The Triple Stack: EVs + Solar + Battery = Maximum ROI
Most fleet managers evaluate EV economics in isolation — comparing the cost of an electric vehicle against its petrol equivalent. That's a mistake. The real business case emerges when you stack three technologies:
- Fleet EVs — Eliminate fuel costs entirely
- On-site solar — Generate free electricity during business hours
- Battery storage — Store excess solar for overnight/evening charging
When combined, these three technologies create a closed-loop energy system where your fleet runs on free, self-generated electricity for 60–80% of its charging needs.
"We installed a 30kW solar system on the depot roof in January. Our 8 fleet EVs now charge for free between 9am and 3pm. The battery handles the morning top-up before drivers leave. Our electricity bill for fleet charging dropped from $1,500/month to $280/month — an 81% reduction." — Fleet Operations Manager, Property Services Company, Parramatta (Cable Co client, installed March 2026)
The Numbers: 10-Vehicle Fleet, 5-Year Analysis
Scenario: Property Maintenance Company, Western Sydney
| Parameter | Value |
|---|---|
| Fleet size | 10 passenger EVs (BYD Seal, $52,000 each) |
| Daily driving | 80km average per vehicle |
| Charging need | ~160kWh/day total fleet |
| Solar system | 30kW rooftop (depot) |
| Battery storage | 20kWh (peak shifting) |
| Grid electricity rate | $0.35/kWh (business rate) |
| Solar generation | ~120kWh/day average (Sydney) |
5-Year Total Cost Comparison
| Cost Category | ICE Fleet (10 × Corolla) | EV Fleet (No Solar) | EV Fleet + Solar + Battery |
|---|---|---|---|
| Vehicle cost (after FBT/grants) | $350,000 | $370,000 | $370,000 |
| Solar + battery system | $0 | $0 | $55,000 |
| Fuel / electricity (5 years) | $90,000 | $30,000 | $8,000 |
| Maintenance (5 years) | $80,000 | $40,000 | $40,000 |
| Registration (5 years) | $40,000 | $30,000 | $30,000 |
| FBT saving (5 years) | $0 | -$155,000 | -$155,000 |
| NSW Kick-start grant | $0 | -$80,000 | -$80,000 |
| Solar export credits (5 years) | $0 | $0 | -$12,000 |
| 5-Year Total | $560,000 | $235,000 | $256,000 |
| Saving vs ICE | — | $325,000 (58%) | $304,000 (54%) |
Wait — the solar option costs slightly more than grid-only EV? Not quite. The solar system continues generating value beyond year 5 (25-year panel warranty), and the $55,000 investment pays back in under 3 years when you factor in building electricity offset (not just fleet charging).
The Real Comparison: Including Building Energy Offset
A 30kW solar system generates ~43,800kWh per year. Your fleet consumes ~58,400kWh per year. The excess solar (weekends, holidays, low-driving days) offsets your building's electricity consumption.
| Year | Fleet Charging Saved | Building Offset | Export Credits | Total Annual Benefit |
|---|---|---|---|---|
| Year 1 | $14,400 | $4,200 | $2,400 | $21,000 |
| Year 2 | $14,400 | $4,200 | $2,400 | $21,000 |
| Year 3 | $14,400 | $4,200 | $2,400 | $21,000 |
| Year 4 | $13,800 | $4,000 | $2,300 | $20,100 |
| Year 5 | $13,800 | $4,000 | $2,300 | $20,100 |
| 5-Year Total | $70,800 | $20,600 | $11,800 | $103,200 |
The $55,000 solar + battery investment returns $103,200 over 5 years — an 88% return, or 2.7-year payback.
Sizing Your Solar System for Fleet Charging
The Formula
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Required solar capacity (kW) = (Daily fleet kWh need × 1.3) ÷ Peak sun hours
Example: (160kWh × 1.3) ÷ 5 hours = 41.6kW ideal system
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The 1.3 multiplier accounts for weather variability, panel degradation, and system losses. In practice, a system sized at 70–80% of ideal still covers most charging needs because:
- Not all vehicles charge simultaneously
- Weekend/holiday generation builds battery reserve
- Grid top-up handles peak demand days
Recommended System Sizes by Fleet
| Fleet Size | Daily Charging Need | Recommended Solar | Recommended Battery | Estimated Cost |
|---|---|---|---|---|
| 5 vehicles | 80kWh | 15–20kW | 10kWh | $25,000–$35,000 |
| 10 vehicles | 160kWh | 30–40kW | 20kWh | $45,000–$65,000 |
| 20 vehicles | 320kWh | 60–80kW | 40kWh | $85,000–$120,000 |
| 50 vehicles | 800kWh | 150–200kW | 100kWh | $200,000–$280,000 |
Use our Solar System Cost Calculator and Battery Storage Calculator to get instant estimates for your specific site.
Government Incentives That Apply to the Full Stack
For the EVs
- FBT exemption: $15,000–$18,000 per vehicle (3-year lease)
- NSW Kick-start: $5,000 per passenger vehicle + $3,000 per charger
For the Solar + Battery
- Small-scale Technology Certificates (STCs): ~$3,500 rebate on a 30kW system
- NSW Energy Savings Scheme (ESS): Additional certificates for commercial solar
- Accelerated depreciation: Instant asset write-off for business solar systems
For the Charging Infrastructure
- NSW Kick-start charging grant: Up to $3,000 per AC port
- NSW Destination Charging (if publicly accessible): Up to 75% of costs
The Operational Advantages Beyond Cost
1. Energy Independence
Grid outages don't stop your fleet. Battery storage provides backup charging capacity for 1–2 days of normal operations.
2. Peak Demand Reduction
Battery storage shifts charging load off-peak, reducing your building's maximum demand charge — often the largest component of commercial electricity bills.
3. Vehicle-to-Grid (V2G) Revenue
Emerging V2G technology allows parked fleet EVs to export stored energy back to the grid during peak demand events. Early V2G trials in Australia are paying $0.50–$1.00/kWh for peak exports — a potential future revenue stream.
4. Carbon Reporting
Solar-charged EVs produce zero Scope 1 and Scope 2 emissions for fleet transport — increasingly important for ESG reporting and government tender requirements.
Cable Co's Integrated Approach
We design and install the complete system — solar, battery, chargers, and electrical infrastructure — as a single integrated project. This matters because:
- Single point of accountability — One contractor, one warranty, one maintenance contract
- Optimised design — Solar, battery, and charger sizing calculated together for maximum efficiency
- Load management — All systems communicate to prevent overload and maximise self-consumption
- Grant maximisation — We identify and apply for all applicable incentives across the full stack
Get Started
- EV Charger Cost Calculator — Estimate your fleet charging infrastructure
- Solar System Cost Calculator — Size and price your rooftop solar
- Battery Storage Calculator — Calculate battery payback with fleet charging
- Talk to our fleet team — Free site assessment for fleets of 5+ vehicles
Frequently Asked Questions
How much solar do I need to charge a 10-vehicle EV fleet?
A 10-vehicle fleet averaging 80km/day per vehicle needs approximately 160kWh of daily charging. A 30–40kW solar system in Sydney generates 120–160kWh per day on average, covering 75–100% of fleet charging needs. A 20kWh battery stores excess generation for early morning or cloudy day top-ups.
What's the payback period for solar + battery on a fleet depot?
Typically 2.5–3.5 years when the solar system offsets both fleet charging and building electricity. A 30kW system with 20kWh battery ($55,000 installed) generates approximately $21,000 in annual energy value, delivering payback in 2.6 years.
Can I charge my fleet entirely from solar?
In summer months, yes — a correctly sized system covers 100% of fleet charging. In winter, solar covers 50–70% with grid top-up for the remainder. Annual average self-sufficiency is typically 70–85% for a well-designed system.
Does battery storage make financial sense for fleet charging?
Yes, for two reasons: (1) it stores daytime solar excess for overnight/early morning charging when vehicles are parked, and (2) it reduces your building's peak demand charge — often saving $200–$500/month on commercial electricity bills independent of fleet charging.
What maintenance does a solar + battery + charger system need?
Solar panels: annual inspection and cleaning ($300–$500). Battery: monitoring only (no moving parts, 10-year warranty). Chargers: annual inspection and firmware updates ($150–$250 per charger). Cable Co offers bundled maintenance contracts covering all three systems.