Tuesday, August 20, 2013

Reducing Military Fuel Use with Solar Power

The US military have tried a number of energy saving programs, under the DoD Facility Energy Strategy. These are for energy reduction and alternate energy production schemes on fixed military bases. There are also deployable systems such as one from Lockheed Martin for the US Air Force Basic Expeditionary Airfield Resources (BEAR) program, which fits in three standard shipping containers. There is a trade-off between the portability of a power system and its cost: at one extreme the power system can be permanently installed on a base, at the other it can be something an individual soldier can carry around (or wear on their uniform).

The Australian Defence Force (ADF) can't afford to spend too much building many such systems. I suggest one "sweet-spot" is for deployable, shipping container sized modules (as used for the US Air Force system). A shipping container sized module can be built in a factory and transported to a military base and set up to operate. When needed, it can be packed up and shipped to a bare base to supply power. Shipping containers can be transported by civilian trucks, trains and ships, as well as military helicopters and fixed wing aircraft.

As a target size I suggest an ISO 20 Foot Shipping container. This is large enough that commercial off the shelf power systems can be used, but small enough to be moved easily. The industry standard for a shipping container allows 30,400 kg maximum
gross weight. However, the RAAF's larget helicopter, the Boeing CH-47 Chinook, can only carry 12,700 kg, allowing for 10,500 kg of equipment in the container. The weight is unlikely to be the limiting factor, as while diesel generators are heavy, solar panels are not.

The USAF containerized power supply requires three containers and considerable setup. This is not ideal for deployment on a military operation, where speed is of the essence and there is limited skilled labor available. I proposed the Australia unit should be usable with one container (but expandable with multiple units). It should be able to be assembled, or disassembled, by one technician who has received three hours of familiarization, supervising four military personnel who have received no special training, in six hours. There should be no tools or additional equipment required, apart from what comes in the container.

Container Contents

The container would have mounted in it a conventional diesel generator, power regulating electronics and a fuel tank (for seven days supply). There would also be space for solar panels, the framework to mount them, cables, tools and manuals.

A container has a volume of 33.1 m³. Assume a design which provides a conventional diesel generator and 20% solar power (a cost effective combination) and seven days fuel supply (on diesel alone). It is then necessary to calculator what capacity system would fir in the container.

Solar Panels

The Sharp NU-A188EY solar panel has a typical output of 188W and is 1328 x 994 x 57.5mm and weighs 16.5kg. Assuming an adjustable stand (which doubles as a cradle in the shipping container) and cables for this doubles the volume and adds 25% to the weight of the panel, this makes volume of 0.15 m³, or 0.807 m³/kw and 110 kg/kw. Assuming the entire container was filled with these panels, there is room for 220, providing 41kw. However, there has to be room for a generator and fuel.

Generator and Fuel

A typical generator set (CAT 300 kVA : 3406C) is 4.3 x 1.1 x 2.2 m,10.2  m³, or 0.034 m³/kw. It weighs 3,454 kg or 12 kg/kw. The fuel required, running at 50% power is 38.5  l/hr. Assume the solar panels replace 25% of the fuel, reducing consumption to 29 l/hr, or 4.9 kl per week, or 0.016 m³/kw and 163 kg/kw (allowing for tank).

Calculating Capacity of a Containerized System



m³/kw Weight kg/kw
Solar panels 0.807 110
Generator 0.034 12
Fuel 0.016 163
Total 0.857 285

ISO Container

Volume ISO m³ 33.1
Possible kw 37
Volume m³ 32
% total capacity 86%
Equipment kg 10545
Container kg 2200
Total weight kg 12745
CH47 Capacity kg 12700
% total capacity 100%

So allowing for solar panels, generator and one week's fuel, a shipping container could hold a 37 kw power supply. The capacity of the container would be limited by weight, rather than volume.

However, the ADF  already has diesel generators. So a simpler alternative energy supply would be one purely solar powered. This would remove the safety  issues around transporting liquid fuels. An ISO container could hold a 41 kw solar array, which could then be linked to one or more diesel generators.


Assuming $2,000 per kw for solar panels, mounting hardware and cables. A diesel generator costs about $300 per kw. Allowing for the cost of the container and construction, the cost would be about $200,000 per unit.

Cost $/kw
Solar panels $2,000.00
Generator $302.00
Fuel $25.00

Total per kw $2,327.00
Total for module $86,099.00
Shipping container $5,000.00
Total Materials $91,099.00
Build factor' 200.00%
Total $182,198.00

Number of Containers

A reasonable deployable solar capacity for the ADF to aim for would be 200 shipping container sized modules, producing 7.4 MW, at a cost of $40M. That might sound like a lot of shipping containers and money, but they would all fit in the Navy's two LHD ships, now under construction at a cost of $2B.

Smaller Containers and Modules

Smaller containers might be a more practical option, allowing for more flexible use and transport on smaller vehicles. A ten foot ISO container could hold a 18.5 kw PV system, using a standard military generator such as Advanced Power's 16 kVA, APD016. Also for maximum flexibility, the equipment should not be permanently mounted in the container. The container could have minimum modifications from a standard unit, with a generator and fuel tank which can be removed for separate use. The PV panels which could be in packs which can be carried out by two personnel and set up by hand, with no lifting equipment required.

PV Panels to Supplement Small Generators

An area for research would be solar panels designed to supplement smaller standard military diesel generators, regulate their voltage output and make them "smarter" and more fuel efficient. 727 Watt PV modules with built in power conditioning electronics could be made light enough to be moved by two personnel (about 80 kg). Two modules could be paired with a small diesel generator, such as Advanced Power's 1.3 kW APD1300, or four with the 2.5 kVA, APD2500. These configurations would be small enough to be transported by the Light Cargo Trailer of a Mercedes-Benz G-Wagon and a medium utility helicopter.

Normally connecting a PV array to a generator is a complex process requiring a trained technician. Instead the modules could be fitted with their own electronics and a simple plug and socket to connect in between the generator and the load. There would be no need for any controls on the PV panel: it would be simply plugged in and supplement power from the generator, lowering fuel use and providing a constant voltage for sensitive systems.

Scope for Research

Packing a solar array into an ISO shipping container would require some design and engineering, but is not particularly difficult. Further work could suit the system more for the military environment. In particular commercial solar panels are bright blue with a glass cover. Research could produce a camouflaged panel which was also less liable to breakage.

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