I don't know how the setup is on this thing, but the roof has 40m2 of suitable angle and at 150W/m2, this is only 6kW or 42 kWh a day in winter, up to 60 kW in summer per car.
A 80-100kW motor is likely more than enough to get it moving, but it will need to have its battery boosted on arrival to each station like the Newcastle tram.
The solar panels on the train itself are little more than show. They keep the auxiliary battery charged up. The majority of the energy actually comes from the grid at the depot where the railcar set is plugged in and the batteries charged overnight.
The depot roof is covered with solar panels and over a day produces enough electricity to cover what the charge cycle uses at night, but they don't store it at the depot, but push it into the electricity grid.
They are basically using the electricity grid as a giant battery. I believe at a later stage if funding is forthcoming, a battery bank will be installed at the depot so the power would be PV solar -> (depot)battery -> (railcar)battery
One of the 2 diesel engines has been replaced by an electric drive, leaving the other engine and transmission in place to allow the train to get back to the depot if it has an electrical problem or the batteries get critically low.
At the moment they can only claim it's a 'solar train' by accounting fiddle.
It's really a technology demonstrator test bed and not a commercially viable system on it's own, but as a technology demonstrator it's providing valuable data on possibilities.
Of course once the rail-trail people take over the railway alignment, they will fight any proposal for the railway to be reinstated in the future as they won't want to lose their nice level trail. While I like the idea of disused rail alignments becoming cycle touring paths, the cycle touring lobby then become vocal opposition to rail reopening and I'd rather a functioning railway than a touring cycle route.