Posted: Fri Mar 21, 2008 1:27 pm
As you say, battery technology still has a long way to go before we can convert Jeremy Clarkson.
Here are some figures for my motorcycle that might help a little. All-up weight including me is around 200 kg.
I currently have a 1.68 kWh lead acid battery pack (5 x 12V/28 Ah), which weighs 47 kg. If I'm careful with the throttle I can actually get 1.20 kWh hours out of this pack, giving a range of 15 miles at 80 Wh/mile. That means a useful energy density of 25 Wh/kg for lead acid.
Lead acid will typically only deliver around 60% of its rated capacity at EV discharge rates. It's not the ideal chemistry for this application.
When prices come down I plan to switch to lithium ion, probably lithium iron phosphate. From all the reports I've read, including user experience, these cells should deliver the current I need with only a 10% reduction in nominal capacity. Nominal energy density is 80 Wh/kg, so a conservative estimate of useful energy density would be 70 Wh/kg. That means almost a threefold improvement over lead acid.
Lithium polymer cells are even lighter and have a nominal capacity of 100 Wh/kg and higher, but they can't yet handle high discharge rates and they require careful management.
Here are some figures for my motorcycle that might help a little. All-up weight including me is around 200 kg.
I currently have a 1.68 kWh lead acid battery pack (5 x 12V/28 Ah), which weighs 47 kg. If I'm careful with the throttle I can actually get 1.20 kWh hours out of this pack, giving a range of 15 miles at 80 Wh/mile. That means a useful energy density of 25 Wh/kg for lead acid.
Lead acid will typically only deliver around 60% of its rated capacity at EV discharge rates. It's not the ideal chemistry for this application.
When prices come down I plan to switch to lithium ion, probably lithium iron phosphate. From all the reports I've read, including user experience, these cells should deliver the current I need with only a 10% reduction in nominal capacity. Nominal energy density is 80 Wh/kg, so a conservative estimate of useful energy density would be 70 Wh/kg. That means almost a threefold improvement over lead acid.
Lithium polymer cells are even lighter and have a nominal capacity of 100 Wh/kg and higher, but they can't yet handle high discharge rates and they require careful management.