Features: This solar Windmill Model operates without battery, automatically rotating when heated. Designed to be used with a solar film testing lamp, this solar Windmill effectively showcases the thermal penetration and insulation properties of different film materials, offering more intuitively understanding. The fan's rotation speed changes before and after applying the solar film, allowing customers to easily comprehends the product's heat insulation performances. Ideal for physics classes, science education, and energy knowledge teaching, this Desktop Wind Mill Model allows students to experience the fascinating process of thermal energy conversion. With its mechanical operations requiring none power sources or battery, this structure is suitable for children to operate and display. Specifications: Component: Solar Panel Base Size: about 10x7cm/3.94x2.76inch Package Includes: 1pc solar Windmill Model note: Please allow 1-2cm errors due to manual measurement, make sure that you do not mind before you order. Due to the difference between different monitors, the picture may not reflect the actual color of the item.