By Ebele Orakpo
Professor Michael Chendo is the Head of the Department of Physics, University of Lagos. In this chat with Vanguard Learning in Lagos, Chendo, who had worked with EU Joint Research Centre in Ispra, Italy, says solar energy could be used to empower women and improve the nation’s economy. Excerpts:
THE first part of my research was in this area of solar irradiation in Lagos because prior to that, there was virtually no information on that and in solar business, you have to know the amount of energy you have to enable you to plan. That was the first thing I did in 1979/80 after which I also introduced a new concept in terms of graduating the performance of solar steel used for distillation of water. We introduced what we call MTF, modulation transfer function. Then later, we embarked on how to make more efficient solar cells by ensuring that the solar cells get appropriate/optimal photons.
Professor Chendo said there were three options open to them to achieve their aim. “It is either by what we call tandem arrangement for the solar cells or selective filters. Either we do it by beam splitting or beam shifting of the solar spectrum. Normally, if you allow the entire solar radiation to fall on a particular cell, the unwanted portion will heat up the cell causing some damage.
The idea then was to determine the optical window from this particular cell and then devise a means o f making the unwanted portions of the spectrum to perform maximally. So in spectrum shifting, first of all, the sunlight is focused on a particular target and then that target will absorb certain portions of the spectrum and then shift whatever is left to the solar cells.”
Continuing, Chendo said; “I eventually zeroed down to beam splitting technique. Again, there were two main aspects. As I said earlier, if you allow the entire spectrum of the sun to fall on the solar cell, the unwanted portions will heat up the solar cells and cause damages so why not extract these unwanted portions and convert them to heat? So the idea was to develop a complete system. There were two options – either develop what we call optical absorption filter or interference filter.
Absorption/ Interference filters: “What we did was to get a plate which we coated with different layers of tinting material. Let me give you a practical example, you have seen a tinted car. You cannot see those in the car but they can see you. So we coated the materials with different layers so that whatever the first layer rejects, will get to the second layer until eventually it gets to the last layer and that will be just what the cell requires. It is highly technical and very involving.”
“Then we came to absorption filters. We looked at the same chemicals to see how we can optimally utilise them to match the windows. What we did was to use optical spectrometers and then manipulate the thickness with the volume of the lens of the cylinders to see how we can eventually get what we want. With that, we were able to get some good results.”
Chendo said the results he got in 1987 became very useful to the science community. “When I went to Norway in 2003, a group from Australia was quoting what I did, not knowing I was in the conference and when they found out, they were very excited. Then in 2006, I went to another workshop in Italy, they were talking about these concentrated solar cell devices. You know in concentration, all they want to do is to minimize the space which means the cell has to be of thicker texture. A group used the concept to develop concentrated solar cells. I was excited because I saw the fruit of my labour in the 80s,” he enthused.
He noted that using concentrated solar cell devices in places like Lagos, might not be readily adopted “because the sunshine here is very diffuse because of pollution unlike a place like Sokoto with less pollution where you will be able to track the sun.
Algae fuel or Algal biofuel:
Prof. Chendo said he is working on the troublesome algae, to make it useful. “Right now, we are working on a material that seems to be a nuisance, the algae, which we will use to generate energy. A lot of work has been done on algae worldwide. It has been shown to be very potent in terms of biofuel. The question now is; how do we cultivate algae in commercial scale?
We know there are different species of algae. What we are doing now is first of all identify these different species of algae and then determine the portion of the spectrum where they are most sensitive. They don’t all require the same amount of sunshine. The spectrum goes from about 3 to 1.5 micrometre so everyone takes what he wants. Whatever he does not want is a waste just like I said of the solar cells. We have already identified some portions of the spectrum where they can thrive.