Phase IIB Research
November, 2015 – Solar Roadways Incorporated was awarded a Phase IIB SBIR (Small Business Innovative Research) contract by the U.S. Department of Transportation. The 2-year $750,000 Phase IIB contract included additional civil engineering tests performed at Marquette University in Milwaukee including:
Freeze/Thaw Cycling: Panels were placed in an environmental chamber and exposed to extreme temperatures to make sure the mechanical/electrical systems held up. For this test, six SR3 panel, were placed in two tubs of water inside an ESPEC walk-in environmental chamber. The first tub contained three SR3 panels in fresh water, to assess moisture conditioning capabilities, and the second tub contained three SR3 panels in a salt water solution (i.e. ~ 3 % by weight NaCl) to assess performance in an expected real-world corrosive environment. The test consisted of 10 cycles where the chamber temperature was set to -20 °C for 48 hours and then increased to 50 °C for 48 hours. This approximate five-day period constituted one test cycle.
Moisture Conditioning: Three SR3 panels were subjected to long duration moisture testing as follows: 1) a 24 hour test, 2) a seven day period, 3) a 14 day period, and 4) additional 14 day periods as needed. The panels were submerged for the required time period(s), removed from the water tank, dried with a lint free towel and weighed. The panelss were then placed back into the water tank to begin the next test cycle.
Moisture testing was accomplished until the measured weight increase, after three consecutive weigh-ins, was less than 0.1% of the total paver weight or 5 grams, whichever is greater. The moisture conditioning duration testing resulted in essentially no measurable weight gain using a 100lb load cell with 0.02lb resolution.
Picture on the left is at Marquette University. Picture on the right is test we conducted on our own by submersing two SR4 panels into a tub filled with water. The panels were powered up and ran underwater for over five months. They never failed.
Shear Testing: Panels were subjected to high shear forces to simulate heavy vehicle braking.
Advanced Loading: Simulated 15-years of truck abuse in three months. A weighted (9500-pounds) truck tire made over one million passes over six Solar Road Panels. No panel breakage and no wear. Notice how the tire keeps the panels clean.
All tests were passed successfully – see Technologies article below.
While we plan to begin with non-critical applications such as driveways, parking lots, sidewalks, bike paths, etc., these civil engineering tests moved us closer to being ready for public roads and highways – our ultimate goal.
SR3 prototypes
Higher intensity LEDs replaced those of the SR2 panels. The mounting holes were also removed to allow for more surface coverage with the solar cells. SR2 was a 36-watt panel and the SR3 was a 44-watt panel of the same size. The edge connectors made installation easier. SR3 had an onboard microprocessor to read temperature sensors and an ambient light sensor. It used this information to automatically activate the heating elements and the adjust the light intensity of the LEDs.
SR4 prototypes
Better high intensity LEDs replaced those of the SR3 panels. SR4 was also increased from 44 to 48-watts. Cyber security was added to avoid any sort of hacking.
Artist’s conception of an SR3 panel
Actual SR3 prototype