The end of summer

Every year in August there's another of those numerous Swedish traditional occurrences: the kräftskiva or crayfish party. Since I enjoy the crayfish, I've never missed eating them in August. But unlike the earlier years - I've been in Sweden since 1998 - I no longer attend parties in which large quantities of brännvin or aquavit are consumed and the requisite drinking songs are sung. Mostly now I just down a kilo of crayfish with a friend or two.

Since crayfish eating happens at the end of August, it also signifies the end of summer. However, there are still the apples and pears to pick from the trees and the blackberries are ripe now, so it's not quite over yet. Tomas and Ariana will be over this weekend to help put the Åkerö apples in the food cellar. They should store well there and be edible until Christmas. Good thing it's loaded with spiders to keep the flies away.

I've also been watching the weather to see if it's time to transfer my 16 cubic meters of wood to the wood shed. When it's time, I'll have have a few people over for a wood stacking party. If it's anything like previous years, my friends do all the wood stacking and I make the food, an arrangement that seems to have been fairly satisfactory in past years.

And then, brrrr, darkness and cold settle in to stay.

Badger in garden

Camping at Fjällnora

Nanosolar

I'm not always aware of which topics are hot at any given time since I don't own a television (hmm - a future blog topic?) although I do get the daily Dagens Nyheter. But I've been curious about a company called Nanosolar for a while and I've decided get some perspective about their technology and claims in fabricating CIGS solar cells, the same kind that I research. The suggestion to do so at this time came from Bengt Axmacher's comment to my post about building a solar charger. If I'm surmising correctly, he's wondering how a company such as Solibro that uses expensive vacuum deposition equipment in a relatively slow and materials inefficient manner to painstakingly produce solar modules one glass pane at a time could possibly compete with Nanosolar's cheap ink printing method using a metal foil roll-to-roll process with 100% materials utilization to produce solar cells that are - apparently - just as good.

Some fact gathering is needed here and I started at Nanosolar's website. Before getting into their technology, I first was curious about the end result: the efficiency of their solar panels (I'm one of those people who likes to find out how the story ends before reading the book). That's apparently a secret - I couldn't find it anywhere even in a broader web search. But they do advertise the efficiency of their absolute best cell as being 14.6% in a paper published March 2006. It was a half square centimeter in size and was made on a glass substrate. Incidentally, March 2006 was also when I fabricated my own record cell of 18.5% efficiency using a process identical to Solibro's. Unfortuneately, it can be very tricky to compare results between two different cells. In this case, the Nanosolar cell was actually measured to be only 13.95% efficient but was calculated to be 14.6 had it not had a top metal contacting grid on it. Similarly, my cell would have been 19.1% if I'd used the same trick of calculating away the contact area. Other things can also affect efficiencies such as antreflective coatings or whether the cells are encased for durability. When making large cells there will be more inherent losses and they are also more difficult to manufacture uniformly. Modules compound the losses due to the interconnects of the individual cells and problems in cell matching. Trying to calculate what the efficiency of a fully assembled solar panel might be based on the results of a weentsy little lab cell is not straightforward. If you take a look at my posting about a solar module you'll see it was 14.8% efficient, i.e. not even close to the 18.5% I got for the single cell. So here goes: I'm going to guess wildly and predict 8 to 9% efficiencies for Nanosolar's fully assembled panels.

On to some technology. The copper-indium-gallium-selenium ink that Nanosolar uses to print their solar cells is proprietary, but apparently it's made of nanoparticles of metal selenides which are printed onto a metal foil which forms one of the electrical contacts. It then goes through a heat treatment of 4 or 5 hundred degrees. Additionally, solar cells require a buffer layer and a top contact to form a structure that I described in a CIGS solar cell. I couldn't find out which method is used to deposit these layers, but Nanosolar emphasizes that vacuum deposition is not it. Hopefully, I'll get around to describing the vacuum deposition method someday since it's the way I make my solar devices.

I'm undeniably intrigued by Nanosolar's process. Vacuum deposition methods are indeed wasteful. Materials usage can only be minimized when huge glass panels are processed since the waste is mostly at the edges. Applied Materials makes thin film silicon on glass panes that are 5.4 square meters - I think it's the biggest in the industry. But vacuum equipment is terribly expensive, takes a tremendous amount of energy to run, corrosive selenium gets into everything and, in my experience, the heaters for the metals keep burning out - I don't just melt copper, I evaporate it at about 1500C. It's difficult to get uniform coating and control the respective quantities of copper, indium and gallium in the resultant films. And this is just for one of the layers needed to make cells. Modules also require patterning steps to form the interconnects between cells. Nanosolar doesn't require this in their process, but instead they have to assemble cells into modules and make interconnects. As far as esthetics go, I think Solibro has the upper hand. I suspect their sleek black panels are easier for an architect to place on buildings.

Back to the original question of whether Solibro can compete with Nanosolar: I conclude that it would be entirely premature to predict the demise of Solibro.

But neither company has yet made a product available to the public.

The Carpool

I just realized the significance of the empty halls in the lab. Four very particular co-workers are missing, at least for a while. Ventsi has gone back to Bulgaria for the summer, Tomas with wife Ariana to Prague, Per-Oskar is somewhere on vacation and poor Uwe's vacation request has been denied and he's been sent to Solibro in Thalheim, Germany where he's probably the most important person right now to get high efficiency solar modules coming off the production line there. But I'm rubbing my hands with glee. Why? These four co-workers are also the other four members in our carpool. With no one here but me, the car is all mine!

I should explain a bit about how our carpool works. The five of us all bicycle as our main means of transportation but we jointly own a car, the red Skoda Octavia in the pic. In reality Per-Oskar is the official owner having been chosen because he was the one able to get the cheapest car insurance despite being the youngest at 27. He's also the only Swede (hmmm... this couldn't possibly be correlated to getting a good deal on insurance, could it?).

The way it works is fairly simple. We maintain a group on yahoo where we can book the car as needed. We have no quotas since any conflicts are easily resolved by a trip down the hall at the lab. In the car we keep a journal of our driving and we pay 16 crowns per mil (this is Swedish for 10 kilometers). Gasoline is paid for with credit cards drawn on the carpool bank account which is maintained by P-O. Then we share all other car costs such as maintenance, insurance and the very expensive Uppsala parking which allows us to park at the lab - you didn't think that employees were allowed to drive to work and park in the lot for free, did you? The two car keys are kept in my office to which everyone has their own key.

The car's upkeep is shared, of course. Tomas and Uwe are particularly good at fixing things on it. Tomas is actually not the official member having given that honor to Ariana. He's also very willing to let her do all the driving but I believe this is due to the fact that he has no license and has never, in fact, learned to drive. When it's been time to change summer/winter tires I have always managed to get out of helping by offering to cook dinner for the other members. Tire changing happens at my house since I store the tires there. P-O handles the book keeping and gets us to pay up whenever the account becomes empty. A quick look at the log book reveals that in the first six months of this year the car has been driven 6800 km. So, on average we've each driven 6800/5 = 1360 km. In reality, we're often teaming up with each other when we go shopping or go on weekend trips since we're friends and not just carpoolers.

Now that I've gleefully used the car all week for my 5.5 km commute, I'm realizing that I very much miss my bicycle. I'm now starting my fifth year as a carpooler and have become entirely used to bicycling in all kinds of weather. When the weather gets too extreme - my personal temperature limit is -15C in winter - there's usually, but not always, a bus. Otherwise a quick call to a fellow pooler to come rescue me from someplace usually solves the problem.