Energy regulator Ofgem has fined two of the UK's biggest energy companies a total of £4.15 million for failing to meet energy efficiency targets.
Scottish Power will pay £2.4 million and SSE £1.75 million for failing to fulfil its obligations under the Government's Community Energy Savings Programme (CESP).
Under the scheme, energy firms were required to make customers' homes more energy efficient and thus lower carbon emissions by the end of December 2012.
However, Scottish Power only fulfilled 70% of its obligation by the deadline, leaving several thousands households to miss out on the energy efficiency measures in the cold winter of 2012/13. The company finally reached the target in April 2013.
SSE hit 90% of its obligations before the deadline and completed the rest by May 2013. The fines will go towards charities that will benefit vulnerable customers, Ofgem said.
Sarah Harrison, Ofgem's senior partner with responsibility for enforcement said: "Today's redress package sends a clear message to the energy industry that late delivery of obligations is unacceptable."
A third company, GDF Suez/IPM, was also fined £450,000 after it delivered 38.6% of its obligation on time but was also the quickest to make up its shortfall by March 2013.
Last week British Gas agreed to pay £11.1 million for missing the same targets.