microgrid system and a 10-kilowatt tracking microgrid system. With a total investment of 1.35 million yuan, the overall installed capacity amounts to 30 kilowatts. It is expected that the daily power consumption will range from 15 to 20 kilowatts; this electricity will be used entirely for production and lighting purposes at the gas station within the Panzhihua service area along the highway. 5. Others: Since 2011, some companies in China have also begun to work on the research, development, production, and promotion of solar sound barriers and solar parking canopies. One of the greatest advantages of solar energy is that it can be used almost anywhere, on any scale. Given that the sound insulation panels on both sides of the road are not being utilized fully, and considering that road sound barriers have large areas exposed to sunlight, installing photovoltaic modules on these sound barriers is undoubtedly an excellent option.

VI. On Cost and Benefits 1. Cost Estimation Since there are very few solar highways that have been built abroad, and many are still in the exploratory and experimental stages, it is difficult to provide accurate cost estimates. The author has only managed to gather some scattered data from abroad for reference. The Brusaw couple, who came up with the idea of “solar roads”, believe that the cost of solar roads is about three times that of constructing traditional roads. Generally, the cost of constructing the pavement for experimental solar highways abroad is about $500 per square meter. Based on this calculation, the cost of constructing one kilometer of roadway is $1.75 million. For a four-lane solar highway, the cost per kilometer amounts to $7 million; at current exchange rates, this is equivalent to approximately 44 million RMB. According to estimates by Commissioner Liu Hanyuan, at the current level of construction, the cost of building a photovoltaic power plant along each kilometer of roadway can be kept at around 2.3 million yuan. 2. Benefits: Since no complete, true solar highway or solar road has yet been built abroad, there are no exact figures regarding its benefits; most of the information available is based on estimates or assumptions, but it can still be used as a reference. As for the social benefits, they are widely recognized: environmental protection, sustainability, energy savings, safety, significant land conservation, and the ability to connect to the grid to supply electricity to residents. Regarding economic benefits, some points have already been mentioned in the previous introduction: how much electricity can be generated, how many tons of standard coal and petroleum can be saved, and how many tons of carbon dioxide emissions can be reduced…… ； Based on the current subsidies and desulfurization electricity prices, it can be calculated how many hundred million yuan in economic benefits can be generated each year. Below are some estimated figures for reference: 1) Abroad – A one-kilometer-long four-lane highway in the United States can generate enough electricity to power 300 households. -Seven solar-powered overpasses on Highway 101 in California, USA, have photovoltaic systems that can generate 15 megawatts of electricity. -The 18-kilometer-long, 30-kilometer-wide stretch in Italy will have solar photovoltaic installations along its length; these will meet 100% of the electricity needs of the 800,000 facilities located along it. The photovoltaic devices on the road surface generate 12 million kWh of electricity annually, which is equivalent to saving 310,000 tons of oil per year and reducing carbon dioxide emissions by 100,000 tons. -The solar roads installed in the Netherlands are capable of generating around 50 kilowatt-hours of electricity per square meter. Since each household in the Netherlands consumes 3,500 kilowatt-hours of electricity per year, 70 square meters of such solar roads can meet the electricity needs of one household. ………… 2) Domestic situation: Committee member Liu Hanyuan analyzed that by the end of 2012, China’s total highway length had reached 96,200 kilometers, with the total length of highway lanes across the country amounting to 424,600 kilometers. Based on 3.5 meters per lane, the space area for a single lane is approximately 3,500 square meters. If the actual installed capacity is calculated at 15 m2 per kilowatt, then the photovoltaic capacity per kilometer is 230 kilowatts. Meanwhile, the total area of lanes on all highways in the country amounts to 1.486 billion square meters. If solar photovoltaic power plants were built along these highways, the total installed capacity would be nearly 100 billion watts ； Even if only 50% of the highways meet the requirements for installing such facilities, the installed capacity could still reach 50 billion watts, which is far exceeding the country’s current total installed capacity. The annual electricity generation would amount to 49 billion kWh, accounting for about 9% of the country’s total annual consumption. Additionally, 19.53 million tons of standard coal could be saved each year, and 52 million tons of carbon dioxide emissions could be reduced. Based on the current subsidies and prices for electricity produced through desulfurization, this could generate an economic benefit of 45 billion yuan per year. By installing solar photovoltaic power plants on highways, each lane can generate approximately 250,000 yuan in revenue per year; in contrast, farmland of the same size per kilometer generates only around 2,000 yuan in income per year. Liu Hanyuan said that making full use of the areas along China’s highways, as well as their service areas and parking lots, to promote the construction of solar photovoltaic power plants can meet the electricity needs for communication facilities, video surveillance systems, and other services along those highways. “The physical structure of photovoltaic power plants can also provide shade and protection from rain on highways, preventing drivers from being dazzled by strong light. Meanwhile, preventive maintenance of highways is crucial for reducing maintenance costs and minimizing the risk of serious traffic accidents resulting from declining road conditions. ”

VII. Main Problems Existing As mentioned above, to implement solar highways, two key issues must be addressed: road surface structure and cost. 1. Exploration of road surface materials: As previously mentioned, the road surface of a solar highway consists of three layers, with the top layer being a transparent protective layer. This layer serves two purposes: one is to protect the internal solar photovoltaic modules, and at the same time it allows sunlight to pass through ； Secondly, it must allow for the normal passage of various loads on the road surface; in other words, it must meet all the requirements associated with being a road surface, such as hardness, roughness, and friction. It can be seen that the surface of a solar highway must not only meet the specified traffic requirements (such as sufficient strength, stability, durability, as well as smoothness and skid resistance), but also ensure that an adequate amount of solar radiation is received, thereby maintaining the conversion efficiency of the photovoltaic panels. Currently, scientists and technicians abroad are researching and searching for this special new type of optical material for road surfaces. It is reported that transparent ceramics, focusing lenses, or tempered glass are the most likely to meet the above requirements. Transparent ceramics are a type of optical ceramic that is as transparent as glass. Transparent ceramics possess high mechanical strength and hardness, as well as the ability to withstand very high temperatures; they do not soften, deform, or crystallize even at temperatures of 1,000 degrees. It has high electrical insulation properties and chemical stability. It is reported that after numerous experiments, the Brusso couple have successfully developed a type of glass with high hardness and a textured surface, to be used in solar panel-covered roads. This special glass is very different from traditional glass. Currently, some foreign institutions are researching and developing transparent ceramics and concentrator lenses suitable for use on solar highways. 2. High cost: The high cost of solar highways is one of the main factors affecting their development and widespread adoption. It is reported that the cost of the pavement for experimental solar highways abroad is around $500 per square meter. Based on this calculation, the cost of constructing one kilometer of roadway is $1.75 million. For a four-lane solar highway, the cost per kilometer amounts to $7 million; at current exchange rates, this is equivalent to approximately 44 million RMB. U.S. agencies have calculated that if all of the country’s roads could be converted into solar roads, while the U.S. energy sector might be able to break free from its dependence on oil, the cost of doing so would still be in the trillions of dollars, according to conservative estimates! Therefore, only by **reducing the cost of solar panels can the aforementioned plan be truly realized. According to Committee member Liu Hanyuan, at the current level of construction technology, the construction cost per kilometer of lane-mounted photovoltaic power stations can be kept around 2.3 million yuan. 3. Complex road surface maintenance: The road surface maintenance of solar highways involves two main issues: repairing damage to the road surface and regularly cleaning the light-transmitting surfaces (transparent ceramics or focusing lenses). Since the surface of solar highways consists of individual units, maintenance is relatively simple – only the damaged units need to be replaced. The regular cleaning of the light-transmitting surfaces is essential to maintaining the conversion efficiency of solar photovoltaic modules, with the specific methods varying depending on the circumstances. 4. Security issues Security issues fall into two main categories: damage (caused by human action or natural forces) and theft. Generally speaking, this problem exists in the outdoor facilities of highways; it is a common issue. It is believed that as the construction of socialist spiritual civilization in our country progresses and people’s quality continues to improve, coupled with effective supervision measures, such problems will be continuously resolved. In 2014, the **Energy Administration issued the \"Notice on Further Implementing Policies Related to Distributed Photovoltaic Power Generation\" (Guoneng Xinneng No. 406), encouraging the development of various forms of distributed photovoltaic power generation applications. The notice states that \"it is encouraged to promote the use of photovoltaic power generation in public facilities such as railway stations (including high-speed rail stations), highway service areas, airport terminals, large comprehensive transportation hubs, large sports venues, and parking lots,\" and that \"abandoned land, barren hills and slopes, agricultural greenhouses, tidal flats, fish ponds, lakes, etc. should be utilized according to local conditions to build distributed photovoltaic power plants for local energy consumption.\" It is evident that **distributed photovoltaic power generation is highly encouraged and supported, with many relevant policies and regulations introduced in recent years. It is believed that as technology continues to advance and more funding is invested in research and development, key technical challenges and materials issues will be gradually resolved, thereby reducing the construction costs of solar highways. It is expected that in the near future, the first solar highway will appear in China. The author suggests that the relevant authorities and organizations give high priority to this issue, organize relevant personnel to conduct research and planning, assess the feasibility of its implementation, carry out necessary pilot projects based on the existing conditions, and gradually promote it. References: 1. Liu Hanyuan: Utilizing domestic highways to build solar photovoltaic power stations, Sina Finance, March 3, 2013. 2. Ou Yinglei: The concept of using highways for solar photovoltaic power generation, Guangdong Science and Technology, August 2012: 218–219