How does the company pay zakat on materials it sells occasionally to some customers, knowing that its main business is installing generators and lighting and providing non-commercial services?

The materials purchased by the company for sale are considered trade goods, and Zakat (definition) is obligatory upon them. They should be valued and added to cash or other trade goods, and the Zakat should be paid in cash. However, if the contract includes the installation of generators along with the provision of materials, it is a manufacturing contract (Istisna'), and Zakat is not obligatory on the materials unless they are sold to craftsmen.