Posts tagged with: thin film

Solar panels fall into two main technological categories. The incubant, established tyoe are called crystalline silicon solar panels and the exciting but unproven type are known as ‘thin-film’ solar panels. To understand the advantages and disadvantage of each technology I’ll briefly explain how each type of solar panel is made. Crystalline silicon solar panels are made from 50 or so ‘solar cells’ connected together and encased in glass. Each solar cell is in fact a thin slice of large crystal of pure silicon (called an ingot). These large crystals are grown from a seed crystal surrounded by molten silicon at very high temperatures. The silicon used must first be extracted from silicon dioxide (also known as sand) and then purified to a very high level. Once the crystal is formed it can be sliced into wafers. The wafers are then specially treated to make a junction between a positive and negative type semiconductor, and then other layers such as the conductive contacts are added to make a working solar cell. This process has many steps and consumes a lot of energy. However, many companies have spent a lot of time refining the process to make it as efficient as possible so almost all parts of the process are now automated.

Thin film solar panels are made using a radically different process. The underlying physics is similar in that they still use a junction between a positive and negative doped semiconductor, however thin film solar panels have the potential to be made in much fewer steps than crystalline silicon. The idea is to take glass (or sometimes foil or plastic) and coat it directly with a series of layers, including the active semiconductor layers to produce a working solar cell. The glass is then encapsulated with a protective plastic and a second sheet of glass as protection. This process saves having to make lots of small cells and connect them together. The other advantage is that the layers are very thin, hence thin film solar cells. The active layers of the cell are only a few nanometers (billionths of a meter) compared to 0.2mm for each silicon wafer.

The important point of all this is that the manufacturing cost of thin film solar cells has the potential to be significantly lower than crystalline silicon. Unfortunately, there are some catches. Firstly, they are not as efficient as crystalline silicon. Crystalline silicon reaches 16 – 18% efficiency in modern solar panels, whereas the most efficient thin film solar panels on the market today  are under 11%. The next drawback is reliability. Thin film solar panels have had less time to prove themselves and have been known to suffer from degradation meaning that their performance gets significantly worse over time.

Despite these drawbacks, several companies have managed to become very successful in manufacturing thin film solar cells. The most notable is called First Solar who are now one of the top two largest solar panels manufacturers in the world and have a significant advantage over rivals due to their low manufacturing costs. First solar make thin film solar cells made from cadmium telluride, one of a number of semiconductor materials that can be used for thin films. First Solar’s panels are less efficient but are very popular for large scale solar installations because of their low cost.

Before the financial crisis, when silicon was in short supply and very expensive, all thin film solar panels were a good idea. First Solar could not produce enough and billions were invested in a large number of thin film solar companies aiming to follow in their footsteps. Now that the silicon shortage is over and the price of crystalline silicon solar panels has fallen, the environment for thin film solar cells is more challenging. First Solar will remain a strong player as they have managed to get to high volume and have a reliable production process. Many of the 200+ start-ups hoping to replicate their success will struggle however. For thin film solar cells there are a wide range of different manufacturing processes and materials that can be used, and there is still a lot of research being done to improve our understanding of the underlying physics. This means that there is a lot of opportunity to invent a ‘unique’ technology and start a company but only the best thin film solar companies will make it however. They have to show not only that their technology is efficient and reliable, but also demonstrate that large scale production is feasible and low-cost. Many ideas that look good on paper or in the lab turn out to be impractical when it comes to volume manufacturing.

At present, it seems like crystalline silicon will retain a strong market share for the foreseeable future (it current represents 80-90% of the market) but I believe that eventually certain thin film technologies will begin to displace crystalline silicon. There is a lot of potential for efficiency improvement in thin film, as well as lower manufacturing cost. Some technologies, particularly that usce solution processing are really very exciting.

What does this mean for the UK solar industry? Very little actually. I would expect over 90% of the UK market will be crystalline silicon for a long time. The reason is that the UK market will be dominated by smaller rooftop applications (partly due to the structure of the tariff as discussed last week). In such space-constrained applications you want to use the most efficient technology to maximize the energy generated from the available area. For now, this means always choosing crystalline silicon as it’s efficiency is significantly above any thin film solar panel out there.

Keep an eye out for breakthroughs in solar technology as some are surely bound to occur, but beating high quality crystalline silicon solar panels made in China for cost, efficiency and reliability is not easy.

Good question. There is a huge amount of innovation happening everywhere in renewable energy and although solar technology has evolved rapidly in the last few years there is still a long way to go. There are lots of different aspects of a photovoltaic system that can be improved, and I will cover as many of them as I can on these pages.

First of all though, what is the basis on which we can judge these improvements? What is the ultimate goal here? Everyone can have their own opinion, but my ambition is to see solar energy compete economically with conventional energy sources, and for that to happen requires just one thing, lower cost of energy. Now you can get to lower cost of energy either by reducing the cost of the solar energy system or by increasing the amount of energy you get out of it. As we shall see, people everywhere are coming up with a lot of cool technology to go down both of these routes, but lets start with a company that I like called Nanosolar, who may eventually make the key step that makes solar power cheaper than coal.

First a bit of background: Solar panels are the most expensive part of a Solar electricity system, making up between half to two thirds of all the upfront costs. Most solar panels (sometimes called photovoltaic panels) are made from 50 or so ‘solar cells’ which are thin slices of silicon crystals specially treated so that they can turn sunlight into electricity. Its basically the same process that’s used to make electronic chips, which is fine for making tiny things that go inside your computer, but quite expensive for covering a small fraction of the earth’s surface with. Therefore a phenomenal amount of research has and is being done to find cheaper alternatives. So far the leading candidate for a replacement is the called ‘thin-film’ solar cell. In this case you start with flat panel of material such as glass, and coat the whole thing in a series of super-thin electronic layers that convert the sunlight into electricity. This process is cheaper than making normal silicon panels, however they are not as efficient at producing electricity.

Nanosolar are a frontrunner in developing thin film solar panels and are taking the technology to the next level. Most makers of thin-film solar panels need to use big vacuum chambers to deposit the semiconductor and can only process one panel at a time. Not so Nanosolar; they’ve cleverly developed a special electronic ink that they can literally ‘print’ onto big rolls of flexible metal sheets. Their factory in Silicon Valley looks very similar to a newspaper printing press – it’s much more suited to covering large areas.

When running at full speed the printing press should be able to cover XX football fields a day. Once the electronic layers have been printed on the foil they are cut into 6-inch squares and flown to another, newly opened factory in Germany where they are laid out into modules sandwiched in glass. Nanosolar claim their process is much cheaper than existing manufacturers out there, so cheap that it doesn’t matter that their panels are less efficient than traditional silicon solar panels. If this is really true be good news for consumers in the future, as Nanosolar could significantly bring down the price of solar panels.

Its not all plain-sailing for the US company however. They’ve been working on their process for nearly ten years and so far spent around half a billion dollars and have very little in the way of earnings. They’ll have to sell a lot of solar panels before their investors can start to relax. As with all new technologies, it takes time for customers to overcome reliability concerns, so getting to high sales volumes may take a bit of time.

Whether it’s Nanosolar that succeeds or one of the few dozen other firms pursuing similar strategies is not so important. What is important is that technology makes solar power economically viable without subsidies, and as we shall discuss on this blog, there are a lot of people out there dedicated to making that happen.