Solar LED Technology
Finally, the technology to combine very low voltage LED lights with a rechargeable solar-powered NiCad battery system is here. While there have been solar panels used to charge batteries of various sizes for many years, powering standard 12v or 110v lights quickly drained all but the largest batteries that could be quickly recharged with solar power.
We have designed a very small, lightweight, elegant system that combines the new technologies of low voltage LED lights, solar panels and rechargeable solar powered NiCad batteries. The result is a selection of lights that burn bright, long, inexpensively, cool and safe. And we have many more new and exciting products in development!
You can find more information about solar LED lights, the NiCAD batteries used in our solar lighting systems and solar panels below:
WHAT IS AN LED?
An LED, or Light Emitting Diode, contains a chemical compound that gives off light when an electric current passes through it. They’ve been around for many years, but only recently has the technology advanced so that rather than just an ‘indicator’ light on your stereo amplifier or phone, they can be made bright enough to actually use as an independent light source.
LEDs put out a tremendous amount of light for their size and energy draw. They create almost no heat and use very little electricity. White LEDs were only developed in the past few years; before that they were only available in red, green, yellow and a few other colors. Best of all, an LED will last thousands of hours; some have been tested to over 50,000 hours (vs. a standard flashlight bulb that will only last a few hundred hours).
On a more technical basis, the centerpiece of a typical LED is a diode that is chip-mounted in a reflector cup and held in place by a mild steel lead frame connected to a pair of electrical wires. The entire arrangement is then encapsulated in epoxy. The diode chip is generally about 0.25 mm square. When current flows across the junction of two different materials, light is produced from within the solid crystal chip. The composition of the materials determines the wavelength and color of light.
The shape, or width, of
the emitted light beam is determined by a variety
of factors: the shape of the reflector cup, the
size of the LED chip, the shape
of the epoxy lens and the distance between the LED chip and the epoxy lens.
We designed our LED for a fairly
wide dispersion of light (rather than very focused).
For this reason, if you look directly into our LEDs they might not appear as
bright as ones that have a very narrowly focused
beam (better for headlamps and flashlights). If
you look from the side, however, you will find
they display much more light than a focused beam,
and are thus better for a lantern application
where you want light in a wider area.
HOW MUCH POWER DO LED LIGHTS DRAW?
Different colored LEDs use different amounts of electricity. In general, an LED uses about 1/10th the power of an incandescent bulb and they are up to 90% more efficient than both fluorescent or neon bulbs of similar wattage.
If you wired your house to use LEDs instead of incandescent bulbs you could run the lights day and night for a year with just a 12 volt car battery. Therein lies the beauty of our system: finally we have LEDs bright enough for task lighting that can be powered by a very small, easily recharged power supply.
Most LEDs draw between 20-30mA of current. A typical rechargeable AA battery will supply between 500-1,500mA, meaning 15-50 hours of light. Allowing for varying voltage regulating circuits, the actual burn times are about 20% less.
The voltage required to
power an LED depends on which
end of the light spectrum it’s color lies:
red LEDs take the least (about 2 volts) while
blue take the most (up to 4 volts). When the available
voltage drops below the minimum required by more
than 10% the LED will not work.
This is one of the more curious electrical anomalies
of LEDs: Ohm’s law—one
of the most basic laws of electricity—does
not work.
WHAT ABOUT THE BATTERIES?
Sollight's solar LED lights use rechargeable NiCad battery packs because for overall performance they provide the best solution for storable power.
NiCads have an observable memory effect (meaning they will tend to only charge a certain amount based on what they are used to). However, this has only been observed in situations where the battery has been discharged to the EXACT same level for numerous cycles (more than 50 cycles). NASA experienced memory effect in its early satellites that orbiting the earth for several months, when they tried to charge the batteries to a greater charge (fuller), the batteries where not able to take this charge. The solution was to drain the batteries below the level that they had been repeatedly drained to, then they where able to receive a greater charge.
In the case of Sollight's LED lights, it is unlikely that the batteries will receive either the exact same charge or discharge for more than 50 cycles, so the memory effect should not be a problem. Regardless, it is a good idea to charge your LightCap FULLY before you first use it, and to keep it charged as much as possible when not in use.
NiCad batteries lose (discharge) 1-2% per day while inactive. This also depends on the level of charge (faster when full), and temperature (faster when hot)). So even if the batteries are fully charged, they will essentially be dead in 90 days. We recommend that you keep your LightCap fully charged whenever possible, and that you give it a good direct sunlight charge at least once a month if you keep it stored.
Finally, while there are
several other types of battery/charging systems
available, NiCad batteries have the best shelf
life of the declarable battery family. NiMh batteries,
often used in items that will receive a daily
recharge (cell phones, laptop computers, VHF radios,
etc.), discharge at a rate of 3-4% a day.
WHAT KIND OF SOLAR PANELS WE USE?
There are two basic types of solar panels (also referred to as a PV - photo voltaic cell): mono-crystalline and poly-crystalline. Each has it's own output characteristics.
Our Siemens solar panel is made from Polycrystalline silicone. It yields a slightly higher charging output than a mono-crystalline in direct sunlight, slightly less in overcast conditions.
Our solar panel is rated at 90mA (milli-amperes), meaning it will put out 90 mA of power each hour in high intensity light or direct sunshine. In overcast conditions, and even when the PV is not oriented directly at the light source, the output is greatly reduced. They may go as low as 6mA on an overcast day, in the shade or indirect sun.
Why is this important? Our NiCad batteries each hold 800mA of power; we use two of these, for a total capacity of 1,600mA. Thus, if the PV is putting out an average or 50mA per hour, it will take approximately 32 hours to fully charge the batteries. This, in turn, should power the WHITE LED for up to 20 hours, and the RED LED (which draws less energy) for up to 30 hours. As the batteries discharge, the output voltage will also decline slightly, along with the brightness of the light.
For this reason it's always good to keep the batteries charged, and to keep the PV exposed to light whenever possible (to top off the batteries). Even a few hours in a well lit room can add a half-hour of burn time to your Sollight solar powered LED lights.
