For all their calamitous outcomes, wars — and the military which wages them — have long been a source of radical new technological developments. Navies throughout history, for example, have been early adopters of new technologies and were the driving force in the transition from sail power to coal in the 19th century, and from oil to nuclear power in the post-war era.

But the military's adoption of new technology had its greatest and most enduring impact in 1912 when Winston Churchill, then the UK's First Lord of the Admirality, ordered the British Royal Navy to switch its fuel source from coal to oil in its new battleships. This was not only a defining moment in the history of warfare but it also led to the development of the oilfields of the Persian Gulf and the growth of the Anglo-Persain oil company, an antecedent of the modern-day BP, and put the world on a path towards growing oil dependency that has defined energy economics in recent decades.

Fast-forward 100 years and the military is again looking to switch energy sources in a shift away from hydrocarbon dependence and with a nod on renewables playing an increasingly important role. And, as with Churchill's decision, the move is likely to have repercussions well beyond the battlefield.

An Urgent Military Priority

The military has two main reasons to be interested in renewables, both of them compelling. The first is cost. According to figures from the US Defense Energy Support Center, the country's military spent about US$18 billion on fuel in 2008.

Added to that is the oil price, which while not yet at 2008 levels, has been creeping inexorably upwards to remain stubbornly above $100/barrel for the past few months. This puts an enormous strain on the US defence budget with every $10/barrel price increase translating into a massive $1.3 billion/year rise in spending.

But while cost is a key factor, an even greater imperative is the fact that the US military's insatiable need for hydrocarbons is having a negative impact on its ability to fight. Fuel supplies severely restrict battlefield mobility and fuel convoys themselves make relatively easy targets for insurgents, while tying up the key front-line troops that are necessary to protect them.

The problem was seen as so serious that in 2006, the top US military commander in western Iraq, Major General Richard Zilmer, urgently requested the Pentagon to send more renewable energy systems to the country to make use of solar and wind power to produce power for bases and outposts.

Zilmer's decision was seen as the opening shot in the push for a greater role of renewables in the military. And while the US involvement in Iraq is now winding down, the ongoing war in Afghanistan is proving an even sterner testing ground for renewable energy technologies.

Mainly this is due to a lack of infrastructure. Afghanistan has no national electricity grid and much of the country's power comes from diesel generators. This means that fuel often has to be transported long distances in convoys of trucks from Pakistan or flown in by plane. Both options are expensive and supply columns are often attacked, sometimes with devastating consequences. Indeed, fuel supply problems are often cited as one of the reasons for the defeat of Soviet forces in Afghanistan during the 1980s.

Moreover, the cost of providing energy in war zones is often calculated as a 'fully burdened' cost, which means not just the initial cost of buying fuel, but also the cost of transporting it to where it is needed. Per gallon estimates range anywhere from $20 to $1000.

Then there is the human cost. General Steve Anderson, a senior logistician in Iraq for the US military, estimates that more than 1000 Americans have been killed in Iraq and Afghanistan as a direct result of transporting fuel to power tents and buildings.

To combat this, renewable energy, particularly solar photovoltaics and solar water heating, are attractive options. The US Defense Department is evaluating mobile solar and wind generators to replace fuel trucks in combat zones, but its ambitions do not end there. In total, it has projects in various stages of development for hundreds of megawatts of renewable energy.

It has also backed several programmes to reach a renewable portfolio standard, according to a recent report: 'Reenergizing America's Defense' published by the Pew Project on National Security, Energy and Climate. The report describes efforts by the US military, which uses nearly 80 percent of the US government's energy consumption, to reduce dependence on fossil fuels and cut pollution by enhancing energy efficiency and using clean energy technologies. The goal is for the US military to produce 25 percent of its energy needs from renewable sources by 2025.

Order of the Day: Big Projects, Tough Targets

Solar is leading the charge. The US Army is developing a 500 MW solar power generation plant in Fort Irwin, California, that will help power the base and reduce its vulnerability to power supply disruptions as well as using solar shades with tents to better insulate them in an effort to reduce cooling costs. The army believes this could cut energy usage by up to 50 percent by lessening the need for air-conditioning.

Not to be outdone, the US Air Force is also keen to get in on the act. The Nellis Solar Power Plant near Las Vegas, Nevada is already operational. The plant covers a huge 57 hectare area of land leased from the US Air Force at the nearby Nellis Air Force Base, which is home to advanced fighter training. Operations began there in 2007 and it will eventually produce 25 percent of the power used at the base, which is currently more than 25 GWh/year. Its ground-mounted PV modules employ a sun-tracking system, with around 70,000 solar panels, and the peak power generation capacity of the plant is approximately 13 MW.

Even the famous Top Gun fighter school at Miramar, California has felt the need for solar and has installed solar technologies on base buildings, which has put the base on track to achieve a 43 percent reduction in energy usage by 2012, against a goal of a 90 percent reduction by 2017.

One of the largest operating PV installations in the US is located at Nellis Air Force Base (Source: USAF)

And solar energy is by no means restricted to American soil. Solar water heating has provided warm showers for American soldiers on active service in Afghanistan's Helmand province as part of a programme overseen by the US Department of Energy's National Renewable Energy Laboratories. NREL is also looking to utilise the potential of rooftop and brownfield options for photovoltaic arrays in the country.

The military is also looking at alternative fuels. The US Navy plans to use alternative sources to provide half of the total energy consumption of its ships, aircraft, tanks and other vehicles by 2020.

It also has plans for a 'green' carrier strike group that runs completely on alternative fuels by 2016. The US Navy introduced its first hybrid vessel last year, the USS Makin Island, which at low speeds runs on electricity rather than fossil fuel, and has also started experimenting with fuel made from algae on some of its vessels, the theory being that biofuels can be produced wherever raw materials are available, including within war zones.

The US Air Force has also set itself some tough renewables target and is aiming to acquire half of its domestic jet fuel requirements from alternate sources by 2016. To achieve this, it is currently developing some of the biggest biomass plants in the US, one at Florida's Eglin Air Force Base and another at Georgia's Robins Air Force Base. An F/A-18 Super Hornet fighter jet flew on biofuel in 2010 and, more recently, an F-15 Eagle fighter had its first biofuel test flight in Florida using a blend of Hydrotreated Renewable Jet, an eco-friendly alternative from sources including animal fats or plant extracts such as camelina, with traditional JP-8 jet fuel.

Another massive renewables operation is happening at one of the US Army's biggest camps, in reality a small town of 120,000 people, at Fort Benning in Georgia. The plan is to install two power stations to convert the facility's landfill gas into electricity. Fort Benning will be working with FlexEnergy using a technology known as Powerstation. Designed to be easily transported between different theatres of operations, the device also allows the harvesting of weakly-concentrated gases that could be missed by conventional approaches to landfill.

Solar Power Gives Infantry the Battlefield Edge

Not all the projects are large-scale. Some are designed to meet the needs of individual soldiers in theatre. Rechargeable batteries are important because they give soldiers the ability to power systems anywhere on the battlefield, and reduce the amount of money the army spends on replacement batteries. To achieve this, the US Army's Communications-Electronics Research, Development and Engineering Center's Army Power Division (CERDEC) has developed a solar kit that consists of a panel and different adapters that allows soldiers to recharge any military battery. A biological battery that uses sucrose as an electrolyte to power systems is also in development.

Last year, Sky Built Power, a company specialising in renewable and mobile power generation won a contract to provide the US military in Afghanistan with power units. The systems, known as SkyStations, can be mixed and matched according to requirements and include solar modules, a small wind turbine, a back up electricity system, water purification and communications capabilities. Another solar technology is the PowerShade, a larger solar tarp that fits over a standard Marine Corps tent, which can provide enough energy to power the tent's lighting system.

The technology is catching on with other militaries. The British Army is currently exploring the use of solar and other renewables to power forward military bases in battle areas such as Afghanistan, while the US Marine Corps has launched the '10x10' campaign aimed at reducing energy intensity, water consumption and increasing the use of renewable energy. The Israel Defense Forces are also looking to introduce hybrid models of jeeps and introduce green courses aimed at saving water supplies and boosting the use of renewables on the battlefield.

Innovation — The Most Potent Weapon of All

Because the military has moved into renewable energy so rapidly, much of the technology currently being used is commercially available or has been adapted for the battlefield from civilian models. But the military is starting to look at more innovative technologies, a move that could have enduring consequences beyond the battlefield.

One of the most unusual projects the military is looking at is a scheme to use temperature differences between warm surface waters and deep, cold water to generate power. The idea behind what is known as Ocean Thermal Energy Conversion (OTEC) technology is not new but the military has hired Lockheed Martin to develop it at a time when commercial development of the technology has stalled due to the relatively high cost of extraction and the relatively low levels of power produced. The military is optimistic that the technology can eventually be refined to work more efficiently - a gamble that a commercial operator would probably be unwilling or unable to contemplate. The military also favours OTEC because it could eventually guarantee a constant baseload power supply, unlike variable solar and wind.

Also receiving investment is solar-powered hydrogen production, both as a way of powering vehicles and to store energy generated from wind until there is demand for it. Solar powered hydrogen generation could also be used to power military bases in a bid to overcome issues associated with the reliability of wind and solar.

Both hydrogen energy storage and OTEC are expensive technologies that are not going to be used for large-scale power any time soon, but by investing in these technologies, the military may be performing a very useful service for clean energy.

Combating the Cyber-Threat

The US is also aware that a cyber-attack on its power facilities could severely damage its fighting ability. To combat this, the military is keen to roll out a system of micro-grid technology that will combine energy from existing diesel-powered generators alongside alternative and renewable energy sources. The idea is that renewables would keep military bases running in the aftermath of any cyber attack or natural disaster.

The project is known as the Smart Power Infrastructure Demonstration for Energy Reliability and Security, or Spiders, and will be tested at various bases in Hawaii over the next two years. The US state is also likely to be a testing ground for many new technologies owing to both its isolated location and expensive (often diesel generated) power as well as its status as home to the US Pacific Command. It is therefore a prime location for renewables and as it relies heavily on imported oil, power prices there are much higher than in the continental US. The military plans to cut its fossil energy use in Hawaii by about 70% by 2030 using a combination of renewable energy, biofuels and energy efficiency measures.

An Allied Effort

While the US military is at the forefront of the great renewables push, its allies are also playing an increasingly important role.

The Australian Navy is pioneering the use of CETO, a wave-powered electricity generation technology developed by Carnegie Wave Energy, which currently supplies energy to a defence communications station in Western Australia. CETO's underwater buoys are moved up an down by ocean swell which drives pumps and, in turn, pressurises seawater that is delivered ashore by a pipeline. Once onshore, the high-pressure seawater is used to drive hydro turbines and thus generating electricity.

Exmouth uses very low frequency radio transmissions to communicate with ships in the western Pacific and Indian Oceans. If the scheme is successful it will prove CETO's viability for the provision of power into a remote system.

In addition, Ocean Power Technologies (OPT) is building the first buoy-to-grid connection in the US, bringing wave power ashore at a Marine Corps base in Hawaii.

The company is also set to provide power for an anti-terrorism and maritime surveillance programme off the New Jersey coast. This will not be connected to the grid but the wave energy will power technologies including at-sea sensors and communications with the overall aim of a self-powered vessel detection system. Such a system could provide an early warning of any seaborne terrorist attack or drug smuggling at a low cost and requiring very little maintenance.

Traditional UK defence companies are also embracing renewables. Qinetiq and BAE systems are using their expertise in the military sphere to branch out into the wave and tidal energy sector. Qinetiq has also been working with Vestas to reduce the radar signature of wind turbines and their potential impact on military and civilian air traffic control systems.

This is a very real concern in the UK's crowded airspace were the radar signature of wind turbines often threatens to disrupt existing radar facilities.

British scientists are also working on a solar-powered drone for airplane manufacturer Boeing in partnership with Qinetiq. Engineers from Newcastle University will build the engine for the massive SolarEagle, which will have solar panels that its designers say will allow it to remain airborne for five years at a time. The SolarEagle will also have the biggest wingspan of any aerial vehicle in the world at 120 metres. Using solar will allow the plane to fly at an altitude of more than 60,000 feet (20,000 metres) where temperatures can be below minus 60oC, all the while providing valuable intelligence for ground forces.

The Newcastle University team previously collaborated with Qinetiq on Zephyr, an earlier drone that held the previous endurance record for unmanned aerial flight after two weeks in the air. SolarEagle's first test flight is scheduled for 2014.

What Are The Limits to Military Power?

The military is having less success in extending the use of renewables to civilian populations. The US Army National Guard has tried to bring renewable energy to Afghanistan for civilian use, with forays into wind and solar built by army units, the Afghan government, and NGOs. However, the results have been mixed and a lack of trained civilian personnel has lead to some projects being abandoned.

But the military is more accustomed than the commercial sector to dealing with setbacks. It also has the advantage of acting fast when it needs to without the need for lengthy debates.

Just as importantly, the military has the buying power to create products and markets. Solar and wind technologies have benefited from government subsidies and are already becoming much cheaper.

The main beneficiaries of the military's gung-ho approach to renewables are alternatives like OTEC which have a lot of potential but are not yet commercially viable.

By stepping in as an early adopter with immense purchasing power the military has the ability to make such technologies practical and affordable and therefore propel them into the mainstream.