Thursday, September 14, 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.

Thursday, September 7, 2017

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.

Thursday, August 17, 2017

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.

Wednesday, August 16, 2017

Canadian researchers use Energy3D to design renewable energy systems for mobile hospitals in Libya

Fig. 1: A H-shaped mobile hospital designed using Energy3D
Prof. Tariq Iqbal and his student Emadeddin Hussein from the Department of Electrical and Computer Engineering at the Memorial University of Newfoundland in Canada published a paper in the Journal of Clean Energy Technologies titled with "Design of Renewable Energy System for a Mobile Hospital in Libya."

The researchers recognized that the United Nations' efforts to provide field hospitals have recently decreased in areas that face a high risk in transportation, lack of power, and lack of security for field officers, such as war-torn countries like Libya and Syria. In those unfortunate parts of the world, lack of aids and health resources have a major effect on people's lives. Their paper proposes a photovoltaics (PV) hybrid system for supplying an electric load of a mobile hospital in an area where there is no grid. Such a hybrid system is believed to be a cost-effective solution to power a mobile hospital capable of providing uninterrupted power to support a doctor and two nurses.

Our Energy3D software was used in their research as a simulation tool to study the heat load and optimize the design solution. Figure 1 shows a H-shaped design from their paper (I guess the H-shape was chosen because it is the initial of the word "hospital").

Fig. 2: Energy3D supports 450 regions from 117 countries.
We highly appreciate the researchers' efforts in finding ways to help people living in remote areas and war zones in the world. We are glad to learn that our software may have helped a bit in providing humanitarian aids to those people. Inspired by their work, we will add more weather data to Energy3D to cover areas in the state of unrest (455 regions from 120 countries are currently supported in Energy3D, as shown in Figure 2). In the future, we will also develop curriculum materials and design challenges to engage students all over the world to join these humanitarian efforts through our global drive and outreach.