This review emphasizes the critical need for accurate integration of solar energy into power grids. It meticulously examines the advancements in transformer models for solar forecasting, representing a confluence of renewable energy research and cutting-edge machine learning. It evaluates the effectiveness of various transformer architectures, including single, hybrid, and specialized models, across different forecasting horizons, from short to medium term. This review unveils substantial improvements in forecasting accuracy and computational efficiency, highlighting the models' proficiency in handling complex and diverse solar data. A key contribution is the emphasis on the crucial role of hyperparameters in refining model performance, balancing precision against computational demands. Importantly, the research also identifies critical challenges, such as the significant computational resources required and the need for expansive, high-quality datasets, which limit the broader application of these models. In response, this review advocates for future research directions focused on standardizing model configurations, venturing into longer-term forecasting, and fostering innovations to enhance computational economy. These proposed pathways aim to surmount current challenges, steering the domain towards more accurate, adaptable, and sustainable solar forecasting solutions that can contribute to achieving global renewable energy and climate objectives. This review not only maps the present landscape of transformer models in solar energy forecasting but also charts a trajectory for future advancements. It serves as a pivotal guide for researchers and practitioners, delineating the current advancements and future directions in navigating the complexities of solar data interpretation and forecasting, thereby significantly contributing to the development of reliable and efficient renewable energy systems. •Addressing the critical need for accurate forecasting of solar irradiance and photovoltaic generation.•Examining transformer advancements in solar forecasting, critical for integrating solar energy into power grids.•Analyzing model capabilities in diverse environments, highlighting their role in forecasting accuracy and deployment issues.•Identifying future research in model standardization and computational efficiency to improve solar forecasting.