February 15, 2017


Solar-powered trains are closer to reality than we might think (Leo Murray, 15 February 2017, The Guardian)

Solar giant Lightsource, for example, recently signed a 25 year power purchase agreement (PPA) with Belfast airport that underwrote a neighbouring £5m solar farm, using a private wire to supply a quarter of the airport's electricity needs. [...]

The UK's electrified rail routes have all of the features needed to support this kind of PPA-based renewable development, and more. Network Rail is the UK's single largest electricity consumer, with internal decarbonisation targets and a strong incentive to reduce operational energy costs. Alongside Transport for London (London's largest electricity consumer), these companies spend around £500m every year on traction power for their trains.

There are already over 5,500km of electrified tracks in the UK, with a major electrification programme building or converting hundreds more over the coming decades.

Early indications suggest it should be possible to connect virtually anywhere on the approximately one-third of this network that uses the direct current (DC) traction power system, unlocking access to thousands of potential new sites that have previously been out of bounds to new renewables.

What's more, the universe apparently wants this to happen: the standard operating voltage of the third and fourth rail DC routes is 630v-750v, while the standard output voltage of a solar PV array tends to be between 600v and 800v.

This serendipity makes the engineering challenge of connecting the two look very manageable, and the likely cost of the power interface equipment competitive with typical grid connection costs.

Conversion of renewable DC to grid alternating current (AC) results in something like 3% of the electricity being wasted, so supplying DC power direct to trains saves that loss too. Some of these DC routes already suffer from "under-powering", meaning train operators cannot add more passenger capacity to these routes because the grid cannot supply the extra electricity needed to power the trains. At scale, our innovation could solve this problem as well.

Posted by at February 15, 2017 6:06 AM