Monthly Archives: September 2017

Deciphering a solar array surprise with Energy3D

Fig. 1: An Energy3D model of the SAS solar farm
Fig. 2: Daily production data (Credit: Xan Gregg)
SAS, a software company based in Cary, NC, is powered by a solar farm consisting of solar panel arrays driven by horizontal single-axis trackers (HSAT) with the axis fixed in the north-south direction and the panels rotating from east to west to follow the sun during the day. Figure 1 shows an Energy3D model of the solar farm. Xan Gregg, JMP Director of Research and Development at SAS, posted some production data from the solar farm that seem so counter-intuitive that he called it a "solar array surprise" (which happens to also acronym to SAS, by the way).

The data are surprising because they show that the outputs of solar panels driven by HSAT actually dip a bit at noon when the intensity of solar radiation reaches the highest of the day, as shown in Figure 2. The dip is much more pronounced in the winter than in the summer, according to Mr. Gregg (he only posted the data for April, though, which shows a mostly flat top with a small dip in the production curve).

Fig. 3: Energy3D results for four seasons.
Anyone can easily confirm this effect with an Energy3D simulation. Figure 3 shows the results predicted by Energy3D for 1/22, 4/22, 7/22, and 10/22, which reveal a small dip in April, significant dips in January and October, and no dip at all in July. How do we make sense of these results?

Fig. 4: Change of incident sunbeam angle on 1/22 (HSAT).
One of the most important factors that affect the output of solar panels, regardless of whether or not they turn to follow the sun, is the angle of incidence of sunlight (the angle between the direction of the incident solar rays and the normal vector of the solar panel surface). The smaller this angle is, the more energy the solar panel receives (if everything else is the same). If we track the change of the angle of incidence over time for a solar panel rotated by HSAT on January 22, we can see that the angle is actually the smallest in early morning and gradually increases to the maximum at noon (Figure 4). This is opposite to the behavior of the change of the angle of incidence on a horizontally-fixed solar panel, which shows that the angle is the largest in early morning and gradually decreases to the minimum at noon (Figure 5). The behavior shown in Figure 5 is exactly the reason why we feel the solar radiation is the most intense at noon.

Fig. 5: Change of incident sunbeam angle on 1/22 (fixed)
If the incident angle of sunlight is the smallest at 7 am in the morning of January 22, as shown in Figure 4, why is the output of the solar panels at 7 am less than that at 9 am, as shown in Figure 3? This has to do with something called air mass, a convenient term used in solar engineering to represent the distance that sunlight has to travel through the Earth's atmosphere before it reaches a solar panel as a ratio relative to the distance when the sun is exactly vertically upwards (i.e. at the zenith). The larger the air mass is, the longer the distance sunlight has to travel and the more it is absorbed or scattered by air molecules. The air mass coefficient is approximately inversely proportional to the cosine of the zenith angle, meaning that it is largest when the sun just rises from the horizon and the smallest when the sun is at the zenith. Because of the effect of air mass, the energy received by a solar panel will not be the highest at dawn. The exact time of the output peak depends on how the contributions from the incidental angle and the air mass -- among other factors -- are, relatively to one another.

So we can conclude that it is largely the motion of the solar panels driven by HSAT that is responsible for this "surprise." The constraint of the north-south alignment of the solar panel arrays makes it more difficult for them to face the sun, which appears to be shining more from the south at noon in the winter.

If you want to experiment further, you can try to track the changes of the incident angle in different seasons. You should find that the change of angle from morning to noon will not change as much as the day moves to the summer.

This dip effect becomes less and less significant if we move closer and closer to the equator. You can confirm that the effect vanishes in Singapore, which has a latitude of one degree. The lesson learned from this study is that the return of investment in HSAT is better at lower latitudes than at higher latitudes. This is probably why we see solar panel arrays in the north are typically fixed and tilted to face the south.

The analysis in this article should be applicable to parabolic troughs, which follow the sun in a similar way to HSAT.

Exploring hurricane datasets in the classroom

In August 2017, Hurricane Harvey evolved from a series of thunderstorms to one of the first major hurricane landfalls in the United States since early 2005. Right on the heels of Harvey, Hurricane Irma blasted through the Caribbean and onto the U.S. mainland, striking Florida in early September.

The National Oceanic and Atmospheric Administration (NOAA), which aims to understand and predict changes in weather, provides educational resources and datasets about hurricanes.

The dataset for 2005-2015 is available in our Common Online Data Analysis Platform (CODAP), a free and open-source web-based data analysis tool, geared toward middle and high school students.

Screenshot of NOAA hurricane data embedded in our Common Online Data Analysis Platform.

With all the current catastrophic news about hurricanes, students have lots of questions. Use the data to help them understand the history and characteristics of storms.

  • To investigate the paths that hurricanes generally follow, use the slider to change the year from 2005 to 2015, and watch the data points on the map, which represent the general path of the storms.
  • To determine the storm with the highest wind speed, click the top data point in the wind speed graph, which plots year against highest wind speed. Since data is linked across multiple representations, the data point is highlighted on the graph and in the table, so you can find the name and date of that particular storm (e.g., Wilma, October 15, 2005, with top wind speeds of 160 mph).
  • To learn which year had the most or least number of storms, look at the storms per year graph. Notice an outlier in the data with year 2005, which had 15 storms during that season. (Note: This was the same year as Hurricane Katrina. Select KATRINA in the table and make sure the slider is set to 2005, then see the path of the hurricane graphed on the map.)
  • To see a relationship between wind and pressure, click on the Graph button. Drag the Maximum Wind column header from the table to the vertical (y) axis until the axis turns yellow. Drag the Minimum Pressure to the horizontal (x) axis until the axis turns yellow. (Note: you may need to scroll to the far right of the Case Table to see these columns.) 

Analyzing and interpreting data is one of the key science and engineering practices of the Next Generation Science Standards (NGSS), and representing and interpreting data are featured throughout the Common Core State Standards (CCSS) for mathematics. Students can use publicly available datasets from storms and other weather events to learn more about the world around them.

STEM Resource Finder: Part I – Register for a Teacher Account and Add a Class

Our updated STEM Resource Finder (previously called the Learn Portal) at learn.concord.org now allows you to search for resources, create classes, assign activities, and track student progress with reports. All in one place. All for free.

Register for a Teacher Account

Follow these easy steps to create an account in the STEM Resource Finder.

  1. Click the Register button in the upper right-hand corner.
  2. Complete the registration form with your name and create a password.
  3. Select the radio button for “Teacher,” create a username, and provide an email address you can access easily.
    • Complete the fields about your location and school.
    • If you don’t find your school listed, or you are a homeschool, click “I can’t find my school in the list” to enter the name of your school.
  4. After registering, you’ll receive an email from help@concord.org. Click the “Confirm Account” button in the body of the email to activate your account.
    • If you do not receive the activation email in your inbox, please check your junk or spam mailboxes, or any quarantine set up by your email provider.
    • If you cannot access the email in your junk or spam mailboxes or quarantined email, please contact help@concord.org for assistance.
  5. By clicking the link in the activation email, you’ll be directed to the STEM Resource Finder. 
  6. Click the Home icon in the upper right — that’s your own home page, where you can create and manage your classes, and track student progress.

Add a New Class

  1. To get started, Add a New Class by clicking the link on the left and enter Class Setup Information. Provide a class name, description, and applicable grade level(s). (Note: Please disregard the Term field as it’s currently not working. We’re working to update this soon.)
  2. Create a unique Class Word, which students will use to enroll in this class. Class words can be more than one word, but cannot include any special characters (such as *, @, and %). The Class Word is not case sensitive.
  3. You’re now ready to assign resources to this class. Click the Concord Consortium logo in the upper left to search all resources or view curated collections of resources by clicking the Collections link in the top navigation bar.

Additional information is available in the User Guide.

Let us know if you have any questions!

Designer dragons? Talking to students about the ethical implications of editing DNA

University of Michigan School for Environment and Sustainability, Flickr (CC-BY-2.0)

A breakthrough in medical research has allowed a team of scientists to edit the DNA of human embryos to repair a version of a gene that causes cardiomyopathy, a genetic disease resulting in heart failure. While some see this genome editing technology—known as CRISPR—as a remarkable tour de force, others find the practice extremely alarming.

Meanwhile, some middle school students are already practicing genetic engineering in the classroom with inexpensive kits. Geniventure, our dragon genetics game for middle and high school students, also allows students to manipulate genomes, but the DNA in Geniventure is virtual and the species is a mythical creature called a “drake,” the model species for dragons.

Working with drakes and dragons allows us to combine various real-world genes without having to be restricted to the genome of a specific species, a problem that scientists in many countries often run into. We’ve combined real genes from mice, fruit flies, lizards, and other model organisms into the genome of our fantastical creatures. Students thus experience many of the same real genes that scientists around the world are also studying. Importantly, using dragons also allows teachers to talk about ethical issues, including the implications associated with modifying DNA.

CRISPR incites fears of designer babiesthe idea that parents will someday want to choose particular traits for their unborn children. In Geniventure, students do “design” drakes in challenges that require them to change alleles to match a target. Teachers guiding students through these challenges have an opportunity to discuss the notion of modifying an organism’s genes for a particular purpose. They can pose questions to get students thinking about the ethical implications of gene editing: Are there circumstances where you wouldn’t want to edit a drake’s genes? What might happen if you changed the wrong gene and you couldn’t change it back? What effect would that have on the drake’s future offspring?

“Designing” drakes. Geniventure tasks students with manipulating drake genes by selecting alleles from pull-down menus in order to match a target drake.

It’s easier to discuss these issues when we are talking about drakes and dragons because humans aren’t anything like these fictitious creatures. But since the genes are modeled after real genes (e.g., the the albino gene is modeled after skin color in humans), we can translate conversations about dragons to similar debates by scientists and regulatory officials about human gene editing. In Geniventure, students change an albino drake’s genes from producing a broken enzyme so that it can create a functional protein and generate a drake with color distributed throughout its scales. Albinism is also an inherited genetic condition in humans, so there is a significant parallel that could bridge the conversation.

Scientists are using CRISPR to investigate the prevention of inherited diseases like Huntington’s disease, cystic fibrosis, and even some cancers, though there is opposition and concern over this technology. One major fear is the safety to a developing embryo. DNA that’s been modified in an embryo would be passed down for generations, which raises concerns that any mutations as a result of the gene editing could cause new diseases and become a permanent part of that family’s genetic blueprint. Geniventure enables students and teachers to start discussions about these important topics.