Powering a 10-star home

A new Christchurch home has received New Zealand’s first-ever 10-star Homestar rating, an award that recognises its energy-neutral, sustainable footprint. Schneider Electric designed its innovative electrical infrastructure, enabling the home to switch seamlessly between mains and solar power.

The 140 m², two-storey home was designed by Christchurch architectural designer Bob Burnett, a leading advocate of sustainable homes. Its thermally efficient design includes solar walls that preheat ventilation air through an energy recovery ventilation system, a dual-heat hot water and hydronic underfloor heating system and fully insulated foundations and slab edges (to reduce heat dissipating from concrete floor slabs). 

Complementing these are numerous eco-friendly features: rainwater harvesting, re-usable greywater, water-efficient fittings, solar power and energy-efficient lighting and electrics. The reduced use of heating and electricity should keep the home energy-neutral, leaving it free of power bills. 

The 10-star rating was awarded by Homestar, a system run by New Zealand’s Green Building Council. It uses a 1–10 scale to measure factors such as energy and water use, waste, materials, ventilation and health and comfort. Homes built to New Zealand’s current building codes typically rate three on Homestar’s scale.

“Energy efficiency doesn’t have to be costly. As this home illustrates, it’s actually about using existing technology in a cleverer way — simple, but smart,” said Burnett.  

The electrical solution

The home’s electrical supply is split between conventional 240 VAC from the grid and a 24 VDC system from 18 roof-mounted solar panels. Evening of the demand is met by the batteries — the home automatically switches to 240 V mains when the batteries run low. The overall configuration demanded a relatively simple electrical design, but it came with a caveat. 

To meet the architect’s energy-efficient, sustainability brief, says Schneider Electric’s Dave Chapman (channel manager — residential), “we had to think a little differently. Considering that the home is designed for a family, affordability was key. Energy-efficient technology often carries a cost premium. Bob wanted a solution using standard, off-the-shelf technology.” 

Chapman’s team opted for energy-saving techniques such as motion detectors — sensors which switch off lights if no one in the room. To support that, they enhanced conventional wiring templates.

“For example, we introduced a sunset switch to specific circuits. It automatically renders these circuits active or inactive depending on whether its day or night. By ensuring that specific lighting circuits can’t be used, any chance of accidental wastage is eliminated.”

The home is equipped with Schneider Electric’s Saturn White range of switches. “Again, while this is one of our standard models, we’ve wired the switches in an unconventional way. Using a relay in the switchboard, we’ve created an ‘all-off’ functionality. The home’s entire lighting system can be shut down from one switch, again eliminating any possibility of lights being left on.” 

To help the home owner keep track of electricity consumption and solar power availability, an Ecomind energy monitor has been installed. It gives owners an easy-to-read-and-understand tool for managing and modifying their energy use patterns. 

Because mobile technology has become so prevalent in the modern lifestyle, the home has been equipped with multiple USB charging ports to service devices such as phones and tablets. With a five-star rating, the USB chargers are particularly energy efficient.  

“While the technology we’ve installed doesn’t meet the conventional definition of home automation,” says Chapman, “in effect the design and the way it’s been configured delivers a similar outcome.”

Solar 

The home’s solar component was supplied by one of Schneider Electric’s specialist partner companies in Christchurch, Canterbury Power Solutions (CPS). The system’s 18 photovoltaic panels are each rated at 260 W and charge two sodium-ion 24 V batteries housed within a wardrobe. The panels’ combined output of 4.16 kW is easily sufficient for servicing the two batteries, said CPS owner Murray Marquet. 

The DC power is converted to 240 VAC by a Schneider Electric inverter connected to a battery management system (BMS). When the BMS senses that battery power is too low, it switches back to the national grid supply. It does this with the help of a simple DIN rail device mounted in the home’s switchboard.

“The switchover is automatic and seamless,” says Marquet. “And as a grid-tied system, the solar configuration also feeds electricity back onto the national grid when there is excess battery power. It’s clean electricity delivered to the grid at the standard 50 Hz frequency. There are no rogue waveforms.”