Electric vehicles are silently coming over the horizon to put petrol-powered four-wheelers to the sword. As they arrive in bigger and bigger numbers, a massive capacity of battery storage will be available to support the grid.
Australia is rich in resources to use to generate electricity to power EVs, so we’ll be better off than we have been relying on fuel, 90% of it imported. And road transport accounts for about 17% of CO2 emissions, so our air will also be less foul. So, there are many reasons why the electrification of transport is a good thing. But is it enough?
Researchers at the Digital Grid Futures Institute at the University of NSW think we can do better than plug-in EVs and in early February hosted a seminar to set out the possibilities for “vehicle-integrated photovoltaics”, or cars that have solar cells plastered all over them.
We’ve been seeing this stuff for years, of course, with PV-panelled rigs on skinny wheels racing up and down the outback to cross the line before sunset. But the dream of passenger vehicles powered by their own PV generation, with plug-in charging in reserve, is a real pursuit. One step further, however, is the ultimate challenge – a non-plug-in perpetually powered production vehicle.
The grid is changing, where a one-way traffic system of electrons is being replaced by “multiple directions of energy flow and information flow”, said UNSW Digital Grid Futures Institute director Professor Joe Dong. The energy and transportation systems are major contributors to global carbon emissions, and their transition to clean energy is a pivotal step towards pushing back the tide of global warming.
Electrified transport, destined to replace the petrol- or diesel-powered alternative, can serve a dynamic role as a source of stored energy. “The electric vehicle links the transport system to the electrical system … and EVs will be playing a critical role in the future.”
No-one’s sure exactly how and when owners will charge this huge fleet of plug-in EVs about to hit our roads, but we can at least expect a rise in overall electricity demand – and non-renewable generation. “People charge vehicles overnight, when there is no sun.”
The UNSW team’s efforts to design a solar-powered car for mainstream use – along with other developers thinking along the same lines around the world – will restrain drivers’ demand on the grid … so long as solar-powered cars actually work.
First few laps
Toyota moved early in the field of integrating PV into the shell of a car when it mounted stiff solar panels on a Prius, including its sides. The latest prototype of the Toyota is far more elegant, with PV moulded onto the roof and bonnet. In tests in Japan the vehicle is averaging 30km a day under its own power. That’s a great result in a country where 70% of daily car travel is less than 30km. “Most of us day-to-day don’t drive very far,” said UNSW associate professor Ned Ekins-Daukes. “People take long road trips on holidays but most of the time we’re making short trips.”
In last year’s Bridgestone World Solar Challenge UNSW’s latest Sunswift car, “Violet”, averaged 110km/h and managed a top speed of 140km/h. Loaded up with three passengers and a driver, all a minimum 80kg, the vehicle weighs 800kg.
Toyota’s PV-covered Prius can cover 17km/kWh, while “Violet” achieves 33km/kWh, said Ekins-Daukes (standing on the right in the main picture). The world record, set by Duke University, is more than 1,000km/kWh. “That shows us what is potentially possible with vehicle efficiency.”
An easy route to greater efficiency is to add more solar cells, but no-one wants an oversized car these days. Another route would be a pliable PV surface material, applied to bodywork not covered with solar cells. “Solar paint”, if it existed, could fit the bill.
Professor Martin Green, UNSW’s inhouse solar pioneer, is determined to unlock the mystery of how solar paint might work but first of all he set out the difficulty implicit in creating enormous singular cells. An area about five square metres painted to become a single solar cell would generate about 2,000 amps of current, he said, and require improbably large conductors. “Obviously a simple application of paint to structures is not going to work, because of the mismatch in generation characteristics of the cells,” said Green (standing on the left in the main picture). “It starts getting very complicated.”
One way around it might be to think about “scavenging” power from small areas, where a micro-electric up converter collects power from a small painted region and boosts it to a voltage that can be transmitted with smaller conductors. “It wouldn’t be too much of a stretch to imagine a sophisticated process for applying different layers of paint that were photovoltaically active,” he says. “That led to this concept of a solar-paint car whereby the whole car is essentially one big solar cell but the boosting of the voltage is done electronically by microelectronic chips.”
Under the sun
Cost-wise, rooftop PV clocks in at about 20 cents per watt at 20% efficiency, said Ekins-Daukes. At the extreme premium end, 3-5 multi-junction technology used in space applications and aircraft costs more than $100/w for efficiency up to 47%. Ekins-Daukes proposes an appropriate PV efficiency for solar-powered cars will be somewhere between standard rooftop and top-shelf space-age.
When the fuel comes from the sky, every solar-powered car’s performance will rely on how much time it spends under the sun. Vehicles parked in leafy boulevards, covered bays or underground car parks will be hardly as energetic as those parked out in the open. “The opportunity for putting photovoltaics on a vehicle means you don’t have to charge it very much at all if it’s sitting in the sun,” Ekins-Daukes said.
But how many cars do sit in the sun? Researchers at UNSW have developed a device that gathers irradiance data for cars and are collecting results from any motorists they can sign up, here and around the world.
Cars are more than utilitarian devices that deliver us from A to B, however. They signal freedom, adventure and status (if you buy into that whole thing). Governments may regulate the uptake of EVs, by setting targets for their replacement of all emitting alternatives as new vehicles – as is happening in Europe – but buyers’ and drivers’ anxiety about the time it takes to charge, and how that impacts their plans for the day, are yet to be tested. A car that carries its own energy generation plant could ease their concerns.
Research presented by Dutch research organization TNO program manager Bonna Newman, visiting from the Netherlands, showed a 750-watt solar-powered car can get by largely without plugging in to charge over the summer months, even in the cloudy Holland. “You can go from having 59 charging moments during the year [without PV on the roof] to 33 charging moments during the year [with PV], according to this simulation,” she said.
In sunny Madrid, the researchers found an EV can go from 62 charging moments in a year down to 20, with 750 watts of PV installed.
TNO is working with Dutch carmaker Lightyear, a spin-off of World Solar Challenge team University of Eindhoven, on a prototype for a car roof 90% covered with solar cells with 19% efficiency. “We should be able to get at least 1,000 watts on this vehicle,” Newman said.
The ultimate challenge, of course, is to produce a car that never needs charging and never stops. UNSW professor of practice Richard Hopkins hopes to apply all he learned as head of operations for the RedBull Formula 1 team to design and build the first non-plug-in perpetually powered production vehicle. “A lot of the technology is here and now,” Hopkins says. “Can we do it today? My answer is no. Will we be able to do it? Yes. How are we going to do it? We’re working on it.”
A car that relies on its own smarts to propel it along will be powered by a combination of sources. “It might be solar, it might be PV paint, it might be kinetic energy, induction charging, power sharing between vehicles,” Hopkins says, “and a whole lot that we don’t know about today, because we are living in a world that is innovating at a faster rate than ever before.”