While the cost of renewables plays a part, the principal driver for this is, ironically, gas itself. The UK energy mix at any one moment usually includes plenty of renewables, but some gas is still frequently still needed. The way the market works, generators bid to supply power in half-hour blocks, with the cheapest bid accepted first. But all successful bidders end up being paid the price of the most expensive source needed to meet demand.
Source:
www.bbc.com
