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Solar fiber optic lighting for daylighting of high-rise intensive buildings and military shelters

Conventional daylighting scheme employing windows and skylights are no longer so useful especially for daylighting of high-rise and intensive buildings. Residential buildings with limited natural lighting are generally lit by fuel-based electricity which contributes to increase of CO2 concentration in the atmosphere. Alternatively, the concentrated solar energy can be transmitted via fiber optic technologies deep inside the buildings. Fiber optic daylighting system is developed as an aggressive and flexible approach to harvest sunlight for dimly-lit spaces in various circumstances.


Solar fiber optic lighting setups are an alternative to traditional indoor lights using fiber optic technology. Fiber optic cables are designed to carry light from point to point by internally reflecting said light along their length. Solar fiber optic setups allow you to capture sunlight, transmit it inside, and emit it in your home or business. While more expensive than traditional lighting setups, a fiber optic lighting installation can help you save money on electricity costs while providing high-quality, natural light throughout your property.


As a good option for off-grid electricity supply, the photovoltaic (PV) solar lighting system has provided noticeable benefits after adopting solar home lighting system, such as reduction in kerosene consumption, increase in children’s study hours, extended working hours of small business and income generation.


Costs for solar fiber optic lighting systems will vary by brand. Lighting boxes themselves can cost $500 or more depending on their size. The fiber optic cables are usually priced by length, so lighting an area of your building that’s further away from your roof will cost more than an area close to it. Additionally, the material you use for the cables will influence pricing. Glass cables are higher quality and last longer, but can cost around $10 per foot. The other option for cable material is acrylic, which provides lower quality light at about half the cost per foot. For most property owners, solar fiber optic lighting won’t be worth the initial upfront cost. However, as costs fall and the technology becomes more widespread, fiber optic lighting options will become more and more viable for all kinds of properties.


Solar fiber optic lighting system

There are three major components to these systems

1. Solar collectors/receivers

Much like photovoltaic solar panels and solar hot water systems, solar fiber optic systems need to collect sunlight, usually on top of a roof. The solar collectors used for fiber optic lighting are usually made of several small mirrors that focus sunlight into the fibers that actually transmit light. Similar to ground-mounted tracking systems, many solar collectors for fiber optic setups track the sun throughout the day. This allows them to capture as much sunlight as possible to funnel down into your building.

2. Fiber optic cables

Once solar collectors capture sunlight, they focus it into the actual fiber optic cables that transmit any captured light throughout your building. Solar fiber optic cables are like electrical wiring, but instead of transmitting power, they transmit light by reflecting the light internally along their entire length. Cables are usually made from glass or plastic, and the glass versions generally carry light more effectively but come at a higher price point.

3. Indoor lights

The last major components of a solar fiber system are the lights themselves. Light can travel up to a few hundred feet through fiber optic cables, and at the end of each cable is a lighting apparatus that disperses sunlight, just like a traditional electrical lighting setup. Fiber optic lighting companies often have multiple types of lighting products that provide different lighting experiences, from spotlights to large area lighting.


DOD requirement

Fiber-optic hybrid day-lighting system has also military applications such as  military shelters in order to cut energy use and the use of fossil fuels. The DoD management has duly recognized the scope of the energy problem in its operations and has undertaken several initiatives on renewable and alternative energy technologies.However, there are still energy issues that need to be addressed. According the DoD SBIR 2011.3 solicitation, more than 4,600 gallons of JP-8 fuel is used for lighting shelters in a 600 person base camp. All this energy could be saved by developing a compact, lightweight, and sufficiently ruggedized solar lighting system for military shelters.


Steven Winter Associates, Inc. (SWA), an award-winning energy and sustainability small business, considers the development of a solar lighting technology for Army shelters is a timely opportunity and joins Energy Focus, Inc. (EFOI), a leading supplier of energy solutions such as and fiber-optic lighting and LED lighting, in proposing to develop an advanced fiber-optic daylighting system by transforming their prototype passive, fiber-optic daylighting technology to meet the demanding needs of the military shelter application based on the teams collective experience in fiber-optic daylighting, remote-source lighting and energy efficient lighting.


During the phase I project, the team established the technical feasibility of developing a fiber-optic daylighting system by building a pre-prototype solar light collector with a low-cost dual-axis motorized tracker, and a hybrid (solar-LED) light fixture.The overall objective of the phase II project is to design, build and demonstrate a reliable, cost-effective fiber-optic daylighting technology for military shelter application based on phase I research undertaken by SWA and EFOI.There are three key components in the fiber-optic daylighting systema solar light collector/concentrator (SLC) that focuses IR/UV filtered solar radiation onto optical fibers, a motorized tracking system to align SLC normal to solar radiation reasonably accurately, and light delivery system comprising fiber-optic cables and hybrid light-fixture.In addition to undertaking phase II research, the team is committed to rapid commercialization of the technology to be developed.


Chinese Researchers designed Hybrid fiber-optic daylighting and PV solar lighting system

Engineers have developed hybrid fiber-optic daylighting and PV solar lighting system for household applications. The system is composed of a light collecting subsystem, a light guiding subsystem, an optical fiber light diffuser subsystem and corresponding control system.


Light collecting subsystem

Light collecting panel is the critical component of the light collecting subsystem, and it is made of aluminium sheet due to its high strength and light weight. Nine Fresnel lens with the same specifications are mounted on the light collecting panel and utilized as the solar concentrators. Thus, the sunlight can be focused from a relatively broad collection area onto the fiber optic receiver unit and then distributed by optical fibers. To ensure that sunlight always vertically radiates onto the Fresnel lens, the light collecting panel shall be driven by the stepping motor to rotate continuously. In addition, PV cells are embedded in the residual area of light collecting panel. The power generated by PV cells during the day time drives the hybrid lighting system, and most electricity is stored in the accumulator to meet lighting demands in the night or cloudy weathers.


Light guiding subsystem

Polymethyl methacrylate (PMMA) fiber optic is selected in this paper to convey and distribute sunlight throughout the buildings due to its advantages, including high light transmittance, low dispersion, high stiffness and resistance to ultraviolet irradiation. The temperature at the sunlight spot focused by the Fresnel lens can reach up to 140°C in sunny weather, which might exceed the melting point of PMMA (130°C-140°C) and further result in damage of PMMA fiber optic interface. Therefore, an innovative fiber optic receiver unit is specially designed to
minimize the temperature at fiber optic inlet. the aluminium fiber optic receiver unit is composed of sunflower cooling fins and hollow
cylinder. The area and quantity of the cooling fins can be adjusted based on the practical cooling requirements to achieve good dissipation effect.


Light diffuser subsystem

Generally, the launched sunlight is emitted at angle of 58° from the fiber optic end with high luminance, which could directly illuminate the space but the illuminated space is limited due to the low-angle incident light. Meanwhile, the luminance level depends on the outdoor conditions, resulting in unstable and non-uniform indoor lighting effects. Therefore, researchers have designed a fiber optic diffuser subsystem which consists of diffuser lens, panel, shell, base board, light-emitting diode (LED) light and fiber optics.


Twelve diffuser lens providing 120° wide angle ensure the light emitted from fiber optic ends and LED to be scattered uniformly, enlarging the lighting area and simultaneously providing conformable natural light. Nine fiber optic emitting ends and three LED lights are mounted on the base board. Solar-powered LED could meet the lighting demands in case of insufficient outdoor sunlight and night.


Preliminary system performance shows that, the developed system could provide comfortable and natural indoor illumination. Meanwhile, the hybrid lighting system can provide an average of 9h of electric lighting under clear sky conditions, and reduce 158.2kg of carbon dioxide emission in a year within the tested dark room of 5m2.


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