Tag Archives: Solar radiation modeling

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 plants using 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 no concern of outdated or degraded efficiency. 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 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 reflecting area of more than 3,000 square meters). The last figure demonstrates 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).

In the months to come, we plan to enhance Energy3D's ability to model various kinds of heliostats and various configurations of solar thermal power (e.g., parabolic trough and Fresnel reflectors). Currently, only the alt-azimuth tracking mechanism and flat mirrors are implemented.

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.

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!

Energy3D makes designing realistic buildings easy

The annual yield and cost benefit analyses of rooftop solar panels based on sound scientific and engineering principles are critical steps to the financial success of building solarization. Google's Project Sunroof provides a way for millions of property owners to get recommendations for the right solar solutions.



Another way to conduct accurate scientific analysis of solar panel outputs based on their layout on the rooftop is to use a computer-aided engineering (CAE) tool to do a three-dimensional, full-year analysis based on ab initio scientific simulation. Under the support of the National Science Foundation since 2010, we have been developing Energy3D, a piece of CAE software that has the goal of bringing the power of sophisticated scientific and engineering simulations to children and laypersons. To achieve this goal, a key step is to support users to rapidly sketch up their own buildings and the surrounding objects that may affect their solar potentials. We feel that most CAD tools out there are probably too difficult for average users to create realistic models of their own houses. This forces us to invent new solutions.

We have recently added countless new features to Energy3D to progress towards this goal. The latest version allows many common architectural styles found in most parts of the US to be created and their solar potential to be studied. The screenshots embedded in this article demonstrate this capability. With the current version, each of these designs took myself approximately an hour to create from scratch. But we will continue to push the limit.

The 3D construction user interface has been developed based on the tenet of supporting users to create any structure using a minimum set of building blocks and operations. Once users master a relatively small set of rules, they are empowered to create almost any shape of building as they wish.

Solar yield analysis of the first house
The actual time-consuming part is to get the right dimension and orientation of a real building and the surrounding tall objects such as trees.
Google's 3D map may provide a way to extract these data. Once the approximate geometry of a building is determined, users can easily put solar panels anywhere on the roof to check out their energy yield. They can then try as many different layouts as they wish to compare the yields and select an optimal layout. This is especially important for buildings that may have partial shades and sub-optimal orientations. CAE tools such as Energy3D can be used to do spatial and temporal analysis and report daily outputs of each panel in the array, allowing users to obtain fine-grained, detailed results and thus providing a good simulation of solar panels in day-to-day operation.

The engineering principles behind this solar design, assessment, and optimization process based on science is exactly what the Next Generation Science Standards require K-12 students in the US to learn and practice. So why not ask children for help to solarize their own homes, schools, and communities, at least virtually? The time for doing this can never be better. And we have paved the road for this vision by creating one of easiest 3D interfaces with compelling scientific visualizations that can potentially entice and engage a lot of students. It is time for us to test the idea.

To see more designs, visit this page.

Making sense of non-optimal solar panel orientations seen on Google Maps


Figure 1: Google Map
If you are thinking about putting solar panels on your roof, the conventional wisdom is that your house probably would be automatically disqualified if its roof does not have a large south-facing side for installing solar panels. If you have no idea about this, the sales representatives from solar companies would probably tell you this based on their training.

While it might be a smart strategy to target houses with most promising returns at the beginning of the solar energy industry back a decade ago, the old rules may not hold any longer. With the solar cell efficiency of commercial panels climbing above 20% and, more importantly, the environmental awareness of homeowners increasing, the solar energy market has changed a lot.

Thanks to Google Map, it is just a few mouse clicks away to get an idea about the current status of the market. So I surveyed my neighborhoods in eastern Massachusetts and was surprised to find that a significant amount of rooftop solar panel arrays do not actually face south (Figure 1). This is understandable because a significant percentage of buildings do not have a roof that has a south-facing side. So if homeowners living in those houses want to contribute to solving the environmental problems, they do not have any other choice except putting solar panels wherever they can be mounted. If you take a look at your own neighborhood in Google Map, you should spot a lot of west- and east-facing (or even north-facing!) solar panels.

Figure 2. Solar simulation in Energy3D
Figure 3: South-facing vs. west-facing
I have heard some solar installers accusing competitors of coaxing homeowners into this kind of less effective configurations in order to increase their profits at the expense of the homeowners' running cost. Before we start pointing fingers at one another, let's stop and think: Is it really such a horrible idea to put solar panels on a non-south-facing side? The problem is that few people really have an idea about how much less energy those non-ideal configurations would entail compared with the optimal south-facing situation. An estimate of this is critically important to helping homeowners make up their mind whether to go solar or not. And, by the way, it also demonstrates your business ethics and technical capability as well. Unfortunately, in reality, you cannot re-orient people's houses or roofs to figure that out.

Thanks to the funding from the National Science Foundation, this kind of estimation can be easily done using our Energy3D software, which has a decent crystal ball when it comes to solar modeling and prediction (Figure 2). I have been blogging about this capacity of the software for a while. It is time to finally put this tool into practice to help people evaluate their solar options.


Let's start with a very simple house and a 5kW solar panel system (Figure 3). The first step is to get a sense of how accurate Energy3D's prediction may be. In situations similar to the standard test conditions (STC), this system -- when oriented to the south -- should generate about 6,000 kWh per year in Boston, Massachusetts and about 8,000 kWh per year in Los Angeles, California. The results from Energy3D agree exactly with these widely-cited numbers, as shown in Figure 4.

Figure 4: BOS vs. LAX
With this validity, we can then ask the following question: What if we have only a west-facing roof? This can be easily done by rotating the model house in Energy3D 90° and then redo the calculation. It turns out that the homeowner in Boston will get about 80% of the maximal output (when the panels face south), as illustrated in Figure 5. The folks in LA will fare slightly better -- about 82%.

Figure 5: South-facing vs. west-facing outputs
I believe a large number of homeowners, if informed by the results of this simulation-based analysis, may consider 20% performance reduction as acceptable. Yes, their panels will generate less electricity than those on the roofs of houses with the optimal orientation, but many would like to do whatever they can to help reduce carbon emission. To them, doing it at a pace that is 20% slower is infinitely better than doing nothing at all, letting alone that many houses do not face exactly west and the actual performance reduction will be less than 20%.

The results of this study should give you a sense about how simulations may be useful in fostering the growth of the solar energy market. Even better, through years of development, we have made solar simulation in Energy3D so easy that anyone can do it. As an experimental step, we are now collaborating with high schools in Massachusetts to pilot-test the feasibility of engaging students to evaluate the solarization potential of their own houses. Our goal is to create an integrated education-business model that benefits both sides. We hope that the success of this project will help the world reach the goals set by the Paris Agreement.

Personal thermal vision could turn millions of students into the cleantech workforce of today

So we have signed the Paris Agreement and cheered about it. Now what?

More than a year ago, I wrote a proposal to the National Science Foundation to test the feasibility of empowering students to help combat the energy issues of our nation. There are hundreds of millions of buildings in our country and some of them are pretty big energy losers. The home energy industry currently employs probably 100,000 people at most. It would take them a few decades to weatherize and solarize all these residential and commercial buildings (let alone educating home owners so that they would take such actions).

But there are millions of students in schools who are probably more likely to be concerned about the world that they are about to inherit. Why not ask them to help?

You probably know a lot of projects on this very same mission. But I want to do something different. Enough messaging has been done. We don't need to hand out more brochures and flyers about the environmental issues that we may be facing. It is time to call for actions!

For a number of years, I have been working on infrared thermography and building energy simulation to knock down the technical barriers that these techniques may pose to children. With NSF awarding us a $1.2M grant last year and FLIR releasing a series of inexpensive thermal cameras, the time of bringing these tools to large-scale applications in schools has finally arrived.

For more information, see our poster that will be presented at a NSF meeting next week. Note that this project has just begun so we haven't had a chance to test the solarization part. But the results from the weatherization part based on infrared thermography has been extremely encouraging!

Solarizing a house in Energy3D

Fig. 1 3D model of a real house near Boston (2,150 sq ft).
On August 3, 2015, President Obama announced the Clean Power Plan – a landmark step in reducing carbon pollution from power plants that takes real action on climate change. Producing clean energy from rooftop solar panels can greatly mitigate the problems in current power generation. In the US, there are more than 130 million homes. These homes, along with commercial buildings, consume more than 40% of the total energy of the country. With improving generation and storage technologies, a large portion of that usage could be generated by home buildings themselves.

A practical question is: How do we estimate the energy that a house can potentially generate if we put solar panels on top of it? This estimate is key to convincing homeowners to install solar panels or the bank to finance it. You wouldn't buy something without knowing its exact benefits, would you? This is why solar analysis and evaluation are so important to the solar energy industry.

The problem is: Every building is different! The location, the orientation, the landscape, the shape, the roof pitch, and so on, vary from one building to another. And there are over 100 MILLION of them around the country! To make the matter even more complicated, we are talking about annual gains, which require the solar analyst to consider solar radiation and landscape changes in four seasons. With all these complexities, no one can really design the layout of solar panels and calculate their outputs without using a 3D simulation tool.

There may be solar design and prediction software from companies like Autodesk. But for three reasons, we believe that our Energy3D CAD software will be a relevant tool in this marketplace. First, our goal is to enable everyone to use Energy3D without having to go through the level of training that most engineers must go through with other CAD tools in order to master them. Second, Energy3D is completely free of charge to everyone. Third, the accuracy of Energy3D's solar analysis is comparable with that of others (and is improving as we speak!).

With these advantages, it is now possible for homeowners to evaluate the solar potential of their houses INDEPENDENTLY, using an incredibly powerful scientific simulation tool that has been designed for the layperson.

In this post, I will walk you through the solar design process in Energy3D step by step.

1) Sketch up a 3D model of your house

Energy3D has an easy-to-use interface for quickly constructing your house in a 3D environment. With this interface, you can create an approximate 3D model of your house without having to worry about details such as interiors that are not important to solar analysis. Improvements of this user interface are on the way. For example, we just added a handy feature that allows users to copy and paste in 3D space. This new feature can be used to quickly create an array of solar panels by simply copying a panel and hitting Ctrl/Command+V a few times. As trees are important to the performance of your solar panels, you should also model the surrounding trees by adding various tree objects in Energy3D. Figure 1 shows a 3D model of a real house in Massachusetts, surrounded by trees. Notice that this house has a T shape and its longest side faces southeast, which means that other sides of its roof may worth checking.
Fig. 2 Daily solar radiation in four seasons

2) Examine the solar radiation on the roof in four seasons

Once you have a 3D model of your house and the surrounding trees, you should take a look at the solar radiation on the roof throughout the year. To do this, you have to change the date and run a solar simulation for each date. For example, Figure 2 shows the solar radiation heat maps of the Massachusetts house on 1/1, 4/1, 7/1, and 10/1, respectively. Note that the trees do not have leaves from the beginning of December to the end of April (approximately), meaning that their impacts to the performance of the solar panels are minimal in the winter.

The conventional wisdom is that the south-facing side of the roof is a good place to put solar panels. But very few houses face exact south. This is why we need a simulation tool to analyze real situations. By looking at the color maps in Figure 2, we can quickly figure out that the southeast-facing side of the roof of this house is the optimal side for solar panels and we also know that the lower part of this side is shadowed significantly by the surrounding trees.

Fig. 3 Solarizing the house
3) Add, copy, and paste solar panels to create arrays

Having decided which side to lay the solar panels, the next step is to add them to it. You can drop them one by one. Or drop the first one near an edge and then copy and paste it to easily create an array. Repeat this for three rows as illustrated in Figure 3. Note that I chose the solar panels that have a light-electricity conversion efficiency of 15%, which is about average in the current market. New panels may come with higher efficiency.

The three rows have a total number of 45 solar panels (3 x 5 feet each). From Figure 2, it also seems the T-wing roof leaning towards west may be a sub-optimal place to go solar. Let's also put a 2x5 array of panels on that side. If the simulation shows that they do not worth the money, we can just delete them from the model. This is the power of the simulation -- you do not have to pay a penny for anything you do with a virtual house (and you do not have to wait for a year to evaluate the effect of anything you do on its yearly energy usage).

4) Run annual energy analysis for the building

Fig. 4 Energy graphs with added solar panels
Now that we have put up the solar panels, we want to know how much energy they can produce. In Energy3D, this is as simple as selecting "Run Annual Energy Analysis for Building..." under the Analysis Menu. A graph will display the progress while Energy3D automatically performs a 12-month simulation and updates the results (Figure 4).

I recommend that you run this analysis every time you add a row of solar panels to keep track of the gains from each additional row. For example, Figure 4 shows the changes of solar outputs each time we add a row (the last one is the 10 panels added to the west-facing side of the T-wing roof). The following lists the annual results:
  • Row 1, 15 panels, output: 5,414 kWh --- 361 kWh/panel
  • Row 2, 15 panels, output: 5,018 kWh (total: 10,494 kWh) --- 335 kWh/panel
  • Row 3, 15 panels, output: 4,437 kWh (total: 14,931 kWh) --- 296 kWh/panel
  • T-wing 2x5 array, 10 panels, output: 2,805 kWh (total: 17,736 kWh) --- 281 kWh/panel
These results suggest that 30 panels in Rows 1 and 2 are probably a good solution for this house -- they generate a total of 10,494 kWh in a year. But if we have better (i.e., high efficiency) and cheaper solar panels in the future, adding panels to Row 3 and the T-wing may not be such a bad idea.

Fig. 5 Comparing solar panels at different positions
5) Compare the solar gains of panels at different positions

In addition to analyze the energy performance of the entire house, Energy3D also allows you to select individual elements and compare their performances. Figure 5 shows the comparison of four solar panels at different positions. The graph shows that the middle positions in Row 3 are not good spots for solar panels. Based on this information, we can go back to remove those solar panels and redo the analysis to see if we will have a better average output of Row 3.

After removing the five solar panels in the middle of Row 3, the total output drops to 16,335 kWh, meaning that the five panels on average output 280 kWh each.

6) Decide which positions are acceptable for installing solar panels

The analysis results thus far should provide you enough information with regard to whether it worth your money to solarize this house and, if yes, how to solarize it. The real decision depends on the cost of electricity in your area, your budget, and your expectation of the return of investment. With the price of solar panel continuing to drop, the quality continues to improve, and the pressure to reduce fossil energy usage continues to increase, building solarization is becoming more and more viable.

Solar analysis using computational tools is typically considered as the job of a professional engineer as it involves complicated computer-based design and analysis. The high cost of a professional engineer makes analyzing and evaluating millions of buildings economically unfavorable. But Energy3D reduces this task to something that even children can do. This could lead to a paradigm shift in the solar industry that will fundamentally change the way residential and commercial solar evaluation is conducted. We are very excited about this prospect and are eager to with the energy industry to ignite this revolution.

Daily energy analysis in Energy3D

Fig. 1: The analyzed house.
Energy3D already provides a set of powerful analysis tools that users can use to analyze the annual energy performance of their designs. For experts, the annual analysis tools are convenient as they can quickly evaluate their designs based on the results. For novices who are trying to understand how the energy graphs are calculated (or skeptics who are not sure whether they should trust the results), the annual analysis is sometimes a bit like a black box. This is because if there are too many variables (which, in this case, are seasonal changes of solar radiation and weather) to deal with at once, we will be overwhelmed. The total energy data are the results of two astronomic cycles: the daily cycle (caused by the spin of the Earth itself) and the annual cycle (caused by the rotation of the Earth around the Sun). This is why novices have a hard time reasoning with the results.

Fig. 2: Daily light sensor data in four seasons.
To help users reduce one layer of complexity and make sense of the energy data calculated in Energy3D simulations, a new class of daily analysis tools has been added to Energy3D. These tools allow users to pick a day to do the energy analyses, limiting the graphs to the daily cycle.

For example, we can place three sensors on the east, south, and west sides of the house shown in Figure 1. Then we can pick four days -- January 1st, April 1st, July 1st, and October 1st -- to represent the four seasons. Then we run a simulation for each day to collect the corresponding sensor data. The results are shown in Figure 2. These show that in the winter, the south-facing side receives the highest intensity of solar radiation, compared with the east and west-facing sides. In the summer, however, it is the east and west-facing sides that receive the highest intensity of solar radiation. In the spring and fall, the peak intensities of the three sides are comparable but they peak at different times.

Fig. 3: Daily energy use and production in four seasons.
If you take a more careful look at Figure 2, you will notice that, while the radiation intensity on the south-facing side always peaks at noon, those on the east and west-facing sides generally go through a seasonal shift. In the summer, the peak of radiation intensity occurs around 8 am on the east-facing side and around 4 pm on the west-facing side, respectively. In the winter, these peaks occur around 9 am and 2 pm, respectively. This difference is due to the shorter day in the winter and the lower position of the Sun in the sky.

Energy3D also provides a heliodon to visualize the solar path on any given day, which you can use to examine the angle of the sun and the length of the day. If you want to visually evaluate solar radiation on a site, it is best to combine the sensor and the heliodon.

You can also analyze the daily energy use and production. Figure 3 shows the results. Since this house has a lot of south-facing windows that have a Solar Heat Gain Coefficient of 80%, the solar energy is actually enough to keep the house warm (you may notice that your heater runs less frequently in the middle of a sunny winter day if you have a large south-facing window). But the downside is that it also requires a lot of energy to cool the house in the summer. Also note the interesting energy pattern for July 1st -- there are two smaller peaks of solar radiation in the morning and afternoon. Why? I will leave that answer to you.

Energy3D in Colombia

Camilo Vieira Mejia, a PhD student of Purdue University, recently brought our Energy3D software to a workshop, which is a part of Clubes de Ciencia -- an initiative where graduate students go to Colombia and share science and engineering concepts with high school students from small towns around Antioquia (a state of Colombia).

Students designed houses with Energy3D, printed them out, assemble them, and put them under the Sun to test their solar gains. They probably have also run the solar and thermal analyses for their virtual houses.

We are glad that our free software is reaching out to students in these rural areas and helping them to become interested in science and engineering. This is one of the many examples that a project funded by the National Science Foundation also turns out to benefit people in other countries and impact the world in many positive ways. In this sense, the National Science Foundation is not just a federal agency -- it is a global agency.

If you are also using Energy3D in your country, please consider contacting us and sharing your stories or thoughts.

Energy3D is intended to be global -- It currently includes weather data from 220 locations in all the continents. Please let us know you would like to include locations in your country in the software so that you can design energy solutions for your own area. As a matter of fact, this was exactly what Camilo asked me to do before he headed for Colombia. I would have had no clue which towns in Colombia should be added and where I could retrieve their weather data (which is often in a foreign language).

[With the kind permission of these participating students, we are able to release the photos in this blog post.]