Data aggregation protocols play a crucial role in enabling real-time monitoring of the smart grid's operational status by the power control center. To ensure robust security, a data aggregation protocol should provide features such as data privacy, fault tolerance, lightweight computation, and fine-grained data aggregation. However, existing data aggregation protocols employing techniques such as homomorphic encryption, masking, or differential privacy fail to deliver these features concurrently. To address this challenge, we propose a novel lightweight privacy-preserving data aggregation scheme based on proxy reencryption and asymmetric scalar product-preserving encryption, in which encryption operations only involve addition and multiplication over the integer field, thus avoiding time-consuming exponentiation and pairing operations and achieving lightweight computation. Furthermore, through the use of an asymmetric scalar-product-preserving encryption scheme, we effectively align aggregation policies while maintaining the privacy of power consumption data. Finally, when compared to three recent data aggregation schemes with analogous structures, experimental results demonstrate that our proposed scheme outperforms others regarding computational and communication overheads, thus enhancing its efficiency.