This is the fourth version of CSP.guru produced during the openCSP project and reflects the state of play in the middle of 2021. As requested by CSP.guru users, we include for the first time a Microsoft Excel ".xlsx" for quick analysis, but also retain the data-package for machine readability. This release has three new data fields: "Local_spelling", especially relevant for the Chinese plants, indicates the name in Mandarin or other alphabets. Second, we added two fields "hybridisation_capacity" and "Hybridisation_comment" to collect data on co-location of CSP plants with other power sources. Early plants often had a fossil fuel burner to increase the capacity factor, ISCC plants are integrated with a natural gas combined cycle, and modern CSP plants are often co-located or integrated with other renewable power sources, especially low-cost power generators from PV and wind. In terms of projects, in the first half of 2021 one plant, Cerro Dominador in Chile, went online. To that, we added three plants in China as under construction namely Supcon Delingha 135 MW Tower, Shouhang Yumen 100 MW Tower and the Shenzhen Jinfan Akesai - 50MW Trough. For an upcoming analysis we also added some additional pilot plants. Additionally, we updated some data entries as better sources were available, including for the Hami project. The location of Duba Green ISCC was updated and the status set to under construction, as it is not clear that the plant is operational. Finally, it is important to point out that the field "operational" means something different in China than in other countries. In China grid connection and first power production suffice to be eligible for the Feed-in-tariff, while in other contexts operational indicates the completion of the plant.