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!