The key distinction between drones and other aircraft is their ability to fly and operate autonomously, hence the name unmanned aerial vehicles (UAV). With neither the risks nor limitations of having a human onboard, drones can reach higher altitudes and operate for extended periods of time, while controls are “manned”, or monitored, by remotes and computer systems on the ground. The combination of autonomy and advanced technology has allowed drones to take on a variety of functions, such as carrying and delivering goods, surveilling areas of land, collecting data and capturing images for both military and civilian missions (1).
Engineering a power source that can last for days/weeks and not burden the device with excessive weight is a constant challenge in aeronautics. Drones for civilian use are usually powered by removable battery packs that last for less than an hour before returning to the ground for replacement (2). Those used for extended surveillance and reconnaissance require much larger power sources to carry the weight of multi-rotors and actuators (i.e. cameras, weapons, radars, sensors), which in total can range from below 2kg and over 600kg (1). For high endurance missions lasting days or weeks, 80-90% of the gross weight is in fuel capacity and 10-20% of the weight in the actuators (1).
Solar-powered drones have proven to be a much more efficient source of energy for drones traveling long distances and over extended periods of time. The use of solar cells not only offers a constant stream of energy to operate the vehicle, but also greatly reduces the overall weight. AeroVironment, a leading energy and aeronautics company in California, designed some of the most groundbreaking solar-powered aircrafts—Solar Challenger, Pathfinder, and Pathfinder-Plus (3). Although these were manned aircrafts, AeroVironment also has a division for unmanned aircraft systems, which may foreseeably be integrated with their solar-energy initiatives.
Solar-powered drones still require research and experimentation before they can be fully implemented. However, the opportunities and benefits are clear and the industry has become increasingly competitive, with energy, aeronautic innovation, and even digital media companies involved. Solar Impulse is one company working towards clean energy aircrafts. Most recently, the company’s Solar Impulse 2 completed a 43,000 km flight on no fuel and solar energy alone. Bertrand Piccard, the 58-year-old seasoned pilot, told reporters, “We have shown that the plane could fly forever. The limit is the pilot.” (4) Facebook and Alphabet, Google’s parent company, are developing technologies in their projects known as Aquilas and Google Titan to deliver internet connection to any part of the world that still lacks access (5). These missions require devices to sustain itself at high altitudes, 18,000 to 27,000 meters above the ground, and adapt to unexpected weather conditions for a continuous 3 months; current tests remain far from the goal, as Aquila has flown up to 655 meters above ground and for a 96-minute period (6).
The vision for solar-powered drone technology has yet to be perfected and authorized under government regulation. As mentioned earlier, photovoltaic technology has proven to be sufficient for fueling aircrafts without interfering with the vehicles’ aerodynamics. However, the conditions for which drones are expected to experience include high pressure, extreme temperatures, and fluctuating weather conditions. With this in mind, researchers have identified that only 5 out of 20+ technologies (crystalline silicon (c-Si), gallium-arsenide (GaAs), amorphous silicon, copper-indium-gallium-selenide and thin gallium-arsenide based photovoltaics) can withstand the conditions described above (7). Furthermore, research around photovoltaic technology specifically for drones requires a different standard for measurements and data collection because the optimal solar panel for powering a drone is not necessarily the technology with the highest energy yield, but the highest power-to-mass and power-to-area ratios (PUAV) (7). Currently, solar-powered drone technology is somewhat dependent upon existing photovoltaic research, until more data can be collected and solar energy systems can be understood in collaboration with aerial vehicles.
Finding a balance between mass and power sources in drone technology is not the only challenge that innovators are faced with. Researchers and engineers are also racing against the clock as more competition enters the industry and increasing government regulation is put in place. The U.S. Federal Aviation Administration’s (FAA) UAS Rule (Part 107), due to take effect on August 29th, 2016, limits vehicles’ weight at 25kg and altitude at 121.92 meters off the ground unless approved under a certificate of waiver (8). Increasing government regulations may hinder the progress in solar-powered drone research, especially for purposes of testing high endurance and high altitude vehicles. On the other hand, as more companies and organizations occupy the aerial landscape, partnerships across sectors will rise. Facebook and Alphabet are just two of many companies that have found opportunities through such partnerships.
Incorporating solar energy with drone technology has shown benefits beyond providing clean energy. Solar-powered systems will allow vehicles to spend longer durations in the air and maintain constant surveillance, leading to greater data and accuracy of information collected. These aspects are appealing to industries that may not have had a part in drone technology before, like those in media or telecommunications. Although this new area of research may lead to some interferences from competitors and regulators, other businesses and governments can also offer great networks and opportunities for solar-powered drone technology.
(1) Gupta, S., Ghonge, M., Jawandhiya, P. M. “Review of Unmanned Aircraft System (UAS)” International Journal of Advanced Research in Computer Engineering & Technology (IJARCET), vol. 2, no. 4, 2014. Accessed on 5 Aug 2016.
(2) Pullen, John Patrick. “This Is How Drones Work.” TIME. TIME Inc., 3 Apr. 2015. Web. 1 Aug. 2016.
(3) AeroVironment. AeroVironment, Inc., 2016, www.avinc.com. Accessed 1 Aug. 2016.
(4) Burgess, Matt. “What’s next for Solar Impulse? Pilots reveal where their iconic plane is going to take them now.” WIRED. Condé Nast Publications, 27 July 2016. Web. 3 Aug. 2016.
(5) Cuthbertson, Anthony. “Google Tests Solar-Powered ‘5G’ Internet Drones” Newsweek. Newsweek LLC. 1 Feb. 2016. Web. 1 Aug. 2016.
(6) Vanian, Jonathan. “Facebook’s Solar-Powered Drone Just Hit a Big Milestone” Fortune. Time Inc. 21 July. 2016. Web. 1 Aug. 2016.
(7) Alta Devices. “White Paper: Selecting Solar Technology for Fixed Wing UAVs” 2015. pdf. 3 Aug. 2016.
(8) Small UAS Rule, Federal Aviation Administration § 107 (2016). Print.
Image: © Ivan Cholakov | Dreamstime.com - <a href="https://www.dreamstime.com/stock-photo-drone-over-us-city-surveillance-flying-image57023398#res14972580">Drone over US city</a>
The idea of using sunlight and radiant heat to source electrical and heating/cooling systems is no new phenomenon. Solar powered technology has been developing for decades, since the introduction of solar photovoltaics (PV), a medium of conductive materials (i.e. silicon, cadmium, gallium) designed to convert absorbed sunlight directly into electricity (1). Solar engineers later found that the alternate form of solar energy, radiant heat, could generate solar thermal electricity (STE) through concentrated solar power (CSP) technology. CSP structures are strategically placed to reflect and focus sunlight upon a “heat transfer fluid” (i.e. molten salt, synthetic oil), which then transfers the energy to an engine that produces electricity (1). Although solar technology has existed for several decades, solar engineers continue to make material, installation and distribution improvements on existing PV and CSP structures to stimulate and sustain growing demands for renewable solar technology.
Between solar PV and CSP technology, households and businesses prefer PV energy conversion systems because they are easier to install, show rapid returns on investment, and are compatible with existing policies/markets (1). CSP technology remains as a major source of renewable energy, but requires much more area and maintenance, making it most effective in arid climates.
At 2015 year-end, the worldwide capacity for solar PV was 227 gigawatts, approximately 185 million solar panels, while that of STE was 4.8 gigawatts (3). The U.S. alone increased capacity by more than 10 gigawatts in 2015 and totaled over 800,000 distributed PV systems installed (4). These trends were attained through technological advancement, as well as increasing dialogue around the subject of renewable energy in politics, businesses, and civil engineering. The past decade has shown rising numbers of operating solar energy systems in the U.S. and worldwide due to both scientific and systemic progress.
Material and Manufacturing Improvements
Solar CSP and PV systems are both constructed with large amounts of metal, where CSP structures have also shown a “high metal depletion burden”, “greater than for other power generators” (1). PV systems generate the most waste during the manufacturing process of using crystalline silicon to build PV modules (1). Developments in solar technology materials and manufacturing processes are foreseeable, as it is in solar technology companies’ best interest to find alternative materials and designs that will increase efficiency and durability.
Solar Energy Systems for the Long Haul
Solar power systems’ variability to sun exposure, based on geography, climate, and date, is a continuous challenge for engineers. To account for periods and locations that receive minimal to zero sunlight, solar power engineers have experimented with different materials and chemicals’ power load capacities, battery and storage technology, and transmission systems (1). A broader approach is a systemic change that places solar and wind energy on the power grid, alongside existing electricity grids that are primarily powered by coal and fossil fuels, also known as system value (SV) (5).
Progress in solar power technology has been driven by increasing awareness of climate change, initiatives to counter act global warming, and economic incentives through lower utility costs and public policy standards. Solar engineers are expected to meet the rising demands of government officials, consumers, and businesses by mid-century (5). Engineers and manufactures will be held responsible for increasing production in the coming years, while continuing to develop solar technology that will maximize energy efficiency, sustainability, and distribution.
(1) Hertwich, E.G., Alosisi de Larderel, J., Arvesen, A., Bayer, P., Bergesen, J., Bouman, E., Gilbon, T., Heath, G., Pena, C., Purhit, P., Ramirez, A., Suh, S. Green Energy Choices: The benefits, risks and trade-offs of low-carbon technologies for electricity production.
(2) “Renewables: About solar photovoltaics.” International Energy Agency. n.d. 14 Jun. 2016.
Renewable Energy Policy Network for the 21st Century. Renewables 2016: Global Status Report. REN21, 2016. 13 Jun 2016.
(3) Cantwell, Maria, Sen. Hearing on Near-Term Outlooks for Energy and Commodity Markets, U.S. Senate Committee on Energy & Natural Resources. 366 Dirksen Senate Office Building, Washington D.C. 19 Jan. 2016. Opening Statement. 13 Jun 2016.
(4) Mueller, Simon. Next Generation Wind and Solar Power, From cost to value. International Energy Agency and Clean Energy Ministerial, 2016. 14 Jun. 2016
Image: © Tangencial | Dreamstime.com - <a href="http://www.dreamstime.com/stock-photos-solar-thermal-power-plant-image23345363#res14972580">Solar thermal power plant</a>