Quis Custodiet Ipsos Custodes: Bringing More Transparency to the ENTSO-E TP Data and Forecasts on Transmission System Operations

The ENTSO-E Transparency Platform (TP) is an ambitious data sharing platform to bring more visibility to transmission system operational data and forecasts. This information is important not just for transmission system operators, but also market players planning their operations in a grid-informed manner. This paper examines the quality of data and forecasts made available on this platform across four European bidding zones (BDZ): Belgium, the Netherlands, France, and GermanyLuxembourg. It reveals data gaps and instances of implausible values (e.g., exceeding installed capacity). Error metrics applied to available day-ahead forecasts also highlight significant performance differences among the BDZ for wind onshore, wind offshore, solar, and load, including outliers such as Dutch solar forecasts, which perform 36 times worse than a simple persistence model. These findings underscore the need for data verification and improved forecasting methods. To increase transparency and future improvements, we also introduce Transparency ++, a freely accessible dashboard that continuously tracks data quality and forecast accuracy in near real-time for several European BDZs.