Some 25 class 717 trains on the Great Northern service, which runs from Peterborough to King's Cross - via Huntingdon and St Neots - have on-board systems which recover more energy than previous generations of trains. This energy was otherwise lost in the heat from friction on the trains they replaced, with the feature returning half of this energy to help power the network. A total of 115 Siemens class 700s trains on the Thameslink service are also equipped with the technology. The energy returned to the network, 15.8 GWh, is the equivalent of almost two weeks of domestic energy consumption in one of the towns on the operator's network. The green improvements come as the rail operator releases its 2019 sustainability report, with other energy-cutting initiatives such as the upgrade of platform lights at all stations to LEDs, which cut energy use by up to 80 per cent, as well as new seasonal lighting controls to further reduce consumption. Some 33 retailers at stations also participate in the national 'Refill' campaign offering free tap water to passengers with reusable water bottles. Govia Thameslink Railway's head of environment, Jason Brooker said: "We are committed to operating a more sustainable railway by embracing initiatives to tackle energy and water consumption, manage resources more efficiently and reduce waste to ensure we lower our impact on the environment." With the upgraded fleet of trains now in operation,15.8 GWh of energy is returned to the network from regenerative braking, an extra 5.6 GWh every four weeks compared to 18 months ago. According to Govia Thameslink Railway, which runs the Great Northern service, this is enough to power domestic energy consumption in Cambridge for 11 days, or Peterborough for seven days.