So yesterday I was cycling again and I looked at the distant wind turbines and they were standing still etc. you know the story. It was pretty much exactly like Monday from the week before, except it was even sunnier and wind blew harder. Except one thing was different: this was a regular Tuesday, a work day, when demand is higher. Making it more baffling.
Germany had a low of -83.94 EUR/MWh. At peak that night, 11.17 EUR/MWh - which is also low. The Netherlands was at worst -8.5 EUR/MWh, which is not that bad. Belgium had -90.13 EUR/MWh, France at -8.44 EUR/MWh, Spain 5 EUR/MWh, Great Britain -7.2 GBP/MWh(about 8.18 EUR/MWh eq.), West Denmark at -0.09 EUR/MWh, Czechia 13.99 EUR/MWh, and Poland at 35.01 EUR/MWh. It doesn't seem that renewables penetrated the grid significantly there.
Update 2021-04-09: This day was featured as an example of negative day-ahead prices on page 11 in an annual report of transmission system operator Tennet.