While the price of renewable power performs a task, mockingly the primary driver is fuel. The UK's power combine at any given time usually consists of ample renewable power, however some fuel continues to be typically required. The manner the market works is that mills bid to provide energy in half-hour blocks, with the most cost effective bid accepted first. But in the end all profitable bidders are paid the value of the costliest supply required to satisfy the demand.
With inputs from BBC