Solar, batteries and the all-electric home

The orderCut the load, then generate

Every kilowatt-hour the house doesn't need is cheaper than one you generate. A well-insulated, well-oriented house with efficient heat pumps for heating and hot water needs far less electricity, so it needs fewer panels and a smaller battery to cover it.

Canberra has a seasonal catch. Across the year, a solar system here produces about 4.3 kWh a day for each kilowatt of panels. In summer that rises to about 7 kWh a day. In winter it falls to about 3, less than half the summer figure, at exactly the time the house needs the most heating. Solar is very good at covering summer cooling and daytime use. It can't fully cover a cold, poorly insulated house in July. The envelope does that.

Solar also counts toward the NCC Whole of Home rating, which offsets the energy used by the heating, cooling, hot water and lighting. It doesn't change the star rating. Panels on the roof won't stop a west-facing bedroom overheating or a cold room losing heat.

The roofDesigning a roof that suits solar

Most of what makes a good solar roof is decided at sketch stage, long before anyone chooses a panel.

• Facing. North-facing panels produce the most over a year. Panels facing directly east or west produce about 15% less. That isn't always a bad result: an east–west split spreads the output across the day, which can suit a household that's home in the morning and late afternoon.
• Pitch. In Canberra, the best fixed angle is about 31°. A typical pitched roof of 20° to 25° works well. Flat panels produce noticeably less and don't wash clean in the rain, so a flat roof needs tilt frames.
• Area. Allow roughly 5 m² of clear roof for each kilowatt of panels. A 10 kW system needs about 50 m² of unbroken roof, which is more than many complicated roofs offer.
• Keep the solar plane clear. Vents, exhaust outlets, flues, skylights and roof ventilation openings all take panel space. Group them on the south or another unused roof plane. Under NCC 2025, most roofs in Canberra also need ventilation openings at the high point, so plan where they go and where the panels go at the same time.
• Avoid shade. A chimney, a taller neighbouring house, a tree or your own upper storey can shade part of the array. Shade on even a small part of a panel string can pull down the output of the whole string. Electronics on each panel reduce the loss, but avoiding the shade is better. The same 3D sun study used for windows and eaves can check the roof at midwinter.
• Keep the form simple. One large, unbroken north-facing plane works far better than a roof cut into many small hips, valleys and dormers. A simple roof is also cheaper to build and easier to keep watertight.

BatteriesStoring the midday sun

Solar output peaks in the middle of the day, when many houses are empty. Without storage, much of that energy goes back to the grid, and the house buys power back in the evening. A battery stores the midday surplus for the evening and overnight. Size it to the household's evening and overnight use, not to the size of the solar system.

Where a battery can go is set by the Australian Standard for home battery installations, AS/NZS 5139. Under that standard, a battery can't be installed:

• in a habitable room, such as a bedroom, living room, kitchen or study
• in a ceiling space or wall cavity
• under stairs or a walkway, or on an escape route
• within 600 mm to either side of, or 900 mm below, a door, window, vent or appliance such as a hot water unit or air conditioner

If the battery sits on a wall with a habitable room on the other side, the wall needs a non-combustible barrier, such as brick, concrete or fibre cement, extending 600 mm beyond each side of the battery and 900 mm above it. In practice that usually means an outside wall or a garage. A battery in a garage may also need a bollard to protect it from the car.

Temperature matters too. Lithium batteries shouldn't charge below 0°C, and many switch off charging when they're too cold, which on a Canberra frost is exactly when you'd want them working. Hot afternoon sun shortens their life and can void the warranty. A wall inside an attached garage, out of both frost and afternoon sun, is usually the best spot. Plan it in the design, rather than leaving it to whatever wall is free on the day.

All-electricWhat the house needs

New homes in the ACT have been all-electric since new gas connections stopped in December 2023. An all-electric house typically runs reverse-cycle heating and cooling, a heat pump water heater, an induction cooktop and an electric oven, and often charges an electric car.

• Single phase or three phase. Most homes can go all-electric on a single-phase supply, because heat pumps, induction cooktops and reverse-cycle systems are designed for it. Three-phase power is worth considering for a fast car charger, a solar system of more than about 10 kW, or a very large heating and cooling system. The network also limits how many high-powered appliances can run on a single-phase connection. Decide during design. Adding three-phase to a finished house is expensive.
• The switchboard. Size it for the whole house, with spare space for circuits you may add later.
• Timing. Running the hot water, dishwasher and car charger in the middle of the day uses your own solar and keeps capacity free for cooking and heating in the evening.
• Cooking. Induction is fast, precise and burns nothing indoors. It still needs a good rangehood ducted outside to clear steam and cooking fumes.
• The car. Even if there's no electric car yet, run a dedicated circuit to the garage or carport now.

DeliveryGetting it built and running

• Draw the equipment. Show the panel area, inverter, battery, switchboard and conduit routes on the drawings, along with the roof vents and other penetrations. If they aren't drawn, they get decided on site.
• Place the inverter well. Put it on a shaded wall near the switchboard, away from bedroom walls, because many inverters hum and run hot. Heat reduces their output.
• Coordinate the roof. Panel fixings and cable entries pass through the roof, so they need to be planned with the roofer, flashed properly, and kept clear of the roof ventilation the code requires.
• Match the rating. If the Whole of Home rating assumed a certain amount of solar, that system has to be installed. Check the certificate before the electrical package is finalised.
• Monitor it. Use the system's monitoring app to check output in the first months. A fault or a shading problem shows up quickly against the expected figures.