Just a few weeks short of five years since IndyCar announced the impending introduction of hybrid power to the series, the premier American open-wheel racing series will finally step into the racing trend that’s existed globally for a decade and made its North American debut with IMSA in January 2023.

And it will do so with a wholly unique spec system that brought two of the fiercest competitors in the series – Honda Racing Corp. USA (formerly Honda Performance Development) and Chevrolet and Ilmor – together in late-2022, each taking one half of what is in its most simplistic terms a two-part ‘Energy Recovery System,’ investing in it, developing it, tinkering with it and, in August 2023, testing it together to push IndyCar to the hybrid starting line.

That debut comes this weekend at the Mid-Ohio Sports Car Course, four months later than planned to cap a project that was delayed multiple times due to the global pandemic, production and shipping delays, parts failures and shortages and, at times, an overzealous timeline. In the end, it comes with a never-before-used hybrid system that, along with IndyCar’s 2.2-liter twin-turbo V6 internal combustion engine, brings electronic propulsion to IndyCar for the first time in the series’ century-plus history.

Below is a detailed look at how the system works, how and why we got here and what fans can expect to see, hear and experience at the racetrack or their couches this weekend while watching the 80-lap race Sunday afternoon in-person or on NBC.

How did we get here?

Days before Will Power won the 2018 Indianapolis 500, IndyCar officials, in concert with its pair of longtime engine manufacturers, announced the future of IndyCar’s next engine formula: a 2.4-liter twin-turbo V6, to debut in 2021, that would upgrade the 2.2-liter ones that first rolled onto the grid in 2012 and which had run in twin-turbo form since 2014.

When using the push-to-pass overtake system, drivers would be equipped, under the new regulations with more than 900 horsepower – a level of power the series hadn’t seen in decades.

Curiously, though, hybrid power wasn’t at all part of the plan.

Fifteen months later, IndyCar came out with more news about the future of its engine – adding hybrid technology that would be rolled out in 2022, timed to the simultaneous release of a new car design that is yet to have remotely publicly taken shape.

Another year later, in October of 2020 and the throes of the COVID-19 pandemic, the three parties delayed the project to give themselves breathing room after a year of little progress due to shipping and production delays. In March of 2022, yet another delay was announced roughly one year before it’s then planned rollout, moving back the debut to March 2024. In December of that year, the three parties announced the largest change since the initial hybrid plans were onboarded – shelving the addition of the 2.4-liter engine and keeping the 2.2-liter version at least through 2026, to cut costs and free up Honda and Chevy to each take half of the ERS to develop with third parties unable to deliver for a variety of reasons.

The ERS that we’ll see on-track this weekend began testing at Sebring Aug. 16, 2023 with a pair of cars run by Penske and Ganassi. Despite logging more than 15,000 miles by late in the year, the system continued to have reliability concerns, preventing the manufacturing of enough parts for all 10 teams to participate in a planned 10-car test in early-December. With uncertainty as to when all 10 teams and their 27 full-time cars would be able to get a reliable version of the system to test, IndyCar’s hybrid system was delayed once more, pushing its debut beyond this year’s Indianapolis 500 and into early-July.

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What makes up IndyCar's hybrid system?

Among many, many smaller pieces and systems that make the ERS function, it’s essentially two parts that work in concert with each other: the Motor Generator Unit (MGU) and the Energy Storage System (ESS). The MGU, made by Empel in collaboration with Chevy and Ilmor, captures energy derived by the car under braking that would typically be lost as heat, turns it into electricity and sends it to be stored in the ESS.

The latter unit is made up of 20 supercapacitors – highly effective, small, powerful tubes used for storing energy designed by Skeleton alongside HRC USA.

Where are the MGU and ESS in the car?

The components that make up the ERS are housed in a previously open space in the back of the car – the bellhousing – situated between the ICE and the gearbox that used to act as a spacer and a decade ago housed now defunct engine equipment. The space is roughly the size of a milk crate and adds just over 100 pounds to the car compared to the minimum weight it ran at two weekends ago at Laguna Seca.

How does the system work?

The process to fill the ESS with energy that can be deployed back into the rear wheels of the car and produce quick bursts of energy, a process called regeneration (or ‘regen’ for short), starts in one of two ways: either automatically by how the engine control unit (ECU) is programmed to harvest energy at certain levels of throttle or brake pressure, or manually by the driver, either by pressing a button (for a standard pre-set amount of ‘regen’) or squeezing a clutch paddle on the back of their steering wheel that gives the driver true control of how much regen they want to see. The latter process almost acts as an additional brake pedal that can marginally slow the car and then hold onto that energy derived under braking.

That built up energy harvested under braking is then sent by the MGU to the ESS where it’s stored until a driver wishes to deploy it – a process that drivers have full manual control over and which is sparked by the press of a button similar to the push-to-pass overtake system. When a driver wishes to deploy the stored hybrid energy, the ESS delivers that energy back to the MGU, which then delivers more power to the engine, gearbox and driveshaft to make for an additional 60-horsepower boost.

When combined with the separate 60hp push-to-pass system, IndyCar drivers will now have as much as 800hp at their fingertips if using the ERS and the P2P system simultaneously.

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How will this work on ovals?

Because drivers do so little – if any – braking under natural driving conditions on an oval (where six of the final nine races of the season will be run) the parties involved in the development of the ERS imagined the clutch paddle system that will receive the bulk of its use on IndyCar’s various oval tracks. When cars run along in the draft and wish to stay there, rather than trying to pull a run on the car ahead and make a pass, they’re typically lifting their foot off the throttle rather than dragging the brake.

Now, by squeezing the clutch paddle, drivers can keep their foot on the gas and still slow down, with a squeeze of the paddle dragging the brake at a level determined by the pressure the driver delivers. This builds the energy stores in the system without the driver having to mess with braking on an oval – an action that is largely foreign under typical racing conditions.

In a perfect world, drivers will ride along in the draft on ovals, fill up their battery stores and then at their preferred moment, deploy that extra energy in an attempt to make a pass, giving IndyCar drivers the use of an overtake-like system on ovals that they haven’t had in several years. Ideally, this could generate more passing in oval races.

How much power does the system possess?

At a 100% state of charge, the ESS operates at 60 volts and 2,000 amps, a relatively safe amount of power that doesn’t necessitate any kind of special safety equipment – unlike IMSA’s GTP hybrid systems that feature 700-800 volts. The ESS can hold up to 320 kilojoules per lap as the maximum amount of energy a car can store and use during a single lap around a given track, but IndyCar plans to vary that actual ceiling on a race-by-race basis, depending on track length and other factors.

It takes roughly 4.5 seconds to fully charge the ESS and the same amount of time to deploy all that energy. Within the per-lap limits, drivers can use this an unlimited amount of times during a race – different than the push-to-pass system that allows for longer bursts of a similar amount of horsepower, but only a maximum of 150 or 200 seconds of that energy use per race, depending on the specific rules for that course.

And this whole system can be charged by a simple 12 volt wall plug-in back in the garage, or with the engine running on idle.

Other than additional horsepower, does the system come with any other capabilities?

The system retains 30 extra volts of power so cars can be started on their own after a spin or stall on-track – ideally meaning we’ll see fewer short yellow or red flag stoppages during practice, qualifying and races. It also means drivers can start the car themselves on pit lane.

That extra reserve bank of power will also now power the car running in reverse. Instead of a specific gear in the gearbox meant for driving backwards out of a barrier or gravel trap – like one would have in their everyday road car – drivers will shift into first gear and trigger the MGU to spin the driveshaft in reverse so the car rolls backwards – ideally it’s easier than finding the tough-to-trigger reverse gear.

Separate from its use on race days, drivers will also have this additional boost during qualifying rounds. Mastering that, at least initially, may be the most impactful way the ERS is felt across race weekends.

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How will we know when a driver is harvesting or deploying hybrid power?

Indy cars won’t sound any different in this new hybrid era. They won’t almost silently roll off pitlane like IMSA’s GTPs or WEC’s LMDH machines do, and there is no ‘whirring’ sound when they’re harvesting. But NBC is rolling out a new graphic for the remainder of the race weekend broadcasts this year as it closes out its time as IndyCar’s exclusive media partner to illustrate when and how each car is using the system. Similarly, IndyCar’s mobile app will now have a similar function.

Will the cars be faster?

Not yet, at least – or, at least not because of the addition of the ERS. IndyCar’s next two race weekends come at tracks that have been partially (Iowa Speedway) or wholly (Mid-Ohio) repaved since last year’s races, meaning the paddock is destined to set recent-term records and flash faster speeds overall.

But elsewhere, drivers suggest that at best, speeds will be relatively flat – and could even be slower. In addition to the fact that the system is still in its relative infancy and teams, drivers and OEMs are working to discover how to best extract maximum performance, the system’s brief bursts of 60 extra horsepower are not enough to counteract the additional 100 pounds it brings to the car.

Series and engine manufacturer officials have said, though, that there exists a belief that the system, when fully turned up in a year or two when its reliability isn’t being protected so fiercely, the system could produce bursts of 150 horsepower, which could lead to the retirement of the push-to-pass system while still allowing for an extra 30 horsepower of speed when in use.

This article originally appeared on Indianapolis Star: Explaining IndyCar's new Energy Recovery System that delivers hybrid technology