Just like how the Market Price Cap (MCP) sets the maximum price for a region and a commodity, there is also a price floor that sets the minimum price.
Unlike the market cap which changes every financial year in line with inflation, the market floor remains unchanged at -$1,000/MWh. As electricity supply and demand need to be at or near equilibrium at all times of operations, having a price floor that is negative (as opposed to $0/MWh) helps to create a disincentive for generation in times where there is over-supply.
The market price floor of -$1,000/MWh applies only for the energy commodity, FCAS commodities have a floor price of $0/MWh.