RCH: The Near-Perfect Transit Compromise
If you're a city planner or transit administrator, you may be trying to figure out how to not just keep your bus system operating on every tighter budgets, but also how to introduce new, cleaner, less carbon-dependent technology, which is expensive any way you look at it. Frankly, your options are pretty limited starting with cleaner diesel engines all the way up to all-electric trams, trolleys and light-rail: platinum-level solutions. Between this spectrum are buses running on natural gas, hybrids, and all-electric. These can be configured to run on dedicated lanes as part of Bus Rapid Transit systems, first pioneered in Curitibo, Brazil, which couldn't afford, like many cities the cost of rail-based systems.
While cleaner diesel, natural gas, and even hythane -- a blend of methane and hydrogen -- powered diesel buses are the least expensive option, they are still largely dependent on fossil fuels. Emissions are certainly far fewer compared to older technology, but the future price and availability will remain serious concerns for planners looking out over the next decade or longer.
Electrically-powered buses that use overhead lines to continuously provide electricity to run the vehicle have been around for well over half a century; and many are still in operation around the globe. However, the cost of upkeep, not to mention the new construction expense -- and unsightliness -- of these overhead wire systems makes them a problematic option to consider.
Now a Spanish company, Opbrid Transporte Sostensible S.L. has come up with what could be the perfect compromise for many cash-strapped cities: RCH or rapid charge hybrids. They have adapted a diesel-hybrid bus to operate autonomously using a fast-charging system they called Busbaar. As depicted in the accompanying video, the bus is equipped with lithium titanate batteries mounted on the roof. Also engineered into the vehicle is a pantograph that is used to rapid-charge the batteries, similar to those found on high-speed European trains. This can retract when not recharging the bus.
Also key to Opbrid's system is a +200kW charging station that can be installed at either or both ends of the buses route. Because the lithium titanate batteries -- in Opbrid's case, supplied by AltairNano -- can be rapidly recharged thousands of times with little battery degradation -- the bus can operate virtually all of its route without having to fire-up the onboard diesel generator, depending on terrain and driving conditions. The company estimates in a White Paper presented at EVS 24 that the bus should run 70-90% of the time in electric-only mode. Recharge time is just 5 minutes.
The key advantage of this approach over a all-electric bus is that the the pantograph model only requires about 20kWh of battery capacity compared to an estimated 360kWh, a significant savings in weight 200kg versus 3600kg, as well as cost: US$15,000 vs. US$270,00 at $750/kWh.
In terms of operating cost, Opbrid estimates that over a 10 km long route, typical in many European cities, for example, the bus would recharge 18 times a day, taking 20kWh per charge. That equates to 360kWh of electricity per day. In Europe the average cost of kilowatt is estimated at 0.15€. This means it would cost €54 a day ($75/day) in energy costs. A conventional diesel bus over the same route and getting 5 mpg would burn 36 gallons of diesel fuel at $4/gal. It's daily fuel cost would be US$144 or €103. Opbrid estimates the daily diesel fuel costs at €162 (US$225).
The company estimates that as many as six buses could share a single charging station over a one period with each bus allocated a 10-minute charging window. The cost of each station would be between €150,000-200,000. Assuming the operated would want a second charge station at the far end of the route, the per bus of pair of stations is about $92,000.
There is also the additional cost of eventually replacing the batteries about every two years, according to the White Paper, which estimates the prorated recharge cost at €6.60 or at 18 charges per day total of €120. Total combined costs for electricity and battery replacement works out to be €174. Although diesel could be €12 less expensive than the electric model on a daily energy cost, it ignores the environmental penalties of burning diesel, as well as the discomfort of riders and the driver, not to mention that the batteries may have secondary use applications as energy storage for the charging stations, providing local grid regulations services.
If you combine the concept of bus rapid transit and the Opbrid approach, you begin to have a system that not just clean, but also far more flexible than most of the more expensive alternatives.
blog comments powered by Disqus