Solar Lantern Programmes - A brief watchlist.

Too many people and bodies, unfortunately including media like NDTV Green Campaign, seem to carry an impression that a chargeable torch or battery-powered lamp is a solar lamp by itself and that, donating one to a village family means immortality to all concerned. To top it, some of them have displayed ignorance of the difference between a solar thermal and SPV or photovoltaic panel. Nothing is more damaging to the credibility of the solar energy programme than these amateur freebies.

1. The lantern, most importantly, needs to be compatible to a solar SPV panel, which often costs more than the lamp itself, in the region of Rs 250 per Watt. Typical power ratings of crystalline silicon panels manufactured in India are 6W, 10W and 35W, for this purpose, by Tata BP, SELCO, Solkar, CEL, BHEL, Udhaya Semiconductors, etc. You may thus calculate the budgetary costs. More notes on techno-economic calculations for SPV systems can be found at http://micropower.blogspot.com/2003_11_23_archive.html



2. The energy drained from the lamp's battery each night, in Watt-Hrs should match the panel power rating in Watts X 4.5 hrs, i.e. the solar panel must feed its power in 4.5 hours what has been drained all night by the lamp's battery. This calls for correct matching and supply of a solar panel of adequate capacity and correct voltage for safe and reliable charging.



3. For battery durability and system-level reliability, the battery must not be drained for more than 20% of its stored capacity in a day, on average. While we provide for this in indoor and outdoor stationery lighting systems by using slow-drain Class-100 or Class-120 batteries, compact lantern manufacturers typically use a hi-drain, hi-charge C-5 battery which drains its full charge in just 5 hours. This is why batteries in solar lamps wear out in 3 years or less.



4. Another issue is the light source. Reading and activities involving inspection require 300 Lux i.e. 300 Lumens per Sq Mtr. The recent trend is to use white LEDs, which deliver mostly in the region of 20-30 Lumens per watt consumed, as against a filament lamp that delivers 15 Lumens and a 230V Commercial-grade CFL that delivers 44 and a tube-light that delivers 40 Lumens per watt respectively. Often, the quality of LED lights are questionable for eye safety, unless certified by a manufacturer.



5. Beside quality and quality of light, each light source has a limited life. A standard replacement should be available locally or provided for, the battery as well as LED, tube or bulb used.



6. The beneficiaries need to be taught to connect and place the panel correctly and clean it daily, in order to get the right amount of power. Often, there is no indication of light source or output in Lux or Lumens of the lanterns in the manufacturer's information. We do not even know how for many hours the lamp will glow on full charge, in one day.



7. The manufacturer or donor must address the above issues.



8. In India, it may be wise to contact the appropriate State Nodal Agency for a list o0f their approved manufacturers, because State Nodal Agencies typically undertake execution and follow-up of such programmes, even privately and charitably funded.



9. Alternately, I would suggest procuring the smallest rated but reliable, warranty-supported solar panel and approaching a manufacturer like Eveready, who have recently entered the solar lantern space and have a reasonably penetrated rural marketing network, for support in lantern servicing as well as replacement of battery and light source.

The Barefoot College in Rajasthan under the stewardship of Bunker Roy is a good example, where local persons are first trained and micro-entrepreneurs enabled to service solar lanterns. So is GEDA in Gujarat, for community-owned lighting installations like streetlights.

The country's first State to take up solar energy in earnest saw good and bad cases too. While Gujarat's State Nodal Agency GEDA (www.geda.org.in) managed few hundred streetlights a year in the late 80s by providing solar stills for distilled water to refill lead-acid batteries (sealed batteries were not available locally then), training owners and incentivizing local monitors, the SEBs or State Electricity Boards including GEB bombarded the villages with 1000-3000 streetlights and never bothered to check, with the result that all had failed by 1991-92, causing a massive loss in monetary and credibility of the SPV program. However, on the other hand, a good proportion of the ones installed and facilitated by GEDA with the village administrations' enthusiasm, continue to light up their habitats, to this day.

CHEAT SHEET ON SMART LIGHTING

We now have plenty of light sources to choose from as the days of the ubiquitous bulb and Yard-long tube for all seasons are gone. Here is a quick guide on picking the best one for your needs.

1. First, we should make it a point to insist on knowing the Lumens of illuminating power produced by any light source - bulb, tube, etc; and compare it with the Watts consumed by it.
   
   
2. Typically, a filament bulb delivers 15 Lumens/watt, as against a commercial LED (unless otherwise specified) at 25-30 Lumens/Watt, a TL grade tubelight at 50 Lm/W, and PL lamp (without ballast) at 80 Lm/W and a sodium lamp, as found in streetlights at 100-120 Lm/W. This way, we know that a good tubelight of 40W rating delivers 2000 Lm.
   
   

   The slew of popular CFLs or Compact Fluorescent Lamps available in the market that fit into your regular 230V bulb holder come with a built-in ballast and deliver about 40-50 Lm/W.
   
   

   Hi-Luxage LEDs from LumiLEDs, Philips, Nichia are entring the market now and they are known to deliver as much as 70-90 Lm/W but need to be accompanied with a test certificate or have the Lumen output marked on their assemblies. Another disadvantage lies in the narrow beam angle of an LED, though wide-beam versions are coming into the market. heat dissipation is an issue with hi-power LEDs of 1-3 Watt rating, even if these mostly come with heat sinks.
   
   

   Yet, single LEDs have very low power consumption, LED hence matrices and strips can be configured, to meet various intensity and power needs, almost like a set of dominoes. Here lies an advantage of scalability. One can configure LED arrays and clusters for lighting up passages, stairways, lobbies, even kerbs and pavements, beside wash-lights and up-lights outdoors. One can also use them for safety signage in remote locations, since LEDs use DC which can be stored in batteries and hooked on to a signalling or control network.
   
   

   LEDs also have the flexibility advantage. Advertising signs can incorporate arrays such that they can switch off an alternate LED during late nights to save on power.
   
   

   All this lets us select the light source according to its use without over-providing to waste power or under-illuminating as a misfired power-saving measure.
   
   

3. Next, we need to know the intensity, or how many Lumens and square-feet we need in each of our working/living spaces. A number of standards exist for this. As a thumb rule, it is -
   
   li750 Lux or Lm/SqM for intricate work like embroidery or detail drawing,
   
   • 500 Lux for reading & office work,
     
   • 200 Lux for casual work and 150 Lux for storage spaces etc
     
   • Passages, doorways and gate-cabins need to be lit according to the above work associated with them.
   
   
   

   Each working area in Sq metres multiplied by intensity required will give us the total Lumens.
   
   

   We need to remember from Inverse Square Law that intensity drops 4 times for 2 times increase in distance. So, for high-intensity lighting. This way we need to correct our Lumen requirement.
   
   

   Finally, we can select and space each light source and from ts Lumens, estimate the number of watts these will consume, or the electrical energy per hour. Typically,
   
   

   Tubelights distribute 2000 Lm over a length of 1 Mtr or 1000 Lm over 500 mm. These make for shadow-free lighting. Accordingly, LED strips can be used to deliver similar luxages. The comparative economics are evolving. These can be hung or wall-mounted. Lighting power gets distributed by the square of its distance. This way you can get economy when basic illumination is used.
   
   

   PL lamps and CFLs provide as much as 1000-1200 Lumens but from a single source. If these are required for intricate work, these need to be mounted on the desk, work-table or machine. The same holds for lanterns and LED combo bulbs, several of which are available.
   
   

4. Shades and reflectors not only protect the lamps, they also direct more light toward the lit space. Besides, in low-lit areas, translucent shades can be used so they can be seen from a longer distance. This helps in street lamps and marker lamps in power-scarce areas.

For another example, your walls and ceilings may typically act as a reflector for the white light of a tubelight, else the 2000 Lumens may be halved. Using a bright wall or ceiling colour helps the light behind the source to be reflected forward, so as to improve illumination. Such a combination of reflected and direct light works to diffuse any shadow.