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There are many reasons solar powered robots are touted as alternatives to human-operated machinery. Solar robots can go into hazardous areas with minimal risk to human life. They can deal with bomb threats, chemical spills, and even surveillance in a dangerous region.
However solar robots have limitations affecting global adoption of the technology. Despite improvements in perovskite material, the majority of solar energy technology uses silicon photovoltaics and stubbornly remains at a maximum 25% efficiency. Until manufacturers can improve that efficiency, solar robots will not be widely adopted by industry and/or government.
The Limits of Solar Cells
Silicon is the leading material used for constructing solar panels and cells. Whilst there is no shortage of the silicon dioxide used to create the silicon photovoltaic cells – head down to the beach and grab some sand - it takes an enormous amount of heat to eliminate the oxygen attached to it. Manufacturers have to use an electrode arc furnace to heat silicon dioxide to the required temperatures of between 1500-2000 degrees Celsius. Viable perhaps, but the unfortunate side effect is a higher emission of greenhouse gases.
Perovskites have been widely touted as an alternative material to manufacture solar cells. With no silicon dioxide required, perovskites represent a clean method of solar cell production and can be made at a lower cost with fewer emissions. Perovskites are made using materials where organic molecules (primarily carbon and hydrogen) bind with a metal (such as lead) and halogen (such as chlorine) to form a 3-D crystal lattice. As perovskites can be mixed into liquid solutions, they can be deposited as thin films on the surface of almost any shape – making them perfect for use on robots. However, perovskite solar energy conversion efficiency is still only just above 20% - a full 5% lower than silicon photovoltaics can produce. There is also the question of perovskite durability. Concerns remain over how they can weather different environments or how to industrialize manufacturing to produce perovskites in the same quantities as silicon. Whilst perovskites represent a positive step in the right direction, their lower energy conversion efficiency means they are less likely to be widely adopted.
One overriding factor that always exposes the limits of solar powered robots lies in the environment itself. Climatic conditions always mean the energy conversion and storage remains at the mercy of solar exposure. For a robot to have a useful operating time, a battery is required to store solar energy when little may be available. Battery costs are high and most are big and bulky. Small-scale solar powered robots like drones and ground-based vehicles work incredibly well when there is plenty of sunlight but operating time drops significantly when little sunlight is available. Battery storage does work, but for robots to run for longer the battery needs to be bigger making a small scale robot unviable. To prove the limitation, one only needs to index the various amazon pages online where solar powered robots are targeted towards hobbyists rather than business or government.
Another limitation to solar powered robots can be found in the market dominance of silicon photovoltaics (PV). As it is the most widely adopted solar power, any new technologies being developed are complementing rather than replacing PV, making solar powered robots harder to scale down in size. As silicon PV works best on a large scale (eg. flat panels), building a solar powered robot with this method means the robot can only work in short bursts. Until the market for PV alternatives is there, this limitation will remain, and there are developments in the pipeline. The use of supercapacitors as an alternative storage method for robotics and small scale electronics could work. Connecting a capacitor to a solar engine has shown that the capacitor maintains the voltage at a nearly constant level. Unfortunately, this doesn’t work for applications that need more energy whilst retaining a light weight.
Solar powered robots do work, and the possibilities for what they could help us with in the future remain exciting. However, until global markets adopt alternatives to silicon photovoltaics, solar robots will likely remain as curiosities and experiments used mostly by enthusiasts and hobbyists.
Sources and Further Reading
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