[Reading Science] In Future Cities, Buildings Are Power Plants

Rapid Growth of Building-Integrated Photovoltaics (BIPV) Technology
Power Generation Using Windows with Transparent Thin-Film Solar Cells
The Future Smart City Managing BIPV with AI Is Coming

The Korea Institute of Science and Technology (KIST) developed a high-efficiency thin-film solar cell with light-transmitting capabilities in July of last year. The photo shows a building model made using this technology. Photo by KIST

[Asia Economy Reporter Kim Bong-su] Achieving the 2050 carbon neutrality (net zero) target to prevent climate change is an essential task for humanity. Among alternative energy sources replacing oil and coal, solar power generation is the most actively developed. However, in South Korea, where the population is dense, the land is limited, and most of the territory is mountainous, securing installation space poses a significant challenge. It has become a subject of controversy in many places due to issues such as destroying mountains, eliminating farmland amid anticipated food shortages, and becoming eyesores covered with bird droppings or dust. As an alternative, building-integrated photovoltaics (BIPV) technology has emerged.

The idea is to install lightweight, thin, and transparent solar panels on windows, walls, roofs, and rooftops to produce electricity used by the building itself. This method is much more advanced than the existing rooftop or balcony types. There is no need to install large-scale power generation and transmission facilities. It is attracting attention as next-generation energy technology for eco-friendly and smart cities. However, besides technical limitations such as securing efficiency and durability, challenges remain in price, construction convenience, and safety. In South Korea, research is actively underway, with the recent development of high-output and stable transparent solar cell technology and the construction of pilot houses.

Thin-film solar cell for windows developed by KIST for building-integrated photovoltaic technology.

Essential Item for Future Cities

Imagine future cities where humanity has overcome the climate crisis by finding alternative energy sources. These will be smart and eco-friendly cities where advanced ICT and artificial intelligence (AI) technologies have revolutionized transportation, environment, safety, housing, and welfare. These cities will be built with state-of-the-art buildings equipped with BIPV technology that produces and stores energy independently and is efficiently managed by AI optimization. There will no longer be a need to cover lakes, rice paddies, or forests with unsightly solar panels to secure solar power generation sites. This is a future that integrated solar power generation systems utilizing idle spaces such as building windows, walls, and soundproof walls throughout the city can create.

South Korea has already begun preparations. Since 2020, it has been legislated that public buildings must produce a certain portion (32% as of last year) of their annual energy consumption using new and renewable energy facilities when newly constructed. Private buildings are also pushing for mandatory certification to expand zero-energy buildings by 2030. By 2025, public buildings with a total floor area of 500㎡ or more and private buildings with 1000㎡ or more must adopt zero-energy building designs. By 2030, all public and private buildings with a total floor area of 500㎡ or more must obtain zero-energy certification to achieve greenhouse gas reduction targets.

Globally, the BIPV market is also growing rapidly. According to an R&D briefing report by the National Research Foundation of Korea (NRF), the global market research company Grand View Research estimated the global BIPV market size at $16.62 billion in 2021. It is expected to grow rapidly at an average annual rate of 20.5% from 2022 to 2030, reaching $88.38 billion by 2030. A report by Airzton projected that South Korea’s BIPV power generation market would grow from $110 million in 2020 at an average annual rate of 21.19%, reaching $360 million by 2026.

Thin-Film and Color Expression Technology Essential

To commercialize building-applied solar power generation technology, technologies that surpass the existing simple silicon solar cell modules must be developed. First, developing thin, lightweight, and high-efficiency thin-film solar cells that can be processed into curved or roof shapes and installed on walls or soundproof walls is urgent. Especially for use as windows, they must maintain high efficiency while allowing appropriate light transmission. Because they are used as building materials, technologies that allow color application are also required. Price competitiveness is essential. Currently, window-type and wall-type solar panels are priced at least 5 to 10 times higher than rooftop solar panels. Among building-integrated solar technologies, the highlight is the window type, which accounts for an average of 45% of the building area. The concept is to attach very thin, light-transmitting solar cells to glass for power generation.

The challenge is that it is a difficult technology that must catch two rabbits: power generation efficiency and light transmission. In this regard, in July last year, the Korea Institute of Science and Technology (KIST) attracted global attention with notable research results. The research team led by Jung Jeung-hyun, head of the KIST Next-Generation Solar Cell Research Center, and Dr. Yoo Hyung-geun developed a transparent solar cell using CIGS material that maintains high efficiency (23.4%) comparable to widely used crystalline silicon solar cells while securing transparency by applying transparent oxide electrode and silver (Ag) precursor technology. CIGS stands for Cu(InGa)Se2, a compound composed of four elements: copper, indium, gallium, and selenium.

Schematic diagram of KIST's luminescent thin-film solar cell.

Although CIGS compound solar cells had been developed previously, they had the disadvantage of being opaque due to the molybdenum metal back electrode. The research team applied a laser process capable of etching down to a few micrometers (㎛) to uniformly form fine patterns, removing the opaque thin-film material and enabling light transmission. They also used indium tin oxide (ITO) as the back electrode and applied a silver (Ag) precursor to reduce interfacial electrical resistance, securing high efficiency. Director Jung explained, "Window-type thin-film solar cells must achieve both transparency and electricity generation efficiency. If technology is secured to transmit about 50% of light and use about 50% for power generation, it will be possible," adding, "There are challenges ahead to improve power generation performance and laser etching capability."

The NRF report also pointed out, "To rapidly and massively disseminate solar energy, it is necessary to shift from existing silicon solar cells to thin-film solar cells that can be applied to buildings, automobiles, and everyday products," and emphasized, "It is essential to secure core technologies that can realize various colors based on low-cost solution processes."