|Fig. 1: An up-close image of the prototype solar roadway panels. (Source: Wikimedia Commons)|
The majority of outdoor surfaces that can be walked or driven on today sit in the sun absorbing massive amounts of heat. What if we could simply pave these surfaces with solar panels capable of harnessing this energy? Instead of using roads solely for transportation purposes, solar roadways could also provide a source for energy production, safer road conditions, and less maintenance cost.
The idea of solar roadways is relatively new, originating from a startup company from Idaho called Solar Roadways Incorporated that started in 2006. Solar roadways use solar panels which are made up of photovoltaic cells that use semiconductors to absorb light and create a flow of electrons, creating power to be used for homes, business, street lights, etc.  As shown in Fig. 1, solar roadways consist of solar panels, impact resistant glass and LED lights that can be programmed for road signs and lanes.  These panels also heat themselves, removing the need for salt and plows during the winter.
The United States has 43,000 square miles of impervious surfaces, 65% (27,950 square miles) of which are roads and other paved surfaces.  The goal for companies like Solar Roadways Incorporated is to eventually cover all paved surfaces with reinforced solar panels. All obstacles aside, how much energy would doing this produce? The most solar cell efficient, commercially available solar panel is a 230 Watt PV module with 23.8% efficiency.  Each panel has a surface area of 13.4 ft2. To cover the entire 27,950 square miles of impervious surfaces, we can use the previously mentioned information to figure out the wattage produced:
|27,950 mi2 ×
(5280 ft / mi)2
13.4 ft2 / 230 W
|=||1.34 × 1013 watts|
On average, there is about four hours of peak daylight hours each day, so 1460 hours a year. This gives an energy delivered per year of 1.34 × 1013 kW × 1460 hours = 1.96 × 1016 kWh. When factoring in that the panels on the roads will mostly be horizontal, unlike most solar panels on roofs, this figure reduces to 1.35 × 1016 kWh. According to the EIA (Energy Information Administration), the United States used approximately 3.86 × 1012 kWh of electricity in 2015.  This means that if we were to successfully achieve complete coverage of all impervious surfaces in the U.S. with solar panels, we would produce more than three times the electricity used.
While all of the previously mentioned benefits of solar roadways sound great, the cost of installation does not. The lowest cost per square foot of solar panel in the market is around $9.44. Here is how much it would cost to install solar panels on all 27,950 square miles of roads and pavements in the U.S.:
|27,950 mi2 × (5280 ft / mi)2 × $9.44 per ft.2||=||$7.35 × 1012|
To put this cost of installation into perspective, the U.S. national GDP of 2015 was $17.94 × 1012.  Keep in mind that this calculation is a low estimate, not factoring in maintenance and replacement costs. To say this cost is astronomical would be quite an understatement.
Although solar roadways offer many benefits and possibilities, it is hard to ignore the ridiculous cost of installing them. It will take a serious cost reduction to even make solar roadways somewhat of a possibility for the future. Considering the idea of solar roadways is still in it's infancy, the progress made so far is promising.
© Matt Klassen. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 "Solar Technologies: Solutions for Today's Energy Needs," Solar Energies Industry Association, 4 Nov 14.
 "On the Not so Sunny Side of the Street," The Economist, 5 Jun 14.
 L. Frazer,"Paving Paradise: The Peril of Impervious Surfaces," Environ. Health Perspect. 113, A465 (2005); ibid. 114, A21 (2006).
 M. A. Green et al., "Solar Cell Efficiency Tables (Version 48)," Prog. Photovoltaics 24, 905 (2016).
 "Monthly Energy Review November 2016," U.S. Energy Information Administration, DOE/EIA-0035(2015/11), November 2016.
 "Gross Domestic Product 2015," World Bank, 11 Oct 16.