Rush to energy harvesting for electric vehicles
Nov 08, 2011 Dr Peter Harrop
Those designing electric vehicles have much in common, whether they are hybrid or pure electric, on-road, off-road, on-water, underwater or in the sky. That is true for unmanned and manned vehicles. All of them have on-board power that limits performance, whether the usual battery or battery-supercapacitor pair or, more rarely, supercapacitors alone. It is not enough to wait for the promised reduction in battery manufacturing cost of two thirds in ten years from now or even the greater drop in battery price that may be caused by a price war before the end of the decade, triggered by over-supply. We need work rounds as well, including many forms of energy harvesting. The importance and emphasis on energy harvesting now makes it one of the key enabling technologies for electric vehicles in addition to the usual ones of batteries, electronics and motors.
Range extenders for hybrids, as they become more like pure electric vehicles, are also a new key enabling technology. However, the trend with these is for them to be the equivalent of an emergency can of fuel for the rare long journey of lack of a fast charging station at the right place when needed. In some models, the range extender has to provide extra power when stationary such as warming up frozen batteries and heating the vehicle and/or charging the battery at destination when the vehicle is stationary but providing a large amount of power to other devices such as utility tools or military equipment. Nevertheless this all adds up to the capacity and power delivery of the range extender being much less than that of the conventional engine that used to be in such a vehicle but range extender weight and cost need to be disproportionately less still so the range extender designers have a tough challenge.
Many things are being done to improve the situation so we do not hold up a whole industry because batteries are improving too slowly. Examples are more efficient motors, much lighter weight electrics and electronics through printing and more advanced structural composites. Energy harvesting is becoming available in many forms that do not steal from each other. For example, both asynchronous and synchronous traction motors easily provide regenerative braking returning typically 15% of forward kinetic energy during braking and flywheel-based versions based on the Formula One racing KERS Kinetic Energy Recovery System are now being trialled in family cars, both purely mechanical (tough to control but returning 20%) and via electrical storage. There are many trials of dampers (shock absorbers) capturing vertical kinetic energy from bumps in the road, 500W per car damper and 1000W per bus or truck damper being in sight with full energy-capturing active suspension to follow. Light and later outside and inside heat hitting the vehicle is captured by bendable solar cells but traditionally only over one square meter or so of roof resulting in a mere 100W peak or less. Next stage is more efficient and larger conformal silicon roof panels as recently demonstrated by Webasco for example, then translucent photovoltaics in windows gets added followed by transparent PV over windows, lights and body. Finally we shall get conformal photovoltaic skin over the whole vehicle including underneath because it will be broader band, harvesting infrared as well as light.
For hybrids, thermoelectric harvesting on the engines and exhaust pipe is being prepared for market but electric motors and batteries also get hot - though not a hot - which means that thermoelectric harvesting will eventually be prepared for these as well.
As always, we can glimpse the future in in military vehicles and Formula One cars. Autonomous Underwater Vehicles UAVs already come to the surface from time to time to garner light and wave power to charge their batteries and there is more to come. For example, Monterey Bay Aquarium Research Institute believes that the principle of energy harvesting dampers can also be deployed on and under the sea. Boeing is working on an Autonomous Aerial Vehicle AUV that can be deployed in the upper atmosphere for five years thanks to more advanced structural solar cells and other harvesting. Regenerative soaring, where the propeller goes backwards to charge the batteries, has been demonstrated by electric aircraft developers.
Very flat multiple batteries are increasingly used with energy harvesting to improve charge and discharge speed and cooling. This was first seen in solar aircraft but it is now appearing in electric racing cars. Call those structural batteries, a precursor of smart skin for vehicles with many layers of electrics and electronics including printed logic and power controls, which brings us to electric racing cars.
Lola Group and Drayson Racing Technologies DRT recently announced further detail on the groundbreaking Lola-Drayson B12/69EV all-electric prototype. The major partnership between Lola and Drayson to build an electric powered Le Mans Prototype LMP car was announced in July. The Lola Drayson all-electric sports car will be the fastest electric powered race car to lap a circuit. Showcasing technology such as inductive charging, composite battery power, moveable aerodynamics and electrical regenerative damping, the B12/69EV will be one of the most advanced zero emission competition cars to have run.
BAE Systems Advanced Technology Centre ATC will be developing 'multi-functional materials' for integration into the vehicle. These multi-functional materials combine the structural strength of composites with the ability to store electrical energy able to power onboard electronic devices and systems. BAE Systems is already leader in series powertrains for hybrid buses and very active in military electric vehicles. Research activity has already successfully demonstrated the ability to amalgamate standard battery chemistries with composites to create a "Structural Battery".
This novel and innovative multi-functional material is manufactured in the same way as normal composites and can be shaped into complex 3D structures. Unlike concepts that embed traditional batteries into structures, BAE Systems structural power capability uses patented technologies to incorporate the chemicals that batteries contain directly into composites. The integration of energy storage into structural elements also provides notable weight savings over traditional solutions.
Currently energy densities - the amount of energy stored per unit of weight - that have been demonstrated are comparable to existing traditional commercial vehicle batteries. Further development of the technology will continue to push the energy storage density available.
The exploitation of Structural Battery technologies within the defence environment can be used to reduce or remove the need for batteries across a wide range of applications. The material could be used in virtually anything that requires electrical power, from small electronic devices in a soldier's kit, to a complete vehicle. This will provide potentially significant benefits to military platforms and equipment, making them lighter in many instances and reducing the logistical footprint associated with supplying batteries to the frontline.
For the Lola Drayson B12/69EV, Structural Battery technology offers the opportunity to house power for some onboard electronic systems within the structure, allowing the main batteries to be dedicated to propelling the car. We are working in partnership with Lola's engineering teams to develop the manufacturing processes and techniques to scale the capability from existing laboratory demonstrators to meet the structural and power requirements for large scale applications.
For more attend Energy Harvesting USA, which also covers miniature energy harvesting technology for sensors and actuators that are becoming very widely deployed in vehicles. Indeed, Fiat sees photovoltaics around rear lights providing their energy as energy harvesting becomes fragmented and distributed around the vehicle rather than just charging the batteries. We are therefore seeing energy harvesting from milliwatts to kilowatts all being useful in vehicles.
Uniquely, the forthcoming "Energy Harvesting USA" will cover all these aspects from Ford, Volvo, Levant Power, Electric Truck, Electric Aircraft Corp and others covering harvesting that charges traction batteries and over 30 speakers dealing with harvested power for small sensors, actuators, lights and so on in vehicles and other locations.
Electric Vehicles Land Sea Air USA concentrates more on the vehicles and the place of harvesting in the fuller picture. A large number of electric vehicle manufacturers not seen in conventional EV events will present including WheelTug aircraft electrification, MotoVolta motorbikes, SolTrac farm tractors, Monterey Bay Aquarium Research Institute AUVs and manufacturers of industrial, commercial, military, e-bike, cars and other EVs.
Read "Energy Harvesting 2011-2021", Energy Harvesting for Electric Vehicles 2011-2021, Energy Harvesting and Storage for Electronic Devices 2010-2020 for more.