"Churn rate" (also known as the "churn factor") is used as a measure of liquidity. The concise description of the role of churn rate in the context of the European Internal Energy Market contains the ACER/CEER Annual Report on the Results of Monitoring the Internal Electricity and Natural Gas Markets in 2014, November 2015 (p. 198).
The said document elaborates on this issue in the following way:
"A frequently used indicator of liquidity is the churn rate (i.e. the number of times electricity generated in a market is subsequently traded). The churn rate is also calculated as the ratio between the volume of all trades in all timeframes executed in a given market and its total demand. In particular, ID liquidity can be expressed as the ratio between ID-traded volumes and demand."
Another way of defining a churn rate is the volumes traded through exchanges and brokers expressed as a multiple of physical consumption.
There is no consensus on the level of churn factor that indicates sufficient market liquidity.
A churn factor of three is considered to be a minimum value (ACER/CEER Annual Report on the Results of Monitoring the Internal Electricity Market in 2015, September 2016, p. 34).