The widespread adoption of electric vehicles (EVs) has accelerated the development of social internet-of-things vehicle-to-grid (sIoT-V2G) technology, yet it has simultaneously introduced significant privacy and security challenges. For instance, attackers may illegally access or tamper with sIoT-V2G transaction data, jeopardizing data integrity and disrupting grid operations. Furthermore, the interaction between EVs and the Smart Grid (SG) lacks robust authentication mechanisms, and the frequent occurrence of identity breaches exacerbates privacy risks. Existing authentication schemes predominantly rely on certificate authorities (CAs) or private key generators (PKGs), which lead to challenges in key escrow and certificate management. To address these issues, this paper proposes a privacy-preserving authentication scheme based on certificateless aggregate signatures. The certificateless mechanism eliminates the need for certificate management and key escrow, while the use of aggregate signature technology reduces the verification time for individual signatures. Additionally, ring signature techniques are employed to anonymize the sender’s identity, thereby achieving conditional privacy protection. Through these measures, the proposed scheme ensures high security while improving authentication efficiency. Experimental results validate the effectiveness of the proposed solution.