The Problem
Trucks are the biggest CO2 emitters on the road. They account for 5% of the vehicles on the road but produce 20% of the transportation sector’s emissions.
The trucking industry consumed 54.3 billion gallons of fuel and spent $142.9 billion to buy that fuel in 2015.
One of the biggest operational costs for trucking is fuel. Eliminating even 1% of those fuel emissions a year would save the industry $1.43 billion dollars a year.
While many of the newer trucks on the road are far more fuel efficient with the latest and greatest aerodynamic and drive trains efficiency increases, most trucks are not as efficient. These are the trucks that use the most fuel and cost the most money to drive.
Solution
Putting a wind generator in a big rig’s airfoil will further increase the semi’s fuel savings and help save the industry billions in fuel costs over the years it is in use. When the driver applies the brakes the baffle on the airfoil opens up and the wind rushes through rapidly spinning the turbine. The turbine drives a generator to store the energy in batteries for later use by the driver at night or to help refrigerate the trailer en route.
For mountainous routes and routes with many traffic lights this system could significantly reduce fuel consumption. Assuming an average of 40 mph wind speed on a 16 square foot paddle wheel wind turbine blade surface for 30 minutes in a single day would generate 86 kw of instantaneous power and 43 kwh of energy.
Depending on the route and how much time is spent going downhill much more energy could be generated. If this energy were going directly to refrigerate the trailer is could refrigerate the trailer with far less diesel consumption due to diesel’s efficiency losses being converted to electricity for the trailer cooling system.
Unlike many other truck efficiency innovations the truck airfoil wind turbine does not rely a heavy investment to adopt a partially electric drivetrain for the cab or retrofitting a trailer the driver would be stuck with for every job. This is a small addition to the truck with large savings over time.
Why an Airfoil?
The key question was how can you increase a truck’s fuel efficiency without forcing the driver to commit to large upfront costs?
Aerodynamics are the obvious place people start when tackling this question. There are hundreds of innovations out there from trailer airtabs to cab airfoils themselves truckers invest in to save money.
We decided to focus on something most truck drivers are familiar with and buy— an airfoil. The sloped fiberglass on the top of some trucks that allow them to pass through the air more efficiently. We noticed many trucks still do not have this aerodynamic addition and most of those that do don’t have anything behind the airfoil.
Furthermore, when a truck is braking, the airfoil is playing for the wrong team helping increase wear and tear on the brake system. If we could make something that would detect when the truck was braking and convert some of that energy it would help save fuel costs for the driver because of the sheer inertia of a 30 ton big rig slowing down.
Tesla’s cars and Toyota’s Prius can convert this brake energy to recharge the batteries to extend the vehicle’s range. They can do this because of their electric motors which double as electric generators. To enable an existing diesel truck to do the same would be a massive undertaking since the back wheels would need to be retrofitted with electric motors, batteries, and the electronics to handle to massive power influx from the braking truck.
So what other way can we slow down the truck that wouldn’t cost the driver an arm and a leg? Open the airfoil and use the wind to help slow the truck and put a wind turbine there to generate electricity.
What to do with Electricity on a Truck?
Electricity on a truck isn’t really all that useful for moving the vehicle. It could be used to reduce the load on the alternator, but a more efficient use would be to simply store it so the driver can use it during the 14 hours he is not on the road.
An even better use for the power is to help cool a refrigerated trailer. Many trucks such as those that supply Safeway, Kroger, and most other grocery stores around the country do not use airfoil sleeper cabs. Every one of these tens of thousands of trucks on the road need to keep their haul cold.
Today these refrigeration cabs are powered by the truck’s diesel engine. Using the power from the airfoil wind turbine instead you can save more fuel. Diesel to electricity conversion is not nearly as efficient as a fully electric generation system, so while the wind produces less power than is stored in the generator’s diesel tank, the energy conversion from chemical to kinetic to electricity energy results in high efficiency losses. Wind’s kinetic to electric on other hand is far more efficient.
Design
So now we have decided making a wind turbine in a wind turbine airfoil how do we make it?
Starting with the wind turbine, most turbines you see are called horizontal wind turbines. They produce electricity from ambient wind and are able to generate power at wind speeds anywhere from 12 mph to 55 mph depending on the turbine. They are good getting energy from low to medium wind speeds but have a theoretical wind to motion rate of about 59% although in reality closer to 35–40%.
Not good enough for the truck. That means given an area of 24 square feet with two wind turbines they would produce about 51 kwh of energy and have more difficulty handling higher speeds such as the 80 miles per hour a truck is likely to be driving at.
On the other hand a paddle wheel design would be able to maximize the wind to power conversion since it can harvest the full force to spin the generator. The downside is that it uses half the airfoil surface area. If both sides of the turbine are exposed at the same time it will just shake rather than spin.
So that halves our surface area from 32 square feet to 16 square feet but allows us to increase our energy generated to 86 kwh over a day if we assume 1 hour of spinning at 40 mph during a 10 hour drive.
Great we are generating power, but generating 86 kw is a ton of power for a battery to store at one time so it needs to be buffered. The easiest way to do that is to take a page out of the electric car playbook and use a couple ultra capacitors. Ultra capacitors can be rapidly charged up and slowly discharged to charge the batteries.
The batteries would need to be a 12v 200 ah cell to store enough energy for the driver for the night to run the entertainment and HVAC systems while he is off the road all without using a drop of diesel. The system can alternate between cooling the refrigerated trailer and the charging the battery depending on the trailer’s temperature.
Now we need to figure out how the airfoil should open when the driver is braking or presses the button to open up the baffle. If the baffle is insecure the wind will violently shake the panel and damage it, but a smaller opening would significantly reduce energy production. We decided on a rail system for a reinforced cover panel that slides above the airfoil. This way it doesn’t encroach on the turbine’s area and we add a couple extra precious inches to the blade length.
So the driver hits the brakes and the motor on the airfoil pulls the panel back. Wind rushes in to spin the paddle wheel wind turbine which turns the electric generator. The power gets stored in ultra capacitors then goes to either help refrigerate the trailer or charge the battery for the driver at night.
The driver then releases the brake and the motor turns off and the springs snap the panel back over the opening in the airfoil bring it back to its aerodynamic form.
The airfoil and wind turbine generator cost to the driver would be about $2,500, just $500 more than a conventional airfoil. Furthermore it would pay for itself in the same amount of time as the conventional airfoil while reducing stress on the braking system and saving more money per day.
