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EV charging remains a great question for the burgeoning industry. Michigan's DTE Energy is the first to tackle developing a specialized bill scheme for EVs (Chevy Volt charger is pictured).  (Source: Car Fanatic Forum)
Customers can also opt for cheaper off-peak charging; may have to pay up to $2,500 for high-tech meter

The Tesla Roadster is already prowling the streets while the 2011 Chevy Volt and 2011 Nissan LEAF EV are preparing to launch later this year.  That's familiar news to most, but what might be a little more hazy is how the growing ranks of EVs are getting their power.

Amid all the EV excitement, charging has been one topic that has been decidedly undercovered -- largely due to lack of available information.  However, the Michigan Public Service Commission this week announced that it had approved the state's first experimental rate for residential customers to recharge their EVs.  

Utility DTE Energy Co.'s Detroit Edison unit filed the application.  By having a regimented payment infrastructure and usage monitoring, the utility will be able to better cope with demand and presumably provide customers with more competitive rates than if it left them on their own to install home charging stations and charge off their current connections.

DTE Energy is offering EV customers two options -- either pay a flat rate of $40 per vehicle per month, or sign up for a lower, variable off-peak rate.  The big expense will be the installation of a specialized meter circuit and charging station -- DTE Energy says that customers may be charged up to $2,500 for that.  It's unclear whether automaker-provided chargers will be compatible with DTE's system.

The trial program will run through December 31, 2012 and can cover up to 2,500 consumers.

For moderately heavy drivers (40-100 miles per day), assuming $40/week in gas expenses and the full charging station cost, it looks like customers will start to see savings in about 2 years.  While those savings have a long way to go towards justifying the large cost premiums on the Volt and Leaf, they're a start, at least.

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By Solandri on 8/12/2010 1:59:50 AM , Rating: 2
At $0.10 per kWh the Volt (on electric) costs about 2.2 cents per mile.

I see a lot of people making the error you just did. Charging a battery is not a 100% efficient process. In fact, the faster you want to charge a battery, the less efficient it is.

According to this site, the 240 V charger will send 32 Amps to the battery for 3 hours to charge it from a depleted state.

240 V * 32 A * 3 h = 23 kWh. The Volt's battery pack is only supposed to have 8.8 kWh usable capacity, so this is a charging efficiency of 38%. In other words, your electricity price is going to be about 5.8 cents per mile, not 2.2. That puts the break-even mileage at 250,000 miles.

The 120 V charger is supposed to operate at 12 Amps, and take 8 hours. That's 11.5 kWh, for a much better 77% charging efficiency. See? Slower charging = better efficiency. That yields 2.9 cents per mile, and a break-even mileage of 185,000 miles.

The LEAF and probably the Tesla vehicles suffer from this deficiency in particular. Due to their longer range, they have larger capacity batteries. That means to get charging efficiencies >70%, they need charging times on the order of 20+ hours. Not practical for a vehicle driven daily. To get around this problem, someone needs to design a switching unit in these battery packs to let you draw power from the individual cells in series, but charge them in parallel. Unfortunately, charging in parallel means duplicating the charging circuitry for each individual cell, increasing the cost of the charger.

By namechamps on 8/12/2010 8:36:56 AM , Rating: 2

While charging a battery isn't 100% efficient it is closer to 95%-98% efficient. Sometimes what is quoted is charge/discharge efficiency however we are only interested in charge efficiency because discharge efficiency is already included in miles per kwh rating.

Just because the charger is 32A peak doesn't mean it pulls 32 AMPS continually.

I mean come on man. Battery charge non-linearly. They have a high current flow when at a low charge. As charge builds the current flow slows. Near the end of the charge the output of the charger is a tiny fraction of peak power.

32% efficient batteries? If the battery is 32% efficient that means roughly 70% is converted into heat. 15 kWh of heat (50,000 BTU). Really? Thats more than the peak output of furnances in many smaller homes.

Maybe the reason you keep seeing people make the "error" of not including a 32% battery efficiency is because no such battery that crappy exists.

By othercents on 8/12/2010 4:20:06 PM , Rating: 2
The LEAF and probably the Tesla vehicles suffer from this deficiency in particular. Due to their longer range, they have larger capacity batteries. That means to get charging efficiencies >70%, they need charging times on the order of 20+ hours.

Buy two. Problem solved.

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