Transportation infrastructure is traditionally considered a means of fulfilling the mobility needs through connecting communities via commerce and moving people. Financial resources to build and maintain these infrastructures come, for the most part, from fuel taxes (for example 20 cents/gal). However, with increasing numbers of lane-miles added to support the expansion of the population away from cities, and as vehicles become more fuel efficient, funding for maintenance is becoming scarce and our infrastructure will, inevitably, continue to deteriorate. Millions of lane miles subject to solar radiation and heat and mechanical vibrations, combined with repeated load strains under normal working conditions, make these infrastructures great sources for energy harvesting. The currently wasted energy can be transformed using efficient systems into usable electric power. Using these infrastructures as a means of harvesting energy is a relatively novel idea that has not been fully implemented yet. Massive amounts of mechanical strain energy is wasted when millions of vehicles are moving on roadways, railways, and bridges. The emerging harvesting technologies can harvest the wasted energy, feed the harvesting energy to the power grid, or save the generated electricity in batteries to charge electric vehicles and power roadside lights, traffic signs, and monitoring sensors. The following list highlights the economic benefits and environmental impact of energy harvesting technologies.
- Energy harvesting technologies are: completely green, having no environmental impact, as opposed to energy generated from burning fossil fuels,
- Take up no public space as the energy harvesting technologies use existing right of way,
- Can be implemented in rural infrastructure providing sources of power to remote areas,
- Use available energy resources from traffic loads, heat, and vibration (not requiring wind, sun, or geothermal sites), and
- Enable a “smart” infrastructure by gathering real-time information on vehicle weight, speed, and traffic volume.
Energy harvesting technologies are not new, but the feasible applications of the technologies in transportation infrastructures are yet to be quantified. Preliminary literature review suggests that the energy harvesting technologies are taking steps for full deployment in European roadways; however, limited studies have considered the application of the energy harvesting technologies in the United States roadways to date. Currently, California is investing in developing Piezoelectric-based technology for potential implementation and Virginia conducted limited field-testing on their smart road. The Piezoelectric-based technology is a great opportunity for state DOTs to consider for an energy harvesting technology as a source of revenue to raise the economic impact and lower the environmental impact of each DOT’s transportation infrastructure.
Revenues for integrating the generated power from energy harvesting technologies can be used for infrastructure maintenance funds and to offset the reduced revenues from gas taxes. Continuous monitoring of infrastructure will save DOT the associated cost of diagnostics. Collected traffic data can be fed into a traffic management system. Incorporating the generated power for improving street illumination will improve safety in remote areas.
Energy harvesting (scavenging) is a process that captures unused ambient energy that would otherwise be lost in the form of heat, vibration, stress, or deformation. Roadways, bridges, and railways are exposed to energy from wheels’ movement, loading, and solar heat. These resources can be potentially converted and stored into usable electric power. Energy harvesting can lead to sustainable transportation infrastructure. Examples of current technologies to harvest energy are:
Energy harvesting using solar collector: The heat in an asphalt pavement surface is accumulated during the day due to the absorption of solar radiation. The concept of an asphalt solar collector involves a piping system that collects pavement heat through an appropriate fluid (Mallick et al. 2009). The piping system can reduce temperature of pavement and surrounding ambient air ultimately reducing the urban heat island effect (De Bondt 2003). However, the structural integrity of the piping system under intense heat and repeated impacts of traffic loads is still a major concern for roadway engineers. The solar collector technology is highly dependent upon climate conditions and may not be universally viable.
Energy harvesting using TEG: The temperature of an asphalt roadway structure is typically higher at surface and lower at deeper layers, creating a thermal gradient across the pavement (Datta et al. 2016). The thermal gradient can activate thermoelectric generator (TEG) materials to generate electric power. Inserting TEG materials in roadway structures can convert the thermal gradient heat into electric voltage using the Seebeck effect (Liang and Li 2015).
Energy harvesting using piezoelectric transducers: Under traffic loading, pavements are exposed to vibrations, strains, and compression forces that form mechanical strain energy. The mechanical strain energy can be captured and converted to usable electric power using piezoelectric transducers (PZT) (Hill et al. 2014; Ali et al. 2011). PZT have the property of generating an electric voltage when subjected to deformation by dimensional alteration or vibration. Xiong (2014) designed and installed nine different PZT energy harvesters for roadway applications. The conclusion was that the output power from PZT was very low but enough for powering structural health sensors network.
Energy harvesting using photovoltaic: The principals of solar roadways is to use embedded (surface) photovoltaic technology for harvesting solar energy. The photovoltaic technologies are incorporated into the surface replacing the traditional asphalt pavement materials currently used. In 2006, Solar Roadways Inc. built a parking lot covered by solar panels (Mehta et al. 2015). The solar panels in the roadway are integrated with heating elements to maintain above freezing temperature. In the Netherlands, the SolaRoad built a 230-feet bike lane with solar panels made of thick glass layers to withstand heavy loads. SolaRoad expects that the power generated from the panels to exceed 3 megawatt-hours after six months from opening (SolaRoad 2016). In December 2016, France constructed the first kilometer-long solar road coated with a clear silicone resin that enables them to withstand the impact of passing traffic. Major concerns are the roads durability to resist traffic impact and preserving surface texture for the safety of motorists. Also, the effect of shading caused by obstructions from buildings, trees, cloudy conditions and from passing vehicles may impact the efficiency of solar roadways.
The reviewed information detailed various technologies, but the technologies did not provide guidance on the best practices of using them in infrastructure for maximizing economic and environmental benefits.
There are numerous technologies that surfaced over the last few years in an attempt to use transportation infrastructure in harvesting energy. Some technologies have unique characteristics and advantages over others depending on their applications. For instance, PZT is a candidate technology for railways and steel bridges to convert mechanically induced vibrations into useable energy, but is not as applicable in asphalt roadways. Therefore, the goal of the study is to “develop a synthesis document on the current energy harvesting technologies and their feasible applications in transportation infrastructure” that meets the following principal objectives:
- Summarizes the state of knowledge on existing energy harvesting technologies with promising applications on transportation infrastructure.
- Develops a guideline document comparing the energy harvesting technologies on the basis of their operation mechanism, energy output, functionality, durability, environmental impact and
- Provide recommendations on their feasibility, obstacle for implementation and potential use in transportation infrastructure.
Tasks to evaluate identified benefits and unintended risks include the following:
- Canvas transportation agencies for energy harvesting success stories
- Obtain sample specifications
- Canvas regulatory agencies for their vision on energy harvesting technologies and the concerns the agencies think need to be addressed to make such implementation of technologies possible
Canvas DOTs to obtain existing analytical data on different energy harvesting technologies
- Ex. Solar collectors, TEGs, Photovoltaic technologies, etc.
- Synthesize characteristics of energy harvesting technologies
- Identify areas of optimal use for the technologies
- Create life-cycle costs and risk analysis for energy harvesting success stories
- Evaluate benefits and risks of implementing energy harvesting technologies within the transportation ROW
- Identify and evaluate existing policies concerning energy harvesting technologies on roadways and ROW to help agencies make appropriate changes to practices, equipment, facilities, or agency policies when using energy harvesting technologies.
- Identify gaps in existing practices and policies
- Convert key information into more “readable” formats
- Compile best existing practices, training materials, or products into a single repository
As vehicles become more fuel efficient and with rising demand for electric vehicles the financial resources from fuel taxes will not meet the demand for keeping up with the construction and maintenance of these infrastructures. Lack of sustainable source of power in rural remote areas is one of the major causes of increased crashes and fatalities nationwide. More importantly, with the next generation vehicle to vehicle (V2V) and autonomous vehicles technology ready for deployment in the near future, the need for a network of sensing and monitoring infrastructure is greatly needed. The guidance document will be a reference for DOTs on how to identify the optimum harvesting technology for a particular application in infrastructure to maximize environmental and economic benefits. The guidance document will also include a process to evaluate the potential environmental impacts and economic gain when key parameters (e.g., traffic load and volume) are identified. The study will answer questions such as:
- What are the potential energy harvesting technologies for transportation infrastructure?
- What are the economic benefits and the environmental impacts of integrating these technologies?
- What are the best-practices or lessons learned from the case studies on implementing these technologies on infrastructure?
- What are the needs for expanding the use of these technologies to maximize their benefits?
State DOTs are aware of the rising costs of maintenance and lower amounts of revenue being provided. The DOTs are learning about possible ways to generate more revenue and have a more comprehensive way of collecting statistics and data about use and deterioration. The DOTs would champion this research since the study would provide new information about the implementation of energy harvesting technologies.
Environmental, Operations and Maintenance Divisions in State DOTs
ADC60, Resource Conservation and Recovery Committee
Samer Dessouky, Ph.D., P.E., F. ASCE, Associate Professor, Department of Civil and Environmental Engineering, University of Texas at San Antonio, SAMER.DESSOUKY@UTSA.EDU, (210) 458-7072.
Energy Harvesting, Environmental Impacts, Sustainability
- Mallick, R.B., Chen, B. L. and Bhowmick, C., 2009. “Harvesting energy from asphalt pavements and reducing the heat island effect”, International Journal of Sustainable Engineering, 2:3, 214-228
- De Bondt, A. (2003). Generation of Energy via Asphalt Pavement Surfaces. Asphaltica Padova.
- Liang, G., and Li, P., 2015, Research on thermoelectric transducers for harvesting energy
- Datta U., Dessouky S. and A.T. Papagiannakis. (2016) “Harvesting of Thermoelectric Energy from Asphalt Pavements” Transportation Research Record: Journal of the Transportation
- Research Board. DOI 10.3141/2628-02
- Hill, D., Agarwal, A., and Tong, N. Assessment of piezoelectric materials for roadway energy harvesting. Energy Research and Development Division Final Project Report, DNV KEMA
- Energy & Sustainability, Oakland, CA, 2014.
- Ali, S. F., Friswell, M. I., and Adhikari, S., Analysis of energy harvesters for highway bridges. Journal of Intelligent Material Systems and Structures, Vol. 22, No. 16, 2011, pp. 1929‐1938
- Xiong, H., Piezoelectric energy harvesting for public roadways, Ph.D. Dissertation, Virginia Polytechnic Institute and State University, Department of Civil Engineering, VA, 2014.
- SolaRoad. Publications, http://en.solaroad.nl/publications/, accessed June 24, 2016.
- Mehta, A., Aggrawa, N., and Tiwari, A., Solar Roadways-The future of roadways, International Advanced Research Journal in Science, Engineering and Technology, Vol. 2, Issue 1, May 2015.