Passage: From 1951 to 1968, it worked every year except in 1961. 1953 was an especially difficult year due to a lack of water supply, which meant the Tejo Power Station had to work for almost the entire year, often overburdened in order to satisfy demand not only from its own distribution network but also to support the national grid. It was also during the 1960s that all the low pressure equipment was shut down and dismantled.

Question: What year did it not work?
1961