LED LIGHTING – THE WAY TO THE FUTURE OF SOLAR?

The world is desperately trying to cut down on its electricity consumption – in an endeavour to reduce our global carbon footprint. Saving on electricity is not just the responsibility of home-owners, but also of industry and government (who consume most of the power anyway!).

Security lighting for Major venues, hospitals, shopping Malls, schools and colledges, Government offices; Stations, etc., is one area where the recent introduction of LED lighting is offering vast savings.

LED (Light Emitting Diodes) have become very popular with both the Solar and, to a lesser extent, the 4x4 fraternity, where power has to be employed sparingly, in order to minimise costs.
The advantges of LED lighting are considerable:

1. They consume about  1/10th of the power of standard CFL lights
2. They last about 10 times as long
3. They are increasing their range of products all the time (Street lights, Strip lighting, Rope lighting, Christmas lights, Floodlights, Spotlights, Vehicle lights, Downlighters, etc.).
4. Prices, expensive at first, are decreasing, as LED lights become more popular and the industry becomes more competitive.

With their low consumption and long life, the LED lends itself to solar street and traffic lights –because, on this application, it does not require too much power and is independently powered by a natural power source – the sun.
Batteries can be mounted high up on the lamp pole, or underground at the base.
Depending upon the required specifications, built-in reserves for rainy or cloudy days can be incorporated into the design.
The unit can be operated from the solar regulator in that when the sun goes down (stops charging) the lights will come on, and vice versa.  Thus there is no need for a light-sensitive switch!

The major points for consideration of any streetlight are:

1. AREA OF COVERAGE : This relates to how big the area to be lit is required to be.  This is also linked to pole height and distance between poles.  The usual range is from 25M-40M for an average streetlight.
2. INTENSITY OF LIGHT : This depends upon the application. Once again, the height and frequency of poles will decide on how this mix is achieved.  There are 2 measurements, or scales employed for these specifications: Centre light intensity and Luminous flux.   In the case of the Centre light, it is usualy on a scale from 11-25 LUX, and for the Luminous Flux from 900-5500LM.  The number and power of the LEDs employed, obviously play a major role in the light’s performance.  Some lights may have in-built heatsinks and cooling fans to reduce excess heat build-up and reduced performance.
3. POLE HEIGHT : These vary from 5-10M and are determined by the application and lighting area required.  The smaller the lighting area, the less bright the light and the lower the pole.
4. POLE TYPE :  Can be made from steel, aluminium, wood, or even plastic.  The first 2 being the most popular.  The poles are usually tapered to the top and usually hinged in the middle for assembly and maintenance purposes.
5. PANEL SIZE :  This determines the amount of charge that the battery will receive on a daily basis and is usully measured in Watts.  The usual range of panels employed is from 40W upto 300W.
6. PANEL TYPE : These can range from Amorphous (or thin film), Moncrystalline, Polycrystaline right upto Hybrid panels.  The specifications for these are determined by budgetary and life expectancy considerations; as in most things in life, the better the quality, the greater the price!
7. BATTERY SIZE : These will be determined by the power consumption of the lights and the size of the panel charging them.  Battery amperages vary from 40AH right upto 400AH. 
8. BATTERY TYPE :  These can vary from ordinary Lead Acid type through to Calcium, Gel, and specialised Spiral wound batteries.  The specifications will determine the life expectancy and depth of discharge demanded by the batteries to be employed.
9. BATTERY LOCATION :  The batteries on the smaller systems are often located near the upper end of the mast and underground for the larger systems.  Access for changing these batteries is always an important consideration
10. HOURS OF OPERATION :  This will vary according to geographic location as well as season.  They usually start at around 6, and can go up to 12 - under extreme conditions.
11. DAYS OF RESERVE :  This relates to the possibility of having a few days of low sun, or even no sun and yet still be able to provide lighting for such a period.  This can vary per country, but usually starts at zero (no, or minimal reserve) and can go up to 5 days.  Any period beyond this would require multiple batteries, and possibly, extra panels.
12. SYSTEM VOLTAGE :  This is the DC voltage of the system which is usually 12V, or 24V.  The bigger systems requiring 150W panels and larger, usually switch to 24V to minimise losses.
13. SIZE OF LIGHT SOURCE :   This refers to the combined wattage of the LED lights employed, to create the lighting required.  They usually start at 15W and can go upto 100W – sometimes even higher.
14. NUMBER OF LIGHTS :  Thius is usually limited to one or two lights on most street lights.  The 180 degree dual units would obviously require more power and larger battery reserves.
15. ON-OFF SWITCHES :  This can be done by timers, light-sensitive switches, or even by the sun itself linked to the solar regulator (as the panel charges the lights will switch off and vice versa).  The latter is the most efficient system, as it allows for seasonal and even daily changes in required lighting

OTHER POINTS OF NOTE:

When sizing up your battery/panel combinations, remember that a battery should not cycle much below 40% - on a daily basis.  Obviously, if there are several days of no sunlight, then the battery will be required to cycle below this level.  It is important that this does not occur on too regular a basis, or else you will need one of the specialised batteries that can support constant cycling below the 40% mark without drastically reducing its life expectancy.

Also, when matching up your panels to the batteries, ensure that you always calculate an extra 15-20% of solar charging power over and above what is actually required.  The reason for this is that, whenever you experience a few ‘bad sun days’ and the batteries start to discharge below the recomended benchmark, the extra power will allow you to operate the lights as usual, but also to have a little surplus to help bring the batteries up to the optimal level.  If you don’t do this, then you will end up ‘deficit charging’ the batteries - which means that after a few bad days they are starting from say, half-full and progressing to flat every day, and this will damage the batteries and considerably reduce their life expectancy. 

In order to optimise battery life, you should attemp to ensure that the battery is charged to full at least once every 2 weeks, and this can only be achieved by designing in extra panel power.

Solar panels only work at their optimum when they are clean, free from dust, and deposits from our feathered friends!  It is a good idea, during the non-rainy season (if you have one, of course!) to arrange to clean them with a quick squirt of a hose from a ‘cherry picker’(for street lights) on a monthly basis.  Rain obviously does this automatically, so it need only be done after several weeks without rain.

COMBINATION UNITS: SOLAR & WIND

It has also become popular to employ combination units which employ both solar and small wind turbines. The obvious advantages for these ‘Combo’ units, is that the wind turbine can still supply power at night, on cloudy and rainy days, as well as obviously on all windy days. The question is whether to ‘share’ the charging load, or whether to use the wind turbine purely as a back-up for solar. 

This again is up to the client, as it will determine the cost of the unit directly related to what the ratio of power supply would be from either system.  An important factor would be the wind patterns, and sunny day patterns, for any given location.  If you are located in a very windy area (refer to your local wind map) but get many cloudy days, then you would go for the wind turbine as your primary charging source, and solar as a back-up and vice versa.

Employing a Combo unit also cuts down on your reserve battery size requirement, as the wind will probably supply something everyday - thus keeping your battery ‘topped up’ overnight whilst the sun is not contributing but the street lighting is consuming power.  
These units start at around 200W and don’t usually exceed 500W - because of the pole factor limiting weight at the top of the pole.