Just as crucial to propulsion, and fully integrated with the turbocharged 1.6-litre V6, is an Energy Recovery System (ERS) that dramatically increases the unit’s overall efficiency by harvesting (and redeploying) heat energy from the exhaust and brakes that would usually go to waste.
The internal combustion engine itself is a stressed component within the car which is bolted to the carbon fibre 'tub'. Despite its relatively diminutive size and 15,000rpm rev limit, direct fuel injection, a single turbocharger and some remarkable engineering make it capable of producing around 700bhp.
ERS accounts for an additional 160bhp and helps ensure that the new units are not only just as powerful as the 2.4-litre V8s they succeeded, but considerably more efficient, using approximately 35 percent less fuel.
The new power units are a far cry from Formula 1 engines in the early 1950s which produced power outputs of around 100 bhp / litre (similar to what a modern 'performance' road car can manage now). That figure rose steadily until the arrival of F1 racing’s first 'turbo age' of 1.5 litre turbo engines in the 1970s when anything up to 750 bhp / litre was being pumped out. Then, once the sport returned to normal aspiration in 1989 that figure fell back, before steadily rising again. It wasn’t long before outputs crept back towards the 1000 bhp barrier, with some teams producing more than 300 bhp / litre in 2005, the final year of 3 litre V10 engines.
From 2006 to 2013, the regulations required the use of 2.4 litre V8 engines limited to 18,000rpm, with power outputs falling around 20 percent. However, the introduction of a Kinetic Energy Recovery System (KERS) in 2009, which captured waste energy created under braking and transformed it into electrical energy, ensured the teams had an extra 80bhp or so to play with for just over six seconds a lap.
Today’s ERS take the concept of KERS to another level, combining twice the power with a performance effect around ten times greater. ERS comprises two motor generator units (MGU-K and MGU-H), plus an Energy Store (ES) and control electronics. The motor generator units convert mechanical and heat energy to electrical energy and vice versa.
MGU-K (where the ‘K’ stands for kinetic) works like an uprated version of the previous KERS, converting kinetic energy generated under braking into electricity (rather than it escaping as heat). It also acts as a motor under acceleration, returning up to 120kW (approximately 160bhp) power to the drivetrain from the Energy Store.
MGU-H (where the ‘h’ stands for heat) is an energy recovery system connected to the turbocharger of the engine and converts heat energy from exhaust gases into electrical energy. The energy can then be used to power the MGU-K (and thus returned to the drivetrain) or be retained in the ES for subsequent use. Unlike the MGU-K which is limited to recovering 2MJ of energy per lap, the MGU-H is unlimited. The MGU-H also controls the speed of the turbo, speeding it up (to prevent turbo lag) or slowing it down in place of a more traditional wastegate.
A maximum of 4MJ per lap can be returned to the MGU-K and from there to the drivetrain - that’s ten times more than was possible with KERS, the ‘bolt-on’ recovery system ERS replaced in 2014. That means drivers have access to an additional 160bhp or so for approximately 33 seconds per lap.
For regulatory reasons the power unit is deemed to consist of six separate elements. These are the four ERS components, plus the internal combustion engine and the turbocharger. Should a driver use more than their permitted allocation of any one component he faces a grid penalty ranging from 10 to five places.
During a race drivers may use steering wheel controls to switch to different power unit settings, or to change the rate of ERS energy harvest. Such changes are controlled and regulated by the standard electrical control unit (ECU), mandatory on all F1 cars. But for all the things the driver can change from the cockpit, one thing he can’t do is start his own car. Unlike road cars, Formula One cars do not have their own onboard starting systems so separate starting devices have to be used to start engines in the pits and on the grid.
For safety, each car is fitted with ERS status lights which warn marshals and mechanics of the car’s electrical safety status when it is stopped or in the pits. If the car is safe, the lights - which are situated on the roll hoop and the rear tail lamp - will glow green; if not, they glow red. The lights must remain on for 15 minutes after the power unit has been switched off.