Electric Truck Hydropower

Currently, hydropower is limited to systems with two water levels connected through canals, tunnels and penstocks, a turbine and generator convert the potential energy of the water into electricity. To ensure a large installed capacity and capacity factors greater than 30-40%, the catchment area must be high. This significantly reduces the technology's potential in steep mountain regions. In addition, storage reservoirs may also be needed to regulate river flow to increase the capacity factor and economic viability of the plant. 

Despite the complexity of hydropower development, its role in the power system remains crucial. Hydroelectric generation helps to integrate variable renewable energy sources into the grid, and reservoirs also provide water management, flood control and entertainment services. In steep mountain regions, the potential for generating electricity from a small stream of water is high due to the large power outages available. However, the catchment area of these streams is small, resulting in a highly variable flow, which lowers the capacity factor of the plants, reducing the return on investment.

Electric trucks

We propose a more flexible alternative to hydroelectric plants with electric trucks. The proposed system consists of using the existing road infrastructure that crosses mountain ranges to transport water down the mountain in electric truck containers, transforming the potential energy of the water into electricity with the truck's regenerative braking and using this electricity to charge the truck's battery. Once the battery is charged it can be replaced by a partially charged battery so that the truck can drive up the mountain again. The fully charged battery supplies electricity to the grid (Figure 1). The system generates a positive electricity balance because the weight of the truck going up the mountain is 20-30% of the weight of the truck going down the mountain. The trucks’ batteries can also be used to provide peak generation or short-term energy storage to the grid, when required. 

Figure 1: Electric truck hydropower (ETH) system. (a) axial description of the system where the empty truck moves up the mountain to collect the containers filled with water, and the truck with the full container goes down the mountain generating electricity. (b) aerial view of the ETH system compared with an existing hydropower project, highlighting the flexibility of ETH systems.

Small streams of water on mountains are not appropriate locations for conventional hydropower due to its highly variable river flow and the usual gains in scale observed in conventional hydropower. This is where electric truck hydropower (ETH) shines.

The ideal system configuration is in mountainous regions with steep roads, where the same electric trucks can be used to generate hydroelectric power from different locations. This increases the chances that water will be available to generate hydroelectric power and thus increase the capacity factor of the system. Another benefit is that no barrier is needed to draw water from the river and there is no need for reservoirs to regulate the flow of the river. 

Containers parked by a river at the top of the mountain are supplied with water extracted from the river (it could take ten minutes to six hours to fill the container up). Once filled, trucks transport the containers down the mountain generating electricity. When the truck arrives at the base of the ridge, the container is parked next to the river, and water from the container is slowly returned to the river to minimise the impact on aquatic life. 

If electric truck hydropower is combined with cargo transportation, it could substantially reduce fuel consumption in regions with high mountains. For example, a good application for this technology is for a truck that delivers a full container from Washington state to Pittsburgh in the US. On the return trip, just after the truck crosses the Appalachian Mountains, the truck can be filled with water, as shown in Figure 2, and drive down the mountain charging its battery. When it reaches the bottom of the mountain, the truck would release the water and continue its trip with its battery charged.

Figure 2: Hybrid cargo, hydropower truck. (a) fully loaded with cargo and empty water tank. (b) cargo and water tank partly loaded. (c) empty cargo and fully loaded tank.

Inspiration

The electric truck hydropower concept is a result of ten years of experience in hydropower and energy storage, plus a son that loves cars, buses, and trucks. Once we filled a little toy dump truck with water on a slope and the weight of the truck and water lifted a wooden block. After writing many papers on gravity storage, I realised that this was a form of hydropower. Being a fan of Tesla and electric vehicles, the electric truck hydropower concept materialised. 

Writing a scientific paper is not an easy task. One can’t just write a research paper on an original idea. To write a scientific paper requires a theory, a robust methodology and interesting results. As I could not test the technology because I don’t have access to an electric truck, I thought of using assumptions from the literature to estimate the energy losses in the system and the overall efficiency of the technology. As the methodology would not be such a high contribution to the literature, we developed a methodology to estimate the global potential for Electric Truck Hydropower. 

We firstly submitted the paper to Nature Energy, however, received feedback saying that the technology is too new and would require validation prior to being published in the journal. Working at IIASA, the Austrian government pays for open access to papers published in Elsevier or Springer journals. We chose the Energy Journal because it is particularly interested in innovative concepts. Even though the authors and I are strong advocates of hydropower, we tried to show that electric truck hydropower has advantages, as it is modular, flexible and can be a viable solution in small streams.

To implement the idea on a large scale would require many electric trucks. Assuming that a truck has a capacity of 0.25MW, it would require 4000 trucks to generate 1GW of power. With a capacity factor of 35%, 4000 trucks can generate 3066GWh in a year. An electric truck costs around US$150,000, and so 1GW of EVH would cost US$600million (today). The same capacity for wind power would cost around US$1200million dollars. 

Due to the low lifetime of the electric trucks and the batteries of three to seven years, and assuming that the trucks are driven autonomously, the levelised cost of electricity can be as low as US$30/MWh today. Adding the cost of drivers would significantly increase the cost of the system in developed countries, but not so much in developing countries. Given that the cost of electric trucks is expected to reduce significantly in the coming years, the viability of the technology will further increase. 

Potential

Figure 3 presents the potential for ETH divided into seven different continents in cost curves, assuming a generation cost lower than US$100/MWh. The continent with the highest potential is Asia with 617TWh, South America with 466TWh, Central America with 65TWh, Europe with 56TWh, Africa with 17TWh, North America with 5TWh, and Australia with 0.7TWh. The global potential for ETH is estimated to be 1226TWh.

Figure 3: World potential for electric truck hydropower. (a) Topographic data (SRTM). (b) Surface runoff data (ERA5). (c) Road infrastructure (GRIP). (d) Conversion of minimum ETH generation road slope into road slope applied. (e) ETH system efficiency at different road slope gradients and speeds. (f) Road slope gradient applied. (g) ETH levelised cost with road slope. (h) Minimum ETH generation costs of the region. (i) Maximum ETH potential of the region. (j) ETH cost vs potential curve of different continents

The proposed ETH technology is an innovative, clean, renewable source of electricity that is competitive with solar, wind and conventional hydropower. It is particularly interesting with high flexibility. For example, if a country like Argentina with high potential is in an energy crisis, it can buy several electricity trucks and generate electricity with a CAPEX of US$600/kW. After the crisis is finished, the trucks can then be used to transport cargo. 

The current advance in battery technology is opening a vast world of new possibilities. Electric truck hydropower is just one of them. We are writing a similar paper named Electric Truck Gravity Energy Storage where we combine electric truck hydropower, with gravity energy storage. The main concept is that, as the truck must go up the mountain to collect water, it might as well carry some sand to store gravity energy in case there is not enough water in the future. This is proposed as a long-term energy storage alternative.

We do hope that someone reading this article has an electric truck and will test the concept to see if the estimates presented here are correct. If they are, we will be able to generate hydropower to reduce the current global dependence on natural gas and fossil fuels with a newly proposed renewable energy technology.

The author is a research scholar at the International Institute for Applied Systems Analysis in Austria. Email: hunt@iiasa.ac.at

Electric Truck Hydropower, a flexible solution to hydropower in mountainous regions by Julian David Hunt, Jakub Jurasz, Behnam Zakeri, Andreas Nascimento,  Samuel Cross, Carla Schwengber ten Caten, Diego Augusto de Jesus Pacheco, Pharima Pongpairoj, Walter Leal Filho, Fernanda Munari Caputo Tomé, Rodrigo Senne, Bas van Ruijven. Energy. Volume 248, 1 June 2022, 123495 https://doi.org/10.1016/j.energy.2022.123495