Case study·Newmarket, Ontario·Tesla Certified Installer

Newmarket Home Microgrid
54 kWh of Powerwall, solar, and a garage built around it

Q: Why two Powerwall 3s and two Expansions instead of one?

For power and for solar inputs. Each Powerwall 3 supplies 11.5 kW, so two give 23 kW, enough to run the whole house with the heat pump, hot tub and pool pump on. The Expansions add stored energy, for 54 kWh in all. Two Powerwalls also bring six solar inputs, one for each string on this roof.

Q: Does a home battery over 12 kW need an ESA plan review in Ontario?

Yes. A battery or solar system with an output rating over 12 kW needs an Electrical Safety Authority plan review before the work starts. The threshold rose from 10 kW in July 2026. An export limit does not lower the rating, so this 23 kW system went to plan review.

Q: Does the EV charge from the batteries during an outage?

No. A contactor wired to the Gateway disconnects the charger the moment the grid goes down, and reconnects it after five minutes of steady grid. A full car charge would otherwise use a large part of the stored energy.

Q: Can solar connect straight to a Powerwall 3?

Yes. The Powerwall 3 has a solar inverter built in. On this home the six strings land on the six inputs of the two units, so there is no separate solar inverter on the wall.

Q: Did the house need a bigger electrical service?

No. The demand calculation on the home's own utility data came to 136 A on its 200 A service, with about a third in reserve.

Q: Why put a subpanel in the garage?

Because that is where the new loads are. One feeder from the house serves the heat pump, lighting, receptacles and roof de-icing over short runs, and leaves spare spaces for the next addition.

A family home turned its garage into the energy centre of the house: four Tesla battery units, 13.5 kW of rooftop solar, an EV charger, a ductless heat pump, new LED lighting and a subpanel to run it all. We engineered it end to end, from the home's own utility data to the utility connection and the Electrical Safety Authority plan review.

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Garage subpanel, two Tesla Powerwall 3 battery stacks and a Level 2 EV charger in a Newmarket home — Subpanel and Powerwalls, Newmarket

54 kWh

Two Powerwall 3s plus two Expansions

23 kW

Output: the whole house, every circuit

13.5 kW

Rooftop solar, about 90% of a year's use

200 A

Service kept: 136 A calculated

In the garage

Newmarket Home Microgrid

The house

A garage that became the energy centre

The owners were renovating their three-bay garage into a gym and workshop, and wanted the house ready for what comes next: solar, an EV, heat pump comfort and backup for the whole home, without a generator.

The house uses about 13,200 kWh a year and already had a hot tub and a pool. Rather than bolt equipment on one piece at a time, we planned it as one system: a garage subpanel for the new loads, and batteries sized to carry the whole house and store its solar.

What they asked for

Whole-home backup, automatic, no generator
Solar that pays its way all year
A heated and cooled garage gym and workshop
EV charging that never drains the backup

What we brought

Load assessment on a year of utility data
Engineered single-line drawing and layouts
Utility connection, start to finish
ESA permits, inspections and plan review

The systems

Six systems, one plan

What went in, and why each one is there.

Battery storage

Two Tesla Powerwall 3s and two Expansions

54 kWh stored · 23 kW output

What we did: Four Tesla battery units on the garage wall, each Expansion mounted behind its Powerwall. Two inverters supply the house; the Expansions add stored energy.
Why: Whole-home backup with no load left out, and enough storage to move the house's evening use to cheaper hours every day.

Rooftop solar

13.5 kW of solar, straight into the Powerwalls

27 panels · about 11,500 to 12,000 kWh a year

What we did: Four roof faces, six strings, wired into the six solar inputs built into the two Powerwall 3s. No separate solar inverter.
Why: Roughly 90% of what the home uses in a year, and it recharges the batteries during a long outage.

EV charger

48 A Level 2 charger

11.5 kW on a 60 A circuit

What we did: Hard-wired charger on the block wall beside the batteries, fed from the main panel.
Why: A contactor drops the charger the moment the grid goes down, so the car never drains the house battery. It reconnects after five minutes of steady grid.

Garage subpanel

New 100 A garage subpanel

30 spaces, fed from the main panel

What we did: One feeder from the house to a subpanel in the garage. The heat pump, lighting, receptacles and roof de-icing all start here.
Why: Short runs to the loads, the garage's circuits in one place, and spare spaces for whatever comes next.

Ductless heat pump

Multi-zone heat pump, two wall heads

35 A circuit · room for a third head

What we did: A cold-climate outdoor unit with two ductless heads in the garage. We ran the circuit and disconnect; our HVAC partner set the heads and line sets.
Why: The garage became a heated and cooled gym and workshop, all year, with no gas.

LED panel lighting

Nine 2 x 4 ft LED flat panels

Two lighting circuits · three-way switching

What we did: Three panels over the parking bays on three-way switches at the entry, six over the gym and work area. Three spare ceiling boxes are capped for later.
Why: Even, shadow-free light across the whole garage on very little power.

Energy arbitrage

How 54 kWh earns its keep every day

Backup is the insurance. The daily value is timing: make or buy power when it is cheap, use it when it is expensive. Tap a time of day.

Solar runs the house and refills the batteries

Grid

Taking the surplus

Solar

Up to 13.5 kW

Batteries

Charging from the sun

House

Running on solar

Solar feeds the house first, then fills the 54 kWh. Anything left goes out to the grid, up to the 12 kW export limit agreed with the utility, and earns net-metering credit on the bill.

Credits carry forward to the darker months.

ESA plan review

Over 12 kW, so it gets reviewed first

Most home battery jobs never need a plan review. This one does, and we treat that as part of the build, not a hurdle at the end.

Output rating of the systemTwo Powerwall 3 inverters at 11.5 kW each

23 kW

Plan review above 12 kW

Export limit at the meterSet in the Powerwall's power control, agreed with the utility

12 kW

The home's average drawAbout 13,200 kWh over the last year

1.5 kW

The export limit does not decide it, the output rating does. Any battery or solar system rated over 12 kW needs an Electrical Safety Authority plan review before the work. This one is 23 kW, so we prepared the full engineering package: single-line drawing, layouts, the Code demand calculation, the utility's approvals and the equipment certifications.

What we measured

No bigger service, by the numbers

We ran the Code demand calculation on the home's own utility data, with every new load included.

Calculated demand, by the Code method on the home's own utility dataHouse, hot tub, pool, garage, heat pump and EV charger

136 A

Existing serviceKept as is

200 A

Result: no bigger service. 136 A against 200 A leaves about a third in reserve. Solar is a source, not a load, so it does not change the calculation.

The process

How a project like this comes together

1
Data review. A year of the home's utility data shows how the house actually runs, hour by hour.
2
Load assessment and sizing. The Code calculation confirms the service, and the batteries and solar are sized to the real loads.
3
Design and approvals. Single-line drawing, layouts, the utility connection agreement, ESA permits and the plan review.
4
Build. Garage subpanel and circuits, heat pump, lighting and EV charger, then the batteries and Gateway in a one-day service cutover.
5
Commissioning and handover. ESA inspection, an outage test, the export limit set, and the owners set up in the Tesla app.
6
Solar connects. The panels land straight on the Powerwalls' built-in solar inputs, with no separate inverter.

Solar, storage, EV and heat pump, planned as one system

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Straight Answers

Newmarket Microgrid Questions

The kind we would give before you commit a dollar of capital. Tap a question.

Why two Powerwall 3s and two Expansions instead of one?

For power and for solar inputs. Each Powerwall 3 supplies 11.5 kW, so two give 23 kW, enough to run the whole house with the heat pump, hot tub and pool pump on. The Expansions add stored energy, for 54 kWh in all. Two Powerwalls also bring six solar inputs, one for each string on this roof.

Does a home battery over 12 kW need an ESA plan review in Ontario?

Yes. A battery or solar system with an output rating over 12 kW needs an Electrical Safety Authority plan review before the work starts. The threshold rose from 10 kW in July 2026. An export limit does not lower the rating, so this 23 kW system went to plan review.

Why is the solar export limited to 12 kW?

That is the size agreed with the utility for this connection. The Powerwall's power control holds what goes back to the grid at 12 kW. Inside the house the full 23 kW is still available, so the limit only trims exports on the sunniest hours.

What is energy arbitrage with a home battery?

Using power when it is expensive that you stored when it was cheap. Here the batteries fill from solar during the day and top up on the ultra-low overnight rate, then run the house through the 4 to 9 pm peak. Surplus solar earns net-metering credit.

Does the EV charge from the batteries during an outage?

No. A contactor wired to the Gateway disconnects the charger the moment the grid goes down, and reconnects it after five minutes of steady grid. A full car charge would otherwise use a large part of the stored energy.

Can solar connect straight to a Powerwall 3?

Yes. The Powerwall 3 has a solar inverter built in. On this home the six strings land on the six inputs of the two units, so there is no separate solar inverter on the wall.

Did the house need a bigger electrical service?

No. The demand calculation on the home's own utility data came to 136 A on its 200 A service, with about a third in reserve.

Why put a subpanel in the garage?

Because that is where the new loads are. One feeder from the house serves the heat pump, lighting, receptacles and roof de-icing over short runs, and leaves spare spaces for the next addition.

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