Hybrid Solar Lighting

Traditionally photo voltaic solar panels are used to convert the naturally abundant solar light into usable electricity. Though recent advances in the design of such solar panels have been reducing their cost, still it costs about US $ 2.45 per Watt. Taking the US average system size at 5 kW energy needs, the cost of Solar Panel will be about 12250 US Dollars. The energy efficiency in converting the solar energy to usable electricity at the utility socket level is just about 15 %. The chain in the conversion consists of solar panel arrays which feed microprocessor controlled regulators which in turn charge lead-acid storage batteries. These batteries drive inverters which eventually feeds the output into the utility. Every step adds to the overall inefficiency in this process.

Hybrid solar lighting (HSL) is different from the traditional solar power, in that the solar light is directly piped into buildings through fiber optics. Inherently this process of channeling solar light through roof top light collectors has higher efficiency as the light energy is directly used. Thus for the same roof area, you get far higher light output.

Hybrid solar lighting in action

HSL technology concentrates natural sunlight through an array of reflectors into light collectors which pipe sunlight directly into a building or enclosure through fiber optic bundles. The fiber optics eventually drive hybrid light fixtures. These hybrid light fixtures house diffusing rods to disperse the collected light or the light from high power LED lamps powered by standard electric utility. There is a control unit which controls the quantum of light available as set by the end user. On a sunny day, most of the light will come from the sun while on a cloudy day, part of the light will come from the utility.

The hybrid light fixtures have special diffusing rods that spread out the light in all directions. For instance, one collector powers about eight hybrid light fixtures and this can illuminate approximately 10,000 square feet.

The hybrid luminaire diffuse light within the interiors to integrate the natural light with existing artificial lighting; to provide controllable interior lighting.

A daylight harvesting controller automatically increases or decreases the artificial lighting in the interiors, keeping with the sunlight levels prevalent.

The roof mounted collectors have a visible spectrum band pass filter which traps unwanted heat and harmful ultraviolet radiation from the sun light. The light available through the hybrid light fixtures will have broader color temperatures than any artificial lighting. This wide spectrum light has subjectively higher amount of warmer reds and colder blue than the traditional incandescent bulbs or fluorescent bulbs. Artificial lighting - no matter how it is produced - offers only a limited spectrum of light.

Hybrid solar lighting combines the convenience of artificial lighting with the benefits of natural lighting - from lowered energy consumption to improved employee productivity.

Hybrid luminaire

While it has been found that conventional lighting puts out a lot of heat, solar lighting is efficient. When used on the top floor of a building, at least 50 percent of the sunlight that is collected as indoor lighting is delivered by HSL.

In hybrid solar systems, since artificial means are used to generate light, microprocessor controlled system equipped with photo sensors automatically adjust electric current that is required to keep a room uniformly bright.

On a sunny day, even 80 % of sunlight can be harnessed. Contrarily, on a day when the sun is covered with dark clouds, the piped sunlight may drop to only 5 % of the room's lighting requirements.

Advantages of Hybrid solar systems

The advantage with HSL is that even if there is little or no sunlight, these fixtures provide constant illumination.
HSL is found to be far more efficient that photo voltaic cells. With photo voltaic cells, about 15 % of sunlight is converted into electricity and then the electricity has to be changed back to light. Tendency for light bulbs is to lose a lot of energy in the form of heat. Consequently, the end result is only about 2 % of the sunlight that actually gets used.

Another advantage of the HSL light fixtures is that they generate far less heat than conventional bulbs. Therefore, less energy is spent on air-conditioning.
Unlike fluorescent bulbs that emit only at a narrow frequency spectrum , HSL provides a full spectrum of light. This full spectrum of natural light has several health benefits. A study reveals that stores with natural light boost their sales by up to 40 %.
Interestingly, hybrid solar systems are cool enough to touch with bare hands. The collectors remove the infrared light, that part of the spectrum that generates a lot of heat in conventional bulbs. Hence, Hybrid solar system is ideal for commercial buildings where lighting is the cause for huge electricity bills.

According to a study conducted by Duncan Earl, a co developer of the technology and chief technology officer of Oak Ridge startup company Sunlight Direct, the system can save about 6000 kilowatt hours per year in lighting and another 2000kWh in reduced cooling needs for a total of 8000 kWh annually. Over a period of 10 years, for parts of the US where the utility rates are 10 cents per kWh, the savings would be up to $ 8000 per hybrid solar lighting unit.

This translates into energy savings between $1 million and $ 2 million over 10 years and maintenance savings could account for another $ 300,000 in savings for the same period.

Use of Hybrid solar systems in residential areas is yet to catch up as the cost advantages are not as great. However, studies are on to see that homeowners do indeed receive a premium for the solar savings of having a solar energy system at home.

In the US, there has been an instance reported in a newspaper article in Washington DC where a home with hybrid solar systems is able to save $50 to $80 per month on utility bills. Thus a home with hybrid solar lighting system allows the homeowners to save an average of $780 annually.

Other benefits of HSL

When research was conducted on HSL at the Oak Ridge National Lab, it was found that the sunlight from the collectors had a noticeable reddish tint, particularly during sunrise and sunset hours. This has been welcomed by many users who seem to enjoy the softer reddish hues when they are still asleep in the early mornings and also in the evenings when it is time to go home from work.

Studies reveal that natural light is important for body's internal rhythms. Some doctors opine that lack of full spectrum of natural light is the cause for seasonal acquired depression. A full spectrum of light also makes a place cleaner and more spacious subjectively.

Hybrid solar systems provide peak light output even at a time when there is a great demand for electricity. Energy is saved during the day when electricity costs most.

In short, hybrid solar systems combine the convenience of artificial light with the benefits of natural light. HSL delivers the benefits of natural lighting with the reliability of artificial light in an integrated manner.

The world is going green today and daylight is becoming an important lighting source as it consumes zero energy and produces zero emission.