How does the virtual energy tank work in WEC?

A Hypercar dives into the pits despite still having fuel onboard. Another stretches its stint while its rival's energy percentage approaches zero. The explanation lies in WEC's virtual energy tank, a crucial part of endurance racing strategy.

It tracks how much propulsion energy a car is still permitted to deploy, rather than simply how many litres remain in its fuel tank.

What is the WEC virtual energy tank?

In the Hypercar category, each car receives a maximum energy allocation per stint, expressed in megajoules (MJ) and set through Balance of Performance, or BoP.

The virtual tank counts down as that allowance is consumed. On a hybrid Hypercar, it accounts for propulsion from both the combustion engine and electric motor.

This helps regulate cars with different powertrain designs across the WEC Hypercar field.

A reading of 20% means approximately one-fifth of the permitted energy allowance remains. It does not mean the fuel tank or hybrid battery is 20% full.

How is virtual energy measured?

Driveshaft torque sensors allow officials to calculate the mechanical energy deployed through the drivetrain over time.

The system measures propulsion output rather than estimating energy usage from fuel consumption alone. Consequently, deploying hybrid power also uses the allowance. Recovering energy under braking replenishes the battery, but does not simply refill the virtual tank.

For a normal Hypercar stint, the regulated energy accounting runs from pit exit to pit entry.

How does the virtual tank refill?

During a refuelling stop, the virtual allowance increases according to a regulated energy flow rate while the hose is connected, after any applicable additional docking time.

Connecting the hose does not instantly reset the display to 100%. A shorter refuelling connection restores less virtual energy, allowing teams to tailor a stop to their remaining race distance.

Physical fuel and virtual energy must therefore be managed together. Enough petrol to continue does not automatically mean enough permitted energy to complete another lap.

What happens if the virtual tank reaches zero?

The car does not automatically stop because its allowance is exhausted. However, going below zero breaches the energy rules, triggering a penalty and requiring the deficit to be compensated at the next stop.

Teams must pit before exceeding their allocation.

Why does virtual energy matter for race strategy?

Drivers can reduce energy consumption through lift-and-coast, sacrificing some lap time to extend a stint. Traffic, weather and neutralisations can also change how far the remaining allowance will take them.

When following Le Mans and WEC racing, compare energy percentages alongside gaps and lap times. A leader with little allowance remaining may soon surrender track position, while a chasing car with more energy has greater strategic flexibility.