Off‑Grid EV Charging for Fleets — Volt Vault

Fleet electrification runs headlong into a bottleneck — reliable charging power where vehicles actually park. Grid upgrades drag on for months or years. Meanwhile, fleets need solutions today. Off grid EV charging answers that need by bringing power generation to the lot itself. Volt Vault, developed by US Energy and highlighted in a recent Munro session, demonstrates how mobile, fuel-flexible charging can bypass delays, cut costs, and accelerate electrification.

The infrastructure challenge

Parking lots were never designed for megawatts of draw. A few lamps may require 3 kW, but a dozen Level 2 chargers can demand more than 90 kW. Add in a couple of DC fast chargers and the load spikes by another 200 kW. Meeting that demand often requires trenching, switchgear, new transformers, or even substation upgrades. Timelines extend from 18 months to five years, stranding capital in the ground and delaying vehicle deployment.

Fleets cannot wait. Delivery schedules, lease expirations, and regulatory mandates push them to move faster. A mobile charging unit removes the bottleneck by skipping utility construction. It provides immediate power on-site — and relocates if routes or depots change.

Volt Vault’s architecture

Volt Vault is built around a heavy-duty 11.1-liter natural gas engine rated at 180 kW. The generator delivers 480 V three-phase output directly into a DC fast-charging cabinet. Two ports share roughly 170 kW of available load, charging vans, buses, or trucks in minutes. For resilience, a dedicated 60 kWh lithium iron phosphate pack runs HVAC, controls, and monitoring. That pack never charges vehicles — traction charging comes straight from the prime mover.

The design is deliberately simple. Standard industrial parts, coil-on-plug ignition, direct-drive cooling fans, and weather-resistant louvers make service predictable. Operators press a single green button to start the unit, while indicator lights and emergency stop ensure clarity. Lean design minimizes training needs and reduces error risk.

Configurations for every use case

Volt Vault ships in four main versions:

Level 3 Classic — Dual-port DC fast charging up to ~170 kW shared. Ideal for high-utilization fleets needing quick turns.
Level 2 Array — Sixteen 9.6 kW ports for overnight delivery vehicles with predictable dwell. One customer charged 32 vans daily for months with high uptime.
Flex — A hybrid model combining about eight Level 2 ports with two ~30 kW DC fast chargers. Perfect for mixed fleets that require both overnight and mid-day boosts.
Light — A compact 20-foot trailer delivering 60 kW DC via two ports. It can run on propane, making it attractive for rural yards without natural gas pipelines.

All models support NACS adapters, RFID or credit card payment, and remote connectivity via a Cradlepoint 4G/5G gateway. Optional disaster-response kits bundle hoses, grounding cables, and tools so crews can deploy in the field without delays.

Fuel flexibility

Natural gas remains the primary fuel. Units connect to existing pipeline service at low pressure or draw from high-pressure tube trailers — a “virtual pipeline” that delivers compressed natural gas anywhere. Propane variants expand siting options in regions without pipeline infrastructure. Critically, the same engine can operate on renewable natural gas captured from dairies or landfills, reducing lifecycle emissions.

This fuel flexibility positions Volt Vault as more than a stopgap. As RNG supply grows, carbon intensity falls without changing the hardware.

Economics in practice

Energy cost drives adoption. On-site generation via natural gas can deliver electricity for about $0.14/kWh nationally, and sometimes as low as $0.10. By comparison, fleets in California can face $0.40–$0.60/kWh grid rates during peak hours. Running Volt Vault in those windows cuts cost by two-thirds.

In transportation terms, that equates to around $0.04 per mile of delivered energy — far below unleaded gasoline at $0.22–$0.23 per mile in some markets. Beyond savings, mobile charging delivers schedule control. Vehicles charge when they need to, not when the utility says capacity is available.

Environmental considerations

Critics often question burning gas to charge EVs. The math tells a different story. Replacing diesel with gas-fired generation lowers emissions per mile, especially when fleets adopt renewable natural gas. Methane captured from landfills or farms has a global warming potential more than 20 times higher than CO₂. Turning that methane into CO₂ while generating electricity results in net greenhouse-gas reductions.

In Wisconsin, where coal still dominates the grid mix, Volt Vault running on RNG achieves a cleaner carbon profile than utility power.

Operational details engineers care about

Load sharing — DC output automatically splits between two vehicles, maximizing throughput.
Thermal management — Heavy-duty radiators prevent derate even at full 180 kW output on hot days.
Serviceability — Clear compartmentalization and conventional parts keep downtime short.
Controls — Remote telemetry and firmware updates flow over cellular networks.
Safety — Grounding kits, labeled stops, and standard lockout points match industrial practices.

These engineering choices show a consistent lean design philosophy — build around proven modules, simplify training, and minimize hidden factory debt.

Use cases beyond fleets

The mobility of Volt Vault opens opportunities beyond depot charging. Disaster relief is a prime example. A unit and a tube trailer can establish Level 3 charging in a disaster zone within days. Military test ranges have already used the system to electrify remote proving grounds. Leasing companies also benefit — they can recover charging assets when moving to new facilities, avoiding stranded capital.

Emerging applications include car-wash operators that want to share onsite power. By integrating a transfer switch, owners can run building loads when chargers are idle, capturing cheap electricity from the same generator.

Competitive landscape

Competitors typically follow one of two models: large stationary battery packs or smaller generators aimed at passenger vehicles. Battery packs still rely on grid charging, which leaves fleets vulnerable to the same infrastructure delays. Volt Vault’s prime power design avoids that trap. Its focus on B2B fleets rather than retail charging distinguishes it from rivals.

Roadmap

Future designs include compact 20-foot enclosures, a 10 percent power increase, and lower emissions. Waste-heat utilization also sits on the roadmap, potentially providing building heat or hot water from captured thermal energy. Each step continues the lean improvement cycle: reduce cost, improve efficiency, and expand flexibility.

Conclusion — bring the power with you

Off grid EV charging changes the pace of electrification. Volt Vault proves that fleets can sidestep infrastructure delays, cut per-mile energy cost, and deploy vehicles sooner. Its modular architecture, fuel flexibility, and serviceable design align with lean principles Munro & Associates values — immediate impact with long-term adaptability.

Fleet managers facing grid bottlenecks should not wait years for transformers. Instead, they can bring power to the parking lot, pressure-test their electrification strategy, and adapt with data. With Munro’s teardown insights and cost benchmarking, Volt Vault stands as a practical bridge to a fully electrified future.

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