Testing of a five-car Hitachi Class 802/0 tri-mode unit will begin in 2022, and the train could be in traffic the following year. It is expected the train will save more than 20% of fuel on Great Western Railway's London Paddington-Penzance route. The plan is for the '802' to use battery power in and out of stations, and through urban areas. Of the 305-mile route, only 53 miles as far as Newbury are electrified (17%).
Source: wiktionary