The proliferation of Internet of Things (IoT) devices demands cryptographic algorithms that balance security with resource efficiency, especially as quantum computing development threatens classical cryptography. In this paper, we evaluate the energy consumption of post-quantum cryptographic (PQC) algorithms, with an emphasis on lightweight algorithms suitable for IoT environments. Given the critical nature of IoT systems, ensuring both security and minimal energy consumption is essential. We analyzed a selection of PQC algorithms standardized by NIST, comparing their energy performance with classical counterparts such as RSA and ECDH. Using a microcontroller, processes such as key generation, encryption, and decryption were measured. Special attention is paid to how different mathematical structures, such as lattice-based cryptography, influence energy usage. The results highlight the efficiency of lattice-based schemes, such as CRYSTALS-Kyber, in key encapsulation tasks, outperforming classical cryptographic methods in both speed and energy consumption. Our findings are useful for researchers working on the integration of PQC in energy-sensitive applications, such as IoT.