Tuesday, May 27, 2008

Back to work



Alessandro didn't get quite what he expected at the haircutter's! But it is quite the fashion.

I'm back at work 50% and started yesterday by working with my trainee to make CIGS (copper-indium-gallium-diselenide) solar cells. There are many steps in this process, all involving coatings on glass of thicknesses on the order of around a micron (a thousandth of a millimeter)or less. Yesterday's step was the making the CIGS layer itself, the heart of the solar cell. I started at 10am and was done at midnight - it looks like I've almost finished my 50% worktime for this week!

Friday, May 23, 2008

Apple and wood


Finally some sun after a week of wind and rain, with temps going below freezing at night. With 17C right now, it feels wonderfully warm. The apple tree has almost finished flowering, but I managed to catch the last blooms in this picture. 16 cubic meters of cut and split wood was delivered (in pouring rain) which, with the 4 cubic meters left over from last year, should be enough to heat my home for the next winter season. If all goes as planned, of course, I will not be living here for the entire winter, but will be in cow and chocolate country (I didn't mention watches - I don't wear one and am mostly uninterested in the time). The wood will need to be stacked and sun-dried in the summer before it's ready for the fire, but it tends to be too much even in my normal two-handed state and I usually get some friends over for a barbecue and wood-stacking party. This time will be no exception - I've just invited the entire department of engineering sciences, about 30 of us, over for a garden party in three weeks. While I made no mention of the wood stacking activity as yet, I'm sure that sometime between now and party time there will be a few offers of 'Let me know if you need help with anything...'.

Thursday, May 22, 2008

честит рожден ден!

It was my Bulgarian friend Ventsi's birthday today. To celebrate, he invited some friends to lunch in town - four were Bulgarian, two were Czech and then there was me. The Czechs, Tomáš and Ariana, who are also good friends of mine, were shaking their heads at having to listen to a language as incomprehensible as Bulgarian. One of the other Bulgarians, Ilia, is the head of our department at the Ångström lab and also a good friend. During my six years of joining in various Bulgarian activities both at work and elsewhere, I have managed to pick up a smattering of words from the language, especially after Ilia downloaded a number of Bulgarian folk songs onto my computer. One word which never fails to enter the conversation is ракия. However, none was consumed at our lunch today.

Wednesday, May 21, 2008

Thumbthing

Today I was at the hospital to get more x-rays of my thumb and wrist to hopefully discover why the healing process is so slow. There was a new doctor this time, the fifth doctor so far, but apparently it's normal practice at the hospital to get whichever doctor can fit in a bit of time in their overly tight schedules. The new x-rays showed that, in addition to a ligament having been separated from my thumb and removing a piece of bone with it, my skiing accident also caused re-injury to one of the bones in the hand called the navicular bone. The translation from Swedish is simpler: it's the boat bone (båtben). Apparently I injured this bone a couple of decades ago - I sort of remember having to write left-handed for a month due to some injury. Since it was untreated, it never healed, and the cartilage that separates it from its neighbor no longer exists, making re-injury more likely. Apparently I can also expect arthritis in my coming years, if this hasn't already caused it to start now. The result of today's visit is that, instead of returning to work this Monday, it will be three more weeks at home, and therefore a few more blog entries can be expected. Nevertheless, I plan on getting my bicycle out soon and see how well I can ride using the gears and brakes on the left side only. And not actually grasping the handlebar on the right.

Tuesday, May 20, 2008

A solar module

As long as this blog lacks a sense of direction, I expect that I'll be jumping from topic to topic at random with no organization. So today I thought I would show a small solar module that I made at the Ångström Laboratory, which is where I work. The module is a copper-indium-gallium-diselenide cadmium-free device, but I'm not going to explain that at this time. This particular module is about three years old, and unfortuneately, this picture wasn't taken until the device had already started to oxidize. That's why it looks like a map of the earth's land masses was printed on it. I had glued the protective glass on it - encapsulated, in the solar world - rather sloppily. It originally had a satiny black appearance, which is the look any self-respecting solar module should strive for since it's the color that absorbs the most sunlight.
The outer dimensions of the glass are 12.5 by 12.5 cm, but only the black area between the electrical contacts actively contributes to electricity generation. And this is where it starts to get technical. The graph I've included namely shows the module's electrical operating characteristics when under sunlight, although, to be precise, I faked the sunlight by using a light bulb whose intensity and color spectrum more or less imitate that of your basic 'standard' sun. The word 'standard' should, of course, make your eyes roll - maybe I'll say something about it some other day. Anyway, back to the graph: the vertical axis is current, the horizontal one is voltage. There are three little x's on the curve. One marks the point where the device is short-circuited such that the voltage is zero and the current is maximized, noted as Isc in the table. Another is when the circuit is open such that the current is zero and the voltage is maximized, noted as Voc in the table. The third is the one of most interest. It lies in the middle of the curve at the maximum power point where the product of I times V - power, that is - is maximized. Any external circuit that tries to be powered by a solar module should try to draw just the right amount of current at the maximum power point if it wants the most power that can be produced.
The table, besides showing the active area of the module, Isc and Voc, also calculates two other things: fill factor FF, and efficiency. The fill factor is a measure of how 'square' the curve is and is used to calculate the efficiency of a device, although fill factor has a different meaning to my beer drinking friends who are contemplating their beer glasses at our regular Friday night beer gatherings (this could be a topic for another day). The efficiency measures, in percent, how much of the sun's power can be delivered by the device in the form of electricity and is calculated by multiplying Isc times Voc times FF. This particular module is 14.8% efficient. In terms of power output, it can produce 14.8% of the sun's power, which, for a 'standard' sun just happens to be 1000W per square meter. In other words, if this module were as big as 1 square meter it could produce 148W of power (if the sun were 'standard', ha ha). But this particular little module is only 76.8 square centimeters (=0.00768 square meters) so it can produce 0.00768 times 148 equals to 1.14W, a result that makes me glow with pride.
Oh, by the way, I should mention that the I-V curve above was measured at NREL, the National Renewable Energy Lab in Colorado, a former employer of mine where they do such internationally recognized efficiency measurements of solar devices to keep people like me honest.

Monday, May 19, 2008

Forget-me-not

Why have I chosen to sign my posts as Forget-me-not? The simplest reason is that I typically choose some flower name for myself, and when prompted for a name, I went outside and saw the beautiful forget-me-nots in the garden where I just took this picture. Ultimately, of course, I associate myself in some way with the flower I choose. This association is quite straightforward - as I look ahead to changing my job, changing my language (from Swedish to German) and changing my country of residence (Sweden to Switzerland) I'm hoping that I won't be entirely forgotten by the friends and colleagues I leave behind. My many previous moves have already resulted in my friends being located worldwide. This time, the move will be accompanied by my two boys also moving to new countries: the oldest, Daniele, will spend his third year in the physics program at Cambridge, and the youngest, Alessandro, will relocate with his father to Florence where he will start high school (gymnasium, as it's known in Nordic countries). My own move is actually not that imminent, being probable in late fall.

Sunday, May 18, 2008

day 2

My blogging interest has survived into day 2. I have now started to wonder what the content of my blog eventually might be. Will I write about that truly fascinating subject, copper-indium-gallium-diselenide thin film solar cell research or the somewhat more mundane thoughts and events of my personal life in a diary to be read only by myself? Today, it is most definitely the latter. This blog owes its existence to my sheer boredom at being well into my third month of being home from work while waiting for a torn ligament in my right thumb to heal. No apparent (to me) healing has occurred and the thumb remains 100% out of commission. I am now waiting for a professional assessment at my next doctor's visit which will hopefully be this week. However, in the somewhat doubtful event that this blog will still be in existence a month from now, I plan on including some solar cell tidbits, such as excerpts from my recent power point presentation in which I presented the highlights of the last six years of my research activities at the Swiss Federal Institute of Technology (ETH) in Zurich.

Saturday, May 17, 2008

how to

Ok, maybe my first posting wasn't very original, but I figured it was as good of a start to my diary as anything while I'm taking myself through the 'how to' phase of blog creation.
The best things in life are free.