On Sunday 24thMarch at 10.30am, the imbalance or ‘cash out’ price of electricity went negative for six and a half hours (i.e. 13 consecutive Settlement Periods of 30 mins each), reaching a maximum negative price of £70/MWh at around 2pm. 

If the cash-out price is negative, it means more electricity is being produced than is consumed (so energy users are paid to use more while producers are paid to produce less). This matters because a larger price spread, and negative prices especially, create opportunity for price speculators (arbitrage) in the energy market.