Highly efficient lighting
Electrification programs/projects using solar energy generators are being implemented throughout rural areas of developing countries. In general, energy supply networks (electricity supply networks) are not appropriate due to remote locations, impassable terrain and costly line installations.
Although many independent systems provide energy for cooling, radio and television, lighting remains the primary requirement for virtually every photovoltaic system.
A single solar-powered lamp can make a real difference to the life of a family in developing countries. But these families have the lowest incomes in the world. So the base retail price and the overall cost over the life of the system must be kept as low as possible.
Achieving this goal is far more difficult than simply combining the cheapest components. Analytical comparisons of the various electricity technologies reveal some surprising economic realities for system designers.
Lighting technology Various lamp technologies are used in small solar energy systems. The purchase price is often the deciding factor, but the cost-effectiveness should be taken into account when making the selection, as this influences the costs of a suitable panel and battery.
The incandescent lamp Very small, self-propelled incandescent lamps that have no more than 1 watt are commonly used. These lamps are very inexpensive, but provide sparse lighting with very little performance. They use the expensive system components very little, such as the panels and the battery, and represent a false savings.
Halogen This advanced light bulb technology is a substantial improvement in performance over standard light bulbs - but it still falls short when compared to other light sources. Their performance duration is very sensitive to small variations in power supply - both above and below their normal limit voltage.
Light-emitting diode The technology of the light-emitting diode has made many advances in the last decade in terms of its compatibility for light supply - especially in the area where the light is needed in a concentrated beam.
However, high-performance light-emitting diodes such as the 5 watt Luxeon with their parts bundled in glass remain very expensive. In addition, their performance is just that of an ordinary fluorescent lamp. The effectiveness of smaller Luxeon LEDs is still lower and none of the released commercially available Luxeon performance capabilities account for the losses in control circuitry required to convert from the standard 12 volt unit.
Conventional composite plastic LEDs have fairly inconspicuous convincing effectiveness and degrade very quickly due to light emissions that yellow the plastic body.
Fluorescent This gas-discharging device is already established as an extremely effective lighting technology. Progress in phosphorus chemistry has led to a slight improvement in performance, but it is now essentially a mature technology.
The performance of the fluorescent lamp is a question /generally depends on the size /. Large lamps are more powerful due to the fact that the amount of energy used to heat the electrodes is smaller in longer vessels.
As a rule, small solar energy systems use compact fluorescent technology ranging from 3 to 11 watts. They are produced in large quantities and appear to represent good values as they are both effective and reasonably cheap.
Unfortunately, they prefer stable working conditions and are very dependent on deviations from their optimal input voltage and the ambient temperature.
Battery voltages typically reach 15 volts during boost phases and below 11 volts during discharge. Many compact lamps overheat and fail if operated at 15 volts for more than a few minutes. Low voltages destroy the electrodes due to excessive heat, resulting in darkening of the tube and loss of performance.
Cold Cathode The Cold Cathode is an advanced gas discharge technology that provides the highest possible performance with other important additional benefits.
Fluorescent cold cathode tubes operate with much more voltage and less current than conventional fluorescent lamps. The higher voltage eliminates the need to heat the tube while the lower current significantly extends the life of the discharge electrodes.
Eliminating wasteful heating electrodes allows high performance even in a small lamp - typically 30% more performance than a comparable fluorescent lamp.
Cold cathode lamps have a life expectancy twice that of an ordinary compact fluorescent lamp. They are also not dependent on the accelerated drop in voltage supply fluctuations. The lower temperature also contributes to a longer lifespan for associated electronics.
Cold cathode lamps can be insulated indefinitely without causing damage. Without requiring a specific electrode temperature, the cold cathode lamp can be operated to any desired brightness within its maximum capability. They can even be used continuously in lighting applications that would destroy a traditional fluorescent lamp in a day.
The only disadvantage of this cold cathode technology is the higher manufacturing costs. These depend in part on the complexity of building trustworthy electronics for the high tube voltage - but are also dependent on the low production volume compared to that of conventional fluorescent lamps.
Assessment of the lifespan/duration of the system Under good conditions, a solar panel can be operated for far more than 15 or 20 years; this guarantee already exists on much smaller solar panels. As the most valuable and long-lasting component, it also determines the lifespan of the system.
Based on the 15-year PV service life of the system, the rechargeable battery must be replaced several times, which entails high operating costs. The lifespan of the battery depends on the charging and discharging regime but usually a normal SLA with a daily discharge of over 50% of its capacity needs to be replaced every two years.
A simple rule of thumb for matching panel and battery is that approximately 1 watt of solar charging equals each amp-hour in a 12 volt power system. A system typically supports 1 watt of lamp power for 4 hours per night for each watt of solar panel capacity.
Assuming a retail price of US$2 per amphour for smaller 12 volt SLA batteries and assuming US$10 per watt for smaller solar panels, the cost of the battery is actually the highest for life in the system.
Saving a single watt in a lamp would offset approximately $12 in the purchase price of the panel and initial battery and another $12 in the cost of replacing the battery over 15 years of system life.
Rainbow Power's new 7 watt cold cathode lamp can save up to 3 watts compared to a comparable standard compact fluorescent lamp, ultimately resulting in a total savings of $72.
Of course, improvements in lamp effectiveness can go a long way toward reducing overall expenses, both initially and over time. Conversely, a solar powered system can provide significantly more light for the same cost of using a higher power light source.
Further savings can be achieved by using the insulation option of the cold cathode. Useful light can be provided at less than half the full power, thereby also providing opportunities for consumers to tailor their power consumption.
In addition, the cold cathode lamp will usually last for more than 15 years if used for 4 hours per night. The ordinary fluorescent lamp will need to be changed/replaced twice during this period - experience has shown more often when exposed to variations in 12 volt operation.
The new range of economical compact cold cathode lamps from Rainbow Power represents a valuable/worthwhile investment in any photovoltic system. They form an important part of every small lighting system and provide an extended service life. They also minimize/reduce ongoing costs, which represent the biggest hurdle to the effective use of PV lighting systems by the world's poorest people.