Expressway charging hub · 1.92 MW container

The site and the problem

A DC fast-charging hub on the Mumbai-Pune Expressway (NHAI) operated by a Tata Power EZ Charge partner initially planned three 240 kW CCS2 chargers (total 720 kW peak output) on a utility grid connection limited to 200 kW. The initial design pushed load-shedding onto the grid during simultaneous charging events: if two vehicles charged in parallel, the system would slow-charge one bay to 60 kW while running the other at 240 kW, degrading user experience and risking grid violation fines.

The operator faced a choice: either negotiate a costly 800 kW upgrade with the DISCOM (₹45-60 lakh, 6-12 month wait) or use a BESS to buffer the solar and grid trickle, allowing three chargers to run at full 240 kW simultaneously from stored energy. The site had rooftop and canopy space (480 kWp available) but no way to absorb midday PV overage during low-traffic hours.

Sizing the system

Traffic patterns on the expressway showed 60% of charging events occurred between 10 AM and 4 PM (midday, when solar peaks). A 1.92 MW container-scale BESS (IZ-1920K-3P) was sized to store 3.84 MWh of energy. This allowed the system to buffer 480 kWp solar generation during daylight and release it at full 720 kW (3 x 240 kW chargers) for 5+ hours, even if grid supply remained capped at 200 kW. The payback model incorporated avoided DISCOM upgrade costs (₹55 lakh) plus the ability to charge premium rates during peak hours, recovering capex in 4.2 years.

The 1.92 MW IZ-1920K-3P unit was chosen because no smaller Infozeb SKU could sustain three 240 kW chargers simultaneously. A second smaller cabinet would have duplicated control complexity; one large container simplified OCPP (Open Charge Point Protocol) orchestration and thermal management.

Engineering details

The IZ-1920K-3P is a containerised unit housing LiFePO4 cells across 500 x 48 V, 200 Ah modules. The three 240 kW chargers interface directly with the BESS AC output (1.92 MW rated, 2.3 MW peak for 3-second bursts). A 200 kW grid connection provides the baseline supply; the BESS absorbs solar overage and fills in gaps when grid pulls approach 200 kW. The system operates in peak-shaving mode: during high-traffic hours, the BESS discharges to deliver the full 720 kW across three bays without tripping the grid import limit.

OCPP 1.6J and OCPP 2.0.1 protocol integration was critical. The cloud EMS at portal.infozeb.energy runs a smart charging scheduler: it queries charger availability every 10 seconds, estimates state-of-charge, and decides whether to slow-charge (hold SoC at 60% for flexibility) or fast-discharge (bleed the battery at 3 PM when peak solar clouds appear). All three chargers report OCPP status to a Tata Power backend, which logs session revenue and health metrics.

Key technical aspects of the expressway hub:

• LFP cells, 6,000-cycle chemistry (≈12 years in a public charging duty cycle where 90% of days involve 1-2 charge/discharge cycles)
• Peak discharge: 2.3 MW for up to 3 seconds (simultaneous 720 kW charger supply plus 200 kW grid import)
• Three-phase 1.92 MW AC output, 415 V, 50 Hz stabilised supply to chargers
• OCPP 1.6J and 2.0.1 protocol support for charger orchestration
• Modbus interface to existing energy management system for solar forecasting
• Active thermal management rated to 45°C ambient (expressway mid-ground ambient often reaches 42-48°C May-June)

What changed after commissioning

The operator could now run three simultaneous 240 kW charging sessions without grid negotiation or overload risk. During the first 90 days, average charging sessions increased from 24/day to 41/day, a 70% jump. Users no longer experienced slow-charge queuing or "charger unavailable" messages. Peak midday revenue increased by ₹18,000/month because the operator could charge premium rates (₹2.80/kWh vs ₹2.10/kWh) during low-traffic buffer hours, knowing the BESS would supply the burst when travel demand peaked.

Solar self-use improved dramatically. The 480 kWp canopy previously exported 35-40% of midday generation back to the grid at a ₹1.50/kWh buyback rate (poor economics). Now, 86% of solar is stored in the BESS and sold to vehicles at ₹2.40-2.80/kWh, a 60% margin improvement. Grid pull during peak hours remained at 200 kW (as contracted), eliminating violation penalties and DISCOM escalation notices.

Lessons we carried into the next deployment

Public charging hubs operate under different physics than residential or factory sites. The next EV charging deployment benefited from three hard-won insights.

• OCPP orchestration is not optional. Our first draft relied on chargers to "request" power from the BESS. In practice, chargers operate independently and don't coordinate. We now run a command-and-control scheduler that monitors all three charger states in real time and preemptively adjusts BESS discharge to prevent voltage dips. Without this, users see slow-charge fallback and abandon the site.
• Traffic-driven seasonality demands higher battery capacity than solar alone justifies. In December-January (tourist season on highways), peak charging demand is 40% higher than June. We now size the BESS to 1.5-2x the PV peak power, not 1x, to smooth seasonal volatility without relying on grid as backup.
• Thermal management in outdoor containers is harder than indoor cabinets. The 1.92 MW container sits in full sun on an expressway median. We added a 20 kW air-cooled heat exchanger (₹3.8 lakh) to maintain 40°C cell temps even in 48°C ambient. Subsequent hub designs budget 8-10% capex for thermal as standard.