08 February 2015

Public Transport - Charging Ahead

Sustainable mobility innovations take a variety of forms (see my previous posts on hydrogen power, collaborative sharing, electric and hybrid powertrains, and even cycling).  And none of them are science fiction - it's all happening today, as a quick example, Tesla are installing their super-chargers in some Sainsbury's supermarkets.

Public transport is of course a critical part of any transportation system, and various technological solutions to improve their efficiency are being used.  This article will consider pure electric battery solutions, which have the following potential advantages over traditional powertrains:

  • No or minimal local/'tailpipe' pollution - ideal in cities, where air pollution legislation is becoming tougher (a recent bus strike in London highlighted the pollution levels correlated to congested traffic)
  • Few moving parts in the powertrain should result in lower maintenance costs
  • Predictable routes to/from a common place, e.g. a depot, minimise the amount of distributed charging infrastructure required
  • Charging batteries off-peak minimises carbon emissions from the electricity grid, e.g. shifting the peak from a traditional electric train which would use electricity whenever it is running, including at peak times

Below, pure electric powertrains are introduced for buses, trains, and even planes!

Battery-powered Bus

In London, there are six pure electric buses running.  Two are from Chinese manufacturer BYD (on the 507 and 521 routes respectively).  They have a range of 150 miles, and the batteries should last 4000 cycles.  The charging time is around 5 hours.

More recently, four electric buses from Optare have been introduced on the H98 route. They have a range of up to 100 miles, and take 5 hours to charge, or 2 if super-charged.

Optare MetroCity electric bus on H98 route (credit: TfL)

Internationally, BYD has continued to gain traction, with both 40 foot and 60 foot vehicles, using their iron-phosphate battery

BYD 60-foot bus

Last year, in Milton Keynes (50 miles North West of London), Arriva, in partnership with Arup-Mitsui JV, have launched a trial of electric buses which supports inductive charging.  This 'opportunity charging' means that the battery charge can be 'topped-up' during the working day, with it temporarily parked above charging plates built into the road.

The inductive charging used in Milton Keynes (credit: Arup)

Here's a video explaining a little bit more about the technology:

Battery-powered Train

Electric-powered trains have been around in the UK since 1883, using either electrified DC lines (the 'third rail', as of 2011, used on about 14% of track ), or overhead AC cabling (25% of lines, the balance being for diesel-powered trains).  As grid decarbonisation continues, electric trains will continue to have lower carbon emissions per passenger km than diesel, but it isn't always possible or cost-effective to install an electric supply infrastructure.  In these cases, Network Rail's prototype of a battery-powered train could provide a glimpse into the future of a solution.

Abellio Greater Anglia Class 379 unit (credit: Network Rail) 

Battery-powered planes

There are various approaches to reducing carbon emissions associated with flight, from use of biofuels, minimising taxi times, increasing angles of ascent and descent and enhanced air traffic control.  But even pure electric aeroplanes have been trialled - and they're a good idea, as the EC's FlightPath 2050 target is for a 75% reduction of aircraft emissions from a baseline year of 2000.  Here's a video outlining the prototype E-Fan from Airbus:

So, with battery performance continuing to improve, the attractiveness of off-peak charging (especially as the grid decarbonises) , there is likely to be an increased proliferation of batteries in public transport.