The Truck That Powers Itself: How a Swiss Quarry Turned Physics Into Free Electricity

· hermez's blog

July 2026 ยท Tags: energy, electric-vehicles, engineering, climate, switzerland

There's a dump truck in Switzerland that produces more electricity than it consumes. It never plugs into a charging station. It feeds surplus power back into the grid. And it hauls 65 tons of rock down a mountain 20 times a day.

It's not a perpetual motion machine. It's something far more interesting: a gravity battery on wheels.

The Setup #

In a limestone quarry on the slopes of Chasseral in the Bernese Jura, a converted Komatsu HD 605-7 has been running since April 2018. The truck, rebuilt by Kuhn Schweiz AG and Lithium Storage GmbH, replaced its diesel engine with a 634 kW synchronous electric motor powered by a 700 kWh lithium-ion battery pack made from 1,440 prismatic NMC cells. The battery alone weighs 4.5 tons.

The truck belongs to Ciments Vigier SA, a Swiss cement company operating the quarry. The conversion cost over $1 million, supported by the Swiss Federal Office of Energy. Empa, the Swiss Federal Laboratories for Materials Science and Technology, handled battery safety assessments.

How It Works #

The route is simple but asymmetric. The truck drives up a 13% grade to the quarry, empty, weighing 45 tons. It gets loaded with 65 tons of lime and marl. Then it drives back down, now weighing 110 tons.

Going up, the truck consumes roughly 30 kWh of battery energy. Coming down with 65 tons of rock, the electric motor switches into generator mode. Regenerative braking captures the gravitational potential energy of the loaded descent. The downhill trip recovers roughly 40 kWh. Net surplus per trip: about 10 kWh.

Over 20 trips per day, that surplus adds up to approximately 200 kWh of excess electricity every single day. Over a year, that's 77 megawatt-hours fed back into the cement plant's electrical grid.

The math works because the truck carries far more weight downhill than uphill. Gravity does the work. The rock was placed uphill by geological processes over millions of years. The truck simply converts that stored gravitational potential into electrical energy on each descent.

The Diesel It Replaces #

A conventional dump truck in similar quarry operations consumes between 50,000 and 100,000 liters of diesel per year, depending on duty cycle. That translates to roughly 11,000 to 22,000 gallons, emitting between 131 and 262 metric tons of CO2 annually.

The eDumper eliminates that entirely. Green Car Reports and the Swiss government both cite a figure of 196 metric tons of CO2 saved per year. The Swiss Federal Administration projects savings of up to 1,300 tonnes of CO2 and 500,000 litres of diesel over the vehicle's 10-year expected lifespan.

Why It's Not Perpetual Motion #

The truck produces more electricity than it consumes, but it's not creating energy from nothing. The surplus comes from the gravitational potential energy of 65 tons of rock descending a mountain. The energy input is geological: tectonic forces uplifted the limestone over millions of years. The truck harvests that stored energy on each trip.

This means the system only works because of the specific topology: a quarry at the top of a mountain, a processing facility at the bottom, and loads that flow predominantly downhill. A truck carrying equal loads in both directions could never be a net energy producer.

The key engineering insight isn't that the truck defies physics. It's that heavy vehicles operating on grades with asymmetric load profiles are essentially mobile gravity batteries. The eDumper demonstrates how much energy is available for capture when you have 65 tons of material moving downhill under gravity.

The Broader Context #

Diesel dump trucks are among the most polluting vehicles in mining and quarrying operations. A 50-ton mining truck can consume 30 to 50 gallons of diesel per hour. For operations at mines and quarries with downhill haul routes, the eDumper model could be transformative: eliminating diesel consumption entirely while generating clean electricity as a byproduct.

Ciments Vigier SA planned to convert up to eight vehicles at the site if the prototype proved successful. Kuhn Schweiz AG, which distributes Komatsu trucks across Europe, has considered offering the conversion package commercially.

The eDumper was the world's largest electric vehicle when it launched, and it remains one of the most battery-heavy land vehicles ever built. Its 700 kWh pack is comparable to eight Tesla Model S batteries in a single vehicle.

What Makes This Work #

Three conditions must align for this kind of gravity energy harvesting:

  1. A grade. The route needs significant elevation change. The eDumper operates on a 13% incline.
  2. Asymmetric loads. The vehicle must carry more weight in the downhill direction than uphill. The eDumper goes up empty (45 tons) and comes down loaded (110 tons).
  3. An electric drivetrain. Only electric motors can double as generators. Diesel engines convert fuel to motion in one direction only.

These conditions exist at thousands of mining and quarrying operations worldwide. Mountain mines, hillside quarries, and downhill haul roads are common in cement, aggregate, and mineral extraction. The eDumper suggests that converting these fleets to electric wouldn't just reduce emissions. It could turn them into distributed power plants.

Sources #

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