The challenge to solarize the world

More and more nations and regions in the world are planning to switch their power supplies to 100% renewable resources by midcentury. There has been, however, a well-publicized debate among scientists about the feasibility of powering the entire United States with only wind, water, and solar energy, triggered mostly by a recent paper by Stanford professor Mark Jacobson and colleagues. Both proponents and opponents are leading energy researchers who support their claims with sophisticated computational models. Given the magnitude and complexity of the problem, there will likely be no clear winner in the near future. But the debate will continue to influence our energy and environmental policies in the years to come.

Since the world also belongs to the young, we are obliged to find a way to engage them in this high-stakes debate. Regardless of the sides people take, few would dispute the strategic importance of educating and preparing energy consumers and workforce of tomorrow. Motivating youth is so vital in Bill Gates’ call for an “energy miracle” that he urged high school students to “get involved” in the energy quest in his 2016 annual letter. But, apart from becoming a conscientious user of energy, how can students make meaningful contributions?

Fig. 1: Energy3D covers nearly 600 regions in 185 countries.

We envision a cyberinfrastructure that works like an “Energy Minecraft” to inspire and support millions of students to take on the energy challenge at the grassroots level on a global scale. On this platform, students will learn basic science concepts and engineering principles. Equipped with the knowledge and skills, they will then crowd-design an unprecedentedly fine-grained computational model that consists of millions of virtual solar panels, reflecting mirrors, and wind turbines accurately positioned around the world and connected to virtual storages and grids. A multiscale model with all these low-level details does not exist yet, but it may be a holy grail in energy research that can potentially settle the case and even provide a blueprint going forward to a 100% renewable energy future if possible at all.

This article introduces the Solarize Your World program, the first step towards realizing the above vision. Although the program currently focuses on solar energy, it has the essential elements of a computational model capable of supporting both STEM education and energy research. And it can be extended to include other renewables such as wind, hydroelectric, and geothermal energy.

The complexity of modeling solar power in the real world

Fig. 2: Learn, apply, and explore

The sun is a gigantic nuclear fusion reactor in the sky that emits a massive amount of energy. Elon Musk has famously asserted that covering “a fairly small corner” of a state like Nevada with solar panels can generate enough energy for the whole country. This makes you wonder what scientists are really debating about.

It turns out that building a reliable solar infrastructure is not as simple as laying down billions of solar panels in a square of 100×100 miles. There are countless technical, economic, and social constraints for solar deployment in reality. For example, people do not have unlimited space and budgets. Some are concerned about the aesthetics of buildings and landscapes with solar panels in sight. Governmental policies drive the cost of solar energy, hence people’s interest, up and down. Energy storage is needed to overcome solar intermittency to provide electricity after sun-set and grid stability at all time. A significant amount of energy is lost during the transmission from utility-scale solar power plants to population centers. All things considered, we have a problem far more complicated than Musk’s ballpark statement. This is why the National Renewable Energy Laboratory has been conducting research on estimating the solar energy potential of the country (e.g., see "Rooftop Solar Photovoltaic Technical Potential in the United States: A Detailed Assessment" by Pieter Gagnon, Robert Margolis, Jennifer Melius, Caleb Phillips, and Ryan Elmore in 2016).

A crowdsourcing model that integrates education and research

Fig. 3: Photovoltaic solar farms in Energy3D

A more accurate assessment of the planet’s true solar potential is to identify all possible locations where suitable types of solar power can be realistically deployed and compute their minute-by-minute outputs to global grids and storages for a cycle of 24 hours under typical meteorological conditions. To evaluate the cost effectiveness of this giant distributed network, a mix of financing models driven by local economics and policies can be used to estimate the scale of investment that needs to be made over a certain period of time. Creating such a multiscale, time-dependent model with details down to instantaneous outputs and levelized costs of individual solar modules is a daunting task that no single researcher can do. But we can call for help from millions of students who know and care about their corners of the world more than any outsider. The challenge is to teach them the science and empower them with appropriate engineering tools so that they can join the energy quest.

Solarize Your World is based on our Energy3D software, a revolutionary CAD tool for anyone to design any type of solar power system in cyberspace and calculate its hourly, daily, or yearly out-puts based on numerical simulation from first principles. With weather data of nearly 600 regions in 185 countries (Figure 1), Energy3D can produce satisfactory results for most parts of the inhabited world, enabling millions to work on local projects. The ultimate goal of Energy3D is to turn the tedious job of engineering design into a fun game like Minecraft, making learning, discovery, and invention playful experiences for all.

A curriculum for learning and practicing science and engineering

Fig. 4: Concentrated solar power plants in Energy3D

For students to succeed in creating authentic models of solar energy systems valuable to research, Solarize Your World provides comprehensive curriculum materials and classroom-to-afterschool pathways (Figure 2) that lead students to: 1) design solar energy systems for their homes, schools, villages, and cities; 2) design any type of photovoltaic and concentrated solar power plants wherever applicable; and 3) communicate their designs to potential stakeholders whenever appropriate. Figures 3 and 4 show solar power systems of different types and sizes on top of satellite images of the chosen sites from Google Maps (some of these systems were modeled or designed by students in our 2017 pilot tests).

The Solarize Your World curriculum consists of three connected parts. Part I teaches students the needed disciplinary core ideas, crosscutting concepts, and science and engineering practices as defined in the Next Generation Science Standards. The disciplinary core ideas cover earth science, heat transfer, geometric optics, and electric circuits that are fundamental to solar power. The crosscutting concepts include energy and systems that are necessary to understanding how the energy from the sun can be converted into electricity to power the world. This part also strives to familiarize students with the practices of scientific inquiry and engineering design. Part II provides scores of open-ended, real-world projects for students to choose. For instance, students can design solar energy systems for their own homes or schools. If students cannot finish a project within the given timeframe in the classroom or wish to undertake more projects out of school, Part III supports them to continue in an online community, possibly in collaboration with many other participants similar to the case of Minecraft.

The road ahead

The U.S. Department of Energy announced on September 12, 2017 that the 2020 utility-scale solar cost goal set by its SunShot Initiative had been met three years earlier. The price of utility-scale solar energy has now fallen to six cents per kilowatt hour. Despite this phenomenal plummet, the road to a 100% renewable energy future is still unclear and debatable. We invite students and teachers worldwide to join our Solarize Your World initiative to pave the way. Rarely have students been given a chance to help answer a question so crucial to humanity.

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.

Energy3D exports Wavefront OBJ files

Fig. 1: An Energy3D model of a house

Starting from Version 7.2.6, users can export most parts of Energy3D models in Wavefront's OBJ format, which has been adopted by many 3D graphics applications and supported by many 3D printers. This provides a possibility to 3D-print Energy3D models and import them into other software.

Fig. 2: OBJ output

OBJ files can also be embedded within Web pages. This mechanism will be important in developing our Virtual Solar World platform, a Google Map application that collects and displays users' Energy3D models of buildings, solar farms, power plants, and so on. The Virtual Solar World is an important part of our Energy3D ecosystem. Figure 1 shows an Energy3D model and Figure 2 shows its OBJ form. As you can see, most of the features in the original Energy3D model are preserved after the conversion.

Fig. 3: An Energy3D model of a solar tower

Fig. 4: OBJ output

Power plants designed in Energy3D can be exported in the OBJ format as well. Figure 3 shows an Energy3D model of a solar power tower and Figure 4 shows its OBJ conversion.

Caveat: At this point, not all OBJ files exported from Energy3D are 3D-printable. Even when an OBJ model looks fine on the computer, it doesn't always get printed right. We are still investigating why the exported OBJ format is not compatible with some 3D printing services.

National Science Foundation funds citizen science project to crowdsource an infrared street view

We are pleased to announce that the National Science Foundation has awarded us a two-year, $500,000 exploratory grant to develop, test, and evaluate a citizen science program that engages youth to investigate energy issues through scientific inquiry with innovative technology. The project will crowd-create the Infrared Street View, a citizen science program that aims to produce a thermal version of Google's Street View using an affordable infrared (IR) camera attached to a smartphone. In collaboration with high schools and out-of-school programs in Massachusetts, we will conduct pilot-tests with approximately 200 students in this exploratory phase. The project will develop SmartIR, a smartphone app that will guide users to collect IR images on both Android and iOS platforms for synthesizing a seamless street view. Figure 1 shows a prototype of the Infrared Street View and Figure 2 shows a little math behind the scenes.

Fig. 1: A hemispherical infrared street view (prototype)

In essence, an IR camera serves as a high-throughput data acquisition instrument that collects thousands of temperature data points each time a picture is taken. With this incredible tool, youth can collect massive geotagged thermal data that have considerable scientific and educational value for visualizing energy usage and improving energy efficiency at all levels. The Infrared Street View program will provide a Web-based platform for youth and anyone interested in energy efficiency to view and analyze the aggregated data to identify possible energy losses. By sharing their scientific findings with stakeholders, youth will make changes to the way energy is being used. 

We are completely aware of possible legal implications and complications of the proposed citizen science program. In the case of Kyllo v. United States in 2001,  the Supreme Court has ruled that the use of a thermal camera from a public vantage point to monitor the radiation of heat from a person's home was a “search” within the meaning of the Fourth Amendment, and thus required a warrant. The ruling seems to be limited to the use of thermal cameras by law enforcement, however. Back then, IR cameras were available to only a handful of professionals, but they are only $200 nowadays and just a few clicks away on Amazon. The widespread use of smartphone-based IR cameras is making thermal images commonplace on the Internet and it is probably an interesting question for law scholars to study how civilian use of IR cameras should be regulated.

Fig. 2: Math behind the scenes.

Regardless, we will take the privacy issue very seriously and will take every precaution that we can think of to avoid potential side effects resulted from this well-intentioned program. Fortunately, we have a lot of public supports to conduct this research on large public buildings and possible commercial buildings, where the concerns of privacy are far less than private residential buildings and the needs to reduce the energy waste of those buildings and save taxpayer dollars are far more pressing. Hence, we will start with school, public, and commercial buildings in selected areas where performing thermal scan of the buildings and publishing their thermal images for educational and research purposes are permitted by school leaders, town officials, and property owners.  

From a broader perspective, the Infrared Street View program could serve as a pilot test that may shed light on increasingly important issues related to citizen privacy in the era of the Internet of Things (IoT), which features the ubiquity of sensor data collection that could be viewed by many as invasive into their physical space (not just cyberspace). While no one can deny the tremendous potential of the technology in transforming the ways people learn, work, and live, careful research must be carried out to address legitimate concerns. This program could be one of those projects that provide a unique approach to meet those challenges from a citizen science point of view, which integrates many interesting scientific, technical, educational, and legal aspects. The lessons we can learn from conducting this work could be very useful to the citizen science community in the IoT era.