Solar-Powered Trains

Tuesday February 09, 2016

Chase asked me why the MARC Train is not solar powered. I explained one line, the Penn Line, is electric and it gets power from many different sources, but the other two lines are diesel. He asked why we can’t put solar panels on top of the cars and use that for energy. It’s a straightforward energy budget calculation, so I decided to work it out. We’ll also make a series of simplifying assumptions, because, its my analysis and I said so.

Let’s walk through the easier case of a WMATA rail train. For a WMATA train, there is no separate locomotive. Each car is self-propelled, so we can figure out each car individually. The latest 7000-series cars are the most efficient cars WMATA has used to date. Each is 3.05 meters wide and 22.86 meters long. That’s a roof of 69.72300 square meters. At zenith, the sun lays down the most sunlight, and that’s 1050 watts per square meter. Assuming a perfectly efficient solar cell, that’s 73.2 kilowatts per car roof and that’s our budget per car. The best commercially available solar cells are only 20 percent efficient, but let’s be optimistic. According to Wikipedia’s page on the WMATA rolling stock, the 7000-series car requires 560 kilowatts to operate. Swing and a miss.

For comparison, the lowest power-MARC engine delivers 5.1 megawatts. One could panel the tracks themselves, similar to solar cells embedded in the road that are turning up in Europe. Panels at grade are possible, but above the tracks, above the catenary, would be better.

But it wouldn’t make a difference. MARC is getting rid of its electric locomotives and replacing them with diesel.

Image by Ryan Stavely / Flickr.