This document reviews different techniques for predicting solar irradiance levels including: 1) Numerical weather prediction models and statistical prediction for short to long term forecasting. 2) MOS (Model Output Statistics) techniques using sky cover products from weather centers for short term prediction. 3) Satellite-based methods comparing different approaches and error analysis for short term forecasting. 4) Signal analysis techniques including wavelet transforms and artificial neural networks combined with recurrent networks for improved prediction. Future work proposed includes combining these methods along with normalized data and forecasts from weather centers to improve prediction accuracy across timescales.