Can electric truck hydropower be used for energy storage?
Article By : Bill Schweber
Storing large quantities of electric energy is hard; is trucked hydropower and regeneration a viable option?
There are many cases of ideas which were first dismissed and ridiculed, then eventually accepted. For example, when respected mathematician Christian Doppler first presented his analysis of frequency shift due to source/receiver relative motion in the early 1800s, he was more than just ridiculed—he was dismissed from his academic teaching position and was almost expelled from the prestigious Austrian Academy of Sciences (Reference 1).
In a more complicated situation, NASA’s John Houbolt proposed the idea of rendezvousing a moon-orbiting module and “disposable” lunar lander rather than landing on and lifting off the Moon’s surface and returning to Earth using a complete self-contained third stage. His idea was also dismissed as impractical and unworkable, and he was told “the numbers just didn’t add up”—yet ultimately, that was the only solution that could work, and did (Reference 2).
For these reasons, I am hesitant to criticize innovative idea of others, especially as it is so easy and convenient to do so while sitting at a desk and keyboard. Still, I do have to wonder about the practicality of some major ideas.
What do I mean? I recently came across a paper “Electric Truck Hydropower, a flexible solution to hydropower in mountainous regions” published in Elsevier’s Energy (a more-readable PDF version is posted here). The authorship roster consists of individuals from eleven legitimate institutions led by a “think tank” called The International Institute for Applied Systems Analysis in Austria; that, too, is prestigious- and distinguished-sounding in name (if not the reality). Their entire presentation has the appearance of seriousness and credibility, no doubt of that.
Their paper proposed and analyzed an alternative scheme to using dams for storing energy and producing hydroelectric power. We know that storing large amounts of energy is a significant challenge, yet one that must be addressed if renewable energy is to become more widespread and available. Dams are among the options, which also include batteries, flywheels, molten salt phase change, and raising/lowering weights (gravity) to cite a few; but each has technical, implementation, and cost shortcomings.
While dams are a technically viable option and are widely used, they do have drawbacks in the vast size required for the storage reservoir and the need for a suitable siting. Instead, this paper proposes a solution that consists of catching water from streams at high altitudes to fill storage containers, transport them down a mountain in electric trucks while converting the potential energy of carried water into electricity via the regenerative braking systems of the trucks, and storing it in the truck’s battery, Figure 1. (They even have a catchy name for it: Electric Truck Hydropower (ETH)).
Figure 1 Schematic of the electric truck hydropower system. (a) 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 via regenerative braking, which is then stored in on-board batteries for subsequent transfer. (b) An aerial view of a possible ETH system compared with the existing conventional Kaprun hydropower project in Austria, highlighting the presumed flexibility of ETH systems. (Image source: Energy/Elsevier)
At the bottom, the energy stored in the on-board batteries would be “offloaded” and the trucks emptied of their water load, and the recovered energy could be used locally or sent to the grid. The empty trucks would then climb back up the mountain road to obtain more water and start the cycle again.
The lengthy paper (11 pages) is loaded with analysis of all aspects of the proposal including losses, with quantitative presentations, discussions, equations, charts, tables, graphs, and artist renditions. It all seems so straightforward and clear-cut. In the end, they conclude that this radically different approach could provide stored hydropower at a cost of between $30 and $100 per megawatt-hour (MWh). They maintain that is cheaper than conventional hydropower at $50 to $200 per MWh. It all sounds so very attractive and feasible, no doubt of that.
But I really wonder if it is a situation where the broader reality (let’s call it “the forest”) is being obscured if not outright buried in the noise of the abundance of presumed data and analysis (the trees). As I read through the ETH paper, I noticed that they slipped in some real-world caveats (I call them the “oh, well, never mind” factors):
- One of the key efficiency equations assumes that the steep mountain roads are smooth.
- The traffic in the mountain roads and the maintenance of these roads that are continuously used by heavy trucks are not included in the cost analysis.
- It assumes that the electric trucks are autonomous, which significantly reduces the fixed costs of the system.
It seems to me that many aspects of ETH reality have been ignored while providing an abundance of numbers. Mountain roads are notorious to navigate even by skilled human drivers and I suspect we are a long way from having autonomous electric trucks do so. These roads are also subject to natural degradation even without heavy traffic, and 24/7 heavy truck traffic will literally beat them apart. The cost, personnel, equipment, and effort to build and maintain these roads will be significant, I suspect.
It’s not that autonomous trucks are impractical. In fact, they are widely used in open-pit mining to bring ore up from subsurface pits, but these are on wide, engineered roads with smooth slope and curves (Figure 2 and Reference 3). Rugged mountain terrain with narrow, winding roads subject to constant disturbance and abuse from heavy vehicles are a very different reality.
Figure 2: A steady stream of Komatsu autonomous ready-haul trucks bring mined ore to the surface in western Australia. (Image source: Mining Engineering/SME)
Is the ETH idea of using electric trucks to carry water down while capturing the potential energy via regenerative braking, offloading it, and doing it again and again a brilliant idea only on paper? Or does it have some merit despite the harsh realities of trucks, steep mountain roads, 24/7 operation, and more? Is this another case of a detailed academic analysis which uses abundance of presumed data to gloss over the many underlying assumptions and estimates that must be made, all with wide error bands, and then choosing the favorable result? Is a case of doing a very thorough analysis so it all seems so logical and sensible until you step back and take a deep breath, figuratively speaking?
I’m very skeptical, but as they say: “never say never”—ideas that seemed even crazier at first have worked out in more than a few cases.
References
- Physics Today, “The fall and rise of the Doppler effect” (March 2020)
- “Apollo: The Race To The Moon” (ISBN 9780976000808) by Charles Murray and Catherine Bly Cox,
- Mining Technology, “Australia leads the way in autonomous truck use” (August 23, 2021)
This article was originally published on EDN.
Bill Schweber is an electronics engineer who has written three textbooks on electronic communications systems, as well as hundreds of technical articles, opinion columns, and product features. In past roles, he worked as a technical website manager for multiple EE Times sites and as both Executive Editor and Analog Editor at EDN. At Analog Devices, he was in marketing communications; as a result, he has been on both sides of the technical PR function, presenting company products, stories, and messages to the media and also as the recipient of these. Prior to the marcom role at Analog, Bill was Associate Editor of its respected technical journal, and also worked in its product marketing and applications engineering groups. Before those roles, he was at Instron Corp., doing hands-on analog- and power-circuit design and systems integration for materials-testing machine controls. He has a BSEE from Columbia University and an MSEE from the University of Massachusetts, is a Registered Professional Engineer, and holds an Advanced Class amateur radio license. He has also planned, written, and presented online courses on a variety of engineering topics, including MOSFET basics, ADC selection, and driving LEDs.