The Science of the SALt Lamp - It's Not About the Saltwater by Pecier Decierdo


Can a lamp really be powered by saltwater? What is the science behind the SALt lamp that made the news recently and has been making the rounds in social media? How can you make your own saltwater lamp and what else can you do using saltwater?

(As I am writing this, I am playing with a toy car that will run when I put saltwater in its “tank”. I got this toy as a freebie at an event two years ago. It’s like the one in this video.)

A device called the Sustainable Alternative Lighting or SALt lamp received a lot of attention recently after the brains behind it, engineer Aisa Mijeno, was given an audience to US President Barrack Obama and Alibaba chairman Jack Ma during the APEC summit held this week in the Philippines.

Many news reports and online articles have described the device as a lamp that runs on seawater. President Obama himself said, “Aisa… is selling lamps that run on nothing more than saltwater.”

[Photo credit: Saul Loeb, AFP]

These are misconceptions. Saltwater, while an important part of how the lamp works, is not where the energy comes from. In other words, putting saltwater will allow the lamp to “run”, but the lamp does not run on saltwater. In fact, saltwater is not even an essential part of the system. You can replace it with vinegar, lime juice, or sports drink, and the system will still work.

Even the people behind SALt describe the principle behind their product imprecisely when they published the following marketing lines in their website: “Light your way with a lamp powered by saltwater,” and, “You can use the ocean water to power up your lamp!”

An elaboration on the same webpage, however, clarifies that the “lamp uses the science behind the Galvanic cell, the basis for battery-making, changing the electrolytes to a non-toxic, saline [salty] solution…” This means that the principle that makes the SALt lamp work is the same principle behind galvanic cells. 

Reviewing the high school chemistry behind galvanic cells will therefore make us understand what the SALt lamp is really about, so let’s do that by describing how you can make your own galvanic cell, and therefore saltwater lamp, at home. Making your own saltwater lamp will also give you a better appreciation of the work Aisa Mijeno has done and will upgrade your admiration of her work from merely, “Oh, she’s so clever!” to “Wow, I aspire to be an innovator like her!” 

People, especially the young, should stop merely admiring scientists and innovators and start aspiring to be like them. Better yet, young people should aspire to be better than the innovator they admire. That is what innovation is about, after all.


[Photo credit: UC Davis Chemistry Department Chemwiki]

Before we describe how you can make your own galvanic cell, let us describe what goes on in a galvanic cell. This will show why the SALt lamp and similar devices are not powered by saltwater. The galvanic cell is in fact powered by two kinds of metals inside, one called a cathode and another called an anode

The power is generated by the fact that the cathode and anode are playing electromagnetic tug-of-war, jostling for the electrons in the device’s circuit. By definition, the metal that happens to be the cathode wins the tug-of-war and grabs the electrons from the anode. But if that’s just it, then there would be no steady current, because there is no complete loop for the charge to go around.

No current means the lamp won’t light up. This is where the saltwater comes in: it carries the accumulated negative charges from the cathode (remember, the cathode has grabbed the negatively-charged electrons) and brings it to the anode. The saltwater closes the circuit, allowing a steady flow of charges that powers the device. 

Saltwater can do this better than tap water because saltwater has lots of dissolved ions. It is these ions that transport the charges. Vinegar, lime juice, and sports drinks have ions too, and so they will also work. Materials like saltwater and vinegar that have ions that can flow within them are called electrolytes.

[Photo credit: i2.wp.com]

To make a simple galvanic cell, you will need the following. First, find two different kinds of metals. Maybe one would be iron and the other is copper. Or maybe one is zinc and the other is aluminum. In fact, you can experiment on which pair of different metals will make the lamp glow brightest and for a longer time. That’s called doing science!†† 

Second, you’ll need some wires and alligator clips or electrical tape. (Most copper wires are coated with a material that is a poor conductor. Remove this coating using sandpaper.) Third, find a small LED lamp. If you are working in a place that’s too bright, you might want to use a small buzzer instead. Next, find cups or glasses, and tissue paper. Finally look for a suitable electrolyte, like saltwater or vinegar. 

You can also experiment on this by trying different solutions to see which will give you the brightest glow or the longest battery life, just like in the study “Cheaper Electrodes Having Higher Efficiency Using Salt Water and Salt Vinegar Electrolytes” published in the International Journal of Innovative Research and Development last October, 2012.1

People too need electrolytes, but they are not an energy source like
carbohydrates and sugars.
[Photo credit: howstuffwork.com]

Now let us make your saltwater lamp. Put water in the cup. Then, add some table salt and stir to mix. (Try 25 g of salt for every 500 mL of water.2) Dip the two metals in the salt solution, making sure that they don’t touch each other. Connect terminal of the LED lamp to the first metal using a copper wire, then connect the second terminal to the second metal in the same way.

 If the LED lamp is not lighting up, it might be due to one of two things. First, you connected the LED in a reverse way. LEDs are diodes. (LED stands for light-emitting diode.) Diodes have a preferred direction of current flow. Just reverse the way you connected the LED. Second, your saltwater battery is not producing enough power. 

To solve this just make more saltwater batteries! Get another cup, repeat the process above, and connect the two batteries you made. Make sure the connection is end-to-end or series, instead of ladder-like or parallel. If two batteries do not do the trick, try three, four, or even more. You don’t have to limit yourself with an LED light or a buzzer, by the way. Get creative with your devices!

The potato battery works on principles similar to the saltwater battery.
[Photo credit: techengineering.org]

Here’s another variation to the same basic design that uses activated charcoal.†††

Doing this as a project will give you a feel for the challenges faced by people who want to design an improved saltwater battery. If you want to innovate on this, you can try experimenting with the basic design, adding your own modifications to see if it makes the LED lamp shine brighter or last longer.

 A big challenge in making saltwater batteries is the fact that the anode gets consumed – you cannot get energy for nothing! Whenever you are producing energy, something always gets consumed. As they say in physics, there is no free lunch. Like any battery, your saltwater battery will eventually run out of energy when the anode is fully used up.

 In practice, the bulb will stop lighting up even before the anode is completely consumed. This will happen even if you change the saltwater regularly. After all, the saltwater is not its energy source; as I mentioned above, the saltwater lamp does not run on saltwater.

Another challenge in making devices that use this principle is making them more efficient. As with money, you often have to spend energy to gain energy. The question always is do you gain more energy that the amount you invested? 

The more energy you gain per investment, the greater the efficiency of your device. Making anodes and cathodes requires an investment in energy. How can you make a saltwater battery that gives you way more energy that this initial investment? This question can be asked of the SALt lamp as well – does it produce more energy that what was used in creating the device?

Another issue about the SALt lamp would be the waste. This article by TJ Dimacali has an excellent discussion on the potential waste issue of the SALt lamp.

Given the claims of SALt, it would seem that their lamp is a good power source because it produces 90 lumens of light that can glow for 8 hours, and you only have to replace the consumables (mainly the anode) after 6 months of continued use. These are impressive numbers, and are probably brought about by an innovation in the design. 

Unfortunately, the SALt website does not contain information about this possible innovation. I hope they will soon make their innovation open-source, so that tinkerers in the Philippines and around the world, especially the poor who need it, can take advantage of the technology. They can choose to patent their innovation if it is novel enough.

So that, in broad strokes, is the science behind saltwater batteries, how to make your own, and why they don’t “run on saltwater” as many seem to think. I hope it inspires you to tinker and innovate like Aisa Mijeno and hear teammates at SALt. Remember that science is not about geniuses propped up in pedestals of unreachable height, but about hard working folks we should try to emulate. This International Year of Light, I hope that we will find better ways to light up our world, both literally and metaphorically.


 Footnotes:

There is a missing piece to this story which is the role of dissolved oxygen in the solution. For an excellent discussion of the role of dissolved oxygen in galvanic cells, check out this link.
†† For the advanced reader, you can check this table of reduction potentials to guide you. Try to find materials with very different reduction potentials. Good luck on finding gold to experiment on!
††† This design and the one described above are different from the standard chemistry set-up that uses two separate compartments for the anode and the cathode. Each compartment is called a half cell. Each half cell contains a solution that has the ionic form of the anode and cathode. For example, if your anode is zinc and your cathode is copper, the solutions can be zinc sulfate and copper (II) sulfate, respectively.

References: 

1 Ramakanth, S., “Cheaper Electrodes Having Higher Efficiency Using Salt Water and Salt Vinegar Electrolytes”, 2012, IJIRD, Vol 1 Issue 8.
2 Chasteen, S.V., & Chasteen, N.D, & Doherty, P., “The Salty Science of the Aluminum-Air Battery,” 2008, The Physics Teacher, Vol 46. 
3 The Exploratorium, “Saltwater Pentacell”, 2002, Square Wheels: An Exploratorium Snackbook.

4 Bardhan-Quallen, S., Championship Science Fair Projects. Goodwill Publishing, New Delhi, India.


3 comments:

  1. I hope everyone like this information they shared as I do. Really great information.
    Salt lamp

    ReplyDelete
  2. Wow, what a fantastic post. The best post around. Thumbs up
    Salt lamp

    ReplyDelete
  3. It is not so much about the technical aspect but, more about that they were able to make a simple designed utilizing know principle to make it work for the people who really need it and, without going out of the way to get it. I do not think they need to explain too much on the real principle behind as 80% of the public really doesn't care anyway... Kudos to her and her team efforts.

    ReplyDelete