What Is ERS In F1? (How The MGU-K & MGU-H Work)

ERS stands for Energy Recovery System, and it is one of the most important systems on a modern F1 car. First (properly) bursting onto the scene in 2009, it has evolved over time to become integral to the cars’ powertrains. So, what are the MGU-H and MGU-K, and how do they work?

ERS in F1 stands for Energy Recovery System. The MGU-K feeds some of the waste energy lost under braking back to the energy store for later use. The MGU-H uses excess exhaust gases from the engine to feed power to the energy store, MGU-K, or the turbocharger’s compressor.

Although the two systems work in similar ways, there are also some big differences between them. Below, we go through how ERS works on an F1 car in more detail, looking at each part individually.

What Is ERS On An F1 Car?

ERS is the energy recovery system on an F1 car, made up primarily of the energy store, the MGU-K, and the MGU-H. ERS allows drivers to get a boost of 161 HP (120 kW) for a given amount of time per lap (more on the specifics of that later), using energy that is harvested from regenerative braking and waste exhaust gases.

ERS in its current form came around in 2014, when the power unit regulations changed from mandating naturally aspirated V8 engines to turbocharged hybrid V6 power units. However, ERS began as KERS in 2009, when some teams started implementing kinetic energy recovery systems on their cars, and between then and 2013, various teams chose to use it while others avoided it.

The Largely-Unknown First Use Of KERS In F1

But the first potential implementation of KERS actually came back in 1998, when McLaren were developing an energy recovery system for their MP4/13 car. At the time, McLaren were partnered with Mercedes as a works team, and Mario Illien (one of the founders of Ilmor) helped them develop a mighty engine that led them to many wins and back-to-back championships in 1998 and 1999.

However, in 1998, the engine used in the McLaren was set to run with an early KERS system, although this time using a hydraulic system rather than the motor-generator systems used on modern F1 cars. Adrian Newey was one of the car’s designers, and he has since said that, while the hydraulic system is the least technically favorable, it was the cheapest and easiest to implement.

Essentially, under braking, hydraulic pressure would build up, and that pressure could be released under acceleration to provide more power to the rear wheels – enough to allow them to gain 2 tenths of a second per lap!

However, the energy recovery system was outlawed before it could be used in any races (at least that’s what most sources suggest), likely as a result of other teams feeling they wouldn’t be able to keep up with the development costs (although some teams may have implemented and possibly used their own systems too). ERS wasn’t seen on the cars for another decade or so. But this time, hydraulics weren’t the method of recovery and deployment.

Note: This system is not to be confused with McLaren's "brake-steer" system, which is often mentioned in the same context as KERS. This system was used in races and it did not work as an energy recovery system, instead allowing the driver to deploy brake pressure at each of the rear wheels individually.

Modern ERS

The powertrain on an F1 car is the mix of components that drives the car. Many people just think of the engine powering the car, but instead it is actually known as a Power Unit, or PU, as it is made up of several vital components that work together to give the car an enormous amount of power, about 1000 HP.

The powertrain is made up of many different components, but the main ones to consider are the engine, the turbocharger, and both the MGU-K and MGU-H. We will talk about these more specifically in later sections, but MGU stands for Motor Generator Unit, while the K is for Kinetic and the H is for Heat.

An F1 car’s engine can produce around 850 HP on its own (it varies between teams), with an extra ~150 HP coming from ERS

Engine Size

Since 2014, the engines used in F1 cars have been 1.6-liter hybrid V6s. These are internal combustion engines, or ICEs, and they work using a traditional 4-stroke system you would find on your normal car. Using a few extra components, like special spark plugs and precise fuel injection systems, fuel and air are drawn into the cylinders, compressed and ignited, and discharged as exhaust gases.

Where the powertrain differs from your average road car’s is in the power they can provide to the driver, but also in all the various additional components F1 engines have. One of the biggest differentiators is the fact that F1 cars have MGU-H components, which aren’t found even on the most advanced electric road vehicles (as they’re expensive and not as useful at low speeds).

Note: Mercedes were developing MGU-H technology for their road cars, but it's unlikely to become commonplace any time soon

They are capable of more than 1000 HP, which is a massive amount of power for a car that weighs less than a ton. The engine itself produces around 850 HP, with the remaining power coming from the motor generator units that we’ll discuss in more detail below.

Energy Storage

These units generate and make use of energy that is stored in an extra Energy Store (ES), sometimes called an Energy Storage System (ESS), which is essentially a large lithium ion battery (although it’s made specifically for F1 cars). It is regulated to weigh between 20 and 25 kg.

They are also regulated in terms of how much energy they can store and provide, and it must be one component, rather than being split into several throughout the car.

F1 batteries work by taking the energy generated by both the MGU-K and MGU-H and storing that energy for later use (although as we’ll discuss below, the energy doesn’t always go straight from the MGUs to the battery). Drivers do have an overtake button which, when pressed, will give them more battery deployment for overtaking, defending, and simply to make use of it at certain parts of the track.

However, the car’s electronic control unit (ECU) takes care of most of the deployment for them. They can tweak energy deployment maps, for example to change from a high deployment mode for a fast qualifying run to a recharge mode on their cooldown laps, but throughout qualifying and the race, most of the work is done by the computer.

Using That Energy

The power boost from the MGU-K can be used for around 33 seconds each lap (with the MGU-H contributing more energy and allowing for an overall power boost for much longer), which is obviously of massive advantage to the drivers. The MGU-K is used to harvest ‘waste’ energy from the wheels under deceleration (i.e. when the driver brakes) and provide this to the energy store to be used later.

It’s worth noting that the MGU-K is not connected to the brakes in any way, and instead it is connected to the engine’s crankshaft. It recovers energy under braking, but it is not linked to the brakes themselves. The MGU-H works in a similar way, although it is linked with the turbocharger and recovers energy from waste exhaust gases.

The amount of energy each component can recover and release is limited by the technical regulations. The total amount of energy the ES can hold while the car is on track must be no more than 4 MJ*, and this is also the maximum that can be sent from the energy store to the MGU-K during one lap. However, only 2 MJ can be recovered from the MGU-K per lap.

This means a driver could theoretically drain their battery (from 4 MJ to almost 0 MJ) during a lap, such as for a qualifying run or a fastest lap attempt during the race, and then require at least 2 laps to recharge their battery to full capacity. This is why drivers don’t have full power available to them at every point during the Grand Prix, as they need to manage their energy usage.

Key Fact: In reality, drivers will struggle to recover the maximum of 2 MJ per lap via the MGU-K, as they spend so little time on the brakes. At Spa, the longest track on the calendar, the driver is only on the brakes for about 13% of the lap!

* Technically, it’s the difference between the maximum and minimum state of charge (SOC) of the energy store that is limited to 4 MJ. This means the teams can have a battery that can store, say, 6 MJ at most, as long as the minimum amount of charge the battery can ever reach while the car is on track is 2 MJ (6 MJ – 4 MJ = 2 MJ).

This allows teams to ensure the battery will still be able to hold 4 MJ of charge (the maximum they can deploy during a lap) even as the battery deteriorates over time. However, adding more capacity also adds weight, which is turn hinders the car’s performance, so there is a limit to how big the batteries can be without significantly affecting how fast the car can go.

Unlimited Power

The MGU-H on the other hand can recover and deploy a theoretically ‘unlimited’ amount of energy per lap. It can also send an unlimited amount of energy to the energy store, to the MGU-K, or to the turbocharger. The diagram below illustrates the amount of energy that can be sent to and from each component per lap.

The rules permit this unlimited amount of energy in an effort to encourage teams to use the MGU-H well and aid in the overall efficiency of the power units. However, this has led to massive amounts of money being spent on this component, and we will discuss the impact of this at the end of the article.

While there are no limits per the regulations for the MGU-H, it is of course limited by the efficiency of the components and the car’s designers must factor in the effect of thermal degradation on the internal components, as there is a lot of heat stress to consider around the operation of the MGU-H and the high RPM of the compressor.

Note: Increasing the size of the motor could also increase the back pressure in the exhaust system. This could hinder the combustion in the engine, and so it's a fine balance to strike. 

Plus, while the MGU-H can send an unlimited amount of energy to the MGU-K over the course of a lap, the amount of energy that can be sent from the MGU-K to the wheels (via the crankshaft, to which the MGU-K is connected) is capped at 120 kW, or 161 HP. With the modern, fine-tuned MGU-H components teams use nowadays, they can almost get this kind of deployment for a full lap.

33 Seconds Per Lap?

You’ll often find resources online that say the ERS can be used for 33 seconds per lap, but this is not something bound by the regulations. In fact, this figure refers to the amount of “boost time” the driver can typically get from their 4 MJ of energy sent to the MGU-K from the battery.

With the MGU-H system, which is connected to the battery, the turbocharger, and the MGU-K itself, drivers can actually access a 161 HP boost for most of the lap. This is because the MGU-H can recover so much energy through the exhaust gases, and this can be sent directly to the MGU-K when required.

Key Fact: The MGU-H is responsible for about 65-70% of an F1 car's total energy recovery over the course of a lap

F1 ERS Diagram

Diagram illustrating the ERS (Energy Recovery System) in a Formula 1 car, showing the pathways energy can take from the Energy Store through the MGU-H and MGU-K, then to the turbocharger and the rear wheels.
This simplified diagram illustrates the different pathways the energy can take within an F1 car’s energy recovery system

How Do F1 Cars Harvest Energy?

F1 cars harvest energy using the energy recovery system, made up of the MGU-K connected to the crankshaft and the MGU-H in the turbocharger. These motor generator units harvest waste energy lost under braking as kinetic energy, and as heat lost in the exhaust gases, and this energy can be used in various ways.

Waste Energy

We have mentioned the word ‘energy’ quite a lot already, and especially in the context of waste energy. Essentially, the car’s powertrain can only be so efficient, as there is a lot of energy lost at each stage due to friction, which results in heat, which is lost to the atmosphere. This is common of all mechanical equipment and is an ever-present challenge for engineers.

The waste energy in question is not wasted just for the sake of it, as it is inevitable when dealing with combustion engines. The second idea to note concerns the first law of thermodynamics. This states that energy cannot be created nor destroyed, only transformed. Essentially, it can only be shifted from one form to another, rather than ‘made’ or ‘lost.’

So we need to consider what is happening to the energy within a car when it is being driven. The engine uses fuel and oxygen to generate mechanical energy through combustion. This is a result of the chemical energy of the fuel and oxygen being burned, and the mechanical energy of the pistons is converted into kinetic energy in the wheels, driving the car forwards.

At every stage of the process, heat is generated, which is another form of energy. This occurs due to friction of components rubbing against each other, as well as a by-product of combustion itself. The MGU-H makes use of heat energy that would otherwise be lost through the exhaust gases, but the MGU-K converts kinetic energy into electrical energy instead.

We’ll talk more about the specifics of each MGU in the next sections, but first we must understand the basics of the mechanisms they use to make use of this ‘waste’ energy. They do this by converting the thermal (MGU-H) or kinetic (MGU-K) energy into electrical energy by means of a motor system. Hence the name, motor generator unit.

The Motor

A motor is an electrical component that turns when it receives an input of energy. As part of a circuit, that input energy is electrical energy, and the motor turns, converting it into kinetic energy. These motors can be used to turn things like wheels and turbines. But turning the motor mechanically (rather than with electricity) can also turn the kinetic energy back into electrical energy.

This can be seen with the common dynamo that you might have on your bicycle. Essentially, as the wheels turn, the motor in the dynamo turns, which through some complex electronics that we will simplify below, provides power to another electronic device, such as your bike light. This energy can also be stored, which is the basis of the MGUs.

Understanding The Motor

The motor can turn as a result of electrical energy being applied, or it can turn via the input of kinetic or mechanical energy. In simple terms:

  • Send electrical energy to the motor –> Motor spins
  • Spin the motor –> Motor generates electricity
Diagram illustrating a Motor Generator Unit (MGU) working as a motor when electrical energy is supplied, and as a generator when kinetic energy is supplied.
In the top diagram, the unit is functioning as a motor, and in the bottom diagram, it’s functioning as a generator

What happens with both the MGUs in an F1 car is a similar process. They both contain motors, as the name suggests, and these motors can be made to turn via the input of electrical energy from the energy store, like a traditional motor. Or they can be used like a dynamo, using external kinetic energy to turn the motors, and then converting that into electricity.

Generating Current

The way they do this is quite complex. Essentially, the motor consists of wires and magnets. When wires are placed in a rotating magnetic field, current can be generated within the wires, even when they are not connected to a power source. This rotating magnetic field is created by spinning the motor with some sort of external force (i.e. not by sending electrical power to it).

In the MGU-K, the rotation of the rear wheels spins the motor, generating electrical energy

In the MGU-H, the hot exhaust gases passing through it spin the motor, generating electrical energy

What Is The MGU-K On An F1 Car?

The MGU-K on an F1 car is the Motor Generator Unit Kinetic. This is connected to the rear wheels of the car, and it recovers waste energy when the car decelerates. Its motor spins to generate electrical energy under braking, and it can then deploy 161 HP to the rear wheels when required.

As we discussed earlier, when wires are placed within a rotating magnetic field, a current is produced. The faster the motor rotates, the more current is produced. The MGU-K is made of a motor, similar to the MGU-H (which we’ll discuss below). In the MGU-K, it is connected to the crank shaft, which is what turns the engine’s piston movement into the wheels’ rotational movement.

When the wheels are spinning, the motor in the MGU-K is spinning, which means the magnets are spinning. Now, when the MGU-K is in motor mode, it is taking electrical energy from the energy store and convert it into kinetic energy, just like the MGU-H does with the compressor. This provides a power boost to the wheels.

Note: The MGU-K can only provide a power boost at race starts once the car reaches 100 kph (60 mph)

Under Acceleration

The MGU-K is in motor mode when the car is accelerating. In motor mode, the boost of power from the battery is working alongside the mechanical energy from the engine that is driving the wheels constantly.

Now, when the accelerator is released or when the brakes are applied, the MGU-K goes into generator mode. When the car is decelerating, the wheels are still spinning, and they are spinning in the same direction as when they are accelerating. The difference here is that the motor in the MGU-K stops being rotated by the electrical energy from the energy store.

Harvesting Waste Energy

Instead, the motor continues to spin solely due to the rotational energy of the wheels. This means the motor is spinning without an electrical power source, and the magnets in the still-spinning motor rotate, causing the current to flow back to the energy storage system. As we outlined earlier, providing electrical energy to a motor causes it to spin, and spinning a motor causes it to generate electrical energy.

This occurs under deceleration or braking, making use of the ‘wasted’ energy lost from the wheels slowing down. While the MGU-K is not connected to the brakes themselves, the MGU-K takes some of the kinetic energy away from the wheels via the crankshaft, helping slow them down slightly and therefore reducing the energy lost through heat as the brakes are used slightly less.

Note: Different teams may connect their MGU-K to their crankshaft in different ways, and it's a secretive area of development. It's likely that most teams use a gear and clutch system or connect them together directly, but there has been discussion of using chains in the past too.

A Key Distinction

So, while the MGU-K doesn’t directly make use of waste heat energy, it does indirectly reduce the amount of energy lost as heat as the car relies a bit less on the brakes to slow down, thanks to some of the kinetic energy being converted into electrical energy by the MGU-K.

The MGU-K harvests some of this ‘lost’ energy while also aiding in slowing the car down sooner. The MGU-K would not provide enough resistance on its own to completely stop the car, as this would need a massive motor and a large battery to store the huge amount of electrical energy that it would generate. But slowing it down is not its main purpose anyway.

Instead, its main purpose is to harvest otherwise ‘wasted’ kinetic energy from the decelerating wheels and turn it into electrical energy, which can then be sent to the energy store. From there, it can be sent to both the turbocharger’s compressor or the wheels themselves when the accelerator is pressed, giving the car that boost in power.

However, as our earlier diagram illustrated, the MGU-K is also directly connected to the MGU-H, and so the MGU-K can theoretically be used to send energy to the MGU-H, which can in turn spin the compressor. The video below does a good job of illustrating how the MGU-K fits in with the rest of an F1 car’s power unit.

What Is The MGU-H On An F1 Car?

The MGU-H on an F1 car is the Motor Generator Unit Heat. The MGU-H is connected to the turbocharger, and when exhaust gases pass through it a generator turbine spins, turning that kinetic energy into electrical energy. It can then be used as a generator to spin the turbo, boosting engine power.

The turbocharger is a key component of an F1 car’s engine, and it is made up of two main parts. The turbine is the first part, and this is connected to the wastegate of the engine. The exhaust gases from the engine flow out of the wastegate to the turbine, and they then spin the turbine, which is connected via a shaft to a compressor.

This compressor spins with the turbine, drawing in extra air and pushing this air into the engine. This increases the amount of oxygen available to be sent into the engine, which allows the engine to burn more fuel faster for more power (although this is still restricted by F1’s fuel flow limit). The MGU-H sits in between the turbine and the compressor and is connected to the turbocharger shaft.

Note: The MGU-H's rotational speed is limited by the regulations to a whopping 125,000 RPM! The MGU-K is limited to 50,000 RPM.

Turning Heat Energy Into Electrical Energy

The MGU-H has a motor in it that spins when exhaust gases pass through it. This happens when the amount of exhaust gases expelled from the engine exceeds what is required to meet the current demand of the turbocharger. It converts the kinetic energy of the hot exhaust gases into electrical energy through the process we described earlier, with the spinning magnets in the motor generating electricity in the wiring.

This energy can either be sent to the energy storage system for later use or straight to the MGU-K, where it adds additional power to the rear wheels. However, the energy can also be sent to the compressor to keep it spinning at a high RPM even when the driver is off the throttle. It doesn’t provide a boost when the driver is on the throttle, but rather keeps RPM high enough to eliminate turbo lag.

How The MGU-H Eliminates Turbo Lag

When the driver releases the accelerator, the engine stops working so hard, and there are much less exhaust gases coming out of the wastegate. This is not enough to rotate the turbine, so the compressor also stops spinning. This is fine, as the engine doesn’t need extra power when the driver is decelerating. The problem is when the driver puts their foot down again.

When the car starts to accelerate again, the turbine takes a measurable amount of time to get up to speed with the exhaust gases provided to it, so the compressor doesn’t instantly provide the extra air to the engine. This delay from when the driver presses the accelerator pedal to when the engine gets the boost of power from the extra air from the compressor is called turbo lag.

The MGU-H can eliminate this issue by spinning the compressor without requiring enough exhaust gases to be passing through it. This means there is no delay between the driver pressing the gas pedal and the compressor spinning, and therefore the MGU-H eliminates turbo lag. This means the driver can get maximum power as soon as they press the accelerator.

Note: The MGU-H can also be used to improve torque delivery and drivability by allowing for careful control over the airflow into the engine. The teams can pair this with precise fuel injection to optimize the engine's behavior, making the MGU-H yet more complex!

The video below from the Mercedes F1 team does a good job of visualizing this vital (but outgoing) component of the cars.

Why The MGU-H Is Being Removed In 2026

Both the MGU-K and the MGU-H are very advanced pieces of technology, so they are both expensive to build. The MGU-H is one of the most expensive parts of the car, and it is set to be removed from the engines when the regulations change in 2026.

This is largely because it is such an expensive and complex component to develop and put into the cars, and it has limited potential off the track. Lots of the technology used in F1 makes its way into road cars and the wider world in general, with the KERS system now commonplace in electric and some non-electric cars in the form of regenerative braking.

This, paired with the fact that F1 is always trying to cut costs, means the MGU-H simply has no place in the sport beyond 2026. The complex nature of the component, and its implications on the drivability and performance of the cars, means that new manufacturers looking to join the sport would be at a major disadvantage compared to the teams that are now very familiar with the technology.

New Manufacturers Don’t Want It

Any new engine manufacturer looking to join F1 with the MGU-H still a major component would need to spend years of development and a lot of money to try and catch up with the current manufacturers. But development never stops in Formula 1, even for the teams at the front, so new manufacturers would likely never catch up.

So, in order to keep costs down, ensure the cars are as relevant to the wider world as is reasonably possible, and to encourage other manufacturers (like Audi and Ford) to join the sport, F1 decided that 2025 would be the last year the cars would use the MGU-H. From 2026, the cars will depend on MGU-K systems for energy recovery, and we will see in time just how well they do it!

Final Thoughts

The ERS system in an F1 car is very complex, and it’s made up of various different components. The two main ones are the MGU-K and the MGU-H, and while the MGU-H is on its way out of the sport, they are two incredibly complex and fascinating components that contribute to the massive power outputs of modern F1 cars.