Solar Roadways Blog:
Sharing the Journey

Overview - SR3 to SR4

The SR3 testing at Jeff Jones Square in Sandpoint and at Marquette University in Milwaukee has been completed. We are grateful to the city of Sandpoint and all residents and visitors who served as our testers on this pilot project. This “real life test” gave us the information we needed to make important improvements to the design for SR4. We’ll share what we’ve learned, along with some insight into the array of civil engineering tests performed at Marquette.

The biggest challenge that we’ve found has been the manufacturing process. Each individual part worked fine, but putting everything together and subjecting them to the manufacturing process created some problems and a very challenging learning curve.

There are three fundamental features of the Solar Road Panels: the LED functionality, surface heating, and solar harvesting. Here’s what we’ve learned about each from the Sandpoint pilot project:

LED Functionality

SR3 has an array of LEDs, including red, green, blue, white, and yellow. Other colors and shades can be created by mixing the standard colors – we created a few extras for SR3 and will be working with more colors with SR4. These are individual high brightness LEDs designed for outdoor use. They worked great in all preliminary testing. We could turn them up so bright that they could actually hurt your eyes outside on a very sunny day. During SR3 testing, we worked to determine the optimal brightness levels for the LEDs in different situations. Now they automatically adjust themselves to the ambient light and we are pleased with how that is working.

The heavy vacuum of the lamination process is a very harsh environment for small electronics. The tiny LEDs were being damaged during this process. We experimented with many types of clear epoxies to protect them from the lamination process. We eventually found one that could handle the job and began producing panels.

When we initially installed the 30 panels at Jeff Jones Square, we programmed them to rotate through a series of patterns. It resembled a moving dance floor and the kids loved it. Later, we began to create some static images such as this earth design:

Earth Image at Jeff Jones Square
We left this up for 2-3 weeks, when we noticed something unusual: the blue LEDs began to fade (lower their intensity). Experimenting with other patterns, we noticed the same thing happening with the white and yellow LEDs. The red and green LEDs were not affected. This was confusing and frustrating, and we could not continue manufacturing panels until this was resolved.

After many conversations with the LED manufacturer, we learned that the blue, yellow, and white LEDs were made differently than the green and red LEDs. Together, after much testing, we came to the conclusion that the protective epoxy was having a chemical reaction with the LEDs and the sun was the catalyst.

This has been corrected for the SR4 design so that protective epoxies are no longer needed.


After two north Idaho winters, we’ve learned quite a lot with the heat testing results. Although SR3 was able to keep up with the snow in most situations, we’re increasing the heating capability of SR4 to allow for faster heating. This will allow the panels to more easily keep their temperatures up during heavy snowfall.

The Sandpoint installation used anodized aluminum panel retainers between the panels. Since there is no heating in the gaps between the panels, these metal pieces took on the ambient temperature. We learned that they could create an ice bridge during really heavy snowfall combined with extremely low temperatures. We’ve designed a rubber replacement – a “t-channel” for the aluminum units. This new design also greatly simplifies installation and maintenance.

Solar Harvesting

The most disappointing aspect of the pilot project in Sandpoint has been the energy harvesting. In order to increase the number of solar cells in the SR3 panel (SR2 was 36-watts and SR3 is 44-watts), we used a parallel/series combination of cell connections. We also created a Consolidator Board to consolidate the power collected by the panels. We used a parallel/series combination on this board to create the power input requirements for the micro-inverters.

Although all technical solar information I have found says that you can parallel solar power, we found that to be a very bad idea. All of the SR2 panels had their solar cells connected in series, so we’d never seen this problem. What we found was this: every panel produced power, but we couldn’t get them to combine properly to meet the input requirements of the micro-inverters. We were never able to “see” more than 1/3 of the power being produced. In addition, we learned that the extra laminate that was used in SR3 as compared to SR2 due to design changes interfered with solar gain. These problems have been eliminated with the new SR4 design.

For SR4, we found a way to maximize the solar cell area while maintaining a series-connected system. We also increased the wattage from 44W (SR3) to 50W (SR4). In addition, we’ve going from 17.6-percent efficient solar cells (SR3) to 22.5-percent efficient solar cells (SR4). We’ll always be able to increase the solar gain over time as the solar industry continues to advance and make more efficient products for us to incorporate. All of this means that we’ll be able to produce a lot more power with the SR4 panels.

We’ve also replaced the energy monitoring system with a more “Solar Road Panel friendly” monitoring system: one with a much larger input range that doesn’t require the parallel/series configurations.

When we get the SR4s installed, we’ll activate the system on the city’s website. For now, the current energy monitoring system reads zero because the panels have been disconnected from it.

Additional SR4 Improvements

Another hard lesson learned: the cables that were used with the SR3 panels had a plastic jacket. Over time, this plastic jacket became brittle and cracked, allowing water into the cable. After several months, some of the panels began to fail. We’d see only half of the panel lit up. Eventually, the LED patterns would become corrupted and the panel could no longer be communicated with.

We began removing the damaged panels and inspecting them. We found damaged cables where water had entered and began corroding the wires inside. This corrosion creates resistance, which in turn robs the panels of power. This means that the microprocessor, the LEDs, and the heating elements are not receiving the power that they need to function properly.

The new SR4 design uses and molded rubber cable which remains much more flexible after the lamination process.

Civil Engineering Tests Completed

As part of our third contract with the US Department of Transportation, our panels have been undergoing testing at the civil engineering department at Marquette University in Milwaukee, Wisconsin. They performed the following tests:

Shear testing
Freeze/Thaw cycling
Moisture conditioning
Accelerated load testing (simulates 15-years of truck abuse in 3-months)

They were so impressed by the results of the testing that they want to co-author a journal paper with us about the overall test program. We’ll be releasing the findings in a scientific engineering journal.


The Sandpoint pilot project gave us very valuable information: It allowed us time to tweak the LED intensity tables (the LEDs get brighter when the sun does likewise), adjust the heating profile with real time weather patterns, and taught us how to change our manufacturing process to solve the problems that were presented. It also pointed out the weaknesses in the SR3 panels, allowing us to finalize the SR4 design.

We decided from the very beginning of our Solar Roadways journey to be as transparent as possible. We realize that is not the way startups usually operate, but we wanted to be different. We are doing this work for the world and we wanted to allow our fan base to come along with us on the journey. Most people have realized that problems are part and parcel of the learning curve with inventing. We’ve been grateful to have so much support as we’ve worked to improve the panels and get them ready for mass production.

Since we’re done with the pilot project, and since the damaged cables are creating problems for the SR3 panels, we will shut down the Jeff Jones Square installation until spring, when we will replace the system with the new SR4 panels.

The first of the SR4 circuit boards have been received and tested. The first SR4 panels should be completed by the end of January. They will be tested extensively. We’ll put a few in our parking lot on Pine Street in Sandpoint, where everyone will be welcome to visit. Others will go to temporary exhibits. We just announced that one of those events will be the Treefort Music Festival in Boise in March. When the weather warms up in the spring we’ll replace the SR3 panels with SR4 panels at Jeff Jones Town Square in Sandpoint.

The SR4 will become the first commercially available Solar Road Panel.





SR Technology Behind the Scenes

I’m Scott and this is my first blog. I’m so busy with the technical side of Solar Roadways that I don’t have much time for writing. They keep me hard at work and hidden in a windowless office beneath the mezzanine! My formal training is in electrical engineering (MSEE). I’m the engineer who created the circuitry, laid out the circuit boards, wrote the firmware for the microprocessors, and wrote the software to run the devices that we call Solar Road Panels.

While I’ve been busy with the engineering side of things, Julie has been doing a great job of interfacing with everyone on social media. She keeps our followers up to speed on what we’re doing, but she sometimes gets technical questions that she can’t answer. She’s asked me to give a brief overview of what we’ve been working on.

Let’s start with the SR2 panels. Those are the (now famous) hexagonal green panels that you see (in videos and pictures) alongside our electrical shop in Idaho, where this all started. That parking lot/highway section was made of 108 Solar Road Panels and funded by our second contract with the U.S. Federal Highway Administration (FHWA). It was a proof-of-concept project to show that we could indeed generate power, illuminate road lines, heat the road surface, handle stormwater runoff, be modular (ease of maintenance), use recycled materials, can withstand repeated loading, meets or exceeds safety requirements of current paving systems, and offsets its own cost (through power generation, stormwater mitigation, leasing of the Cable Corridor, advertising, etc.).

These SR2 panels had integrated heating elements, LEDs, and solar cells. The LEDs were controlled by an onboard microprocessor which communicated wirelessly to a computer. There were 128 LEDs, including red, green, blue, white, and yellow. The intensity of the LEDs could be adjusted, but only by a direct command from the computer. The heating elements were very basic: I had to climb into the Cable Corridor in the dead of winter to plug them in: functional, but not very practical! The solar cells produced DC power, which was then converted to 240VAC through a micro-inverter and fed into our shop’s load center (circuit breaker box). Our utility company installed a net meter, so whatever power the shop didn’t use was put back onto the local grid. Our proof-of-concept was a success and we were invited back for our third contract with the FHWA. The old parking lot/highway section has been cannibalized for the SR3 testing, but if you visit us, you’ll see an SR2 panel converted into a coffee table in our lobby.

Since that time, we’ve renovated a building in town to serve as a manufacturing facility, purchased and learned how to use manufacturing equipment (a BIG learning curve – no equipment has been made for the type of manufacturing we are doing, so we had to buy existing machinery and create manufacturing processes to get to where we needed to be), and we’ve automated the functionality of the panels. We eliminated the mounting holes from SR2 to make room for more solar cells and devised a new mounting system. The addition of onboard sensors and controls took a tremendous amount of time and effort and testing to get right. Our current SR3 panels have all the features of SR2, but with the following enhancements:

LEDs – a full sized hexagonal panel now has 336 LEDs. That’s 56 clusters of 6 LEDs, including red, green, blue, white (2), and yellow. We experimented with a true RGB LED, but experienced some problems: to make white, you illuminate all three (red, green, and blue). That requires three times the power of illuminating a single dedicated white LED. In addition, if you’re approaching the LED at an angle (as you would in a vehicle), and you’re coming from the side where the red LED is located, the white light takes on a pinkish look. Knowing that the state and federal DOTs wouldn’t put up with “pinkish” road lines, we added the dedicated white and yellow LEDs to get the true line colors and to conserve energy.

The LED intensities are now automatically controlled by the microprocessor (uP). The uP has an onboard EEPROM (Electrically Erasable Programmable Read Only Memory), where I store the intensity tables. I designed in a light sensor on the circuit board which tells the uP the current ambient light conditions on the panel. The uP reads the light sensor, looks up the corresponding intensity and in the EEPROM, and adjusts the LEDs accordingly. That means that the LEDs automatically become brighter as the sunshine gets more intense. At night, the LEDs remain at an intensity of 1. The public installation at Jeff Jones Square was created as a pedestrian gathering plaza, but think of this: for a 2-lane road, with a solid yellow line down the middle and a solid white line on each side of the road, most of the panels would not even be lit up. In fact, less than 2-percent of the LEDs on that road would need to be illuminated for this standard road line configuration, using a negligible amount of energy.

Heating – I designed the heating elements to be controlled by the microprocessor. The hexagon circuit board has four quadrants, each containing a heat sensor and a heating element. The uP is given a temperature threshold (it stores this in its EEPROM). For our winter experiments in Sandpoint, that temperature was set to 3⁰C (or 37.4⁰F). When one of the temperature sensors reported a reading lower than 3⁰C, the uP activated that quadrant’s heating element. Keeping the temperature of the panel at 3⁰C prevented the snow/ice from sticking to the surface. Keep in mind that it’s not even necessary to activate the heating elements unless precipitation is expected.

Interesting story: a snow storm was expected one night, which would be the first real world test of the new heating system. I decided to stay in town until the heating elements kicked in. My software allows me to take readings from the panels: temperature sensors, light sensor, etc. The outside temperature had been hovering around 40⁰F all day, but fell to the upper 20s when the sun went down around 5-6pm. I had to wait until midnight for the internal temperature of the panels to fall below 37.4⁰F, which activated the heating elements. The panels weigh 70-pounds each and therefor behave as 70-pound heat sinks. They’re also mounted to the ground, so it took a very long time for the internal temperature to cool to the point where the heating elements needed to be activated. The system had no trouble keeping up with the snow.

Solar collection – the SR2 panels were 36-watts and the SR3 panels are 44-watts. The energy collected by groups of six panels is brought together in what we call a Consolidator circuit board housed in either an electrical cabinet or a Cable Corridor. The Consolidator board routes power generated by the solar cells to the micro-inverter and provides power back to the LEDs and heating elements. At the Sandpoint installation, the micro-inverters feed the load center which runs the bathroom lights, a water fountain, the kiosk, overhead lights for the public square, etc. The solar installation is too small to run all of that on its own, but it offsets the amount of energy that the public square requires.

The Consolidator board arranges the solar energy collected by the six panels in a series/parallel configuration, including bypass and blocking diodes. This arrangement is done to meet the input requirements of the micro-inverters. By making adjustments to this circuit board, we’re tweaking the energy harvesting capabilities of the Solar Road Panels. We’re also experimenting with moving the solar cells within the panels for more optimal solar harvesting ability. To an engineer, it can always be made better. Years ago, I was designing a product line for a company in Ohio. Someone placed a sign above my door that read, “There comes a time when you just have to shoot the engineer and go into production!”.

The Jeff Jones Square installation in Sandpoint is a pilot project: a small-scale experiment to allow us to get “real world” empirical testing and make adjustments accordingly. When we first installed the panels, we adjusted the intensities of the LEDs under different sunlight conditions until we were able to create our first intensity table for the microprocessor to follow. When the snow was falling, we were experimenting with the best ways to operate the heating elements. Now that the sun is rising higher overhead, we’re tweaking the solar harvesting capabilities (although this seems to be the rainiest spring we’ve ever had, which makes our real world testing difficult!). We’ll post the energy link when we’ve finished tweaking everything for production.

While juggling hardware, firmware, and production, I’m also working on software which will allow the LED lights to be quickly and easily changed. Right now it’s still a cumbersome process, so we are not changing the lights very often. The software will soon change that and we’ll begin to show you all of the possibilities for LED lit surfaces.

We recently sent five of our Solar Road Panels to a university civil engineering lab for shear testing. Later this year, we’ll send out more panels for freeze/thaw cycling, moisture conditioning, and advanced loading (simulates 15 years of truck abuse in 3 months). This is all part of our third contract with the Federal Highway Administration. Stay tuned for the results.

I’ll blog about each subsystem in more detail as time permits. I hope this sheds some light on the technical side of things and on the complexity of our system. These aren’t your typical solar panels!

Welcome Solar Roadies

The time is right for us to add a blog to our other information offerings: website, Facebook, Twitter and Instagram. We love connecting with you through each of those forums. A blog will offer us a chance to go deeper into topics and convey thoughts, feelings and stories with you. We love that so many people from every corner of the earth have been sharing this journey with us.

We are about to embark on a new phase in our journey: it’s almost time to install our first public pilot installation. Our Indiegogo campaign in 2014 left us amazed and overflowing with gratitude. We broke the record on Indiegogo for the most donors: over 48,000 from 165 different countries. We took a solemn vow to use the money wisely and fulfill our campaign promises. We bought a building, equipment, hired employees and worked diligently to improve our product and become ready for public installations.

We worried that we might lose support during this time when we have pulled inward to focus on engineering. We stopped accepting most press invitations and so had far fewer exciting articles to post or news to share. Most of you patiently accepted this part of the journey and sent us notes of encouragement, both public and private. If you ever wonder if that matters… it does. It’s helped keep us energized as we’ve worked on through exhaustion.

Now it’s time for us to move back out into the world and show you what you’ve helped us to accomplish. Our first public installation will be in our hometown of Sandpoint, Idaho at the end of September of 2016 at Jeff Jones Square. The prep work is done there, and we are working with the City of Sandpoint to coordinate the best date for the ribbon cutting ceremony – we’ll have that for you shortly. We’re overjoyed that so many of you tell us you are planning to come and see it with your own eyes! We’ll no doubt see many of you at Jeff Jones Square. If not, we hope you’ll stop by our headquarters so we can meet and thank you in person.

We feel like we are about to crawl out of a chrysalis, just like the butterfly who emerges shakily unsure of her wings. We’re anticipating some unforeseen glitches as we begin our first “real world” testing. Engineering lives by Murphy’s Law! But it’s good - we need to know everything that needs perfecting as we take further steps toward that ultimate of goals: the fast line of a highway.

We’ll continue to post on social media, our website, and here. We’ll be blogging separately as well as together. Other bloggers will be employees, volunteers, and guest bloggers. We’ve got a long list of topics we want to talk with you about, so follow along with us as we go.

Thanks for sharing the journey,

Scott and Julie Brusaw