New radars right as rain

Two new weather radars offer unprecedented sharp and dynamic views of the rain formation processes in clouds. They should help in clarifying the connections between air pollution, rain and climate change.

Cheese, nuts and olives on the tables, people exchanging greetings and colleagues toasting on this memorable day. Last Thursday the international research centre for telecommunications and radar (IRCTR) inaugurated the new radar Parsax with a reception in the foyer of the Electrical Engineering, Mathematics and Computer Science building. IRCTR director, prof.dr. Leo Ligthart, reminded the around sixty people in attendance of a series of firsts by the TU’s telecommunication and radar group. In 1983 for example the group performed the first radar Doppler measurement (enabling the determination of the velocity of clouds), 2005 saw the kick-off of the development of the drizzle radar Idra, and now the official opening of the Parsax radar. This ‘polarimetric agile radar in S- and X-band’ is capable of continuous polarisation measurements of clouds with unprecedented resolution down to three meters.
Whereas the amount of reflection of radar waves is indicative for the amount of water in a cloud, polarimetrics reveal the shape and size of the droplets in a cloud and enables researchers to distinguish between hail, snow and rain. “Using polarisation in radar is not new,” says prof.dr. Herman Russchenberg. “But using polarisation in both directions simultaneously with a resolution of only three metres is unique. It should give us a detailed and dynamic image of the processes occurring in clouds.” 

Russchenberg is a lecturer on the remote sensing of the environment. He studies the formation and disappearance of clouds, the ‘x-factor in climate research’. Clouds have a significant cooling effect that seemingly partially balances global warming caused by rising CO2 levels in the atmosphere.  But the uncertainties are thus far larger than the effect.
Weather radars are vital for learning more about clouds. Not only Parsax, but also the Cesar (Cabauw experimental site for atmospheric research) consortium, which hosts Idra (the IRCTR’s drizzle radar) and a series of rain-measuring equipment on top of a 213-metre high tower.
One of the differences between the systems is that Parsax is a cloud profiler, which can look vertically into the atmosphere. Idra on the other hand scans the surroundings horizontally at one revolution per minute, providing very precise information of where the rain falls.

Idra was developed by the Catalonian engineer, Jordi Figueras i Ventura. It was his PhD project, which he will defend on November 16th. The main feature of Idra is its sensitivity and resolution down to three metres in its sharpest setting. For comparison, the Royal Netherlands Meteorological Institute (KNMI) weather radar has a one kilometre resolution. Idra’s ability to measure drizzle (very fine rain), fog and low clouds is unrivalled. “Drizzle may sound boring,” says Russchenberg, “but it limits the clouds lifetimes. Clouds disappear either by evaporation or by precipitation, which starts with condensation of water vapour on aerosols or fine dust particles of just a few microns across.” Russchenberg aims to clarify the relationships between air pollution (the amount of fine dust aerosols in the air), cloud formation, rain and climate change.

Figueras, who now works at the British Met Office but will soon join Meteo France in Toulouse as a post-doc, believes Idra is now reliable enough for doing long series of measurements. In his view Idra should be able to deliver the best estimates of rainfall rates, because Idra’s images are thirty times sharper than those of the KNMI, and because Idra’s polarimetric capability allows it to obtain better rainfall rate estimates and classify the type of precipitation. Cesar would be the best place to link the presence of aerosols to rain patterns. “Such measurements need to have a long continuity,” Figueras argues. But he also knows that science nowadays is primarily project-based and that it is difficult to get funding for long term monitoring. To set up a long term programmatic research project would require a major change in the current mindset, Figueras writes in his thesis: “But it would benefit the atmospheric remote sensing research in IRCTR and that of the Netherlands as a whole.

“Curiosity and the urge to work on a revolutionary technology,” are the reasons that Dr Miro Zeman, head of the Solar Group at ECTM Electronic Components, Technology and Materials department, gives for his lifetime dedication to the development of solar energy. Zeman, a Slovakian national, came to TU Delft in 1989 to conduct research on a then up-coming material for solar energy, called amorphous silicon.
Fast forward to 2009 and a time when many European citizens are look inward, as demonstrated by the Dutch and French voting no to a European constitution, Zeman, who experienced the Cold War, is living proof that European Union has brought many advantages that are perhaps now already taken for granted.
“In those days, you couldn’t even easily go to Vienna, which is just 50 km from Bratislava, the capital of Slovakia,” he recalls from is office in the Dimes building. Standing up from his desk, he shows his visitor a thin flexible foil in which amorphous silicon solar cells are incorporated. It is a sample of a technology that could enable mass production of solar electricity through its integration in roofs and facades of buildings in virtually every corner of the world.

In 1989 you came to TU Delft to conduct research on amorphous silicon. Why?
“In the late 1970s, many people were interested in this up-coming material, amorphous silicon, and so were researchers at TU Delft. Researchers at Dundey University in England had provided scientific evidence that amorphous silicon could be doped, meaning that its electrical properties could be manipulated in such ways that it could be used for fabricating semiconductor devices such as solar cells. Because there were few people working on amorphous silicon and I had done my PhD on this material, TU Delft invited me to work on a six-month fellowship project. And I have stayed ever since. This project completely changed my life.”

Why did you decide to stay?
“The most important reason is that I knew that I could do better research in Delft than in Slovakia. Another reason was that I could also earn more at TU Delft. At that time the Czech Republic and Slovakia separated peacefully, but there was a lot of uncertainty.”

What makes amorphous silicon so interesting for the generation of solar power?
“The most important reason is that it can be deposited on an underlying or so-called substrate material by a silicon carrying gas, such as silane, and done so at a relatively low temperature. The industry standard (multi)-crystalline silicon is fabricated at temperatures of above 1400°C, while amorphous silicon can be deposited at 200°C. This makes cheaper production of solar cells possible, because less energy is needed and because you can use cheap substrate materials. The company Nuon-Helianthos has built a pilot-line for testing the thin-film solar cell foil, which we and various partners co-developed, and has also decided to build a factory for the production of the solar cell foil.” But its conversion efficiency of 6 percent is quite low compared to the industry standard of approximately 15 percent for multicrystalline solar cells.
“The material properties of amorphous silicon are indeed less compared to those of crystallized silicon. However, by stacking layers of materials with different physical properties the conversion efficiency of up to 10 percent and above can be reached. The issue here is all about making trade-offs. Currently, one of the main challenges in the solar energy industry is to find cheap production techniques. The production cost of the solar foil we developed is a fraction of standard photovoltaic solar panels. In laboratories, conversion efficiencies of 40 percent have been demonstrated. But reaching these values in the real world is something else. We obviously aim for the best of both worlds. But this is not an easy task. It takes a lot of effort and bright minds.”

In 2006 you co-founded the non-profit foundation Slovak Renewable Energy Agency (Skrea). What do you hope to achieve with this organization? “Sadly enough, many Slovakians currently don’t know anything about solar energy. The goal of my foundation is to educate people in Slovakia about solar energy by, for instance, organizing workshops and seminars. Another goal is to create support for the application of solar energy. One project we carried out last year was the called the ‘Sun into schools’ project, in which we installed a 20 kWh PV system in a secondary school in Bratislava and connected it to the grid. This was first-ever system connected to grid in Slovakia. I’m very pleased with our achievements thus far and that many people seem to appreciate our efforts.” 

You’ve experienced the scientific worlds of both the Netherlands and Slovakia. How would you compare them?
“In the Netherlands the focus is much more on trying to unravel the core of scientific questions. In Slovakia, we’re more pragmatic, with the consequence being that research is more superficial. I’ve learned at TU Delft that it’s not only important to make something, it’s also important to understand why things work as they do. However, pragmatism is also important, especially for a technological university. Sometimes researchers focus merely on obtaining interesting research results and not on how society could benefit from their research. I hope my pragmatism helps find solutions to the challenges we face.” 

You’re quite positive about the European integration process. Why?
“In the Cold War era Western Europe seemed a completely different, and maybe even a hostile world for many Czechoslovakians. Probably because the propaganda machines on both sides were working quite well. Europe’s integration process has created grounds for common understanding and cooperation. Now we’re working together on many issues for our common benefit. My presence here in Delft is a result of this integration process, and I hope I have also contributed to an understanding between Slovakian and Dutch people. You know, over the years I’ve developed a feeling of being a real European. I truly feel at home in both countries.”

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