My solar installation

With the introduction I've now given to some nitty gritty solar cell details, I expect you're breathlessly waiting to see my own personal solar installation at home. So I've included a photo of my somewhat funky looking house. In the pic you'll notice the more or less red clay tiles on the roof and the gray-white asbestos "eternit" tiles that make up the siding of the house. Not visible, of course, is the insulation in the walls, which is nearly non-existant in my 1910 house. Also not visible are the solar panels. That's s right - I don't have any! Despite a 25+ year career making a better solar cell, I have never actually owned my own. It's not for lack of interest - solar cell research has always been a passion and never just a job. I suppose I could blame it partly on my nomadic lifestyle, always expecting to pick up and move to some new town, some new country. But that's not a good reason. I've actually been in Sweden for 10 years and before that in Bologna, Italy for 11.

Another reason would seem to be that I live in Sweden, SWEDEN!! Solar in Sweden?? But the reality is that Sweden gets about 30% as much of the sun's energy as does Sahara, even if it does mostly arrive in those incredibly long summer days. Being fairly certain that the lack of solar panels isn't entirely due to my love of procrastination, I'd say that the reason (blame) lies elsewhere. Ultimately I'm just another solar inspired consumer looking for market incentives and a reasonable payback time to buy and install a system. And for this, Sweden is not another Germany or Japan or even the U.S. where solar incentives abound.

So what do these countries, Germany in particular, offer that Sweden doesn't? The list is long, but the one that's most important is the ability of the home energy producer to sell energy back to "the grid". To date, Swedish power companies are not required to buy any electricity from their wanna-be-suppliers aka customers and some have even issued declarations to indicate they will refuse any such requests. Not good news for the poor home producer whose solar installation merrily provides electricity for free all day long to the power companies, and, who, on returning home in the evening from a day's work at the office, discovers the need to buy electricity from the same power company because the sun is low or gone. This is the current situation in Sweden. Talk about a disincentive! And while the occasional political mumble has been heard to address this issue, so far it's been about as effective as a horse's snort. On an aside, I might say the horses have made more headway, having recently snorted effectively about their rights to socialize such that it is now written into law that they must have the company of at least one other horse.

However, the power companies have started to acquiesce: they will now buy electricity once a number of prohibitely expensive conditions have been met and the electricity producer makes enough noise about it. In a report issued by Elforsk http://www.elforsk.se/solel/ (in Swedish, of course!), an organization that researches electricity issues and is owned by the governmentally owned Svenska Kraftnät http://www.svk.se/, the company that controls Swedish electricity (phew, that was a long intro), it would require about 45 square meters of solar panels to reach "break even". The costs involve metering measurements and reporting - one of the requirements is that energy production be reported hourly!

Well, let's see - back to my solar installation. The roof of my house in the pic is facing west - I'd better choose one of my sheds that has both southern exposure and isn't shaded. A quick measurement reveals that the shed in the picture - it once was the goat house under a former owner - has a roof length of 8 meters and is about 3 meters wide. Covering it entirely, that would give me 24 square meters, or about half the area needed for break even. So I can forget about selling electricity! And, darn it, I'm not at home during the day when the electricity is being produced, thus leaving me no choice but to give it away for free or to sell it at a loss. I could, of course, get very expensive batteries to store it, but that defeats the whole purpose or being grid connected. Or I could get inventive about consuming electricity while not at home. Hmmm... maybe I could get an electric car, which is expensive, leave it at home to charge during the day, then drive around with it all night. Or not.

Midsommar

reindeer snack

Uwe, friend, colleague, fellow carpooler, chooser of my digital camera, source of my chili pepper plants, technical and practical wizard in everything electrical, digital and otherwise - and one of many whom I will miss.

.............................solstice, 1 am, the darkest hour

playing "kubb" by twilight

A CIGS solar cell

First, to make one thing perfectly clear: if I had been talking about cigarettes, I wouldn't have capitalized all the letters in CIGS. Nope, CIGS is an acronym for the ingredients in Copper-Indium-Gallium-Selenium solar cells. Actually, CIGS solar cells are made up of a number of micrometer thin layers of which CIGS is just one of those layers. But it's the most important one - it's the so-called absorber layer ie the layer that absorbs sunlight. In the illustration, it's the dark gray layer, gray being a fairly good color to be for soaking up sun rays.
Besides absorbing sunlight, the CIGS layer performs another very important trick. It separates charge. This is what distinguishes CIGS from other grey or black materials such as asfalt (have you ever heard of a solar cell made out of asfalt?). Electrical charges happen to come in two varieties known as positive and negative. If you've ever had to use a battery and were very observant, you would have noticed two things about your battery: it has two terminals and, with some luck, the terminals would have been labeled with a ' - ' and a ' + '. The battery has somehow managed to pile up positive charges at one terminal and negative at the other. A solar cell, aka solar-powered battery, must do the same. The CIGS absorber layer is responsible for the first step: the energy in sunlight is absorbed by electrons, which have a negative charge, giving them such an energetic 'kick' that they can free themselves from the positively charged atoms to which they are normally bound.
So far, so good, but there are a few more steps needed before a solar cell achieves 'battery' status. For one, it needs electrical terminals. Secondly, it needs to get the newly separated charges to their respective terminals. Unfortunately, one of the first things that happens to newly freed electrons is recapture. When this happens, the sun's energy is re-released, usually in the form of heat. This is entirely useless when trying to get electricity! However, a few ingenious people eg at http://www.arontis.se/ think that they can usefully recoup the heat and still produce electricity. But to get electricity, those freed electrons need to get out of the CIGS layer and onto some conducting terminal to eventually make their way into an external electrical circuit. To scientists, the discussion would also include 'holes' which describe the net positive charge created when an atom is deprived of its electron. Even holes can travel and be accumulated at terminals, thus contributing to solar cell function, but I don't intend to delve into that subject here.
Terminals, and how to get the charges there, is what the other layers in the solar cell are for. If you look at the illustration, you'll see the layers that act as terminals. One layer is made of a metal called molybdenum. It's a great electrical conductor just like copper, but it happens to be molybdenum, not copper. The choice reflects the need to satisfy other requirements such as chemical and mechanical compatibility. This layer forms the positive terminal of the CIGS solar cell where the 'holes' accumulate. Attach a wire to that layer and you're halfway there!
The negative teminal is the top layer labelled zinc oxide. By now, you would have noticed that the illustration is labelled in Swedish - that's thanks to Janne Sterner, a former PhD student at the Ångsröm Solar Center, who, besides being able to make really cute illustrations is also terribly Swedish! Anyway, the poor zinc oxide layer has three functions to perform. Firstly, it needs to be transparent to sunlight because it entirely covers the underlying CIGS layer which, as you remember, is the layer that absorbs the light. Secondly, this layer, in partnership with the CIGS layer, is responsible for creating the voltage difference that's so necessary to get the charges to travel to the terminals. And thirdly, it's the negative terminal where the electrons accumulate. Although not as conductive as a metal, zinc oxide can be mixed with a couple of percent aluminum to make it both transparent and conductive at the same time (being both transpartent and conductive is normally a conflict of interest). Attach the second wire to this layer and the solar cell is ready to be used! Oh, and don't forget to face it into the sun.
There's still another layer I haven't mentioned. If you look carefully at the illustration, you'll see a very thin layer labelled cadmium sulfide (in Swedish, of course). It's called a buffer and its purpose is to deal with compatibility and transition issues between the zinc oxide and CIGS. While it doesn't have much purpose in the explanation of how a CIGS solar cell works, it tends to get attention due to the fact that it contains a wee bit of cadmium, making it a possible environmental contaminant. And it's probably unhealthy to lick the solar cell, just in case the urge to do so should cross your mind. A large part of my own research has involved replacing this layer with a cadmium-free alternative, such as was the case for a solar module I wrote about in an earlier post.
I mentioned at the beginning how very thin all these layers are. The entire stack, in fact, is only 3 micrometers thick (there are 1000 micrometers in a millimeter). For comparison, a human hair is 50 to 100 micrometers. Without some supporting base, in this case a pane of window glass, it would be impossible to handle. But, instead of glass, wouldn't it be so much easier to handle if the supporting layer were a sheet of plastic? Being able to roll up solar cells and have them be light enough to carry around would open up so many possibilities! Well, with any luck, I'll get a chance to investigate this at Flisom (http://www.flisom.ch/). To be continued...
ps This picture at the bottom is a scanning electron micrograph photo of what the CIGS solar cell REALLY looks like. The thicker layer is the CIGS itself, characterized with more or less vertical crystals - where each "chunk" is a crystal - and the thinner layer on top is the zinc oxide, where the vertical structure of the crystals is a bit more obvious.

Deer in the daisies

View from the kitchen window

Farewell

Farewell 9th grade Torsviks skola and farewell Sweden!

Not so empty house

With both boys gone the house has suddenly gotten empty and quiet and will remain so until July 15 when Alex will come and stay until school starts again in the fall. To counteract the emptiness I decided to offer to have the Ångström department's summer party at my house. They gladly accepted and yesterday I had 18 guests. The food was catered (smoked salmon, potato salad, caviar appetizers) and my earth cellar, which functions as a summer fridge, was stocked with beer. I thought it was a brilliant way of having great leftovers for the next few days. Too bad I'd forgotten about all the clean-up today! In the pic: Gunilla with Marianne, the party mastermind.

Thumbthings never end

Yesterday was my umpteenth visit to the hospital for more rehabilitation, splints and a review of last visit's x-rays. I have now met five doctors, three of whom have gravely informed me that my condition is very serious. You'd think that I'd been told that I had cancer or aids but what they're referring to is my thumb! While I admit my hand won't be doing any grasping in the near future, despite having already had 3 months to heal, what I can't grasp is the use of the word "serious". Yesterday's doc was #4, the one I first met while lying in a morphine-induced state on the operating table about 30 seconds before being put under and being informed that I was being given the opportunity to ask any questions I might have. I'd woken up afterwards in a cast to my elbow and the doctor explaining numerous times to my dizzy and numbed mind, in Swedish, that he'd decided not to operate after all since it was "too late". The upshot of yesterday's meeting was that, like it or not, the hand was going to hurt but I'd better start using it anyway to regain some mobility and muscle. And the re-injury of the 30 year old damage to the wrist? That could get better, stay the same or get worse, but I'll have to wait and see. Sigh - "serious".

Studenten

I attended another extremely traditional event last week: the high school graduation of my friend Lotta's daughter Sofia. My camera's battery was dead, darn! The photo I have here gives the general idea - graduation caps and partying! Tradition involves a dinner with close friends and family that come from far and wide for the event while the student in question interrupts her partying to attend, at least briefly. The drinking that accompanies the students' celebratory travels through town in decorated trailers, far from being looked down upon, seems more likely to induce nostalgia in the older and sometimes elderly relatives. Sofia herself seemed delirious with happiness and declared her wish that this day would never end!

Solar cells, modules and panels

I've written about a solar module, so this time I'll write about how solar cells are related to solar modules. First of all, what's the difference?
The short answer is that a module is made up of cells that are electrically connected together. In an electrical circuit, each solar cell acts as a temporary battery that operates while the sun is shining on it. There are essentially two ways that cells can be connected together. A series connection has the cells all connected in a row, just like a flashlight can have batteries connected in a row. If a single battery has 1.5 volts, then 4 batteries in a row will have 4 x 1.5V = 6V where the batteries are all touching each other end to end and the external connections are made to one end of the first battery and the other end of the last battery. Likewise for solar cells. Very roughly, a solar cell has half a volt or a bit more. Surprisingly, this is true of most kinds of solar cells, whether thin film or crystalline silicon or any other material - this is by design, not coincidence, but I won't go into the reasons here (ok, it has to do with making the most efficient use of the solar spectrum). If the solar cells are series connected the total voltage of the system can be increased. A typical setup might be to string 24 cells together for an output of 24 x 0.5V = 12 volts.
There's another way to connect cells together. Instead of lining them up end to end, they can be connected in parallel by placing them in a row with the all positive terminals connected together and all the negative terminals connected together. The voltage of this assembly will be just that of a single cell. However, each cell contributes current and the currents will all add up. If you remember from my description of the solar module, the bigger it is, the more current it generates. Connecting cells in parallel is just as if a single cell got bigger.
To get both more voltage and more current, cells can be both parallel and series connected. A string of series connected cells can be parallel connected to other strings of series connected cells. In this way, cells can be assembled to produce a desired current and voltage. Just as a refresher, the electrical power output of a module is the voltage multiplied by the current and is measured in watts.
When you're in the solar store looking at solar panels, what you're seeing is a packaged module with a supporting frame and a little box of circuitry. The circuitry deals with compatibility issues when many panels are interconnected but not performing equally, such as when some panels are under full sun and some are shaded. Partial shading of solar installations can be a real problem, but I'm not going to discuss that this time. In fact, I think I'll stop here, now that I hope I've explained the relationship between solar cells, solar modules and solar panels.

Daniele

Although Daniele turned 21 last Friday, there was hardly any time to celebrate. He had a final in thermodynamics that day and a final in quantum mechanics today, leaving just enough time to blow out a few candles, wolf down some brownies and gratefully pocket his much sought-after present from me: money.
I'm quite convinced Daniele will find some use for money in the near future. His summer adventures begin in a couple of days as he heads for various parts of Europe. During the next couple of months he'll be visiting a friend near Stuttgart, family in Bologna, Papá's new home in Florence, attending a European Youth Parliament session in Liverpool, an EYP party in Berlin, visiting my brother and mother in Munich and meeting up with a Rumanian friend (of the female variety) to drive around Rumania and Greece. He sadly turned down an invitation to spend two weeks in Antigua with another friend (also of the female variety, but not identical to the first) in favor of a return to Sweden in mid-August to start his summer job. The job is at the Ångström Lab working under the supervision of my friend, Tomáš, but he won't be involved with solar cells this summer. He'll be there until the end of September.
On October 4th (coincidental to Alessandro's 16th birthday) his new adventures begin at Fitzwilliam College in Cambridge.

Dissertation party

One of my colleagues (and former carpooler) successfully defended his thesis last week and an extremely traditional party was held at one of the student "nations" in town. It's a formal occasion with all the pomp of a wedding. The dress I wore is one designed and made by my sister, Jane. The dinner involved many speeches and the very Swedish drinking songs accompanied by lots of "snaps". I think we must have had to interrupt dinner about ten times to drink, sing and toast each other. The particular song being sung in the picture below also involved climbing onto chairs and is the song that indicates it's time to leave the table. It was 1 am when I got home and I took a picture of the northern horizon to show how light it was. Darkness no longer arrives here and I expect it will be a couple of months or so before it will get dark again. I notice the picture is fairly blurry - I seem to have had difficulty holding the camera still.