Friday, June 30, 2017

Modeling parabolic troughs in Energy3D

Fig. 1. The absorber tube of a parabolic trough
A parabolic trough is a type of concentrated solar collector that is straight in one dimension and curved as a parabola in the other two, lined with mirrors. Sunlight that enters the trough is focused on an absorber tube aligned along the focal line of the parabola, heating up the fluid in the tube (Figures 1 and 2). If the parabolic trough is for generating electricity, the heated fluid is then used to vaporize water and drive a turbine engine. A power plant usually consists of many rows of parabolic troughs.

Fig. 2. A view from the absorber tube.
Parabolic troughs are another common form of concentrated solar power (CSP), in addition to solar power towers that Energy3D has already supported (there are two other types of CSP technologies: Dish Stirling and Fresnel reflectors, but they are not very common). According to Wikipedia, there are currently more parabolic trough-based CSP plants than tower-based ones.

In the latest version of Energy3D (V7.0.6), users can now add any number of parabolic troughs of any shape and size to design a solar thermal power plant.

Fig. 3: Parabolic troughs at different times of the day

Parabolic troughs are most commonly aligned in the north-south axis so that they can rotate to track the sun from east to west during the day. This kind of trackers for parabolic troughs works in a way similar to the horizontal single-axis tracker (HSAT) for driving photovoltaic solar panel arrays. You can observe their motions when you change the time or date or animate the movement of the sun in Energy3D. Figure 3 illustrates this.

Like photovoltaic solar panel arrays, parabolic troughs have the inter-row shadowing problem as well. So the distance between adjacent rows of parabolic troughs cannot be too small, either. But unlike solar power towers, parabolic troughs do not have reflection blocking issues among mirrors. Figure 4 shows this.

This new addition greatly enhances Energy3D's capability of modeling CSP plants, moving the software closer to the goal of being a one-stop shop for exploring all sorts of solar solutions. In the coming weeks, we will start to build 3D models for parabolic troughs in the real world.
Fig. 4: Inter-row shadowing in parabolic trough arrays

Saturday, June 24, 2017

Robert F. Tinker (1941-2017)

It is in deep sadness that we mourned the passing of Dr. Robert Tinker on June 22, 2017. Bob was the founder of the Concord Consortium and the Virtual High School. For 18 years, he had been my mentor, friend, and supporter. It is hard to accept the fact that he is no longer with us.

My collaboration with Bob began in 1999, when I was doing a term of postdoc in the field of computational biophysics at the newly-established University of Cyprus. My job was to write computer code to simulate molecular motion and quantum transport in proteins. As it is difficult to imagine these nanoscopic processes from raw data generated in simulations, I had to resort to developing real-time, interactive visualizations of simulations so that I could make sense of the results. It was at this point that our trajectories merged. Around that time, Bob and colleague Dr. Boris Berenfeld just got a grant from the National Science Foundation to develop a tool that can visualize the motions of molecules and allow students to mess with them, hoping to create a powerful virtual "microscope" that can bring the obscure molecular dynamics to life on the computer screen for everyone. While Boris was surfing the then-barren Internet to find who had done what in this tiny niche, he came across my Java Molecular Dynamics applet that I created for the purpose of teaching myself Java while experimenting with interactive molecular dynamics. Boris, Bob, and Barbara (Bob's wife) immediately realized that the applet was exactly what they were looking for. After a few rounds of email exchanges, they hired me as a consultant for the project.

While we made progress on the development of what became the Molecular Workbench software later, the plan to employ me as a staff scientist at the Concord Consortium didn't go so well. For some reason, I couldn't come to the U.S. for a job interview (there was no video conference software at that time and it costed more than $3 per minute to make an international call). So Bob decided to stop by Cyprus on his way to an international conference in Israel to make sure that I wasn't just a cat that happened to know how to hit the keyboard in the right places. Even though I didn't know much about the American culture back then, the language of science needed no translation. So we hit it off at the meeting (except that it was kind of weird that the interviewee was actually the host and the interviewer was actually the guest). I made sure that he had enough authentic Mediterranean meze platters and got a chance to submerge himself in the pristine water of the Eastern Mediterranean Sea before he headed back to the States.

I arrived in the U.S. at the end of 2000, basically having nothing but a suitcase. Bob and Barbara welcomed me with an open house and gave me a room to stay for a while until I could find a place of my own. In the next eight years until he "retired," I was fortunate enough to be able to talk to him almost every workday as our offices were right next to each other. As we all remember, he was always optimistic, even in dark times such as September 11, 2001. As the years went by, funding at the Concord Consortium went up and down, but he was such a gifted grant writer that he could always manage to grab some money to keep me focused on the Molecular Workbench project until I became fully independent and found my own path and passion. After he and Barbara retreated to their retirement home in Amherst, they continued to invest their time and energy in the future of the organization. Bob went on to pen many proposals and secured a series of large grants to fund important work at the organization. Unlike many people who think programming and tinkering are "low level" jobs that the Principal Investigators should not have to do, Bob had always been creating his own prototypes and conducting his own experiments all the time to get firsthand experiences. This is probably the reason why he was so insightful with his ideas -- one cannot possibly have a deep understanding about the world if one does not bother to explore in it. He just loved science, programming, and teaching so much that he never stopped learning, thinking, and working until his final days. It is very hard for me to hold back my tears while writing about his last request to me just a few weeks ago, asking me to carry on some work on electronics that he couldn't complete because of illness. With that, he had completely dedicated his entire life to STEM.

Bob's vision about STEM education always put innovation first. He had transcribed the DNA of innovation into the Concord Consortium. His spirit had translated into a culture of innovation that is driving our research and development. With many new emerging technologies, the future ahead of us is full of exciting opportunities. With the combined power and promise of the Internet of Things (IoT), artificial intelligence (AI), and mixed reality (VR/AR/MR), the next decade will undoubtedly bring a new wave of innovation to propel STEM education to a higher level. As a pioneer of probeware for science education who completely understood the pivotal importance of sensors in IoT systems and embedded intelligence, Bob would have been thrilled to set out to explore these new territories with us.

Thursday, June 22, 2017

Khi Solar One

Khi Solar One (KSO) is a 50 MW solar power tower plant located in Upington, South Africa, which was commissioned in February, 2016. KSO has 4,120 heliostats on 346 acres of land. Each heliostat is as large as 140 square meters, reflecting sunlight to a tower as tall as 205 meters. KSO has two hours of thermal storage. The power plant is expected to generate a total of 180 GWh per year.

A low-resolution simulation of Energy3D predicts that on February 28 (close to when the Google Maps image was most likely taken) and June 28 (a winter day in the southern hemisphere), the total daily input to the solar tower (not the output of electricity generated by the turbines) is about 2.6 MWh and 1.9 MWh, respectively, as is shown in the graphs below.

The Energy3D model of the KSO can be downloaded from this web page, along with other solar power plants.



Friday, June 16, 2017

Creating computer models for all solar thermal power plants in the world

Fig. 1: Energy3D models for six solar power towers
Fig. 2: The Gemasolar Plant
One of the unique features of Energy3D is its ability to model, design, and simulate solar power towers. Figure 1 shows the Energy3D models for six solar power towers: Gemosolar (Spain), PS10 (Spain), PS20 (Spain), Greenway (Turkey), Themis (France), and Badaling (China). To support the research and development on concentrated solar power (CSP) -- a solar power solution alternative to photovoltaic (PV) arrays that may be able to provide some baseload capacity, I have been working on creating a library of 3D models for all the existing and planned solar thermal power plants in the world. The ultimate goal is to develop Energy3D into a versatile CAD tool for all forms of CSP (and PV), based on accurate simulation of existing plants first. The acquisition of the capability of reliably modeling both CSP and PV will enable Energy3D to truly support our Solarize Your World Initiative.

Fig. 3: The Gemasolar Plant
Fig. 4: The Gemasolar plant (June 30)
This article shows a bit of progress towards that goal. I have recently added in Energy3D weather data for scores of sites that already have CSP plants or are planning to build CSP plants. Many of these new sites are in Africa, China, Europe, and South America (some of them were requested by our users in Algeria and Chile). These newly added locations bring the total number of sites supported in Energy3D to more than 250. This growing network should provide you weather data that are approximately applicable to your site (but let me know if your site is not currently covered by Energy3D to your satisfaction). When you import your Earth view in Energy3D, the software will automatically choose the supported location that is closest to your site. If there is already a power tower, you can use the length and direction of its shadow in the picture to estimate the date and time when the picture was taken -- this can be done by turning on the shadow and adjusting the date and time spinner of Energy3D until the calculated shadow approximately aligns with the real shadow. After this is done, the heliostats that you add to the scene will approximately point to the same direction as in the image.

In this article, I picked the impressive Gemosolar Thermosolar Plant near the city of Seville, Spain as a showcase. The plant has 2,650 heliostats on 520 acres of land, each of which is as large as 120 square meters. The tower is 140 meters tall. The annual output is approximately 110 GWh. With molten salt tanks, it can store up to 15 hours of energy. Using a low-resolution setting, it takes Energy3D 5-10 minutes to complete a daily simulation and up to a couple of hours to complete an annual simulation. If you can afford to wait longer, you can always increase the simulation resolution and improve the accuracy of results (e.g., more points on the reflectors better account for blocking and shadowing losses).