This study proposes a framework for long-term electricity demand prediction based solely on historical consumption data.The method combines Non-negative Tensor Factorization (NTF) and a Genetic Algorithm to optimize the hyperparameters of time series models.Experiments using real-world electricity data from Japan show that the proposed method achieves lower mean squared error than baseline approaches.The framework offers an interpretable, flexible, and scalable approach to long-term electricity demand prediction.