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a parametric approach for forecast reconciliation, in which homoscedastic Gaussian errors are assumed for a geographical hierarchy consisting of 318 simulated PV systems in California. We are pleased to present this special issue on grid integration, a collection of invited reviews and research articles in the area of Solar Resources & Meteorology—one of the four major subject areas of the Solar Energy journal. Since Solar Energy has been the home journal for many generations of solar scientists and engineers, and has a long history of publishing top-quality solar papers, readers can expect to enjoy the content of this special issue. Grid integration aims at delivering power from renewable energy sources through the grid in a reliable and stable manner. Particularly challenging is the multi-faceted and multi-disciplinary nature of the topic, which has attracted major attention from various scientific communities, such as solar engineering, power and energy systems, meteorology, or computer science. Clearly, without effective communication and constant interaction among these communities, it is hard to see any true progress. To that end, the overarching goal of this special issue is to share the state-of-the-art grid-integration-related research that is happening in various domains with researchers from other communities. According to a recent review by Yang et al. (2018), Solar Energy has published the most solar resource and forecasting papers to date. Since resource assessment and forecasting have become integral to utility operations as solar power generation penetrates power grids, it is natural to focus the special issue on this topic. Therefore, a total of five papers have been included in this topical area.