Is there something in the hair? The tale of a solar cell made with human hair
By Paul Ridden
October 15, 2009
Debate is good. Debate is healthy. Debate is currently raging after an article recently appeared on the UK's Daily Mail website announcing a revolutionary solar cell that's made using human hair. A group of teenage students from Nepal claim to have replaced expensive doped silicon used in conventional solar panels with cheap and readily available human hair to produce a cell capable of generating 9V (18W) of electricity. Curiosity got the better of Gizmag's Paul Ridden, who contacted one of the team to find out more.
Although the Daily Mail article has been used as a primary source reference for many of the subsequent articles that have appeared, it lacked any great detail on how the cell was made and how it was claimed to work. This in turn has led to a great deal of debate on whether such a cell could actually work as claimed, or rather, as reported. Gizmag managed to track down team member and inventor of the cell, 18 year-old Milan Karki and asked about the project.
Working with fellow students from the Science and Technology Guild at the Trinity International College in Kathmandu, Karki appears to have based his innovation on a dye-sensitized solar cell rather than the more familiar layered silicon design. Karki was happy to share some details about his invention with Gizmag but was (naturally) somewhat guarded about full disclosure pending a patent application.
To create his cell he took a piece of glass, stained one end with some silicon dioxide to act as a cathode and fixed oxidized copper to the other (the anode). Human hair was soaked in organic salts and then stretched between the two connections and held in place. A thin layer of graphite covered the silicon end and the copper end left exposed to light (sunlight/UV). A few drops of iodine on the hair act as an electrolyte.
It's said to create electric current when light hits the oxidized copper end and knocks out some electrons which then travel down the salt-soaked hair to the silicon end. The function of the hair is not to soak up sunlight but to act as a bridge in the circuit to help electrical current flow, in other words as a conductor or semi-conductor.
Several of these cells are placed together in series and the power produced when exposed to sunlight is then used to charge a 12-pack of AA rechargeable batteries.
The public speaks
Underneath the Daily Mail article (in common with other sites which have used the article as source for their own stories) you'll find comments from both well-wishers and those who question the validity of the solar cell. The latter having various issues with the science behind the discovery. One commenter, experienced engineer Craig Hyatt, went so far as to create a debunking website where he tackles many of these problems head-on.
Of all the issues, probably the main one is that human hair does not conduct electricity. That hair can and does produce a static charge there is no doubt but as to whether it can conduct an electric current, all the evidence prior to this announcement clearly points to hair being an insulator rather than a conductor, such as the controlled experiments conducted by R A Fischer & Co in 1998.
Karki points to the porous quality of the cortex of human hair and told Gizmag that when pre-soaked in organic salts, the electrons flow through the hair assisted by the conductivity of the salts. He confirmed that while other porous materials had been not been investigated to see if there was a better and cheaper material available, numerous tests with varying colors of hair showed black hair to be the best promoter for those electrons. He attributes this to the higher levels of pigment found in dark hair.
And that leads to another point of contention. Melanin does indeed have electrical properties but as Hyatt points out: "as long as it's bound to the keratin in hair, it is insulated and doesn't come in contact with any electric charge. If there are any active melanin molecules present, they only act as a pigment or convert UV into heat which is how they protect your body from solar radiation." In order to conduct electricity the melanin would need to be "isolated from keratin and concentrated."
Karki says that the melanin merely acts to enhance the flow of electricity and it's the organic salts which actually do most of the work. In fact, he admits that once the hair dries out, the cell stops working but says that getting the cell operational again is a relatively simple matter.
The dark room
Most of the press photographs show the student team holding up the solar panel and powering a light bulb in what appears to be a very dark room. Even the most efficient solar cells currently available need direct sunlight to operate. Olivia Lang, the journalist who originally broke the story, was "out of the office" at the time of writing but Gizmag managed to contact the photographer, Tom Van Cakenbergh. He told us that: "the philosophy of the panel is that it charges a battery first. Indeed I saw it cannot provide enough power for a light directly. The images are shot with the whole set up: panel, battery and bulb."
Experienced teacher of electronics Tony Kuphaldt told Gizmag that this amounted to: "claiming I've made a fantastic new water pump out of human hair, then on the day reporters show up with cameras I demonstrate how a tank full of water - filled the night before with my amazing new pump - is actually full of water today." Kuphaldt also pointed out that silicon dioxide is an insulator too and is "widely used as a nonconducting substrate material in the semiconductor industry for precisely this reason."
However, Van Cakenbergh says that he was also present at a small demonstration where: "the solar panel was connected to a meter (no batteries or whatever) and then we moved it from shadow to sunlight. The numbers on the meter went up a lot." Although, by his own admission no expert in solar energy, he says that on checking the panel over he saw only "the hair, the metal buds, dark paper, electrical wires all attached to a wooden board."
Given that the sacrifice of electrons in a silicon-based cell is not overwhelmingly efficient at converting the sun's energy into electricity and that dye-sensitized cells are even less so, the 2ft by 1.5ft panel featured in the press shots appears to be a bit on the small side to produce the reported output. Karki confirmed to Gizmag that the prototype used to produce the claimed 9V (18W) reading was in fact 6ft by 5ft.
What do you think?
In the absence of any professional technical expertise at the reported demonstration, eye witness reports and the claims of the inventor would lend themselves to the conclusion that the panel doesn't produce enough electricity to power a light bulb but enough to trickle-charge a set of batteries. Exactly how that happens has been and continues to be the subject of much debate and whether the system proves efficient enough and robust enough to have commercial applications remains to be seen.
Karki says that a couple of panels have been sent out to districts in Nepal for feasibility testing. When the patent process is finished with, the Trinity team will be looking to market the invention. More important for some perhaps, at the same time Karki says he will be proving their detractors wrong by disclosing the full details of the solar cell. Something that will no doubt add even more fuel to the debate.
By now you're probably drawing your own conclusions and we'd like to hear them via the comments below.
(All images supplied by Milan Karki)Share
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