Flights of Fancy, and why solar will fly

Humans are by their very nature explorers. For some, the greatest motivation is simply being told ‘it can’t be done’. Even when pioneers have proved it can be done, all too often they are met with the disclaimer that their achievement, however notable, is “simply not practical”.

In 1987, I joined Australian adventurer Hans Tholstrup on the first World Solar Challenge where 14 lightweight cars covered in solar cells raced across the continent’s 3000 km ‘outback’ from Darwin to Adelaide.

The $14 million General Motors Sunraycer won that event with an average speed of 67 km/h and fired more than just the imagination of engineers around the world. The GM effort generated an estimated $200 million in free publicity, and was up to that time, the most successful promotion in the company’s history.

“Inspiring,” said many observers, but cars covered in very expensive solar cells were simply “not practical”.

In the ninth World Solar Challenge held in 2014, however, the cars had advanced to the point where they were faster than the road speed limits and the rules were changed to encourage practical solar vehicles, which has resulted in a number of pre-production prototypes.

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As those cars were finishing their race, another group of explorer’s were preparing an even more ambitious voyage – to circumnavigate the world in an aircraft powered only by the sun.

The idea for the Solar Impulse 2 began after Bertrand Piccard completed the first ever round-the-world balloon flight in 1999 with Brian Jones. Although they started with 3.7 tonnes of propane, they arrived with just 40 kg, and the pilots realized their attempt could have failed for lack of fuel. Piccard promised himself to fly around the world again, but without using any fossil fuels.

“This was a big idea,” explained Piccard, and embraced by many people because the Solar Impulse was a very concrete way to demonstrate the power of renewable energy. “The excitement allowed us to raise the money from private companies and donations, but all aviation specialists told us this project was impossible”.

The team faced formidable hurdles, with no clear benchmarks. They had to start from scratch.

“To fly day and night powered by solar energy alone, and to accomplish a round-the-world tour without fuel, we knew that the plane would require a large wingspan to reduce drag, and a large surface of enough solar cells to produce the energy we need. These had to fit on an ultra-light structure to maximize our energy efficiency, which could then enable us to fly through the night on battery power”.

The team pushed the limits of many technologies and succeeded in developing an aircraft that is as elegant as it is breathtaking. The Solar Impulse has a wingspan wider than a Boeing 747 (72m), the weight of an empty family car (2,300 kg) and the average 24-hour power of a small motorbike (12 kW) fed by the electricity from 17,000 solar cells. When no aviation company could make the aircraft, the team turned to Decision One, a Swiss boat building company specializing in composite and carbon fibre constructions.

Solar Impulse 2 also has a number of practical spinoffs in energy efficiency, aerodynamic performance, and lightweight materials. Better insulation materials, for example, can be used in all homes and household appliances, and the improved motors for electric cars. The team has also progressed the use of advanced batteries.

“All these technologies are used in our daily lives for lifts, cars, boats, and airplanes,” says Piccard. The team’s aim is not to revolutionize the photovoltaic industry but to revolutionize the mindset of people about renewable and efficient energy. “Solar Impulse aims to show that clean energy combined with energy efficiency can allow us to accomplish things that were previously considered impossible,” he says.

Watching the swan-like grace of Solar Impulse as it lightly kissed the tarmac in Hawaii, it was clear to me that their team had completed a circle of technology started by the Wright Brothers.  In so doing, Solar Impulse has trumpeted the Age of Solar.

Sure it was beautiful, some will say, but it’s not practical.

Well, that depends. German company, has developed a single seat light aircraft powered by an electric motor and batteries. Integrating solar cells into the wings gives the aircraft a range of 1000 km. GE is also working on an electric hybrid for 200 seat aircraft, as well as Airbus, whose e-Fan two-seater prototype has just crossed the English Channel

And in my own case, I have developed and flown for 30 minutes at a time, an electric ultralight using an 18 kw brushless DC motor and 12 kilos of lithium polymer batteries charged off my rooftop solar array. As with many EVs, range is an issue and a deal breaker, but when the energy density of those batteries doubles, those issues will begin to evaporate for every EV.

Quite literally, it seems, now is Solar’s turn to fly…

Comments

2 responses to “Flights of Fancy, and why solar will fly”

  1. BroSheffieldBrotherton Avatar
    BroSheffieldBrotherton

    “On December 17, 1903, Orville Wright piloted the first powered airplane 20 feet above a wind-swept beach in North Carolina. The flight lasted 12 seconds and covered 120 feet.”

    Only dreamers could expect anything practical to ever come from that…..

  2. Pedro Avatar
    Pedro

    The future looks good for solar powered flight with increased cell efficiencies maybe up to 40% in the next 5 years and increasing energy density of batteries. It would be interesting to try filling unused voids with helium to give a little extra lift. Could have some excellent applications for companies such as nearmap

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