TAYLOR JOHNSON, SmallWindTips, December 16, 2009
I have been somewhat intrigued by the topic of wind power charging the electric cars of the future as of late. After reading through a number of blogs and different Q&A areas on the internet, I decided to take the question of feasibility into my own hands, so that I can calculate the outcome and offer you the facts.
The first production scale electric vehicle will be the Nissan Leaf, which will hold a charge of up to 24 kilowatt hours. According to Nissan, this 24 kilowatt hour battery can be changed fully in approximately 4-8 hours, and during a quick charge can be 80% charged in only 26 minutes. Wouldn’t that be great, or I guess I should say “won’t that be great” because it is already set for production. It seems that if I were to install a 1.5 kilowatt turbine on my house it should theoretically charge my car over night so it will be ready for me when I head off to work the next day. That’s what I thought too, but the calculations just don’t support it.
Let me first start out by explaining a kilowatt hour and how it differs from the 1.5 kilowatt output of our turbine. So, we have this 1.5 kilowatt turbine on our house, how much power is that really producing? Well, when wind speeds are ideal (usually around 12 mph) your wind turbine will be producing 1.5 kilowatt hours each and every hour, or at least until the wind dies down. As the wind dies down, the power output exponentially decreases until the wind reaches a low speed (generally around 4-6 mph). At this low wind speed no power production will occur, the wind just does not have enough energy to spin the blades on the home wind turbine. Since, the wind doesn’t always blow at 12 mph or higher, scientists have calculated averages for actual wind power production from a turbine. Now I won’t get into all the details, but 40% peak production is very good and we will use that for the calculations to follow.
So now that we know that we have a 1.5 kilowatt small wind turbine and we know that 40% annual power production is near the best we could ever hope for, we can calculate a best case scenario for power output. Simply multiply your turbine’s rated output by the number of hours in a year as well as the 40% annual production statistic.
1.5 x 8,760 x 0.40 = 5,256 kWh’s
This gives us a theoretical annual output of 5,256 kilowatt hours. Now from here, we go back to the car. The Nissan Leaf can store up to 24 kilowatt hours of energy and can travel approximately 100 miles per charge. Since we know that the average American travels 12,000 miles per year, we can accurately deduce that in order to drive the Nissan Leaf as we would like to, we will need to charge it a minimum of 120 times. So, since we are considering best case scenarios, let assume that every time your car is plugged in you will be producing energy at the constant 40%. If that were the case, the Nissan leaf would require 2,880 kilowatt hours (or 120 x 24 kilowatt hours) of energy per year, and that is very do-able.
Now this is where I see a lot of analysis stop. People simply assume that that should work and life should be peachy, however that isn’t the case. As mentioned above and further explained in Understanding the Basics of Windpower, a wind turbine can only produce it’s capacity (in this case 1.5 kilowatts) once each hour. So in the 4-8 hours of charging time for your Nissan Leaf, your 1.5 kilowatt turbine will only produce a maximum of 6-12 kilowatt hours, while the car requires 24 kilowatt hours. And just to emphasize the 6-12 kilowatt hours is a maximum, when output is full and the winds are howling.
I just want to close by saying that in no way am I saying small wind and residential wind systems are not the future of America’s energy policy, nor am I saying that they will not have a large part in powering the cars of tomorrow. I simply wanted to dispell any misconceptions concerning the feasibility of residential wind equipment charging the electric cars of tomorrow.