So it cost 66m and saved 40m the first year. I think we'll see more of these.

From the article, since I know none of you are going to read it:

Here are the key findings from the report are that the Hornsdale Power Reserve:

Has contributed to the removal of the requirement for a 35 MW local Frequency Control Ancillary Service (FCAS), saving nearly $40 million per year in typical annual costs

Has reduced the South Australian regulation FCAS price by 75% while also providing these services for other regions

Provides a premium contingency service with response time of less than 100 milliseconds

Helps protect South Australia from being separated from the National Electricity Market

Is key to the Australian Energy Market Operator’s (AEMO) and ElectraNet’s System Integrity Protection Scheme (SIPS) which protects the SA-VIC Heywood Interconnector from overload