Saturday, September 3, 2011

Photo voltaic Technology


Scientists have known of the photovoltaic effect for more than 150 years. Photovoltaic power generation was not considered practical until the arrival of the space program. Early satellites needed a source of electrical power and any solution was expensive. The development of solar cells for this purpose led to their eventual use in other applications.
DISCOVERY AND DEVELOPMENT OF PHOTOVOLTAIC POWER
The photovoltaic effect has been known since 1839, but cell efficiencies remained around 1% until the 1950s when U. S. researchers were essentially given a blank check to develop a means of generating electricity onboard space vehicles. Bell Laboratories quickly achieved 11% efficiency, and in 1958, the Vanguard satellite employed the first practical photovoltaic generator producing a modest one watt.
In the 1960s, the space program continued to demand improved photovoltaic power generation technology. Scientists needed to get as much electrical power as possible from photovoltaic collectors, and cost was of secondary importance . Without this tremendous development effort, photovoltaic power would be of little use today.

Early photovoltaic development
YEAR
DEVELOPMENT
1839
Antoine-César Becquerel, a French physicist, discovered the photovoltaic effect. In his experiments he found that voltage was produced when a solid electrode in an electrolyte solution was exposed to light.
1877
W.G. Adams and R.E. Day observed the photovoltaic effect in solid selenium. They built the first selenium cell and published “The action of light on selenium,” in Proceedings of the Royal Society.
1883
Charles Fritz built what many consider to be the first true photovoltaic cell. He coated the semiconductor selenium with an extremely thin layer of gold. His photovoltaic cell had an efficiency of less than 1%.
1904
Albert Einstein published a paper on the photoelectric effect .
1927
A new type of photovoltaic cell was developed using copper and the semiconductor copper oxide. This device also had an efficiency of less than 1%. Both the selenium and copper oxide devices were used in applications such as light meters for photography.
1941
Russell Ohl developed the silicon photovoltaic cell. Further refinement of the silicon photovoltaic cell enabled researchers to obtain 6% efficiency in direct sunlight in 1954 .
1954
Bell Laboratories obtained 4% efficiency in a silicon photovoltaic cell. They soon achieved 6% and then 11%.
1958
PV cells were first used in space on board the Vanguard satellite.

CONVERTING SUNLIGHT TO ELECTRICITY
A typical photovoltaic cell consists of semiconductor material (usually silicon) having a pn junction as shown in figure

Sunlight striking the cell raises the energy level of electrons and frees them
from their atomic shells. The electric field at the pn junction drives the electrons into the n region while positive charges are driven to the p region. A metal grid on the surface of the cell collects the electrons while a metal back-plate collects the positive charges.

POWER OUTPUT AND EFFICIENCY RATINGS
The figures given for power output and efficiency of photovoltaic cells, modules, and systems can be misleading. It is important to understand what these figures mean and how they relate to the power available from installed photovoltaic generating systems.
Power Ratings
Photovoltaic power generation systems are rated in peak kilowatts (kWp). This is the amount of electrical power that a new, clean system is expected to deliver when the sun is directly overhead on a clear day. We can safely assume that the actual output will never quite reach this value.
System output will be compromised by the angle of the sun, atmospheric conditions, dust on the collectors, and deterioration of the components. When comparing photovoltaic systems to conventional power generation systems, one should bear in mind that the PV systems are only productive during the daytime. Therefore, a 100 kW photovoltaic system can produce only a fraction of the daily output of a conventional 100 kW generator.
Efficiency Ratings
The efficiency of a photovoltaic system is the percentage of sunlight energy converted to electrical energy. The efficiency figures most often reported are laboratory results using small cells. A small cell has a lower internal resistance and will yield a higher efficiency than the larger cells used in practical applications. Additionally, photovoltaic modules are made up of numerous cells connected in series to deliver a usable voltage. Due to the internal resistance of each cell, the total resistance increases and the efficiency drop to about 70% of the single-cell value. Efficiency is higher at lower temperatures. Temperatures used in laboratory measurements may be lower than those in a practical installation.




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Thursday, April 21, 2011

Illuminance

When it is necessary to access lighting objectively and quantify the lighting ambience of a space, i.e. Low, soft or strong lighting, the concept of illuminance is used. For instance, the luminous intensity which is provided on a single gray wall by a lamp of identical power decreases according to inverse of the square of the distance. The illuminance, in other words the quantity of light incident upon this surface, is a function of the distance to the source (d), its luminous intensity (I), and the angle that exists between the incident light which reaches the material and the perpendicular to the surface.
The illuminance is expressed in terms of lux (lumen/m2). This is a means of comparison which lighting engineers often use to describe the functionality of lighting.
Common Light Levels Outdoor
Common light levels outdoor at day and night can be found in the table below:

Condition
Illumination (lux, lumen/m2)
Direct Sunlight
100000- 500000
Full Daylight
10000-40000
Overcast Day
20,000
Twilight
400
Full Moon
100
Quarter Moon
0.01- 20
Starlight
0.001-10
Overcast Night
0.0001

 Common and Recommended Light Levels Indoor
The outdoor light level is approximately 10,000 lux on a clear day. In the building, in the area closest to windows, the light level may be reduced to approximately 1,000 lux. In the middle area its may be as low as 25 - 50 lux. Additional lighting equipment is often necessary to compensate the low levels.
Earlier it was common with light levels in the range 100 - 300 lux for normal activities. Today the light level is more common in the range 500 - 1000 lux - depending on activity. For precision and detailed works, the light level may even approach 1500 - 2000 lux.
The table below is a guidance for recommended light level in different work spaces:

Activity
Illumination
(lux, lumen/m2)
Public areas with dark surroundings
20 - 50
Simple orientation for short visits
50 - 100
Working areas where visual tasks are only occasionally performed
100 - 150
Warehouses, Homes, Theaters, Archives
150
Easy Office Work, Classes
250
Normal Office Work, PC Work, Study Library, Groceries, Show Rooms, Laboratories
500
Supermarkets, Mechanical Workshops, Office Landscapes
750
Normal Drawing Work, Detailed Mechanical Workshops, Operation Theatres
1,000
Detailed Drawing Work, Very Detailed Mechanical Works
1500 - 2000
Performance of visual tasks of low contrast  and very small size for prolonged periods of time
2000 - 5000
Performance of very prolonged and exacting visual tasks 
5000 - 10000
Performance of very special visual tasks of extremely low contrast and small size
10000 - 20000

Wednesday, March 9, 2011

Reference Efficacy Info

 The  following is a guide of efficacies one might expect from common lamp and luminaire combinations:
Lamp Efficacy:

Incandescent General Service lamps:
50 watts or less-- 11 L/W
50 to 125 watts-- 17 L/W
Over 125 watts-- 20 L/W
Halogen lamp to 250 watts-- 18 L/W

Fluorescent Lamps (based on mean lumens, all at 3,000k color):
Up to 26 watts, retrofit screw base-- 48 L/W
Up to 42 watts, plug in triple tube -- 55 L/W
Long Twin Tube-- 57 L/W
T12 Energy Saving-- 72 L/W
T8 Energy Saving-- 87 L/W
T5 Energy Saving-- 90 L/W
T5 HO -- 86 L/W

High Intensity Discharge Lamps (based on mean lumens):
Up to 100 watt Metal Halide, coated lamp-- 40 L/W
150 to 250 watt Metal Halide, coated lamp, pulse start-- 55 L/W
400 watt Metal Halide, coated lamp, pulse start-- 72 L/W
Up to 250 watt High Pressure Sodium-- 98 L/W
400 and 1000 watt High Pressure Sodium-- 114 L/W

Luminaire Efficacy:
Incandescent downlight with 60W A19 lamp-- 9 to 11 L/W
Incandescent reflector lamp downlight with PAR lamp and reflector trim-- 9 to 17 L/W
Incandescent reflector lamp downlight with PAR lamp and black baffle-- 5 to 12 L/W
Halogen downlight with elliptical reflector and baffle --10 to 15 L/W
CFL Downlight 42W triple lamp-- 28 to 36 L/W
Metal Halide downlight-- 32 to 37 L/W
Fluorescent lensed troffer with T12 lamps-- 41 to 47 L/W
Fluorescent parabolic troffer with T8 Lamps-- 60 to 67 L/W
New generation direct/indirect recessed fluorescent with T5 lamps-- 82 L/W
High Bay Industrial reflector, Metal Halide lamp-- 36 to 47 L/W
Low Bay Industrial reflector, Metal Halide Lamp-- 40 to 50 L/W
Parking Garage luminaire, Metal Halide Lamp-- 38 to 45 L/W
Parking Garage luminaire, High Pressure Sodium Lamp-- 64 to 80 L/W
Decorative wall sconce-- white acrylic diffuser, CFL plug-in lamp-- 13 to 20 L/W
Decorative wall sconce-- white acrylic diffuser, incandescent lamp-- 4 to 7 L/W
Fluorescent under-cabinet light, T5 lamp-- 35 to 47 LW

Saturday, February 5, 2011

Comparison Matrix Between LED versus HPSV Street Light

 

Item60 w LED Street Light150w HPSV Street light
Cost of electricity (KWh)88
Operations in hrs(1 day)1010
Operations in days(1 year)365365
Annual KWh219547.5
Annual Cost of Electricity17524380
Lifetime30000 hrs/3000 days6000 hrs/600 days
Comparative Cost210004500
Total Cost of Ownership over LED lifetime keeping cost of electricity same3540049500

Over All 40% cost saving in LED street Light
 
Salient features of LED lighting
 
  1. High energy efficiency & savings- High power factor> .95
  2. Safe light- no UV or IR in the beam
  3. Low heat dissipation/sink
  4. Vibration resistance- no filament to break.
  5. Instant on - reaches full brightness in nanoseconds.
  6. Long lifespan- 30000- 100000 hrs.
  7. Low -temperature friendly-no issue starting in cold temperature.
  8. Excellent colour rendering
  9. High Brightness- no compromise between efficacy and CRI.
  10. Option of colours
  11. Eco friendly green products-contains no mercury, lead or other heavy metals.
  12. No maintenance cost.
  13. Directional - no wasted light; any pattern possible.

Monday, January 17, 2011

LED Lighting

The use of LED, an acronym for Light Emitting Diode, has greatly spread in the last few years within many diverse fields of application, from traffic lights to infrared TV controls. The increasing use of LED within industry is primarily due to technological progresses, which have permitted LED to be produced in colours other than the original red (which in the beginning was the only colour available), as well as the  fundamental characteristics which LED can boast: being trustworthy, highly efficient and with a long-life span. 
LED today also plays an ever increasing role in the field of technical lighting, as LED lighting systems offer various advantages in respect to traditional sources of illumination:
  • long life
  • no maintenance costs
  • greater efficiency in contrast to halogen and florescent lights
  • secure operation
  • a clean light as it is without IR and UV components
  • easy of installing light points
  • absence of mercury
  • the possibility of a strong spotlight effect
  • no problems switching on
  • insensitivity to humidity and vibrations
  • ease of achieving efficient and effective optics in plastic or glass
LED illuminations have the following characteristics:
  • small
  • dynamic effects (variations of the RGB colours)
  • cost effective shape and size
  • long life and robust
  • concentrated colours
led lightingDue to the characteristics of LED and of the LED lighting systems, light is increasing its value in its ability to create diverse ambiances both publically and privately: such as in the illumination of museums, restaurants, health centres, bars, road signs, safe routes as well as becoming increasingly useful in the naval sector.
The versatility of LED lighting systems make this form of technical lighting particularly adapted to scenography and set design as well as creating original and personalised spaces. Monochrome or multi-colour LED systems perfectly integrate with buildings and their surroundings, becoming an integral part of the design, offering solutions for internal space as well as external spaces, whether in humid environments or very hot atmospheres.
Choosing an LED lighting system brings with it numerous economic advantages in terms of lower costs; the possibility to achieve four times as much light in respect to tungsten flurescent and filament lamps; the increased effeciency and reliability of led is also highlighted in its life span, which is one to two times greater than that of cl;assic lighting sources. 
The Geospec technical team produces and sells a wide range of led lighting systems, which include:
  • LED light fittings
  • LED lighting profiles
  • LED devices
  • LED spotlights
  • Path lamps
  • LED spotlights for swimming pools
  • LED spotlights for gardens and small paths
  • Spotlights for light fittings and/or lighting for stairways and steps
  • Monocrome SMD LED stips
  • SMD RGB Led strips
  • Internal and external Wall Washers
  • Supplies
  • Colours for RGB spotlights