September 12, 2015: Lake County, California. A fire starts and expands rapidly just north of the California wine country. It takes over 200 fire personnel and equipment to finally contain the fire. The aftermath: over 700 square kilometers burned. With over $1.5 billion USD in economic losses, this fire is one of the costliest and largest in U.S. history. Four civilians dead and four firefighters seriously injured. Every year, over 100,000 wildfires occur in the U.S. and they can double in size every five minutes. For wildfires, just as with any emergency situation, early detection and quick response are key to containment.
Solar Power To The Rescue
Although there are many tools currently available for early detection, it is hard to use these same tools in remote or very large areas where events like wildfires occur. Wildfires can be particularly difficult to predict because they can start anywhere at any time. However, if we could bring some of the tools currently available, like smoke sensors, and apply them to vast remote areas it could increase the likelihood of early detection. The biggest obstacle to deploying these tools is the ability to keep them powered. To power these tools, we need a power source that can last years with minimal to no maintenance. Batteries alone do not provide the answer and therefore we must turn to renewable energy sources. The most portable and reliable of these energy sources is solar.
What Is Solar Power
Solar power is a generic term for any material that takes incoming light and converts the light into usable energy. More technically, this material is known as being photovoltaic. In 1954, Bell Labs invented the first practical solar cell using silicon as the photovoltaic material. Silicon is still used in the majority of solar/photovoltaic cells and they are generally assembled into large panels on commercial and residential roof tops or are part of large installations on vast amounts of land. This ubiquitous solar technology generally supplements the electrical power grid. Traditional silicon-based solar is abundant and relatively inexpensive. However, it is bulky, heavy, and provides low to modest power output. In general, silicon-based solar is not practical to power remote tools, like the ones needed for early detection and quick response for emergency services.
A New Type Of Solar Power
To power devices like small remote sensors or unmanned aircraft we need a solar power source that is small, lightweight, and has high power output. One of the best photovoltaic materials on Earth is gallium arsenide (GaAs). In 1970, the first GaAs solar cell was developed by Zhores Alferov in Russia. GaAs has some significant advantages over other materials: it is naturally inert and resilient in most environments and it has a very high power density (more power for the same surface area). GaAs superior performance was immediately evident, but the material had a significant drawback: cost. GaAs was 200 times more expensive to produce than silicon. Additionally, its traditional form is also bulky and heavy, like silicon-based solar. There are methods to decrease the weight of traditional GaAs, but these methods only increase the end product cost. As a result, GaAs has been used almost exclusively in space over the last 45 years. Again, due to its high cost and weight, traditional GaAs is not practical for remote power. But what if there was a way to take all of the great advantages of GaAs and lose all of the disadvantages. Luckily, a solution like this already exists.
In the 1980s, renowned PhD physicist Eli Yablonovitch pioneered a technique to remove thin layers of GaAs from expensive GaAs wafers. By removing thin layers, the GaAs film retained all of the properties of traditional GaAs solar technologies, but the underlying wafer could be reused to save cost. The resulting films were extremely thin and flexible. Today, this process is known as epitaxial lift-off or ELO for short.
One of the companies currently taking advantage of the ELO process and manufacturing these thin film GaAs solar products is Alta Devices (co-founded by Yablonovitch) located in Sunnyvale, California. Gang He, Alta Devices CTO, gives his perspective about thin GaAs, “What makes this technology so special is that it combines the most efficient material for solar applications and puts it into a thin and lightweight form factor. This combination makes it ideally suited for a whole new class of applications that are not addressed by conventional solar technologies.” Thin film GaAs solar can add significant value to existing products by increasing product operability lifetime. Solar can be retrofitted to existing optical, infrared, gas, and smoke sensors. This means that thousands of units of early detection equipment could be placed within disaster prone areas and left unattended.
Combining New Solar Technology with New Tools
Thin film GaAs can also add value to new tools being developed for emergency services such as unmanned aircraft. In late 2014, NASA signed an agreement with the Department of the Interior’s U.S. Fish and Wildlife Service to test small unmanned aircraft for the detection of brush and forest fires. Although results of the tests have not been published to date, the State of Virginia’s Great Dismal Swamp Refuge manager Chris Lowie is hopeful, “…airborne unmanned platforms and their ability to offer a safer and more cost effective alternative for surveillance of potential areas of interest…as well as a reduction in time to detect nascent fires…could potentially save millions of dollars to the taxpayer…” The particular unmanned aircraft being developed uses both visual and infrared cameras to detect fires. However, current flight times are limited to an hour which limits both the range and usability of the aircraft. If this aircraft utilized thin film GaAs solar on its wings, it could potentially quadruple the range making it a better fit for the large areas of land where wildfires normally start.
Keeping Sensors Powered By The Sun
Another new technology that would benefit from the addition of thin film GaAs are wireless sensor networks (WSN). WSN are spatially distributed autonomous sensors that typically monitor environmental conditions. The individual sensors collect data and pass the information to a central hub where data from the sensor network is combined. This collective data is than used to create a depiction of the environment being monitored. The technology emphasizes low cost, power consumption, and promotes the use of solar to keep them powered. In other words, a network of sensors could be placed within fire prone areas to increase the chance for early detection. If the fire grows, the network will be able to track its movement through the collection of environmental conditions. Finally, combining WSN devices with thin film GaAs solar cells allows them to be left unattended for extremely long periods of time without maintenance.
Summary
Imagine if the emergency response team in Lake County, California had a network of remote firefighting tools at their disposal. Thousands of ground sensors capable of detecting environmental changes coupled with small unmanned aircraft patrolling the sky with optical and infrared cameras in search of flames. All enabled and powered by thin film GaAs solar cells. How much destruction could have been prevented through early detection and predictive fire mapping? While we cannot change the past, we are certainly entering an era where WSN and unmanned technologies are converging to provide emergency services with new tools to help fight remote events all powered and enabled thanks to thin film GaAs solar.
For more information, go to www.altadevices.com
About the Author
Rob joined the product marketing and engineering team at Alta Devices in January 2015. His primary role is integrating Alta’s solar technology into their customer’s final products. Prior to joining Alta Devices, Rob served in the U.S. Air Force as an engineer primarily analyzing the feasibility of various next gen defense systems. Rob holds a M.S. in Materials Engineering from the University of Dayton and B.S. in Aeronautical and Aerospace Engineering from Purdue University.
