At the United States Naval Academy’s graduation last week, Vice President Kamala Harris stated, “Just ask any marine today: Would she rather carry 20 pounds of batteries or a rolled-up solar panel?” Indeed, batteries have become a major issue for dismounted soldiers and marines. With all the electronics required on the modern battlefield, the weight of the requisite batteries exceeds that of food or ammunition. And as Vice President Harris stated, green technologies, such as solar panels, have the potential to alleviate some of this burden.
Throughout the Global War on Terror, the US military has evaluated solar panels to allow soldiers to recharge their batteries in the field without a noisy generator. Between the radios, night vision, tablets, weapon scopes, thermal imagers, and array of specialized electronics — it is not uncommon for a soldier to need 15 to 20 lb of batteries for a standard 3-day mission. Additionally, as the battlefield becomes more complex, these squads are going to require more electronics, and hence more batteries.
The Army and Marine Corps procure these solar blankets from companies such as PowerFilm, Inc., which sells an assortment of blankets ranging from 60W to 220W. These thin-film silicon cells have an efficiency below five percent, meaning that it only converts a small amount of the sunlight that shines on it. By comparison, commercial solar cells typically achieve efficiencies around 20 percent, with newer solar cells achieving efficiencies up to 40 percent. Regardless, the thin-film silicon is lightweight, only weighing 6 lb for a 120W solar blanket. However, if soldiers want to use this power to recharge batteries, they require a charging dock and cables that can add 2-3 lb to the overall system weight.
If stationary on the ground for a full day under ideal conditions, the PowerFilm 120W solar blanket provides enough energy to recharge four BB2590 batteries, the standard battery in the radios and large electronic devices used by the US military. Each battery can power a radio for 12 hours or a counter-IED jammer for an hour. Given a standard mission length of 3 days, the 8 lb solar blanket system could offset up to 37 lb of batteries, resulting in a large weight saving. However, this value is highly idealized and decreases with latitude and time of year. In New York during wintertime, the same panel would only recharge one BB2590 battery in a day, due to the decreased the inclination angle with the sun. Moreover, on cloudy days, the panel may not be able to even recharge a single battery.
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But a larger issue comes from the operational implications of using solar blankets. The solar blanket must be deployed for multiple hours, in the middle of the day, in open areas. While there are some operational settings where this would make sense (e.g., an outpost on a mountain performing surveillance for multiple days), most mission sets require that when soldiers are stationary, they maintain cover and concealment. In doing so, they would not be able to deploy a solar blanket in an area that is optimal for sunlight. Moreover, the soldier’s position could be compromised from the glare or heat signature of the solar cells.
As such, the usage of solar blankets has been somewhat limited for this application, as have several other technologies evaluated by the Army and Marine Corps. One technology that showed initial promise was energy harvesting, which generates power through the kinetic motion of a soldier. However, these devices were bulky and did not provide substantial energy with operational usage. The Army and Marine Corps also evaluated wearable, high-efficiency, solar cells that can be attached to a rucksack or helmet. However, these devices only generated a small amount of power in operational use since they were seldom properly aligned with sunlight.
Another “green” technology that shows significant potential is hydrogen-based fuel cells. Ardica Technology has worked with the Army Combat Capabilities Development Command to develop a fuel cell that leverages hydrogen stored in an aluminum-hydride matrix, commonly referred to as alane. The fuel cell itself is only 1.5 lb, and a 0.3 lb cartridge provides the same amount of energy as a 2 lb battery. The major challenge with this technology is the manufacturing the alane, which was originally designed as rocket fuel. However, many different companies, labs, and government agencies are working to develop alane as a potential hydrogen storage mechanism for vehicles. If they are able to commercialize alane, 20 lb of batteries could be replaced with a 4.5 lb fuel cell system.
Electronics are critical on the modern battlefield; as such providing power to these electronics is also critical. While the Army and Marine Corps have traditionally leveraged batteries, advancements in “green” energy technologies from the commercial sector – including solar panels and hydrogen fuel cells – have the potential to lighten the load carried by the warfighter.