Wattway by Colas has a pricing structure of around $6.70 per watt-peak. Watt-peak is a term used to describe peak energy output under optimal sunlight, so if for example a solar panel had a peak power output of 50 watts, according to Colas that panel would cost about $335. However, as Colas itself notes, this cost figure is at the prototype stage and automated manufacturing of Wattway panels has yet to transpire earnestly. As this occurrence can reduce production costs significantly, we'll assume that once Wattway panels are built en-masse we may see a price reduction of up to 15%. That brings the panel cost, over time and on a large scale, to be $5.70 per watt-peak - a figure that will only reduce over time as investments in solar panels continue to bear fruit in terms of efficiency and power output.
According to Colas, 42 slabs (59 m2) had a power output of 6 kilowatt-peak. That would mean each slab has a surface area of 1.4 square meters and a peak power output of 142 watts. As 1.4 square meters has a surface area of just about 15 square feet, that comes to approximately 9.5 watts per square foot at a cost of around $54 per square foot.
Solar Roadways has a more robust prototype with burlier features than Wattway, and their external pricing data isn't approved for public release as of yet. As such, we'll have to make some educated assumptions to determine their cost. Additionally, unlike Wattway where panels are simply glued down, Solar Roadways requires road surfaces to be modified to allow for panel installation. While this is a benefit in the context of advancing the sophistication, longevity and strength of our road surfaces, it's still an additional cost that needs to be incorporated in any pricing model.
The latest Solar Roadways prototype is a 4’x4’ hexagonal solar road panel which has an area of 4.39 square feet (0.4 square meters) that has a peak output of 48 watts. The original prototype was a 10'x10' panel that was estimated to cost $10,000 - so about $100 per square foot. If we were to apply that same price to the hexagonal panels, that's $439 per 48-watt panel. However, the added cost of installation would be an additional overhead cost, which we'll assume to be a 35% increase per-panel. Yet at the same time, mass production reduces costs significantly. If we were to apply the same 15% reduction as we assumed with Wattway, that would mean their 48-watt panel would cost about $500. If we were to scale down to the square foot, that comes to approximately 11 watts per square foot at a cost of $114 per square foot.
With this established, let's assess the performance of both prototypes over a calendar year. Solar panel performance is measured in something called "peak sun hours" which is the aggregate of the amount of solar energy an area receives at a given day if framed in terms of peak output. So let's assume for example a solar panel works for 10 hours a day at varied efficiencies, but what if that entire length of time were condensed into a time period where the panel operated only at maximum efficiency? That's "peak sun hours" for all intents and purposes, and it's the metric most solar systems are rated on. According to the National Renewable Energy Laboratory, the American southwest has up to 6.5 peak sun hours (which can get even higher the closer one gets to the equator), so we'll use that metric to assess maximum performance of solar road panels.
Additionally, solar panels vary in performance based on time of year and temperature (believe it or not solar panels are more efficient when it's colder, and can still work well even on overcast/cloudy days), so we'll assume an across-the-board hit of 15% to account for lapses in efficiency due to climate, weather, traffic, etc. With that in mind, that brings Wattway's peak output to be 8.1 watts per square foot, and Solar Roadways to be 9.35 watts per square foot.
Across an operating window of 6.5 peak sun hours, that brings us to a total of 52.65 watt-hours per square foot generated by Wattway on a given day, and 60.8 watt-hours per square foot for Solar Roadways. With that in mind, across a calendar year that comes to 19,217 watt-hours for Wattway and 22,192 watt-hours for Solar Roadways. Extrapolated into kilowatt-hours, that comes to 19.22 kilowatt-hours for Wattway at and 22.2 kilowatt-hours for Solar Roadways.
With these figures in mind, we'll assume that under optimal conditions Wattway by Colas panels generate 19.22 kilowatt-hours of energy every year per square foot at a cost of $54 per square foot.
In the case of Solar Roadways, we'll estimate they generate 22.2 kilowatt-hours of energy every year per square foot at a cost of $114 per square foot.