In an era of steeply rising energy costs and the approach of peak oil – the point after which global oil production will decline – industry is increasingly seeking lower-energy solutions to cut costs and minimise dependence on non-renewable sources.

The defence industry faces additional challenges. Far-reaching cuts in military spending have seen moves to reduce expenditure on consumable resources, so investments can still be made in essential modernisation programmes to retain the edge on the battlefield.

In addition, one of the greatest risks to life in the theatre of war is in the transport of the massive amount of fuel required across hostile territory. Cutting back the demand will have a direct effect on reducing wartime casualties.

Here we investigate a top ten of military technologies unveiled in recent years aimed towards reducing energy consumption as far as possible.

1. Lithium-air batteries

"Far-reaching cuts in military spending have seen moves to reduce expenditure on consumable resources."

With dismounted soldiers having to carry an increasing amount of sophisticated electronic equipment, the means of powering it can be heavy and bulky, so extensive research has been made into doing so more efficiently.

One development being investigated is the adoption of lithium-air batteries as the energy source of choice.

Lighter and more efficient than current standard issue batteries, researchers at the Massachusetts Institute of Technology (MIT), US, reportedly achieved an energy density of 2,500 watt hours per kilogram within a lithium-air battery in 2011.

This represents a significant improvement over the energy efficiency offered by batteries currently in service.

2. Solar Soldier project

Originally tasked with reducing the weight carried by dismounted warfighters, the Solar Soldier programme could also offer benefits in increasing the environmental efficiency of soldiers.

The programme involves photovoltaic and thermoelectric cells being stitched into a soldier’s clothing, with the cells placed in order to produce and store power as it generates it from the sun.

Backed by the UK Ministry of Defence (MOD) and the Engineering and Physical Sciences Research Council (EPSRC), the project aims to reduce the need for batteries as the electricity stored can be used to power soldier equipment.

In a similar project under the Australian Defence Force’s (ADF) soldier modernisation programme, soldiers are to be equipped with light-weight wearable solar panels based on SILVER solar cell technology to provide portable power.

3. Solar panels

Whether or not the Solar Soldier programme proves viable, the static use of photovoltaic cells at army bases hold potential. Forward operating bases need a large amount of energy to keep them air conditioned and recharge expended soldier batteries and are often situated in areas with long daily exposure to sunshine.

Earlier in 2011, the US Army announced that 160,000 solar panels were to be fitted on military installations in order to reduce their overall power consumption as part of the SolarStrong project at a cost of US$344m.

The push for solar panels is primarily aimed at reducing army consumption from the civilian grid in US-based locations, and the US Army is aiming to make 25% of its energy use from renewable sourced by 2025.

4. Water filtration and re-use systems

Alongside reducing the energy consumption of military installations, the US Army is also working towards improving the overall carbon footprint of army bases with the aim of reducing water demand by 75%.

Testing of a water filtration and re-use system that can be installed at military bases is currently being tested at the System Integration Laboratory at Fort Devens, Massachusetts, US. Once the technology has been proven to be effective, it will be shared with future expeditionary forces for implementation, reducing water consumption at military installations.

5. Organic LED night vision devices

The future of night-vision, now one of the staples of soldier equipment, may also be shaped through the adoption of energy-saving materials such as organic light-emitting diodes (LEDs), used alongside thin-film technology.

Funded by DARPA and developed at the University of Florida, US, ongoing research could see the vacuum tube commonly associated with night vision technology replaced with layers of organic, semi-conductor film materials.

The maximum power requirement is just five volts, allowing the device to be powered by a small battery and reducing the weight of equipment carried by dismounted soldiers.

6. Air conditioning

It was revealed earlier in 2011 that the US military spends US$20.2bn a year to provide air conditioning for bases in Iraq and Afghanistan.

"Introducting insulation and efficiency measures as well as increased use of solar power could save lives and money."

One method of reducing fuel consumption is the use of polyurethane foam insulation for tents in Iraq, which experiments show can cut energy use by 92%, in turn taking an estimated 11,000 fuel trucks off the road.

With the draw-down of troop numbers in Afghanistan, the running cost of infrastructure will decrease, but there will always be similar expenses in future theatres.

By recognising not just the expense but also the risk in running air conditioning, the introduction of insulation and efficiency measures as well as increased use of solar power could save lives as well as money.

7. Landfill methane

The US Army is furthering its use of sustainable power with the commissioning of a power system designed to capture methane from a landfill site and convert it into electricity at the Fort Benning garrison in Alabama, US.

The US$1m system was developed by FlexEnergy under a demonstration programme funded by the Department of Defense’s Environmental Security Technology Certification Programme.

The power station will turn venting gas from the landfill into enough renewable electricity to power the equivalent of 250 homes a year.

8. Decentralising heat plants

An evaluation by engineers of heat plants across the US Air Force found some of the 50-year-old centralised structures to be just 50% efficient, where modern condensing boilers can achieve 95% efficiency.

The Air Force has already decentralised ten of its heat plants and additional projects are underway. The investigation is part of the USAF obligation to meet the US government mandate, which requires all federal agencies to reduce energy consumption by 3% per fiscal year to 2015.

The study found that a US$14 million investment in plant improvements and repairs to the distribution system at one USAF base in Tennessee could improve efficiency at the base by 20% and reduce utility costs by US$920,000 a year.

9. US Navy biofuel programmes

The US Navy demonstrated its ‘Green Hornet,’ an F/A-18 Super Hornet powered by a 50/50 camelina biofuel blend, in April 2010, as an important step in the certification and ultimate operational use of biofuels by the Navy and Marine Corps.

Since then the navy has introduced a number of other programmes to use biofuel more widely. It used the same biofuel blend to power a Seahawk helicopter, an F-22 Raptor aircraft, a fly-past of F-15 Strike Eagle aircraft and most recently the first-ever unmanned flight using an MQ-8B Fire Scout.

The US Navy has committed to obtaining 25% of its energy from renewable sources by 2025. The fuel blend is expected to reduce CO2 output by 75% when compared to conventional aviation fuel.

10. Fuel cells to be installed at US military bases

"In comparison, fuel cells require less maintenance, cut noise and emit fewer pollutants."

The US Energy Department has announced it will install 18 fuel cell backup power systems at eight US military posts, as part of a partnership with the Department of Defence to boost energy security.

Diesel generators are currently used for backup power in military installations.

In comparison, fuel cells require less maintenance, cut noise and emit fewer pollutants.

The fuel cell project will cost the Energy Department US$6.6m. Though fuel cells cost more per unit to install than current alternatives, their operating costs are lower and they pose a lower risk to life due to the dangers involved in transporting conventional fuels.