Power flows both ways.

Send that power to the grid and it is called V2G. A house makes it V2H, an office or a school V2B. Collectively, V2X. What it buys is a car that keeps the lights on through an outage, and a utility with somewhere to draw from when demand spikes. ComEd's two questions were whether any of that beats the alternatives environmentally, and how to site it so that low-income and environmental-justice communities are where it lands first.

Two questions, two methods, and one place they had to meet. The environmental model produced avoided pollution per kilowatt-hour. The spatial analysis knew who was breathing it. Multiplying one by the other gives the criterion the ranking turns on: tons avoided times the population exposed.

The word doing the work is "prospective." Bi-directional charging today works in demonstrations and is still years from a showroom, and the study had to estimate its impact out to 2040 on a grid that changes fuel mix every year. So the model runs the grid three ways. Fast decarbonization, slow, and the middle case. Uncertainty comes from Monte Carlo runs rather than from one confident number handed to a client.

Engineers attack the assumptions that decide the answer, so those went into the pitch first. Every system had to be measured against the same unit, one kilowatt-hour of energy actually delivered, defined separately for each of the five, so nothing could win by grading itself on a friendlier metric. The boundary sat at the use phase, where the disagreements live: what the inverter loses, and how much battery wear you can fairly charge to V2X duty rather than to the daily commute. Every assumption went into a pedigree matrix — the standard way an assessment records how good its own data is — so ComEd's reviewers could grade the inputs without taking my word for anything.

Each scenario then had to carry real numbers. Cycles per year, energy per discharge, round-trip efficiency, battery capacity at end of life. Those four decide the result. The degradation split decides it hardest. Get it wrong and V2G looks either free or ruinous.

All five systems avoid emissions today, and V2G avoids the most: about 0.11 kilograms of CO₂e for every kilowatt-hour it sends back on the 2025 base-case grid. What changes is the ranking. By 2035 the bi-directional systems and the stationary battery have crossed the axis on the base-case and optimistic grids, adding emissions rather than avoiding them, because too little dirty peak generation is left to displace. Managed charging, which only changes when the car draws power, keeps working. It grows about five-fold by 2040, closer to six if decarbonization runs fast and under four if it stalls, and it passes V2G around 2030 on the base-case grid and 2032 on either of the others.

One result argued against a program ComEd already runs. In the optimistic 2030 case the model puts managed charging at plus 0.008 kilograms of CO₂e per kilowatt-hour. It adds emissions instead of avoiding them. Enough clean generation arrives that off-peak hours run dirtier than peak ones, 0.69 against 0.68, so a time-of-use rate calibrated for today's grid would be moving demand into worse power. The fix is to operate against live grid-emissions signals instead of a fixed clock.

Explore the numbers:

Environmental benefit means little if the technology lands only in wealthy zip codes. The second half of the study ranked every part of ComEd's territory for where V2X should go first. That means comparing places on criteria that do not share a unit: income, energy burden, distance to an existing charger, exposure to a peaker plant. An analytical hierarchy process turns ComEd's own priorities into weights by forcing a choice between criteria two at a time. TOPSIS then scores each place by how close it sits to the best achievable profile and how far from the worst. Illinois' environmental-justice, R3 and low-income designations came in as criteria of their own.

The atlas below rebuilds that analysis from the project's own data layers. ComEd-territory zip codes, census tracts bridged through the HUD crosswalk, DOE LEAD energy burden, the 21 peaker plants with their emissions and demographics, and EV registrations per zip from the Illinois Secretary of State for 2019 through 2025, projected forward on a logistic growth curve. It tests one idea: that keeping peaker plants switched off pays its largest social dividend in EIEC communities, Illinois' designation for equity investment eligible communities, where high energy burden and peaker pollution and a growing fleet of dischargeable cars all sit on top of each other.

The study closed in December 2025. ComEd received the full assessment, the spatial equity ranking, the integrated recommendations, and the ArcGIS layers behind them. The uncertainty analysis went over as a working Power BI model rather than as a set of results, so ComEd can change a parameter or drop in the next GREET and NREL releases and re-run the Monte Carlo simulations without us.

Walker-Miller and ICF built the outreach materials with ComEd, working topic by topic through outline and draft. Walker-Miller's practice is going into these communities and doing the engagement in person, so that material came from people who had been in the room. I designed the survey instrument, starting from a review of how other utilities have financed equitable access: on-bill programs, credit-union loans, community co-ops. Then ten rounds of cognitive interviewing against simulated residents from across the territory, revising after each round, until "on-bill financing" read as "small monthly payments added to your electric bill" and the charging question had an answer for people with nowhere at home to charge. It shipped in two versions, a long one for analysis and a short one for town halls. The strategic findings held. Bi-directional charging makes its strongest climate case in the next decade. Its resilience case holds at any grid mix. Time-of-use programs will need emissions-aware controls as that grid changes.

Years of sitting in engineering reviews is what made this one possible. I knew which assumptions they would want to argue with before I wrote them down, and I built the pedigree matrix so they could.