## 7 The Case Study
### Primary Energy Sources  
Due to Saudi Arabia's abundant hydrocarbon resources, the mosque traditionally relies on the regional grid, powered primarily by fossil fuels such as natural gas and oil [102; 103]. While this energy source has proven reliable in meeting the mosque's energy demands, the use of fossil fuels contributes to greenhouse gas emissions, making this approach less sustainable. Saudi Arabia has therefore taken significant steps toward diversifying its energy sources through initiatives such as Vision 2030 [104; 105], which aims to reduce dependence on fossil fuels by increasing the use of renewable energy [106; 107; 108]. This strategy aligns with the country's commitment to sustainable development and has specific implications for energy-intensive sites such as the Al-Haram Mosque. Given the country's high solar irradiance levels, solar power is a primary focus of Saudi Arabia's renewable energy initiatives [104; 105; 106; 107; 108]. Solar panels have already been installed on surrounding buildings and facilities within the mosque complex [109]. However, due to space limitations and aesthetic considerations within the mosque's main areas, the large-scale deployment of solar panels remains challenging [110]. As a result, these solar installations primarily provide supplementary power to auxiliary buildings and nearby administrative offices rather than fully replacing the primary grid supply [110; 111; 112]. Considering the unique requirements of the Al-Haram Mosque, there is significant potential for developing self-powered systems that harness environmental energy sources and energy from pilgrims' movements. Emerging technologies being explored include piezoelectric energy harvesting, triboelectric nanogenerators (TENGs), and hybrid systems combining solar and kinetic energy harvesting. Piezoelectricity, the generation of electricity through mechanical stress--has gained attention for applications in crowded areas [99]. This technology involves embedding piezoelectric materials within the flooring to convert kinetic energy from footsteps into electrical energy [25; 26; 88; 97; 99]. A piezoelectric flooring system could thus be installed in high-traffic areas of the mosque, such as entrances, prayer halls, and passageways, allowing energy to be harvested from the movement of pilgrims. Recent studies [5; 26; 97; 99] indicate that piezoelectric systems could contribute to powering LED lighting or charging low-power devices, although they are unlikely to meet the mosque's extensive energy requirements entirely. Trials conducted in other high-traffic locations have demonstrated that piezoelectric technology can effectively provide supplementary power, particularly when combined with battery storage systems that capture energy during peak usage times [97]. Triboelectric nanogenerators (TENGs) represent another promising approach for creating self-powered systems [99; 62; 92]. TENGs generate electricity through contact electrification, which occurs when two different materials repeatedly come into contact and separate [41]. This technology could be integrated into carpets or mats to capture energy from pilgrims' footsteps, converting mechanical motion into electrical energy. Although TENGs are still at an experimental stage for large-scale applications, they have demonstrated potential in powering small sensors and low-energy lighting [30]. By deploying TENGs in designated walkways within the mosque, energy could be produced to power some low-energy applications. Moreover, the modular nature of TENGs allows them to be easily arranged and scaled according to specific requirements. Last, hybrid energy systems that combine solar power with kinetic energy harvesting might provide a more robust and reliable solution. For instance, integrating piezoelectric materials with solar panels could enable energy collection during both the day (solar energy) and night (foot traffic) [6; 15].