Adding opportunity charging to a Diesel Electric Serial Hybrid Electric Bus (HEB) is probably the best way to build a Nanobus (the acronym for this should probably be OCHEB, for Opportunity Charged Hybrid Electric Bus). These serial HEB buses, such as the Orion(Daimler)-BAE bus, the Mercedes hybrid, MAN, E-Traction and the ISE hybrid already have 99% of what is needed to make a Nanobus. They have electric drive, batteries, and a diesel generator that keeps the batteries charged. In fact in 2008, the Orion will use A123 batteries as their battery storage and ISE is working with Altair on using the NanoSafe in their hybid. Note that some hybrids are so-called "parallel" hybrids. These will not work, only "Serial" hybrids.

 All that is needed to transform a serial hybrid into a Nanobus, is the addition of rapid opportunity charging at one or both ends of the route,  a larger, say 35kwh battery pack, and different programming for maintaining the state of charge (SOC) of the batteries. Instead of the diesel running all the time, as with normal HEV buses, the bus would normally run on electric power alone from the opportunity chargers at one or both ends of the route. The diesel would only turn on in "exceptional" cases, such as when a charging opportunity is missed for schedule reasons, or it is a particularly hot or cold day.

The benefits of using a OCHEB hybrid over a pure battery powered bus, are:

1) You have a diesel backup when a charging opportunity is missed, for example during rush hour when the "make up" time at the route end has to be skipped because the bus was late getting to the end of the route. When this happens, the diesel goes on automatically, and has enough power to keep the batteries from discharging further, so the bus can continue to run the route, albeit on diesel-generated electricity rather than electricity from the grid. The bus can return to all electric operation as soon as the driver has a few minutes to rest and "opportunity charge" the batteries at the end of her route.

2) The diesel generator may also be used during very hot  or cold days when the air conditioning or heating demands are very high. It may not be possible to run the bus the entire route on these days just on battery power alone.

3) If needed, a OCHEB bus can go for long distances, using the diesel generator, such as when the bus needs to be delivered from the factory, or is sold to a new owner in a different city, or needs to go to a far-off depot.

OC should be very easily added by Orion, ISE, E-Traction and Mercedes and immediately transforms these buses from 100% petroleum consumers into potentially 90-100% grid electric consumers - a radical paradigm shift. All this with minimum design risk, and lots of potential profits since hybrid buses are already commanding premium prices!