Mapleton Estate: EV + Battery Integration
A 5,800 sq ft home on Boulder's Mapleton Avenue needed to support a new Tesla Model 3 and wanted resilience during grid outages. We delivered a 200A panel upgrade, Tesla Wall Connector, and Powerwall backup system.
The Challenge
The homeowners—a couple in their early 60s—had just purchased a Tesla Model 3. Their home, built in 1992, had a 100A electrical panel, typical of pre-2000 construction. Adding a Level 2 EV charger (30A) plus existing loads (HVAC, kitchen appliances, water heater) would exceed the panel's capacity. Additionally, they wanted peace of mind: Colorado's Front Range experiences occasional grid disruptions during severe weather. A battery backup system could keep critical loads running during outages.
Timeline: March 2024 (initial consultation) to June 2024 (system commissioning).
Our Approach
- Energy Audit: We reviewed 12 months of utility bills (average 18 kWh/day) and conducted an on-site load assessment. Peak demand was around 32A (heating + AC), leaving minimal headroom for EV charging.
- Panel & Charger Sizing: We specified a new 200A main panel (125 spaces) and a 240V 40A Tesla Wall Connector, allowing simultaneous charging and normal home loads without tripping breakers.
- Battery Integration: We sized a 13.5 kWh Tesla Powerwall for 4–6 hours of critical-load backup (refrigerator, HVAC, lighting, medical devices). A separate critical-load sub-panel ensures the battery isn't wasted on non-essential circuits.
- Permitting & Coordination: We applied with the City of Boulder (electrical and structural) and coordinated with Public Service Company of Colorado for the meter upgrade.
- Installation: Our team removed the old panel, installed the new one with all existing breakers moved and new circuits added, ran conduit from the panel to the Wall Connector, and installed the Powerwall with automatic transfer switch.
- Commissioning & Training: We tested the ATS (automatic transfer switch) by simulating a grid outage. The Powerwall seamlessly took over. We trained the homeowners on monitoring, charging schedules, and backup-power operation.
The Details
System Specifications
| Component | Specification |
|---|---|
| Main Panel | Siemens 200A, 125 spaces, with main breaker disconnect |
| Service Upgrade | 100A → 200A from PSCo meter. Trench work: 60 linear feet |
| EV Charger | Tesla Wall Connector, 240V 40A, hardwired with 6/2 copper wire |
| Battery Storage | Tesla Powerwall (13.5 kWh, 5 kW continuous) |
| Critical-Load Sub-Panel | 60A Siemens sub-panel with ATS (automatic transfer switch) |
| Grounding & Surge Protection | 240V 40A DC disconnect + combined AC/DC surge suppression |
| Monitoring | Tesla app + custom home-automation dashboard |
Project Timeline
- Week 1: Energy audit and initial design ($500 audit fee, credited toward project).
- Week 2–3: Final engineering, 40-page proposal with load calculations, permitting requirements, and ROI analysis delivered.
- Week 4–6: City of Boulder electrical permit approval (3 weeks). PSCo meter upgrade scheduling.
- Week 7: On-site installation: panel replacement (2 days), Wall Connector and conduit (1 day), Powerwall installation and ATS wiring (2 days).
- Week 8: City electrical inspection (passed first-time). Utility meter swap (PSCo technician, 1 day).
- Week 9: System commissioning and homeowner training.
Financial Summary
Costs
- Panel Upgrade (200A): $3,200
- Service Upgrade (100A → 200A, PSCo): $800 (utility charge)
- Tesla Wall Connector & Installation: $1,500
- Tesla Powerwall (equipment + installation): $11,000
- Critical-Load Sub-Panel & ATS: $1,800
- Permits & Inspections: $600
- Labor (design, permitting, installation, commissioning): $3,800
- Total Project Cost: $22,700
Financial Incentives & Payback
- Federal ITC (30% battery credit): $3,300 (applied to 2024 taxes)
- Colorado state rebate (battery storage): $2,000 (PSCo time-of-use program)
- Net Project Cost After Incentives: $17,400
Payback Analysis
Annual Savings: ~$1,800 (EV fuel cost vs. gasoline, plus off-peak charging optimization and reduced peak-demand charges during Powerwall operation).
Simple Payback Period: 9.7 years (based on annual savings and assuming no change in electricity rates).
10-Year Net Benefit: $1,200 (conservative; actual is likely higher due to rising utility rates and gas prices).
Lessons & Key Takeaways
Panel upgrades are capital-intensive but necessary: The homeowners initially balked at the $3,200 panel cost, but without it, the EV charger would have demanded additional expensive circuit-balancing. A 200A panel solved the problem cleanly and future-proofs the home for solar or additional loads.
Battery payback isn't about dollars alone: The Powerwall adds $11,000 to the cost but provides intangible resilience. During a 4-hour grid outage in June 2024, the homeowners' home remained comfortable while neighbors lost power. They valued that peace of mind highly.
Critical-load sub-panels are essential: The ATS automatically isolates critical circuits (HVAC, fridge, lighting, medical equipment) from non-critical loads (pool pump, hot tub, clothes dryer). This maximizes battery run-time during outages.
Transparency matters: We provided a one-line electrical diagram and detailed load calculations in the proposal. The homeowners understood *why* each component was required, reducing scope creep and change orders.
Results & Homeowner Feedback
"We weren't sure if the Powerwall was worth it until the grid went down last summer. The house stayed cool while our neighbors were running to hotels. Now we wouldn't be without it. Solstice's team was professional, transparent, and delivered on every promise."
— Homeowners, Mapleton Ave
System Performance (6-Month Operating Data)
- EV Charging: 125 charges, averaging 25 kWh per charge (consistent with Tesla Model 3 efficiency).
- Powerwall Cycles: 42 charge/discharge cycles over 6 months (averaging 1 cycle per 4–5 days). Battery health: 99% (no degradation).
- Peak Demand Reduction: Home peak demand dropped from 32A to 24A average, due to smart charging scheduling during off-peak hours.
- Outage Resilience: One grid outage (4 hours). Critical loads ran continuously. Backup power reserve: 65% at outage end.
References & Standards
- National Electrical Code (NEC) Article 625 — EV supply equipment
- Tesla Powerwall Specifications
- Public Service Company of Colorado — Service upgrade standards
- City of Boulder Electrical Services — Local code amendments
Ready for Your Own Project?
Contact us to discuss your EV charging, battery backup, and panel upgrade needs.
Schedule Consultation