Investing in more efficient propulsion would seem to be a wiser investment than retrofitted after treatment even if the latter comes with a lower initial cost. The choice becomes less evident between diesel-hydraulic hybrid buses or diesel-electric, serial hybrid buses.
The blog has observed several times, most recently here, about the growth in serial hybrid public transport, so it was good to see someone else say the same thing… sorta.
Bruno Vanzieleghem on AutoBlog Green writes that hybrids are becoming the economical choice for commercial vehicles. One has to be careful with such a statement.
There are major manufacturers that offer hybrid buses. Their sales staff have been known to make what results have shown to be exaggerated mileage claims. So, even if hybrid bus sales are booming, fleet managers may want to be very careful. Diesel-electric, parallel hybrid buses — Big ICE, Little Electric — sometimes demonstrate even worse performance than those conventional diesel buses they replaced — not the kind of report that one likes to take to upper management.
On the other hand, Bruno also made an intriguing statement: “hydraulic energy storage is offered by some manufacturers as an alternative to electrical systems.” Whereas I knew that manufacturers had begun to offer diesel hydraulic serial hybrids for urban delivery and had delivered on the first diesel hdraulic school buses, I was unaware of any diesel-hydraulic, urban transit buses.
There are some that would argue that such a retrofit is the least expensive upgrade for the best ROI (Return On Investment). However, there so far would be seem to be insufficient data. Extrapolations, modeling, and laboratory testing have a place; yet independent, prospective studies can feature a certain validity that other conclusions may lack. There needs to be concurrent comparison made over a greater period of time to say with greater assurance that diesel hydraulic hybrids compare favorably with diesel-electric serial hybrids in terms of ROI over vehicle life cycle.
