I am fascinated by the Tesla roadster car. But some of the specifications don’t seem consistent.
Tesla claims 140 miles of range with “aggressive driving” and 220 miles using EPA city/highway estimates.
Their battery holds 53kWh of charge.
They claim 80% efficiency at peak power, and 90% average efficiency.
They claim maximum power of 185kW of power, or roughly 250 horsepower.
They claim $0.02 per mile for energy usage.
OK, so 53kWh of available energy times 80% worst case efficiency, I get a total of about 42.4kWh available to power the wheels. At 185kW of peak output, isn’t this only 13 minutes of driving before the battery is empty? This is a lot less than 140 miles of range. Am I calculating this correctly? Also, can a Lithium Ion battery really run at this rate (5C!)? I thought that the power tool industry did not like lithium batteries for precisely this reason: they could not provide high levels of discharge current.
Using the 90% efficiency figure, I have 47.7kWh of energy available to power the wheels. So if I drive 55 miles per hour, I should be able to drive 4 hours according to Tesla’s claim. This is an average of about 12 kW of continuous output, or 16 horsepower. I understand that the car is one of the more aerodynamic on the market, and I know that 16 horsepower may be enough to maintain speed. But what happens if I play my music loud or run my A/C or heater while on the freeway? Do I really get 220 miles? Is my calculation correct, will I only get about 16 horsepower of output before I wear out the battery assuming 55 miles per hour constant speed for 4 hours? Assuming that I will accelarate and decelerate routinely during the 4 hours (i.e., pass cars, etc),is 16 horsepower average output enough to drive with real-world creature comforts being powered inside the car? I am assuming zero charge from regenerative braking, since I am assuming that energy transfered will be very low relative to 53kWh battery.
As far as price, 2 cents per mile times 220 miles (?) is $4.40. So this means that a 53kWh recharge should cost me $4.40 according to Tesla. This is 8 cents a kWh. They say these calculations assume time of use meter and night time charging. If I drive 2200 miles per month at 55 miles per hour, using assumptions above I will need 530kWh of charge. Where I live, I get 240kWh of off-peak usage at 8 cents each before I go over my baseline in the Summer. Charging my car, alone would push me into the 4th tier at $0.27/kWh for night charging (weighted average of about $0.20). My day usage would also be billed partially at tier 4, so I’d end up spending about $150/month extra on my day electric bill in Summer, and I’d spend roughly $125 for the 2200 miles at night. This totals an extra $275 to charge my car for 2200 miles, or around $0.13/mile. My current car gets 27 miles to the gallon, or $0.15/mile. If gas goes to $3.50 a gallon, I end up paying $0.13/mile.
Lastly, the Telsa has a 70A charging kit. How do I get 70A through my 30A circuit breakers? Do I need to upgrade (and if so, where do I find 75A circuit breakers)? Is it safe to run 70A? At 70A, they say it needs 3.5 hours to fully charge. Assuming I use 25% of the battery’s charge, I should need under an hour to charge. The problem is that I don’t think I have 70A capability into any of my outlets, I believe I have 15A/30A breakers universally. This would mean that I would need over 2 hours to recoup the energy used to fuel my daily commute. This adds up to a lot of time spent “refueling” each week. I refuel my gas car every two weeks and it takes me under 10 minutes. I understand that the car charges at night just like my cell phone, but I REALLY don’t like the lack of ease towards getting my car refueled. Am I calculating these charge times correctly?