The wholesale price of electricity in the United Kingdom tends to be expensive at 3 p.m. and
cheap at 3 a.m. because
a) Regulators require that prices vary that way.
b) The demand for electricity is high at 3 p.m. and low at 3 a.m.
c) The cost of running an oil-fueled generator is lower at 3 a.m. than at 3 p.m.
d) More producers participate in the auction at 3 p.m. compared to 3 a.m.