Around the world on zero fuel
To fly 35,000 km emission free, without a single drop of fuel.
Let that thought sink in for a moment.
One entire lap of the world, with only the Sun on your back for power. That’s the dream of Swiss aeronaut Bertrand Piccard, and engineer entrepreneur André Borschberg.
It’s a monumental task, but they are not alone.
Meet Solar Impulse 2. A single seat solar powered monoplane, as wide as a Boeing 747, as light as a car, and with the power of a small motorcycle. The 4 large propellers are each driven by a 17.4 horsepower electric motor, each fed by a 41 kWh lithium-ion battery, and topped up by 17,248 photovoltaic solar cells.
This solar-surfing plane can travel non-stop for long day-night trips across oceans and continents. Could this be the future of aviation?
Could solar technology be adapted for commercial flight?
Si2’s entire top surface area is covered by 17,248 solar PV cells. These mono-crystalline cells are the best available at present and can currently generate enough power for energy-neutral flight.
That means, the panels can generate just enough energy to power the motors, and recharge the batteries in time for night. Providing there is enough sunlight, as long as the days remain long, and the Sun keeps shining, the plane could theoretically carry its rather light 2300 kg weight indefinitely.
How do solar cells work?
A photovoltaic cell or Solar PV cell is a sandwich of silicon layers, specially treated to react to light; with more electrons on top (negative charge), and less on the bottom (positive charge). When photons of light strike the top surface, these extra electrons are knocked loose and are attracted to the positively charged side, generating an electric current – like potting balls in a game of pool. Think of the white cue ball as the photon of light and coloured balls as electrons.
Each thin layer of the solar cell sandwich increases the efficiency of the cell by increasing the range of the colours of light the cell can react to, and limiting the amount of light energy wasted, not unlike like having more balls on the table and bigger pockets.
The real issue of solar power is efficiency – at an average of 11 – 15% for commercially available panels there’s a big margin for improvement. Panels of up to 40% efficiency have been proven, however I wouldn’t hold out for these just yet as they are just far too expensive for mainstream manufacture at this time.
Sunlight is free though, so that 15% is still a gift and can easily provide power to domestic appliances on the go. Camping anyone?
The limitations of renewable energy
Sporting 72 meters of wing span; greater than a Boeing 747, covered entirely in solar PV cells, Solar Impulse 2 is capable of generating enough electrical energy to carry a single pilot, essential survival equipment and instrumentation. To store enough energy to continue through the night the plane also carries 633 kg of powerful lithium ion batteries which have to be charged fully each day and will almost completely discharge over-night.
To conserve power, speed and altitude are reduced after dark, there are no environmental controls, no heaters, and no cabin pressurisation.
And the plane can only land at night when the winds are low.
To put this into perspective, the medium-size Boeing 737 800 series passenger plane has a maximum take-off weight of just 75 tons. A rough calculation puts a 737’s engine power at around 20,000 to 36,000 horsepower. Compare this to the 70 horsepower that Si2 is capable of generating and it’s clear that for passenger flight we’re going to need an awful lot more solar cells.
Around 4,910,752 more panels. Roughly.
We need more efficient technology. .
From Inspiration to innovation – but not without its challenges
According to Piccard and Borschberg Solar Impulse is a demonstration of what can be achieved through renewable clean energy. A feat designed to inspire innovation and further advancement of clean technologies and renewable energy.
The reactions on social media have certainly proven inspirational, with the joy and anticipation peaking at every take-off and landing.
Originally planned to complete its journey in 2015, it was time to put theory to practice and the solar-powered circumnavigation attempt started in March 2015.
Departing from Abu-Dhabi, flying east towards India, China, and Japan, the plan was to continue across the Pacific, cross the US, Atlantic, Europe, and return to Abu-Dhabi in around 10 legs.
All was going to plan, however in June 2015 during the 8th leg between Japan and Hawaii the planes batteries were damaged due to overheating caused by the battery insulation, grounding the plane while new parts could be sourced and fitted.
This unfortunate delay so late in the season meant the plane had to be grounded until April 2016 when the necessary long hours of sunlight returned.
And return they did.
The USA stage of the journey was split into 6 flights and began anew on the 21st April 2016.
From bright ideas to energy saving paint
If there’s two things that Solar Impulse demonstrates very well, it’s that renewable energy sources do have a practical place in the world, and it only takes a bright idea to start something wonderful.
One such bright idea came in the form of the photovoltaic paint used by Mercedes Benz on their concept car “G Code”. This sleek, futuristic SUV sports a silver paint job which is capable of generating energy from light, just like a solar cell. Not only that, but it can harvest the electrostatic charge generated by air movement over the cars body.
A more down to earth design from Ford replaces the panoramic glass roof of the C-Max with a panel of enhanced solar cells capable of recharging the car in less time than you probably spend at the office thanks to Fresnel lenses on each solar pv cell.
Its limited electric range makes the C-max more suitable as a zero emission commuter however the conventional engine can take over when the electric runs out.
On Thursday 23rd June 2016, Seville, Spain felt the arrival of Si2 after leaving New York 70 hours earlier. This marks the last waypoint before Si2 sets off on leg 16 to Abu-Dhabi, completing the world’s first manned solar powered, round the world flight. The pursuit of green energy is once again open for business.
As an energy saving expert I am very interested in what the future holds for Solar power and LED’s.
How would solar power change your life? What would you be able to do with one of these?
Images: solarimpulse.com, wikipedia, Mercedes, Ford.