Tag Archives: Solar energy

Designing heliostat layouts of concentrated solar power stations with Energy3D

Fig. 1: PS20 field output heat map (June, 22)
Fig. 2: PS20 field output heat map (December, 22)
Fig. 3: Fermat spiral layout (6/22, Phoenix, AZ)
In an earlier article, I have discussed the concepts and issues (shadowing, blocking, cosine efficiency, etc.) related to the design of heliostat layouts for concentrated solar power (CSP) tower stations. I also showed that these problems can be nicely visualized in Energy3D so that people can immediately see them. Instant visual feedback in design time may be very useful to a designer (in fact, this is known as concurrent analysis in the CAD/CFD community, meaning that the tasks of structure design and function simulation run immediately after each other to shorten the wait time between ideation and analysis). Figures 1 and 2 are the heat map visualizations of PS20, a CSP station in Spain, that instantly suggest the possibility of minor blocking problems for some heliostats in the summer and winter. The heat map on each reflector is based on the reflected portion of the direct solar radiation onto a 8 x 8 grid on the reflector plane. Hence it already includes shadowing loss, blocking loss, and attenuation loss. And you didn't read the image wrong, each heliostat reflector has a whopping area of 120 square meters (12 x 10 meters), dwarfing the vehicle in the image!

This blog post features several new tools that were just added to Energy3D to support the actual design tasks.

Fig. 4: Variations of layouts
The first tool is a field layout wizard that provides basic steps for customizing three different types of layout: circular, radial stagger, and spiral. Of course, you can also easily copy and paste to create a linear array of heliostats like those photovoltaic arrays, but linear layouts are unpopular, perhaps with the exception of the Jülich Solar Tower in Germany. For non-linear layouts, you will need the wizard, which allows you to select the width and height of the heliostat reflectors as well as a variety of parameters to automatically generate a layout.

Note that, in Energy3D, the heliostat field must be built on top of a foundation. The size of the foundation you draw sets the boundary of the heliostat field. As the field layout must be done on a foundation, the layout wizard can only be accessed through the popup menu of a foundation.

The spiral layout that Energy3D supports (Figure 3) is an interesting addition. It currently provides the Fermat spiral, which is the pattern you see from a sunflower head. It is so amazing that solar science seems to always go back to the sunflower. The solar trackers for photovoltaic arrays mimic the motion of sunflowers to follow the sun. The spiral pattern of a sunflower head may hold a key to optimal heliostat layouts (Noone, Torrilhon, and Mitsos, Solar Energy, Vol. 862, pp. 792–803, 2012). This may not be too surprising considering that the sunflower has probably evolved into that particular pattern to ensure that each seed has enough room to grow and fair access to sunlight.

Fig. 5: Superimposed heliostats on top of map images (PS20)
The layout wizard provides a baseline model that you can always modify manually to get what you want (Figure 4). All heliostats can be easily dragged, dropped, or removed.

If you want to model after an existing CSP station, you can use the Geo-Location menu of Energy3D to import a map image of the station and then superimpose 3D heliostats on top of the map image where the images of the actual heliostats are located. Figure 5 shows that an Energy3D model of the PS20 station can be perfectly created using this method. The shadows on the ground cast by the heliostats in the Energy3D model even aligns very well with those captured in the map image (I must confess that I tried to guess the right date and time from the shadow of the tower and the rest just follows).

Visualizing design issues in heliostat layouts of concentrated solar power stations with Energy3D

Fig. 1: Visualizing shadowing loss
As a one-stop-shop for solar solutions, Energy3D supports the design of concentrated solar power (CSP) stations. Although the main competitor of the CSP technology, the photovoltaic (PV) power stations, have become dominant in recent years due to the plummet of PV panel price, CSP has its own advantages and potential, especially in energy storage. According to the US Department of Energy, the levelized cost of electricity (LCOE) for CSP has dropped to 13 cents per kWh in the US in 2015, comparable to the LCOE for PV (12 cents per kWh). In general, it is always better to have options than having none. A combination of PV and CSP stations may be what is good for the world: CSP can complement PV to generate stable outputs and provide electricity at night. As a developer of solar design and simulation software, we are committed to supporting the research, development, and education of all forms of solar technologies.

Numerical simulation plays an important role on designing optimal CSP stations. Concentrated solar power towers are the first type of CSP stations covered by the modeling engine of Energy3D. This blog post shows some progress towards the goal of eventually building a reliable simulation and visualization kernel for CSP tower technology in Energy3D. The progress is related to the study of heliostat layouts (the heat transfer part is yet to be built).

Numerous studies of heliostat layouts have been reported in literature in the past three decades, resulting in a variety of proposals for minimizing the land use and/or maximizing the energy output (see a recent review: Li, Coventry, Bader, Pye, & Lipiński, Optics Express, Vol. 24, No. 14, pp. A985-A1007, 2016). The latest is an interesting biomimetic pattern suggested by Noone, Torrilhon, and Mitsos (Solar Energy, Vol. 862, pp. 792–803, 2012), which resembles the spiral patterns of a sunflower head (each floret is oriented towards the next by the golden angle of 137.5°, forming a Fermat spiral that is probably Mother Nature's trick to ensure that each seed has enough room to grow and fair access to sunlight).
Fig. 2: Visualizing blocking loss

If you haven't worked in the field of solar engineering, you may be wondering why there has been such a quest for optimal layouts of heliostats. At first glance, the problem seems trivial -- well, a tower-based CSP station is just a gigantic solar cooker, isn't it? But things are not always what they seem.

Fig. 3: Annual outputs of the heliostats in Fig. 2
The design of the heliostat layout is in fact a very complicated mathematical problem. We have some acres of land somewhere to begin with. The sun moves in the sky and its trajectory varies from day to day. But that is OK. The heliostats can be programmed to reflect sunlight to the receiver automatically. These all sound good until we realize that the heliostats' large reflectors can cast shadow to one another if they are too close or the sun is low in the sky (Figure 1). Like the case of PV arrays, shadowing causes productivity loss (but luckily, reflectors -- unlike solar panels based on strings of connected solar cells -- do not completely lose power if only a part of it is in the shadow).

Fig. 4: Visualizing cosine efficiency
Unlike the case of PV arrays, heliostats have an extra problem -- blocking. A heliostat must reflect the light to the receiver at the top of the tower and that path of light can be blocked by its neighbors. Of course, we rarely see the case of complete blocking. But if a portion of the reflector area is denied optical access to the receiver, the heliostat will lose some productivity. Energy3D can visualize this loss on each heliostat reflector. The upper image of Figure 2 shows the insolation to the reflectors whereas the lower one shows the portion of the insolation that actually reaches the receiver. Figure 3 shows a comparison of the outputs of the heliostats over the course of a year. As you can see, the blue parts of the reflectors can never bounce light to the receiver because the heliostats in front of them block the reflection path for the lower parts of those heliostats. The way to mitigate this issue is to gradually increase the spacing between the heliostats when they are farther away from the tower.
Fig. 5: Cosine efficiency is lower in the winter

Another problem with CSP tower technology is the so-called cosine efficiency. As we know, the insolation onto a surface is maximal when the surface directly faces the sun (this is known as the projection effect). In the northern hemisphere, however, the heliostats to the south of the tower (the south field) cannot face the sun directly as they must be positioned at an angle so that the incident sunlight can be reflected to a northern position (where the receiver is located). Figure 4 shows a visualization of the cosine effect and Figure 5 shows the comparison of the annual outputs of the heliostats. Clearly, the cosine efficiency is the lowest in the winter and the highest in the summer.

Fig. 6: Semicircular layout in the north field
Does the cosine efficiency mean that we should only deploy heliostats in the north field as is shown in Figure 6? This depends on a number of factors. Yes, the cosine efficiency does reduce the output of a heliostat in the south field in the winter (maybe early spring and late fall, too), but a heliostat far away from the tower in the north field also produces less energy. For a utility-scale CSP station that must use thousands of heliostats, the part of the south field close to the tower may not be such a bad place to put heliostats, compared with the part of the north field far away from the tower. This is more so when the site is closer to the equator. If the site is at a higher latitude to the point that it makes more sense to deploy all heliostats in the north field, dividing the site into multiple areas and constructing a tower for each area may be a desirable solution. The downside is that additional towers will increase the constructional cost.

We now multiply these three problems (shadowing, blocking, and cosine effect) with thousands of heliostats, confine them within an area of a given shape, and want to spend as less money as possible while producing as much electricity as possible. That is the essence of the mathematical challenge that we are facing in CSP field design. With even more functionalities to be added in the future, Energy3D could become a powerful design tool that anyone can use to search for their own solutions.

Choose solar trackers: HSAT, VSAT, or AADAT?

Fig. 1: HSAT and VSAT.
Energy3D now supports three major types of solar trackers: Horizontal single-axis trackers (HSAT), vertical single-axis trackers (VSAT), and altazimuth dual-axis trackers (AADAT). I have blogged about HSAT and AADAT earlier. Figure 1 shows the difference between HSAT and VSAT.

With all these options, which should we choose? The decision is based on the additional output of the solar panels, the space required to operate the system, and, of course, the cost of the tracking system. For instance, AADAT may be more complex as it rotates around two perpendicular axes. Space is always an important constraint and it is even more so for large solar farms considering the issue of inter-panel shading. Fixed arrays and HSAT systems may be more efficient in space usage if the inter-row shading is not significant.
Fig. 2 Energy3D predictions of annual outputs.

Let's first compare the annual output of a single solar panel under different conditions, as shown in Figure 2 and summarized in Table 1, calculated using Energy3D.

Table 1. Comparison of total annual outputs of a solar panel that has a fixed tilt angle equal to its latitude, a solar panel that is rotated by a HSAT, a solar panel that is rotated by a VSAT, and a solar panel that is rotated by an AADAT, at four different locations in the US. The unit is kWh.


Locations
Fixed (tilt=lat.)
HSAT
VSAT
AADAT
Boston, MA
428
520
559
603
Anchorage, AK
258
310
371
380
Miami, FL
507
654
617
711
San Juan, PR
523
694
617
738
 
These results suggest that the AADAT system, not surprisingly, generates the most electricity throughout the year at all four locations, as it always faces the sun. The second best, for low-latitude locations, is the HSAT system and, for high-latitude locations, is the VSAT system. In the case of HSAT, the lower the latitude, the closer the performance of the HSAT approaches that of the AADAT. In the case of VSAT, the higher the latitude, the closer the performance of the VSAT approaches that of the AADAT. This means that, considering the cost factor, HSAT at a very low latitude such as the equator is a better choice than AADAT and VSAT at a very high latitude such as Alaska is a better choice than AADAT.
Fig. 3 Optimal layout through heat map tessellation. 

The above analysis is based on a single, isolated solar panel. For arrays of panels, we must consider the shading area each panel sweeps when it is driven by a tracker. Energy3D's heat map visualization of solar irradiance may be a useful tool for designing optimal layouts for VSAT or AADAT panels that cannot be seamlessly aligned into rows such is in the case of HSAT arrays. From a mathematical point of view, an optimal layout must minimize land use. Hence, it can be imagined as a tessellation of effective shade area of individual panels (Figure 3). This may be something interesting to think about.

Simplifying solar design in Energy3D with Google Map integration

Fig. 1 2D view of Concord Consortium building in Energy3D
Solar design depends on accurate geometry. Rooftop solar panel design requires accurate 3D models of buildings, for example the shape of the roof, the height of the building, and the surrounding objects such as trees. Likewise, solar power station design requires accurate information about the field.

Fig. 2 3D view of Concord Consortium building in Energy3D
The easiest way to obtain these information is through Google Map, from which the dimension of an object can be measured. Although Google Map has not provided elevation data for a point yet, Google Earth does for many towns.

Earlier this year, students who performed solar design with Energy3D in our pilot tests must use Google Earth to retrieve the geometrical data for use in Energy3D design later. Having to master two sophisticated software tools simultaneously in a short time has turned out to be quite a challenge to many students. So an idea came to our mind: Why not just make Google Earth work within Energy3D? (Note: In fact, this is also a common feature among CAD software such as SketchUp.)

Fig. 3 Solar heat map of Concord Consortium building
It turned out that this integration is fairly simple, because Google has done the hard part of providing an easy-to-use Web API for virtually every platform. So in the latest version of Energy3D (V5.8.2 or higher), users will have an internal Google Map ready to help them with their solar designs.

Fig. 4 2D view of a solar farm in Concord, MA in Energy3D
Solar designers can specify a target location in Energy3D and then a Google Map image will be downloaded and used to overlay the ground in Energy3D. They can then draw a 3D building on top of this image by tracing the envelope of the building, eliminating the need to set the dimension of each side numerically. Figures 1-3 demonstrate the result of this new feature using the Concord Consortium's office building as an example.

Fig. 5 3D view of a solar farm in Concord, MA in Energy3D
A remarkable advantage brought by this feature is that it is easy to add model trees on top of the images of surrounding trees. A future version will also allow users to adjust the height and spread of a model tree based on the Google Map image.

Other than assisting designers to acquire site data, the map image also provides a rendering of how a new design may look like in an environment with existing buildings (just pretend for a moment that the building in Figure 2 hadn't existed and were a proposal to build two new houses at the site). Furthermore, with Google Map's elevation API, we will also be able to construct a terrain model of the ground (which is currently flat). Such a terrain model will not only make the energy simulation more accurate by taking all the surrounding objects into account but also make the rendering more realistic by giving the 2D map image a 3D effect (similar to the new 3D view of Google Map).

Based on Energy3D, we have created two solar design challenges for students to make meaningful contributions to the solarization movement. One is to solarize their own houses by designing rooftop solar panels. The other is to solarize their own schools and towns by designing solar farms (Figures 4 and 5). Aligned with the Next Generation Science Standards (NGSS) that require students to think and act like scientists and engineers, our goal is to engage students to practice science and engineering through solving real-world problems. But real-world problems are often complex and difficult (otherwise they are not problems in the real world!). This calls for the development of advanced tools that can empower students to tackle real-world problems. Our Energy3D software provides examples of how technology may knock down the barriers and help students attain the high standards set by the NGSS.

Modeling horizontal single-axis solar trackers in Energy3D

In the last post, I have blogged about modeling dual-axis solar trackers in Energy3D. To be more precise, the trackers shown in that blog post are altitude-azimuth (Alt/Az), or altazimuth trackers, or AADAT in short. In this post, I will introduce a type of single-axis tracker -- the horizontal single-axis tracker, or HSAT in short.

Fig. 1 Solar panel arrays rotated by HSATs
Because single-axis trackers do not need to follow the sun exactly, there are many different designs. Most of them differ in the choice of the axis of rotation. If the axis is horizontal to the ground, the tracker is a HSAT. If the axis is vertical to the ground, the tracker is a vertical single-axis tracker, or VSAT in short. All trackers with axes of rotation between horizontal and vertical are considered tilted single-axis trackers, or TSAT in short. None of these single-axis trackers can help the solar panels capture 100% of the solar radiation that reaches the ground. Exactly which design to choose depends on the location of the solar farm, among other consideration such as the cost of the mechanical system.

Fig. 2 Compare daily outputs of HSAT, AADAT, and fixed in four seasons.
HSAT is the first type of single-axis tracker that has been implemented in Energy3D. HSAT is probably more common than VSAT and TSAT and is probably easier to construct and install. In most cases, the rotation axis of a HSAT aligns with the north-south direction and the solar panels follow the sun in an east-to-west trajectory, as is shown in the YouTube video embedded in this post and in Figure 1.

Fig. 3 Compare annual outputs of HSAT, AADAT, and fixed.
How much more energy can a HSAT help to generate? Figure 2 shows the comparison of the outputs of a HSAT system, an AADAT system, and an optimally fixed solar panel on March 22, June 22, September 22, and December 22, respectively, in the Boston area. The results suggest that the HSAT system is almost as good as the AADAT system in June but its performance declines in March and September and becomes the worst in December (in which case it can only capture a little more than half of the energy harvested by the AADAT system). Interestingly, also notice that there is a dip at noon in the energy graphs for March, September, and December. Why so? I will leave the question for you to figure out. If you have a hard time imagining this, perhaps the visualizations in Energy3D can help.

Fig. 4 Compare wide- and narrow-spacing of HSAT arrays
Figure 3 shows the annual result, which suggests that, over the course of a year, the HSAT system -- despite of its relatively unsatisfactory performance in spring, fall, and winter -- still outperforms any fixed solar panel, but it captures about 86% of the energy captured by the AADAT system.

An important factor to consider in solar farm design is the choice of the inter-row spacing to avoid significant energy loss due to shading of adjacent rows in early morning and late afternoon. But you don't want the distance between two rows to be too far as the rows will occupy a large land area that makes no economic sense. With Energy3D, we can easily investigate the change of the energy output with regard to the change of the inter-row spacing. Figure 4 shows the gain from HSAT is greatly reduced when the rows are too close, essentially eliminating the advantages of using solar trackers. Despite of their ability to track the sun, HSATs still require space to achieve the optimal performance.

Modeling dual-axis solar trackers in Energy3D

Fig. 1: Solar panel arrays in Energy3D
A solar tracker is a system that automatically turns a solar panel or a reflector toward the sun in order to maximize the energy output of a solar power station. It is often said to be inspired by the sunflower.

In general, trackers can be categorized into two types: single-axis trackers and dual-axis trackers. Single-axis trackers have one degree of freedom that acts as an axis of rotation. The axis of rotation of single-axis trackers typically points to true north. Dual-axis trackers, on the other hand, have two degrees of freedom that act as axes of rotation. These axes are typically perpendicular to each other such as those in the altazimuth system. Single-axis trackers cannot exactly follow the sun but dual-axis trackers can.

Dual-axis trackers have been implemented in our Energy3D software for photovoltaic (PV) solar panels, as is shown in the video embedded in this post.

Energy3D has a variety of built-in tools for creating PV array layouts and analyzing their daily and annual yields. Figure 2 shows the comparison of the output of a solar panel rotated by a dual-axis tracker and those of solar panels fixed at different tilt angles (0°, 15°, 30°, 45°, 60°, 75°, and 90°) on March 22, June 22, September 22, and December 22, respectively, in Boston, MA. Not surprisingly, the result shows that the solar panel produces the most energy in June and the least in December.

Fig.2 A tracking PV panel vs. fixed panels at different tilt angles
When analyzing the benefit of using a solar tracker, we found that in June, a fixed panel at the optimal tilt angle produces about 70% of the energy produced by a panel oriented by a dual-axis tracker. That percentage increases to about 75% in March and September and to about 90% in December. This means that the benefit of using a tracker, compared with the maximal output of a fixed panel with the optimal tilt angle, will be significant in the summer but gradually diminish when the winter comes.

Having to manually adjust the tilt angles for a lot of solar panels four times a year sounds like too laborious to be practical. If that is out of the question, it would then be fair to compare the output of a solar panel with a tracker and those fixed at the same tilt angle throughout the year. Figure 3 shows that the total annual yield of a solar panel at the best tilt angle produces only 70% of the energy produced by a solar panel rotated by a tracker. In other words, a solar panel rotated by a tracker generates about 42% more energy compared with a solar panel fixed at the optimal tilt angle on the annual basis.
Fig.3 Annual outputs: tracker vs. fixed

Does the additional energy that solar trackers help generate worth the money (initial investment plus maintenance of moving parts) they cost? You may have heard that, as solar panels get cheaper and cheaper, trackers become less and less favorable. I want to offer a different point of view.

Surely, the return of the investment on solar trackers depends on a number of factors such as the price of solar panels. But one of the most important factors is the solar cell efficiency of the solar panels they rotate. The higher the efficiency is, the more the extra electricity a tracker can yield to offset the cost and make a profit. With the solar cell efficiency for commercial panels breaks record every year (reportedly 31.6% in July 2016), what didn't make economic sense in the past looks lucrative now. The future of the market for solar trackers will only look brighter.

Solar Engineering Summer Camp 2016


Computer modeling with Energy3D
The free Solar Engineering Summer Camp offered by the Concord Consortium was an intensive week-long event that focused on learning and applying solar science, 3D modeling, and engineering design. It featured a solar engineer from a leading solar company as a guest speaker. The activities included hands-on and computer-based activities that were designed to inspire and empower children to solve real-world problems and become change makers who will hopefully create a more sustainable future.

Poster session with parents
This year, eleven children (age 11-16) participated in the event that took place on Concord Consortium's east coast campus. Participants became the science advisors for their parents, investigating how their own houses could be turned into a small power station that supplies the energy needed.

A 3D house created and studied in the event
Using Google Earth and our Energy3D software, they made 3D computer models of their own houses, designed different solar array layouts, and then ran computer simulation to evaluate and compare their yields. They performed cost-benefit analysis of different solutions, based on which they completed solar assessment reports about the solarization potential of their own homes. At last, they presented their results in a poster session and discussed their findings with their parents.

The parents were generally very supportive. Some even helped their kids measure the dimensions of their houses (unfortunately, Google Earth does not provide sufficient information for students to retrieve the geometry of their houses; so some kids must learn how to measure the heights of their roofs using other methods such as photogrammetry).

3D houses created by kids
How did the little science advisors do their jobs in terms of informing their parents then? When asked "Did your child’s Solar Assessment Report make you change your view or interest in solar energy?", a parent responded in the exit survey: "We already have solar panels on our house. This project allowed me to consider our energy needs and additional options for increasing our capacity to generate electricity." This example shows that even for those people who already have solar panels on their roofs, the findings from their kids might have spurred them to think about more possibilities.

As a side note, I noticed an interesting response from a parent: "She enjoyed using the software to design our house. She said it was an interesting topic, but she cautioned me not to rely solely on her calculations to base our decision on whether to convert to solar energy use for our house." The kid is right -- all models have limitations and engineers must use caution. A science advisor should inform her advisee that a model may fail.

Simulating concentrated solar power towers with Energy3D

Concentrated solar power (CSP) systems generate electricity using arrays of mirrors to concentrate sunlight shed on a large area onto a small area. The concentrated light is converted into thermal energy, which then drives a heat engine connected to an electrical power generator. Put it simply, a CSP power station operates like a solar cooker that you might have made in a high school science project. You can think of it as a gigantic solar cooker.


But a small science idea like this could turn into big money. For example, the Ivanpah Solar Power Facility in the California Mojave Desert, which drew $2.2 billion of investment, generates 392 megawatts (MW) -- enough to power hundreds of thousands of homes. As of 2016, the largest CSP project in the world is the Ouarzazate Solar Power Station in Morocco, which is expected to output 580 MW at peak and cost about $9 billion. Globally, CSP power stations will generate 4,705 MW this year.


CSP stations do not need to be only large-scale. Small-scale CSP stations (below 1 MW, on-grid or off-grid) may provide more flexible and affordable solutions to communities, especially those in rural areas. They provide attractive alternatives to photovoltaic power stations. Reflecting mirrors would probably cost less and last longer than solar panels and there is little to no concern of outdated or degraded efficiency (reflectivity loss may be less than 1% after 10 years of exposure to UV). The latter is an issue for solar panels if you consider that, in just six years, the latest 24.1% of solar cell efficiency of commercial panels in 2016 (UPDATE: In July, Hanergy debuted the 31.6% efficiency solar cells for their solar cars!) almost render those 12%-efficiency panels installed in 2010 obsolete and more breakthroughs forecast down the road will only make the old ones look less pretty.

To support the exploration of all kinds of solar energy exploitation, we have added the initial capacity to model CSP power stations in our Energy3D software, which is intended to be a "one-stop-shop" for solar energy modeling and design. This includes the capability of adding mirrors, heliostats, and power towers and analyzing the outputs as a function of time, location, and weather. This article shows some of the graphic effects of solar power towers (with more than 500 reflectors, each of which has the size of 2 by 3 meters, amounting to a total reflective area of more than 3,000 square meters). The four images above demonstrate how heliostats change the orientations of the reflectors at different times of the day (the selected date is June 22 and the selected location is Phoenix, AZ). The images show a simple circular field layout. In reality, radial stagger layouts that minimize shadow loss and block loss and maximize cosine efficiency are commonly used.

In the months to come, we plan to enhance Energy3D's ability to support a variety of field layout designs for power towers and model various configurations of solar thermal power (e.g., parabolic trough and Fresnel reflectors).

I have blogged about Energy3D's capacity to simulate large-scale photovoltaic power stations. This new capacity of simulating CSP stations has enabled Energy3D to model and design two of the three main types of solar power plants (the remaining one is solar updraft tower, or solar chimney, which you will also be able to model in Energy3D in the future).

Updates: 

Integrating Solarize Mass and STEM education through powerful simulation technologies

Fig.1: Solar simulation in Energy3D.
Solarize Mass is a program launched by the Massachusetts Clean Energy Center that seeks to increase the adoption of small-scale solar electricity in participating communities. In 2016, the towns of Natick and Bolton were selected to pilot for Solarize Mass. According to the Town of Natick, "Solarize Mass Natick is a volunteer initiative run by Natick residents. Our goal is to make going solar simple and affordable for Natick residents and small business owners as part of a 2016 state-sponsored program. But it is a limited-time program: the deadline for requesting a site visit is August 1, 2016."

Solar energy does not need to be a limited-time offer. The question is to figure out how residents can do their own site assessment while the guys are not in town to give free consultation. Sure, residents can use Google's Sunroof to quickly check whether solar is right for them (if their areas are covered by Sunroof). But what Sunroof does is only to screen a building based on its solar potential, not to provide a more informative engineering solution to help homeowners make up their minds. The latter has to be done by a solar installer who will provide the PV array layout, the output projection, the financial analysis, etc., in order to run a convincing business. But this is a time-consuming process that poses financial risks to solar installers if the homeowners end up backing out. So we need to find some other creative solutions.

Fig. 2: Student work from a Massachusetts school in 2016.
Funded by the National Science Foundation (NSF), we have been working at the Concord Consortium on exploring meaningful ways to combine solar programs with STEM education that will effectively boost each other. We have been developing a powerful computer-aided engineering system called Energy3D that essentially turns an important part of solar engineering's job into something that even a middle or high school student can do (Figure 1). In a recent case study, we found that Energy3D's prediction outperforms a solar installer's prediction for my colleague's house in Bolton, MA. In a pilot test in an Eastern Massachusetts school in June 2016, we found at least 60% of the 27 ninth graders who participated in the 8-hour activity succeeded -- with various degrees -- in coming up with a 3D model of her/his house and designing a solarization solution based on it (Figure 2). Giving the fact that they had to learn both Google Earth and Energy3D in a very short time and then perform a serious job, this result is actually quite encouraging. Our challenge in the NSF-funded project is to improve our technology, materials, and pedagogy so that more students can do a better job within a limited amount of time in the classroom.

With this improving capacity, we are now asking this question: "What can middle or high school students empowered by Energy3D do for the solarization movement?" Fact is that, there are four million children entering our education system each year in the US. If 1% of them become little solar advocates or even solar engineers in schools, the landscape for green energy could be quite different from what it is now.

Fig. 3: Energy3D supports rich design.
Starting from three years ago, STEM education in the US is required to incorporate science and engineering practices extensively into the curriculum by the Next Generation Science Standards (the equivalent of Common Core for science). The expectation is that students will gradually think and act like a real scientist and engineer through their education careers. To accomplish this goal, an abundance of opportunities for students to practice science and engineering through solving authentic real-world problems will need to be created and researched. On July 8, 2016, NSF has also made this clear in the a proposal solicitation letter about what they call Change Makers, which states: "Learners can be Change Makers, identifying and working to solve problems that matter deeply to them, while simultaneously advancing their own understanding and expertise. Research shows that engaging in real world problem solving enhances learning, understanding, and persistence in STEM." Specifically, the letter lists "crowd-sourced solutions to clean energy challenge through global, public participation in science" as an example topic. An NSF letter like this usually reflects the thinking and priority of the funding agency. From a practical point of view, considering the fact that the choices for engineering projects for schools are currently quite limited, there is a good chance that schools would welcome solar engineering and other types of engineering as an alternative to, say, robotic engineering.

The overlap of timing for the ongoing solarization movement and the ongoing education overhaul poses a great opportunity for uniting the two fronts. We envision that Energy3D will play a vitally important role on making this integration a reality because 1) Energy3D is based on rigorous science and engineering principles, 2) its accuracy is comparable to that of other industry-grade simulation tools, 3) it simulates what solar engineers do in the workplace, 4) it covers the education standards of scientific inquiry and engineering design, 5) it supports many architectural styles (Figure 3), 6) it works just like a design game (e.g., Minecraft) for children, and 7) last but not least -- it is free! With more development under way and planned for the future, Energy3D is also on the way to become a citizen science platform for anyone interested in residential and commercial solar designs and even solar power plant designs.

Exactly how the integration will be engineered is still a question under exploration. But we are very excited about all the possibilities ahead and we are already in an early phase to test some preliminary ideas. If you represent a solar company and are interested in this initiative, please feel free to contact us.

Simulating photovoltaic power plants with Energy3D

Modeling 1,000 PV panels in a desert
Solar radiation simulation
We have just added new modeling capacities to our Energy3D software for simulating photovoltaic (PV) power stations. With these additions, the latest version of the software can now simulate rooftop solar panels, solar parks, and solar power plants. Our plan is to develop Energy3D into a "one stop shop" for solar simulations. The goal is to provide students an accessible (yet powerful) tool to learn science and engineering in the context of renewable energy and professionals an easy-to-use (yet accurate) tool to design, predict, and optimize renewable energy generation.

Users can easily copy and paste solar panels to create an array and then duplicate arrays to create more arrays. In this way, users can rapidly add many solar panels. Each solar panel can be rotated around three different axes (normal, zenith, and azimuth). With this flexibility, users can create a PV array in any direction and orientation. At any time, they can adjust the direction and orientation of any or all solar panels.
PV arrays that are oriented differently


What is in the design of a solar power plant? While the orientation is a no-brainer, the layout may need some thinking and planning, especially for a site that has a limited area. Another factor that affects the layout is the design of the solar tracking system used to maximize the output. Also, considering that many utility companies offer peak and off-peak prices for electricity, users may explore strategies of orienting some PV arrays towards the west or southwest for the solar power plant to produce more energy in the afternoon when the demand is high in the summer, especially in the south.

Rooftop PV arrays
In addition to designing PV arrays on the ground, users can do the same thing for flat rooftops as well. Unlike solar panels on pitched roofs of residential buildings, those on flat roofs of large buildings are usually tilted.

We are currently implementing solar trackers so that users can design solar power plants that maximize their outputs based on tracking the sun. Meanwhile, mirror reflector arrays will be added to support the design of concentrated solar power plants. These features should be available soon. Stay tuned!