Uncategorized

# Charge for 5 minutes, drive 500 miles

This CNN article discusses a company that’s working on a new type of energy storage technology designed for electric cars. If it works as it’s supposed to, it will charge up in five minutes and provide enough energy to drive 500 miles on about \$9 worth of electricity.

Something about that doesn’t sit right with me, and after a bit of maths, I know why. Consider the following, and I will appreciate any advice necessary if I have somehow cocked up these equations.

• Electricity costs around 5.5 pence per kilowatt-hour (kwh) in the UK.
• \$9, at today’s exchange rate, is £4.75.
• £4.75 therefore buys us 86 kwh of electricity.
• The technology claims that it can suck up this amount of electricity during a five minute charge.
• 86 kwh in 5 minutes equates to 1,036 kwh in an hour, meaning that this technology requires a 1,036 kilowatt power supply.
• That’s just over 1 megawatt.
• At 240 volts (where, broadly, amps = watts divided by volts), a 1 megawatt supply requires 4,166 amps.
• 4,166 amps is roughly 70 times that provided to a normal domestic premesis, assuming a 60 amp UK domestic supply.

I’m preparing to wield the big “BOLLOCKS” rubber stamp, but before I do, let’s run those figures again assuming that everything’s in the US, so that differences in cost and specification of electricity supply between the USA and the UK aren’t affecting the judgement:

• Electricity costs around 4 cents per kilowatt-hour (kwh) in the USA.
• £9 therefore buys us 225 kwh of electricity.
• The technology claims that it can suck up this amount of electricity during a five minute charge.
• 225 kwh in 5 minutes equates to 2,700 kwh in an hour, meaning that this technology requires a 2,700 kilowatt power supply.
• That’s 2.7 megawatts.
• At 110 volts (where, broadly, amps = watts divided by volts), a 2.7 megawatt supply requires 24,545 amps.
• 24.545 amps is roughly 204 times that provided to a normal domestic premesis, assuming a 120 amp US domestic supply.

It’s REALLY bollocks then. *STAMP*