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Energy Reducing, Ruggedized, Solar Lighting System


TECHNOLOGY AREAS: Ground/Sea Vehicles, Materials/Processes, Electronics

OBJECTIVE:  To develop a solar lighting system that allows the use of daylight as an interior lighting solution for expeditionary shelters while continuing to satisfy military requirements and mitigating negative solar effects (solar heat gain, UV damage).

DESCRIPTION:  Lighting in deployable shelters is required 24 hours a day and, typically, more power is used on lighting during the daytime hours.  Utilizing sunlight as interior lighting for the daytime hours will enable energy savings and significantly reduce reliance on power management systems.  Unfortunately, the downsides to simple solutions like windows and skylights include solar heat gain, loss of insulation properties, and material fogging/discoloration.  

Current powered lighting systems generate an amount of heat in addition to their power requirements.  The heat generated by current lighting systems, or windows, adds an additional thermal burden to the Environmental Control Unit (ECU).  Lighting loads increase the amount of fuel needed by the shelter for both powering the lighting system and compensating for the heat generated by the lighting system.  A daylighting solution could provide working, living, or emergency lighting during the daylight hours without the need for electricity or generation of excess heat to burden the ECU.

Hybrid Solar Lighting (HSL), which utilizes the fiber optic transmission of concentrated solar light, could eliminate the need for powered lights in shelters through a majority of the daylight hours.  Research performed at Oak Ridge National Laboratory shows great promise for hybrid solar lighting applications [3, 4, 5].  The technology is currently used in some large commercial and industrial buildings [6, 7].  HSL systems are able to monitor the light in the shelter and attenuate the powered lighting according to the amount of fiber optic solar light available, if needed.  The basic concept behind fiber optic transmission is to concentrate sunlight to a bundle of polymer or glass fiber optics.  Fiber optic transmission filters out UV and IR from the sunlight.  Blocking UV makes fiber optics safe to the warfighter and any UV sensitive fabrics or devices.  Filtering IR allows the luminaires to be cool to the touch and produce no excess heat.

Acceptable daylighting solutions are not limited to HSL techniques; this is only used as an example that would be of interest because of its no-heat-gain, blackout compliant nature.   Producing a compact, lightweight, and sufficiently ruggedized solar lighting system is the key to an effective solution for this solicitation.

The currently implemented MIL-PRF-44259D compliant florescent lights are rated at 300 W per system.  If all the light needed during daylight hours is provided by solar lighting than the energy saved is 2.1 kWh/day, or 767 kWh/yr (2,617,234 BTU/yr).  That is about 83 gallons/yr of JP-8 per shelter, or more than 4600 gallons/yr for a 600 man base camp.  These estimates do not include fuel savings via the ECU due to no additional heat load.

PHASE I:  Develop a robust concept for a solar lighting or a hybrid solar lighting system for use in expeditionary shelters.  This concept must demonstrate the feasibility of a solar/hybrid lighting system in a military soft-walled shelter (although the technology could be applied to rigid-walled shelters as well).   The concept must contain a solar concentrating mechanism, a transmission method (fiber optics, reflective material, etc.), and diffuser element to redistribute the light.   Lux measurements must comply with MIL-STD-1472F for the “Office work, general” requirement of 755 lux (recommended)/540 lux (minimum).  The solution will be compared to existing military light system performance found in MIL-PRF-44259D.  A life cycle cost analysis report will be an expected deliverable along with the detailed concept system.   Total packed volume, weight, and cost are all important factors as with any soft walled shelter component and should be weighted heavily during conceptual design.

PHASE II:  Deliverables expected for Phase II will include a full-scale solar/hybrid lighting prototype system and a lighting level/effectiveness demonstration implemented in a 32 foot TEMPER Air-supported shelter [11].  The full-scale prototype should leverage off of the previous detailed concept developed through Phase I.  Investigation of large scale production costs will be reported, this should include additional system improvement recommendations before production would begin.

By the conclusion of Phase II, an acceptable solar lighting system prototype must have the ability to be set up and provide light to a 32 x 20 foot shelter in less than 20 minutes by 4 warfighters with limited/no special tools.  As required by current lighting solutions, the system must be able to function in a variety of applicable environmental conditions discussed in MIL-PRF-44259D.  All blackout requirements must be met by the solution (if applicable).   To be viable as a transition worthy system, the prototype performance must not degrade after 25 strike/erect cycles.

By the end of a Phase II contract, the target cost per system to effectively illuminate a 32 x 20 foot shelter should be $8,000.

PHASE III:  Solar lighting has the possibility to be greatly utilized in both the consumer, commercial, and industrial applications.  As mentioned, most lighting is used during the day at home, at work, in production facilities, and in retail.  Utilizing the daylight as the main source of light will provide significant annual savings in any application, all while limiting solar heat gain and retaining insulation.

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