Solar lamp

A solar lamp in Rizal Park, Philippines

A garden solar lamp

Magnifying glass

A solar lamp also known as solar light or solar lantern, is a lighting system composed of an LED lamp, solar panels, battery, charge controller and there may also be an inverter. The lamp operates on electricity from batteries, charged through the use of solar photovoltaic panel.

Solar-powered household lighting can replace other light sources like candles or kerosene lamps. Solar lamps use renewable energy with infinity supply which is cheaper than standard lamps. In addition, solar lamps reduce health risk as kerosene lamps have a bad impact on human health. However, solar lamps may have higher initial cost, are weather dependent.

Solar lamps for use in rural situations often have the capability of providing a supply of electricity for other devices, such as for charging cell phones. American investors have been working towards developing a $10 / unit solar lantern for replacement of kerosene lamps.

History

In the past solar panels used large crystals mainly made out of silicon which produced electricity when it was exposed to light. When electrons in silicon are exposed to light, they start to vibrate from their fixed positions following thermodynamics rules. Furthermore, it produces heat from the vibration and the movement. Through this, silicon turns a large portion of light energy into electricity. However, manufactures found silicon too expensive to make and to put in as a component of solar lamps.

Photoelectric effect used in solar cells was first noted by Edmond Becquerel, a French physicist, in 1839. Albert Einstein won a Nobel prize in 1922 by exploring the nature of light and the photovoltaic technology based on photoelectric effect. The first photovoltaic module was build in 1954 by Bell Laboratories.

On the other hand, nowadays solar panels are made out of smaller and cheaper crystals. For example, copper, indium, gallium and selenide. These new crystals can be used to form thin flexible films. However these cheaper crystals are less efficient at turning light energy into electricity. Therefore, it is an ongoing project to find a cheaper, efficient silicon substitute material that can be easily mass-produced and convert light into electricity very easily.

Components

The whole structure of solar lamp is shown in Figure 2.

Figure 1

Solar cells/Solar panels

Solar panels are made out of crystals that are made out of covalent bonds between electrons on the outer shell of silicon atoms. Silicon is a semiconductor which is neither metals that conducts electricity nor insulators that do not conduct electricity. Semiconductors normally do not conduct electricity but under certain circumstances they do in this example with exposition to light.

A solar cell has two different layers of silicon. The lower layer has less electrons and hence has a slight positive charge due to the negative charge nature of electrons. In addition, the upper layer has more electrons and has slightly negative charge.

A barrier is created between these two layers however when the stream of light particles called photons enter, they give up their energy to the atoms in the silicon. It promotes one electron from a covalent bond to a next energy level from upper layer to the lower layer. This promotion of an electron allows freer movement within the crystal which produces a current. More light shines through, more electrons move around hence more current flows between. This process is called photovoltaic and photoelectric effect. Photovoltaic systems literally means combination of light and voltage and they use photovoltaic cells to directly convert sunlight into electricity.

Solar panels are made out of layers of different materials, as you can see in Figure 2, in order of glass, encapsulate, crystalline cells, encapsulate, back sheet, junction box and lastly frame. The encapsulate keeps out moisture and contaminants which could cause problems.

Figure 2

Battery

A battery is usually housed within a metal or plastic case. Inside the case are electrodes including cathodes and anodes where chemical reactions occur. A separator also exists between cathode and anode which stops the electrodes reacting together at the same time as allowing electrical charge to flow freely between the two. Lastly, the collector conducts a charge from the battery to outside.

Batteries inside solar lamps usually use gel electrolyte technology with high performance in deep discharging, in order to enable use in extreme ranges of temperature. It may also use lead-acid, nickel metal hydride, nickel cadmium, or lithium.

This part of the lamp saves up energy from the solar panel and provides power when needed at night when there is no light energy available.

In general, the efficiency of photovoltaic energy conversion is limited for physical reasons. Around 24% of solar radiation of a long wavelength is not absorbed. 33% is heat lost to surroundings, and further losses are of approximately 15-20%. Only 23% is absorbed which means a battery is a crucial part of solar lamp.

Charge Controller

This section controls the entire working systems to protect battery charge. It ensures, under any circumstances including extreme weather conditions with large temperature difference, the battery does not overcharge or over discharge and damage the battery even further.

This section also includes additional parts such as light controller, time controller, sound, temperature compensation, lighting protection, reverse polarity protection and AC transfer switches which ensure sensitive back-up loads work normally when outage occurs.

Inverter

Solar energy is produced in DC therefore DC-AC inverter is required to enable people to use AC power of either 220V AC or 110V AC.

Working principles

Figure 3

LED lights are used due to their high luminous efficiency and long life. Under the control of a DC charge controller, non-contact control automatically turns on the light at dark and switches off at daytime. It sometimes also combines with time controllers to set curtain time for it to automatically switch light on and off.

As shown in Figure 3, the chip includes microchip(R), B-, B+, S- and S+. S+ and S- are both connected to solar panels with wire, one of which has plus charge and the other minus charge. B- and B+ are attached to two batteries in this case. The light will be shown through the LED light when all of these are connected.

Properties

Easy to install

Solar lamps are easier to install as often they do not have cable. Not having a cable is a huge advantage as sometimes electricity-run lamps are broken due to the cable lines and reduce the chance of broken lamp. Additionally, LED lighting will provide high-quality illumination.

Cost

There is no maintenance cost required and it is one-time investment as it usually runs itself. Also it can be used wherever and whenever if it is charged. In addition, there is no need to use electricity therefore decrease the charge on electricity bill. Hence, it can be used in areas where there is no electrical grid, for example remote areas or rural areas where they are under-developed.

Using renewable energy

No worries about running out of solar energy to charge the lamps unlike some of the other sources of energy such as electricity or fuel.

Weather dependent

If the weather is cloudy or wet, it will reduce the amount of energy being produced especially in winter there is lower production. In addition, when there are storms or hurricanes, also reduce the efficiency.

Health

In addition, households using solar lamps rather than kerosene lamps are able to avoid the health risk that kerosene can cause. Kerosene often has a bad impact on the lungs.

Pollution

The use of solar energy avoids the creation local pollution and this is especially important where solar lamps replace kerosene lamps indoors, which have been linked to very large numbers of cases of ill-health and deaths. However, photovoltaic panels are made out of silicon and other toxic metals including lead. This is an area scientists nowadays are researching into in order to reduce the harmful impact on environment during their production and final disposal.

Use

Solar street light

Main article: Solar street light

These lights provide a convenient and cost-effective way to light streets at night without the need of AC electrical grids for pedestrians and drivers. They may have individual panels for each lamp of a system, or may have a large central solar panel and battery bank to power multiple lamps.

Solar LED lantern

Rural

In rural India, solar lamps, commonly called solar lanterns, using either LEDs or CFLs, are being used to replace kerosene lamps. Especially in areas where electricity is otherwise difficult to access, solar lamps are very useful and it will also improve life in rural areas.

See also

• Light tube
• Liter of Light project
• Solar device
• Solar Street Lighting
• Solar thermal collector#Evacuated tube collectors