The Ministry of Defence of the United Kingdom has just announced their plan to procure a number of British-built solar-powered reconnaissance drones called the Qinetiq Zephyr from a group now owned by Airbus.
What does this have to do with electric bikes?
Quite a bit, actually.
The Zephyr’s propellers are powered by a pair of brushless 450W electric motors which are quite similar to electric bike motors from an engineering standpoint, and they offer a nearly exact match of the nominal power output of electric bike motor systems from Bosch, Brose, Bafang, Yamaha, and Impulse. Since the Zephyr is designed to stay in the sky for up to two weeks at a time, charging its batteries from solar panels on its wings during the day and using battery power at night, the electric motors in the Zephyr have been designed with reliability in mind. Advances stemming from the research and development of the Zephyr’s motors could translate into big reliability increases for electric bike motors further down the line.
Lightweight, high energy density lithium batteries
The battery pack on the Zephyr is a 3,000Wh unit made from a lithium sulphur chemistry, which offers 2-4X the energy density of the lithium batteries that power today’s electric bikes. The pack was designed and built by Sion Power, a battery company in Tuscon, Arizona, and its partner Airbus, which handled much of the contracting for the Zephyr program. Considering that only military users and drone researchers are willing to pay for expensive high-energy density battery technology at the moment, lithium sulfur batteries are likely to stay in low-rate production for the time being. This could change soon, however. Lithium sulfur could just be the battery chemistry that comes to market and doubles the range of electric bikes within 5 years; Sony, which was the first company to commercialize the lithium-ion battery, has promised to bring lithium sulfur batteries to market by 2020. The catalysts for bringing the lithium sulfur batteries to market in 2020 are likely a combination of lower expected production costs, expiring patents related to the battery technology, as well as increased demand for lithium batteries from the automotive and home power markets. Lithium sulfur batteries will likely cost at least twice as much as today’s lithium cells, with a set of 13 18650-sized cells likely to cost at least $250 ($20/cell), whereas today’s lithium cells cost only $91 ($7/cell). As lithium sulfur cell production increases, though, prices will likely fall by at least 30% sometime by 2025, and even before the pricing of lithium sulfur batteries comes down, lithium sulfur batteries will already be competitive with today’s lithium cells because lithium sulfur cells offer more power per unit of volume and per unit of weight. This means that electric bike makers could offer slimline batteries with just 6 lithium sulfur cells that offer similar range to today’s electric bikes that carry 13 cells, and they could offer the slim packs at a similar cost, though it remains to be seen if the lithium sulfur batteries can offer the higher sustained amperage draw that would be necessary to reduce the number of cells in a pack. Once lithium sulfur cells are released, high-end electric bike makers like Stromer and Haibike might begin to offer extended-range lithium sulfur batteries with more than 100 miles of range at a cost of just over $1,000 per battery, which is approximately double the cost of an average replacement battery today. Lithium sulfur batteries could be a boon to high-end manufacturers that offer the extended range batteries, and later down the line, when lithium sulfur battery prices drop, they could lead to a surge in demand for electric bikes, as their extended range would make them more useful to riders with long commutes.
The Zephyr is build from carbon composite materials, which are somewhat similar to the carbon fiber frames used on carbon fiber electric bikes like the Daymak EC1 and the Easy Motion Neo Carbon. These composite materials offer lots of strength and with minimal weight, and the use of the material has allowed the Zephyr, which sports a 72-ft wingspan, to weigh in at just 117 lbs.
If similar materials were used more often in the construction of electric bikes, it could result in a decrease in frame weight of approximately 10 lbs. Considering that electric bikes weigh approximately 20 to 30 lbs more than their mountain bike counterparts, shaving off 10 lbs would help make electric bikes easier to carry up and down stairs, and might also provide a small increase in range.
Aerospace technology trickle-down
Aerospace technology, including the use of carbon fiber, has already trickled-down to the auto industry, which uses it extensively for the construction of BMW’s i3 electric car and Lamborghini’s Aventador supercar. Bicycles have also benefited quite a bit from aerospace technology, but the technologies shown in use on Qinetiq Zephyr are a clear indicator that there are big technological advances yet to come that will make their way from high-cost aerospace applications all the way to our little electric bikes here on the ground. If Sony and other battery makers can stick to their announced production schedule for lithium sulfur cells, and if carbon fiber electric bike frames come down in price and prove that they can reliably handle the extreme stresses of high-speed electric cycling, then we can look forward to seeing plenty of 40-lb, 100-mile electric bikes on the road just a few years from now.