Solar Decathlon 2023

A house under construction in Rantoul, Ill., is nearing completion. The modest exterior belies the uniqueness of the home, which was designed entirely by University of Illinois Urbana-Champaign (UIUC) students and which features many innovative technologies that make it a model of sustainability, energy efficiency and affordability.

The house is also part of an international competition.

Illinois Solar Decathlon (ISD) is a student organization at UIUC that participates in competitions sponsored by the Department of Energy (DOE). The group is divided into three teams, each of which participates in a different challenge or training period. The Design Team creates a new, innovative design of a residential or commercial building each year that addresses real-world issues like affordability and climate change, then presents their design for judging in April. The Concept Team consists of freshmen and sophomores who lack experience in higher-level engineering and architectural concepts, and spends the year receiving training in preparation for future participation on one of the other teams.

CEE senior Halie Collins, president of the Illinois Solar Decathlon student organization, at one of the weekly meetings held by the group.
CEE senior and ISD president Halie Collins at an early planning meeting.

The third team – featured in this story – is the Build Team. Students on this team design and build a full-size home powered by renewable energy sources. Solar Decathlon groups at universities across the world participate in the Build Challenge, which takes two years to complete: the first year is spent designing the home and submitting the plans to DOE for review and the top designs are selected to move forward to the second year of competition, when the building process begins. 

A truly interdisciplinary effort, the ISD project includes more than 100 students from across campus, including the School of Architecture, who produce the designs, several departments in The Grainger College of Engineering – including Civil and Environmental Engineering (CEE), Electrical and Computer Engineering (ECE), Mechanical Science and Engineering – and others. Students bring knowledge learned from their classes to apply to the collaborative effort. This year, ISD is led by Halie Collins, a senior in CEE.

About the Build Challenge

The Solar Decathlon has been around since 2002, though the competition format underwent a change as a result of the COVID-19 pandemic. As it stands now, all qualifying teams are given $50,000 to start their project, a set of guidelines and criteria on which they will be evaluated, in-person judging by DOE representatives and a period of public exhibition, and a final group presentation in front of a panel of industry experts at the Solar Decathlon Competition Event in Golden, Colo. Solar Decathlon is highly competitive: for the 2023 Build Challenge, 37 teams from around the world originally entered the competition. ISD was one of 15 teams selected to move on to the second year – the build phase – and one of only 11 teams that that progressed far enough with their build to make it all the way through to the final exhibition/presentation rounds. 

Many of the participating student groups design their houses as theoretical or model homes, but some teams – including the team at University of Illinois – take a different approach: they build their houses to be lived in. The team has been working with Habitat for Humanity of Champaign County since the beginning of this project and their design decisions were made with the future residents – a single mother and her young adult daughter – in mind.

Luke Somerville at an ISD planning meeting.
CEE graduate student Luke Somerville.

CEE graduate student Luke Somerville is leading the build team. He oversees all aspects of the construction process, from meeting with Village of Rantoul officials – Rantoul donated the land for the project – to coordinating with contractors to liaising with the local Habitat for Humanity leader.

While all that was going on, Collins was spearheading an effort to raise funds to supplement the starting budget provided by DOE, going so far as to establish a non-profit foundation for the purpose. Even though the teams are provided with $50,000 to start, they must seek funding for the remaining costs through grants and other monetary or in-kind donations. Collins said the group's final budget is approximately $420,000. 

“Coming to college, I never expected that I would be in this position that I am today. I didn't even know this kind of opportunity existed.”

Halie Collins, CEE student and ISD president

The students also deal with cash flow issues, negotiations, contracts and other business-related issues. The business aspect of the project adds an entirely new skill set the students develop as part of their participation in the group.

“Coming to college, I never expected that I would be in this position that I am today. I didn't even know this kind of opportunity existed,” Collins said.

Julie Wang, a Global Studies major in the College of Liberal Arts and Sciences and who serves as ISD's Communications Director, waves from a window during a visit to the construction site.

In May 2023, RENU House is nearing completion.

About RENU House

The ISD team approached their project with four main themes in mind, which also provided the name: the house should be Renewable, Economical, Nourishing, and Universal (RENU).

The home was built using labor and materials sourced/supplied locally, meaning that it should be able to be duplicated in any location. The three-bedroom house is ADA accessible, and a flexible-use room in the center can be open to the rest of the house or closed off and used as an office, home gym, playroom or fourth bedroom. Landscaping plans include a rain garden to help manage stormwater runoff, as well as native plants and a garden bed for vegetables or flowers.

The competition rules say that all the houses must be powered by renewable energy sources. Christine Chung is the team’s Design Engineer, responsible for reviewing all the engineering designs and coordinating with Somerville to ensure that all code – and competition – requirements are met.  She is a senior in ECE, where her focus is power and energy. 

“0ur solar system is completely compatible with what our predicted energy consumption is,” Chung said. “So along the side of when we design the solar production we have to keep in mind how much the house is going to consume in terms of energy load. A lot of that comes from the other teams, and gathering what design choices they made to make the house most energy efficient.”

Christine Chung
Christine Chung

Chung explains that, for instance, choices that the water team makes about the plumbing – the tankless water heater, the types of piping and pumps – all factors into the energy consumption analysis. The same is true for other design decisions the build team makes. Their solar panel system is grid tied, which means that surplus solar power generated is fed into the electric grid, and on low production days – for example, overcast or stormy days – the house can pull power from the grid.  The goal is to produce enough power from the solar panels over the course of a year to offset its energy consumption: that is what makes the house “net zero.” In addition, a battery back-up system means the house will have electricity even during a power outage. 

There are many features incorporated into the design of RENU House that make it both cutting edge and sustainable. The exterior is made from bamboo, a highly sustainable resource due to its quick growth and regeneration. The ductless HVAC system utilizes a noiseless filtration system and will require less maintenance over time. Indoor units control the temperature in each room, all of which are operated by individual thermostats with smart load control that automatically adjusts operation requirements by sensing both indoor and outdoor conditions. The plumbing utilizes a very efficient tankless water heater that uses energy only when hot water is being delivered.  Students in ECE and Computer Science designed an app using open source software that can be used to control and monitor the home's electrical systems. 


House Features

Learn about the house's technical features, as highlighted by Christina Chung:

  • A 9.46kWDC Photovoltaic System that is predicted to produce 13,184kWh/yr
    • This ensures our solar production outweighs our house's estimated energy consumption of 11,789kWh/yr, meaning our house is net-zero!
  • Our house is approved for net metering capabilities with the local utility, meaning that the excess energy we produce can be sent back to the grid and exchanged for solar credits - ultimately lowering our occupant's electricity bill at the end of the year
  • Partnered with SolarEdge to incorporate products with leading technologies 
    • Inverter - can not only serve as the main conversion from the power produced at the solar panels, but also communicates with our backup interface unit and 10kWh backup battery 
    • Power Optimizers - paired with each solar module to maximize power output capable
    • Backup Interface Unit - a central smart hub that can communicate when to switch our system into our "backup" mode
      • in the case of a power outage, this device allows the connection to our battery and critical loads panel 
    • Smart EV Charger - a residential level EV charger to reduce transportation costs and carbon emissions
      • can utilize both grid and available solar simulatenously 
  • Partnered with Mission Solar to have 430W solar modules with PERC (passivation emitter rear contact) technology 
    • improves 6 to 12% more energy production
    • highest PTC ratings of any American-manufactured module
  • Partnered with Unirac's Solar Mount Racking System for optimal fixed tilt angle solar production and low maintenance

  • Passive strategies were used to prioritize the conservation and efficiency of water consumption through an optimal layout integrated into the structural and MEP design
  • The plumbing system uses PEX piping 
    • PEX is flexible with wide range of temperatures and environmentally friendly 
    • average lifespan is about 50 years so very low-maintenance 
  • Designed with a tankless water heater
    • very efficient (99% thermal efficiency rating) as it uses energy only when hot water is being delivered
    • self-modulating technology to adjust flow rate and temperature for optimal energy-efficiency 
    • has double the lifespan of traditional tank heaters at an average of 20 years
    • resilient to sediment buildup and corrosion damage, easier to maintain and replace 
  • Designed with on-demand recirculating pumps
  • Remote controlled pumps at the source of our hot water supply to ensure every fixture has hot water available without wasting any water, reducing energy load at the water heater

  • Heating and cooling system
    • Partnered with LG to utilize a 3-ton LG MultiV system
      • a heatpump that increases flexibility and efficiency
      • wide range in operating temperature
      • provides a 4000CFM airflow
      • requires ZERO ductwork, allowing our system to have water pipes running along the ceiling and avoiding clashes with rest of engineering design
      • rooms are connected through the indoor units that can individually be controlled by a thermostat
      • smart load control that can automatically adjust operation requirements by sensing both indoor and outdoor conditions
  • Ventilation system
    • Partnered with Lunos for the e2 and eGo units 
      • a decentralized and energy-efficient ventilation system that uses ceramic cores to exchange heat between incoming and outgoing air streams
      • allows multi-speed operation to adjust ventilation rates from 10CFM to 35CFM based on individual room needs, conserving energy by reducing ventilation rates when not needed
      • offers low-noise operations and easily replaceable filters for low-maintenance.

  • House uses all dimmable LED lighting for user comfort and energy efficiency 
  • Lighting is dynamic and complimentary to the architecture of the home to minimize energy consumption 
  • All appliances follow Energy Star ratings, ensuring industry approved energy efficiency ratings
  • Carefully selecting lighting and appliances can save a lot of electricity consumption per year
  • The app development team utilizes HomeAssistant, a popular open source software used for non-commercial home automation applications to integrate our system components (such as smart lighting, appliances, solar production, house consumption monitoring) into one app.

One major factor that makes the house net zero is the exterior insulation finishing system (EIFS). Their EIFS uses blown-in cellulose between exterior ZIP panels and interior drywall, which means that very little energy will be required to heat or cool the house because it will be so airtight and able to store heat and cool air effectively.

“People don't think it's very sexy in terms of talking about net zero homes, but more than 50% of building a net zero home is the exterior envelope finishing system,” Somerville said.

Somerville said that for every engineering choice they made, they also had to consider the embodied environmental impact: everything from how much carbon dioxide is produced to evaluating the metals used in equipment and the impact of mining those metals out of the ground. All of that is balanced against economic considerations, sustainability and the human experience.

These design decisions are an important part of the competition because the team needs to explain their choices to the judges and justify them. The team’s decisions are judged in ten categories that make up the “decathlon.”

“You're taking all of these ten categories into account, and they're all weighted equally,” Somerville said. “Each of them is worth 100 points, for a grand total of 1,000. Designing the home becomes a very, very in-depth, thought-out process.”  

Christine Chung works with her crew at the house as work on the interior begins.
Christine Chung, center, and other ISD students work on the home interior.

An additional factor the team is dealing with is the reality of designing a home with a resale value appropriate for Rantoul. That means innovations also have to be low-budget, which is not always easy, and the overall upfront costs for a sustainable house are high. Regardless, the students believe their house could be replicated in similar small towns across America.

“It's been a very big challenge for us to balance our budget with sustainable technology, just because more sustainable technology does tend to be more expensive,” Collins said. “However, just trusting the fact that it does pay back over time with energy savings has been a very important reminder throughout this process. All of our systems combined and the construction of the home… it does come out to be around the average price of a home in 2023. So it's not technically 'affordable,' but it is very affordable in the long run because a family will save tens of thousands of dollars in energy or utility bills.”

But as Chung notes, they have another outcome they are working for that has nothing to do with the competition.

“We are designing with a purpose for an actual family to live there, not just for the sake of producing a really cool energy efficient house to just win this contest,” she said. “We have a long-term purpose for it. So there's a lot of considerations that are taken into our design, where – sure, we want to win this contest – but we also want to make sure it's a reasonably priced house in the long term.”


Home Sweet Home

Civil and Environmental Engineering senior and Illinois Solar Decathlon president Halie Collins talks about working with Habitat for Humanity on their national competition build

Building for a cause (and an education)

For Somerville, who grew up in the Beverly neighborhood of Chicago, being involved in construction is practically in his blood: his father was a bricklayer and all of his uncles worked in trades around the city. 

Luke Somerville at the construction site.
Luke Somerville at the construction site.

"I've been around construction my entire life," he said. "I always really enjoyed that process of a bunch of people coming together and working together to create something new that benefited the people, places, around them. I just think that directly being able to see the rewards of your work, was something that I found hugely inspiring."

That feeling carried over into this project, which is the first Habitat for Humanity house on the block but which will eventually be joined by three more. The neighborhood they are building in is a mix of single-family homes and multi-family residences, of young adults and seniors, of lower income and middle income. Somerville is enthusiastic about being part of a larger effort that is helping to build up a community.

“I think that being fortunate enough at this age to be able to use the engineering knowledge that I've learned from the University of Illinois, and being able to directly impact something as large and influential – and life changing, honestly – as this for people in the local community is really an opportunity you could not find anywhere else,” Somerville said. “It really motivates me on a day to day basis.”

The impact of the build project also goes beyond the future homeowners and residents of the neighborhood: it impacts the students and their education. Each of them is able to apply classroom knowledge to real-world applications, and vice versa.

Somerville notes that his coursework in construction management and design have directly translated into the work he has done on this project. In turn, the hands-on work has expanded his knowledge and understanding of concepts he learned in class. Additionally, the industry connections he made in this process taught him a lot about sustainable construction concepts. In fact, his participation in ISD and interactions with Arup – an engineering design firm that consulted with the team early in the process – led directly to a job offer. He is moving to San Francisco this summer to join the firm.

"I strongly believe that Illinois Solar Decathlon makes the biggest real world impact on the local community as well as the student body that participates in it, compared to any other club on the University," he said. "The projects that we work on are in the hundreds of thousands of dollars, and every two years we have direct industry connections with the Department of Energy as well as a multitude of other national and renewable energy leaders. The people in the organization get hands on experience that you cannot find anywhere else – internship or otherwise. And at the end of the day the thing that I like the most about it is that you get to donate a home to a local family in need."

Halie Collins, foreground left, joins fellow Student members of Illinois Solar Decathlon and Elonda Elston, foreground right, and her daughter, Monae Latchison, center, for a group photo in front of their future home at the RENU Home/Habitat for Humanity site in Rantoul. Habitat Executive Director Chad Hoffman is pictured back row, second from right.
Front row, left to right: Halie Collins with future homeowners Elonda Elston and her daughter, Monae Latchison. Behind them, fellow ISD students with Habitat Executive Director Chad Hoffman (back row, second from right).
In May 2023, RENU House is nearing completion. Photo courtesy Illinois Solar Decathlon.
In May 2023, RENU House is nearing completion. Photo courtesy Illinois Solar Decathlon.

How did they do?

Build Challenge winners were announced during the Solar Decathlon Competition Event in Golden, Colo., April 20–23, 2023. The Illinois Solar Decathlon team placed in the Top 4 in five of the ten categories:


Market Analysis





Embodied and Environmental Impact


Durability and Resiliency

The ISD Design Team qualified for finals in the Design Challenge , but did not place.

See complete Build Challenge results here

Take a virtual tour of RENU House and the other entries here


House exterior photos provided courtesy of Illinois Solar Decathlon; all others by Heather Coit, Grainger College of Engineering. Videography by Nic Morse and Virgil Ward, Grainger College of Engineering.