Dual Battery System FTW
There are about 840,000 buses on the roads of the United States, and while they are a greener way to get around than individual cars (especially for commuting in urban areas - please people, if you live in the city, use transit), the vast majority of them are powered by non-renewable fossil fuels. Some use diesel-hybrid powertrains for better fuel economy and lower emissions, and others run on compressed natural gas to reduce smog-forming tailpipe emissions, but those are just partial solutions. Fully electric buses would be better, but current battery technology can make it difficult to get the right balance of power and range. That's the problem that GE is trying to solve with its dual battery system. Read on for more details.Lembit Salasoo, principal investigator on the FTA Hybrid Transit Bus project, writes on a GE blog:
Why a dual battery system, you ask? Many different battery types exist and most come with a trade-off between power and energy storage capacity. For example, lithium batteries deliver high power, but are less optimized to store large amounts of energy. Sodium batteries, however, can store lots of energy, but are less optimized to deliver high power.
Each type of battery, by itself, focuses on one of the two principal needs for electric vehicles - power and driving range. The beauty of our dual system is that it combines the two to address both needs in the most optimal way. A computerized energy management system splits up the vehicle's power needs between the two batteries with GE's proprietary technology. [...]
We believe our dual system could address the two principal challenges preventing the more widespread adoption of electric vehicles today - the size and cost of the battery. Unlike a single battery, you wouldn't have to over-size your single battery to compensate for more storage or power. Additionally, the dual battery can incorporate less expensive battery chemistries into your battery system. According to modeling studies we have done, these attributes could help reduce the cost of your battery by up to 20%. (source)
So basically, this is a bit like building an investment portfolio; instead of picking only bonds or only stocks, you mix the two to get something that gives you exactly what you need.
Not the most exciting video, but you can see the GE electric bus drive around a bit:
The current prototype has a top speed of 50 mph and a 60-80 mile range under idealized conditions. GE's target is 62 mph top speed and a real-life 100-mile range, which should be good enough for most urban driving conditions.
One of the things that I find promising about this dual battery system is that if only one of the types of batteries improves (say, there's a big breakthrough in sodium batteries), it can still be incorporated. If you have only one chemistry on board, you have to make a choice and can't take advantage of incremental improvements quite as quickly.
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