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13 Aug 2018

If you’re a fan of my long rambling posts then you’re in for a treat, as this is going to be just that. However, what I’ll try to do is segment it off in order that you can take it in, in smaller, more digestible chunks.
  • ERS Explainer
  • Ferrari’s twin battery
  • Free energy tricks & Extra Harvest mode
  • Free load mode / Supercharger mode
  • Potential rear wing ‘stall’
The main idea behind this post is to clarify some of the details and inaccuracies I’ve noted in regard to Ferrari’s alleged powerunit gains. Seeing and being part of various discussions it has become painfully obvious to me that there is somewhat of a knowledge vacuum when it comes to people’s understanding of even the fundamental parts and operation of the Energy Recovery System (ERS).

It’s a failing of the sport, the FIA, the promoters, the teams and the media as they’re not able to elegantly portray the various machinations of the regulations at hand.

I have over the years looked to make these things more understandable with various articles debunking myths that have cropped up and also created a video in 2014 explaining some of the energy flow situations.

I’m a small voice in a very large void though and so I’d urge anyone that’s a fan of the sport, that knows another fan of the sport to read this article, as I attempt to simplify the way in which the ERS works.

Let’s start with the hardware, as understanding the role each of these devices play is fundamental in understanding the overall system.

The MGUK is an electric motor attached to the engines crankshaft and can either recover energy under braking or increase the engines output under acceleration. It has a total output of 120kw (roughly 160bhp).

The MGUH is another electric motor, but this one is paired with the turbocharger in order that energy can be recovered (harvested) when the turbo is spun too hard for the load required of it, or it can be used to spin the turbo to keep it in the optimum speed range.

The Energy Store (ES) is a battery pack housed beneath the driver and offers storage for energy recovered by the the two MGU’s.

At this point I’m going to ask that you forget the fairytales that you’ve read/heard in the past and try to focus on this as if you’ve never even heard of the ERS, as frankly the 4MJ limit and 33.33 seconds of energy usage I continue to read/hear/see are nonsense (and have covered previously).
Let’s take a look at the energy flow diagram from the regulations, as this gives us an accurate picture of what can be done. I’ll start with the basics and then we’ll move onto the more complex energy avenues later.

The MGUK can expend energy up to a rate of 120kw (roughly 160bhp) and unlike KERS, which was a simple power boost, is used as part of the powerunits overall output and mapped alongside the pedal map to produce power as requested by the driver via the accelerator pedal. It can spend 4MJ of energy that’s been stored in the ES per lap (this is where the 33.33 second misnomer came from) but can also draw an unlimited supply of energy from the MGUH through the MGU CONTROL UNIT. However, it can only recover and store 2MJ of energy per lap in the ES.

Perhaps the easiest way to understand the MGUK is that the team and moreover the driver will want the full 120kw/160bhp at their disposal for as much of the lap that is possible (as long as they’re not traction limited) as without it they’re a sitting duck. In order to get that 120kw they will demand it from the ES and MGUH, both of which are programmed to supply energy in a way that is beneficial to the laps overall energy landscape.

That means that although the MGUK is being fed 120kw it could be getting 60kw from the ES and 60kw from the MGUH (or 40/80kw, or any other ratio for that matter). The more energy that can instantaneously be transferred to the MGUK by the MGUH the better, as this extends the depletion ratio from the ES, extending the generally accepted 4MJ/33.33 second figures.

By now you should have realised just how important the MGUH is in the overall energy scheme, as it’s responsible for the ‘infill’ of energy that the MGUK is limited by. Furthermore, the hardware is of little significance when compared with the software, which has to be programmed with various (many of which might seem counter-intuitive) scenarios in mind.

So, let’s play out a scenario in order to explain how the components interact with one another.

Braking into and accelerating out of a slow speed corner/hairpin

  • As the car slows into the corner the MGUK will recover energy, sending some of it to the ES for use later in the lap and the rest directly to the MGUH to keep the turbocharger spooled and in the optimum window for the acceleration phase.
  • Accelerating out of the corner (once no longer traction limited) the MGUK will request the full 120kw to help propel the car forward. The MGU-H, having already kept the turbocharger ‘alive’, will start to recover some energy and send it directly to the MGUK, whilst energy is deployed from the ES to supplement it.
  • As the car accelerates out onto the straight the MGUH will continue to recover energy and feed it to both the MGUK and ES, topping up the latter for use elsewhere around the lap.
As you can see in this fairly innocuous example there is a lot going on, all of which requires the two MGU’s to perpetually feed energy around the system so it performs as expected around the entirety of a lap. In fact it’s the transitional phases throughout a lap that make all of this seem like somewhat of a ‘dark art’, as it’s not a simple and binary energy recovery and deployment tool likes KERS used to be.

As an aside there are a couple of these transitional moments that I’d like to cover in order that you might be able to understand just how pivotal ERS is in the overall powerunit scheme.

It may be strategically advantageous (both from an energy point of view and overall car performance) to recover energy via the MGUK in traction zones, and before you say it, no, it’s not traction control, rather a way of limiting the powerunits overall output and affording the MGUK an opportunity to feed the MGUH and/or ES energy.

Lifting and coasting, whilst normally associated with fuel saving, is another avenue where energy can be recovered by the MGUK and passed to the MGUH for instantaneous use or sent to the ES for later deployment.

Overcoming the cars aerodynamic drag is pivotal in delivering lap time during qualifying, meaning the powerunit will be run at full tilt, but during a race the team/driver will usually opt for a different strategy, forsaking absolute vMax. This often leads to partial throttle being used in order to save fuel and energy (similar to a lift and coast but with more nuance).

On the flip side of these scenarios, the driver can find himself in a position where he doesn’t have enough total energy for the desired demand. Perhaps he’s been running in an incorrect mode or mounted a sustained attack on another driver that has expended more energy than is desirable from the ES’s allocation. Failure to make up this ‘lost’ energy may result in a phenomenon you may have heard before but not fully understood - Derating or a Derate

This is when the driver is requesting the full 120kw energy allotment from the MGUK but the ES and/or MGUH are unable to supply it for the entire time it’s being requested, as explained by Andy Cowell from Mercedes HPP below.

Each circuit will provide an entirely different challenge for the drivers and engineers as they strive to find the perfect way around a lap. Oftentimes it will require sacrifice in one corner or straight in order that the laps overall energy strategy is not compromised, which brings me to another misunderstood concept - SoC.

The other issue that has perhaps led to the assumption that drivers only have 4MJ of energy at their disposal per lap is the SoC (State of Charge) statement relating to energy in and out of the battery pack (ES) per lap.

“The difference between the maximum and minimum state of charge of the ES may not exceed 4MJ at any time the car is on track”.

This simply means that if you started at zero on lap 1 you can’t have more than 4MJ in the ES, but the energy can fluctuate between those figures throughout the course of a lap/race. Think of it like a bank account - you can keep depositing smaller amounts and spending different amounts as long as the sum total does not exceed 4MJ.

This means the amount of energy passing through the ES per lap is only limited by the MGUH’s ability to recover energy, as the MGUK can only recover and store 2MJ (through conventional methods, we’ll get to this interesting caveat shortly).

For 2018 drivers can only use two ES’s per season before being penalized, which puts even more emphasis on their reliability. The ES is a densely packed, liquid-cooled lithium-ion battery made up by a number of cells which will degrade over a period of time and become less or totally ineffective (dead cells), meaning the strategy for using these cells is imperative. The manufacturer will clearly spec the battery pack well beyond the 4MJ hard limit that many associate with the ES, with the overall pack weight really the deciding factor in how much storage can be crammed in there.  

Ferrari’s twin battery layout

From Ferrari’s point of view they’ve opted (since 2014) to run what is known as a twin battery arrangement, but recently, having made large strides up the grid, the team have seen everything they do put under the microscope.
Ferrari's energy store, which ordinarily resides under the driver, was captured here by Craig Scarborough in Abu Dhabi last season, Craig kindly allowed me to use the image
Physically the battery is still only one unit but it’s my understanding that it’s viewed as two ‘virtual’ batteries by the software, potentially improving energy and heat management between it and the two MGU’s.

As such, clarification was sought by various teams and powerunit manufacturers over the use of this battery layout after it was suggested that Ferrari had found a way to exceed the MGUK’s maximum 120kw deployment rate, with a 20bhp figure being put on it. That would require the MGUK to be supplied 135kw, which is clearly beyond the scope of the regulations and something that Ferrari have since been cleared of.

This all came about because the data collected by other teams suggests they’re doing something counterintuitive and not occuring every lap but seems to arise in the secondary phase of acceleration out of a corner.

‘Free energy tricks’

Ferrari, having been cleared of any excessive energy deployment via the MGUK by the FIA have still been the subject of much debate. Nico Rosberg was next in line to throw mud at Ferrari, suggesting he had some ‘insider information’ about a ‘free energy trick’ being employed by the Scuderia ( that was giving them an advantage over Mercedes.

Technically nothing is for free, it just means that Ferrari have found a way to operate the physical hardware within the regulations in a different, or perhaps counterintuitively, when compared to their rivals. But, in short he’s talking about the advantage that can be gained from the MGUH, as it passes energy directly to the MGUK. It’s nothing that at a base level that’s not already understood but that doesn’t mean you can’t get better at it...

It got me to thinking about a less than obvious energy trick that Honda dragged out into the light in 2016 - Extra Harvest Mode. This little nugget of information came via Motor Fan illustrated (a Japanese publication) and showed that if you don’t explicitly write something down in the regulations the teams and manufacturers will exploit it.
It’s a concept that all the manufacturers are believed to be using and that Honda developed and implemented during 2016. Whilst its effect has lessened since (less time on the brakes for harvesting, due to the increase in downforce) it shows that the energy flow diagram can be overcome.

The idea is that you defeat the MGUK’s 2MJ recovery and storage limit to the ES by cycling it through the MGUH, as it both simultaneously deploys and recovers energy (quickly switching between recovery and deployment (ON>OFF) in order to maintain boost pressure and recover energy).

In the example Honda suggest an extra 1MJ of energy is recovered by the MGUK, sent directly to the MGUH for use but immediately recovered and sent to the ES for storage. This trick would only be limited by the amount of energy that can be recovered by the MGUK in the course of a lap and the efficiency and ability of the MGUH to transfer that energy to the ES (which would also have to stay within the SoC limit).

The use of this ‘extra harvest mode’ also opens up the possibility of turning the energy flow in the opposite direction, cycling energy from the ES via the MGUH (OFF>ON) to the MGUK, thus exceeding the Max 4MJ from ES to MGUK.

These methods make a mockery of the regulations designed to constrain the MGUK’s interaction with the ES but have inadvertently led the manufacturers to find ways in which to improve the efficiency of the MGUH and ERS system as a whole.

It’s worth bearing in mind that the ability to recover and store any energy, but particularly this ‘extra’ energy, will fluctuate at each circuit due to the time in corners or on a straight. It’s also affected by other factors, including but not limited to - individual driving style, current fuel targets/ICE operation/modes, car weight and traffic.

Free load mode / Electric supercharger mode

Another area of interest for me is the way in which the wastegate is opened, allowing the turbocharger to be driven electrically by the MGUH, which reduces back pressure and improves the ICE’s output. It’s a strategy we see employed more often during qualifying, as energy management is less critical but often see’s drivers having to do a charge up lap either after a flier or preparing the car during the out lap.

It’s a little more nuanced than simply driving the turbo with the MGUH permanently, with an energy strategy devised that will give the driver the best potential lap time. When you hear the teams or media talk about “Qualifying mode” or “Party mode” this is a key factor in those modes, with fuel and energy maximised for a full on assault.  

You’ll note an audible difference when the wastegates are opened as the exhaust gasses are now escaping in a different way, whilst the turbo is being driven more linearly by the MGUH. It’s become apparent that Ferrari have started to use this mode in short bursts during race situations too, which often see’s their drivers topping the speed traps. Clearly this is advantageous from an overall laptime perspective but it comes at the expense of energy management, meaning it cannot be done lap after lap (at this stage at least). It may come with some minor advantages in terms of fuel economy and/or reliability too but essentially everything that’s done with these powerunits is a trade off.
The audible difference is not something that isn’t ordinarily picked up by the broadcast camera’s / microphones but in the following trackside footage you can hear the difference.

In this great video by Bozzy (he’s definitely worth subscribing to if you don’t already) it can be heard numerous times. But as some quick reference points watch and more importantly listen at 1:02 and 3.55.

This more recent video (from Hungary) also has the audible note change at around 0.17 onwards.

Blown or stalled rear wing

I feel that explaining free load / electric supercharger / qualifying mode was an important task in its own right but, the other reason I did this was to enforce an idea that I’ve already put out there - using the wastegates to ‘stall’ the rear wing. The article kind of of explains the premise but I’d like to add some more thoughts here whilst we are at it.

Again, I’ll also reiterate that this is speculative in nature, others have condemned the idea and I can understand that too, it’s just that the swing toward using the wastegate in the opening phase of the straight at least for me makes it plausible.
This speed plot from Tobi Gruner of AMuS gives us a snapshot of where Ferrari are reportedly faster and got me to thinking about how you could gain top speed, but not directly from the powerunit which is everyone else's immediate leap.

My immediate thought was to turn to a reduction in drag, especially as the concept is still fresh in everyone's minds from the F-Duct and DRD used during the V8 era. However, with no additional/supplementary hardware present around the rear wing to cause a ‘stall’ it seemed unlikely. This did not deter me though (I can be stubborn) and so I tried to think about how using the engine as a pump you might be able to at least cause a destabilisation of the airflow that could lead to a stall.

Of course I had the example of DRD to work with and the fact that the ‘active’ version I’d proposed back in 2015, when the wastegate pipework was originally decoupled from the main exhaust outlet, was also possible, until it wasn’t.... In fact I have a copy of the technical directive that was issued to cover questions that Ferrari required clarification on, in which Charlie subsequently made the idea a non-starter.

What if you didn’t need the pipework though? what if you could cause enough hysteria in the local airflow that the rear wing would lose downforce and with it some of the drag penalty?

In short the exhaust, due to its placement, currently has an influence on the aerodynamic airflow structures it touches (rear wing and diffuser airflow structures ‘talk to one another’, creating an upwash behind the car). Renault use the exhaust to blow the underside of their rear wing, improving downforce at lower speeds, something they’ve tried to enhance by reducing its proximity to the mainplane (which also features heat protection to guard against the increased temperatures it might encounter).

The use of the exhaust flow to drive aerodynamic performance is something teams have been doing for decades, with the rules constantly in a state of flux in order to guard against the activity. Of course, the use of exhaust blown diffusers, during the latter stages of the V8 era is part of the reason why the FIA decided to fix the single exhaust position along the cars centreline, but that doesn’t stop teams trying to gain an advantage.

It’s why the FIA reduced the scope of monkey seat winglets this season, reducing how the localised airflow could be manipulated along with the plume / jet of air that is ejected from the exhaust to improve the diffuser and rear wings performance.

Ok, enough of blowing exhausts for downforce, as we’ve generally accepted that it’s possible, so let’s turn our attention back to stalling the rear wing. The first thing I’ll ask you to note is that whenever teams have looked to do this, they’ve also chosen to add more downforce/drag by running a more aggressive rear wing, as why wouldn’t you take the extra downforce for for little or no drag penalty?..

Ferrari appear to have been doing just that, running more aggressive wing angles than Mercedes, whilst conversely topping the speed traps. Of course, this can be explained away by a difference in overall chassis efficiency or simply more power but it was also that this performance doesn’t seem available lap-after-lap.

So, if we take what we’ve learnt about free load or electric supercharger mode and apply that logic to what’s happening with the wasted exhaust gases we can conclude that you could disturb the natural flow to the underside of the rear wing and potentially cause a reduction in downforce and drag.

Yup, before you say it, I’ve already considered that by virtue of everyone doing this, to some extent, during qualifying with a full-on free load mode use they’d all see the ‘stall’ benefit, but I’d argue that its potential would ordinarily be hampered by a reluctance to run higher rear wing angles of attack that would compromise them in race conditions.

Ferrari, if my assertions are correct have found a way to use more of the free load / electric supercharger mode during race conditions too, which means they’re actively sacrificing some electrical energy for an aerodynamic advantage.
Giorgio Piola captured the wastegate arrangement as the car was torn down after the test in FP1, note the lower wastegate pipe is merely there to comply with the regulations and isn't directly connected, rather merged with the upper pipe

Their yet unraced new rear wing and wastegate position could also add more smoke to this fire, with the wings central geometry less than conventional. You’ll note the leading edge of the mainplane is upturned in the image above, but it also features an odd camber on the underside shown in the image below (highlighted by the shape of the rear wings slot gap separator and marked in yellow by me). Both images were taken by Giorgio Piola when the design was installed on Sebastian Vettel’s car during FP1 at the German GP. 
A rear view of the wastegate setup (red arrow) and the oddly cambered mainplane (line added in yellow to define the surface change) was captured by Giorgio Piola
The general consensus at the time was that Ferrari were testing a high downforce configuration that could be run at a latter point in the season. However, I’d argue the opposite and that in fact we have more chance of seeing it (or a derivative thereof) used at the lower downforce circuits (Spa and Monza), as they mitigate the downforce gains from running the wing by being able to ‘stall’ - reduce downforce and drag through better placement of the wastegate pipes (now installed vertically above the exhaust, rather than either side of it).


I hope this article has been able to break down some of the barriers that have been forged over the years about what I would class as some of the more basic functions of the ERS, whilst also adding further depth on what can be achieved if you take a more sideways view of the regulations.

The gains made by Ferrari over the last few seasons have been astounding but rather than being considered 'cheats' they should be lauded for their brilliance and ingenuity. Afterall, we've all marvelled over Mercedes dominance between 2014-2016, so the Scuderia's resurgence should be admired too.

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  1. In one part of your article you infer the MGU-K is being used to harvest energy other than when braking, is that allows by the rules/regulations? I know that some harvests energy by the K by burning fuel, but still they do that while using the brake pedal.

    1. Yes, there is no specific regulation that suggests the MGU-K must only recover energy when braking.

  2. I would counter that by asking 'what is breaking?' - everywhere where you do not need full power from the engine, you could still run it full tilt, and let the MGU-K sap/recover some energy until you get at the amount you need at the wheels.

  3. Thank you for this article. The idea that Ferrari have managed to take the PU and reduce drag by stalling the rear wing is quite interesting and I can see that it's a pretty touchy arrangement. From a driveability standpoint that could really change up the balance dynamically. Can you tell me .. do teams program specifically for a given track or do they rely on programming the PU for general driveability? Perhaps these dynamic balance issues are somewhat responsible for things like Vettel going "agricultural" in Germany. What was a balanced car at 98% becomes a pusher when brake recovery modes change at 60% capability, like you might find on a damp racetrack.

    1. They will create maps for each individual circuit, these will also be modified throughout a race weekend to tailor them to the driver and conditions. There are numerous maps available for each given circumstance too, some perhaps less honed than others...

  4. Great blog. I am more certain of the gains from improvements in PU electrical management than the rear wing stalling principle. I am still of the view that the 2 battery system that Ferrari use was more to do with mechanical balance, cooling and fitting everything in however time will tell as no development stays secret for long in the fabulous world of F1 technology.

    1. I too believe the energy management tricks mentioned in the article are where Ferrari have made their gains relative to Mercedes, the rear wing stalling tactic is simply me putting out there that it's at least possible. The battery is still one unit, as per regulation, it's just seen as two by the software to improve cooling, reliability and performance.

  5. Hi Matt, I've just discovered the site and have duly learnt several things from this post. I have a few questions though.

    1. Just to clarify: an unlimited amount of energy can be transferred from the MGU-K to the drivetrain each lap thanks to the MGU-H?

    2.I didn't understand what was meant by "It may be strategically advantageous (both from an energy point of view and overall car performance) to recover energy via the MGUK in traction zones". How can the MGU-K recover energy when in anything but a braking zone?

    3. This isn't directly related, but do you know if a push-to-pass button exists with these cars, where a driver can override the deployment algorithm and use the available energy where ever he wishes? Or is there only an overtake mode that the driver would switch to when he requires more aggressive deployment, but with the deployment still determined by an algorithm?

    1. 1. Yes, if energy can be made by the MGU-H it can be either sent to the ES for later use by either MGU (but the MGU-K may only use 4MJ per lap from that source) or the MGU-H can send energy recovered directly to the MGU-K. The only limitation is the amount that can be used at one time, which is 120kw (or 161bhp).

      2. It's broadly understood that the MGUK recovers energy under braking because that's how it's percieved but the MGU is connected to the engine and recovers energy as that slows, meaning it could theoretically draw energy from it at any point, even under acceleration.

      3. Drivers still have an overtake button on their steering wheel but this really just turns everything (fuel and electrical energy settings) upto maximum and shouldn't be seen as P2P. Using it as a P2P would be inefficient IMO as that simply degrades the energy available for the rest of the lap.

  6. "an unlimited amount of energy can be transferred from the MGU-K to the drivetrain each lap thanks to the MGU-H?" Yes when one looks at the FIA official ERS diagram energy flow one can see an arrow between MGU-K (the only part of the ERS that can transfer power/energy to the drivetrain) that says "max 120kw limited".

  7. as there is no "reply" facility to your answering post: "yes there is no specific regulations that suggest the MGU-K must only recover energy when braking". (POWER UNIT AND ERS-FORMULA ONE) "MGU-K (where 'K' stands for kinetic' works like an uprated version of the previous KERS, converting energy generated under braking into electricity (rather then it escaping as heat).

  8. I found a legible version of Figure 1 at

  9. Does that mean that Ferrari runs in the straights partially on waste-gate to stall the wing instead of full time turbo/full throttle?


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