A Sydney student block is humming ahead with a solar-and-storage renewable energy system that includes the 36 Enphase batteries.

Stucco could be any student digs. A vast common room has bicycles stacked at one end and a herd of sofas at the other, all facing a cinema screen that shifts in the breeze from open windows. In one corner a drum kit, in another a couple of guitars. The floor creaks and hasn’t been mopped.

This is Newtown nirvana.

Nearby, young lawyer couples in $2 million terraces agonize about global warming and look at Tesla Powerwall specs on their ipads.

But at Stucco they’ve gone further than that. Up on the roof of the heritage-listed former glass factory 114 solar panels take power from the sun to feed the energy requirements of 40 residents, with any unused electricity saved in a bank of 36 batteries for later use.

A clean energy retrofit in a heritage-listed student housing co-operative wasn’t straightforward, however. Lawyers were required to draft a formal arrangement outlining a power purchase agreement between the tenants and the co-operative and then the Australian Energy Regulator had to agree student co-op Stucco was allowed to sell the electricity generated onsite.

Lastly, the co-op needed approval to become an embedded network, so that the nine existing meters for the common area and eight accommodation units would be replaced with one meter for Stucco, through which it would access electricity from the grid. And that’s where things got held up for a few months.

“That ended up being the approval that proved hardest to get,” says Bjorn Sturmberg, a former resident who led the project. “It was unexpected.”

Group effort

There are plenty of embedded systems in apartment blocks elsewhere in Sydney, but the hard part for Stucco is that theirs was a retrofit – and the AER struggled with that. Sturmberg thinks the stumbling block may have been the consumer rights issue around the tenants’ option of accepting a PPA from the co-op or sticking to grid power as usual.

“It took us about six months to figure out that that was the thing that was holding this whole thing up,” he says. “I think they were confused … and [struggled with the concept] that Stucco was a co-op and a not-for-profit [organisation].”

The AER is used to mediating to what extent an embedded network can “take a cut”, he says. “The fact we were students and a not-for-profit was all very peculiar to them.”

Sturmberg makes it clear he wasn’t pitching the solar-and-battery retrofit embedded system as a precedent to the AER, “but I think they saw it as a precedent,” he says. Either way, he thinks he’s cut a path for others to go down. “It is a precedent and we want it to be a precedent – and hopefully it will be much easier for others [to do the same thing].”

In February Sturmberg launched social enterprise start-up SunTenants, which enables solar to be installed on rental properties with the benefits shared fairly between landlord and tenant.

Study group

Stucco residents are all students at the University of Sydney, who qualified for beds because they or their families just haven’t got the money it takes to live in central Sydney. The eight units each include a kitchen and bathroom, but there is no air-conditioning, no dishwashing machines, hardly any heaters in winter, three shared washing machines and no clothes dryers – which explains why washing is draped over many of the beams and handrails that crisscross the three-storey atrium.

Sturmberg, who’s completed his PhD in physics, had first stab at designing the system and installation was carried out by NSW company Solaray. In January, the system’s first full calendar month, 3.5MWh of electricity was produced, “which is equivalent to 62 trees,” Sturmberg says. His estimate for monthly consumption is about 2.5MWh. The co-op expects the system to have paid for itself in six or seven years.

January brought intense sunshine and half the residents were on holiday, says Stucco president and social work student Sarah King, so there’s no expectation generation will regularly exceed consumption. Stucco’s energy bill for January, for the entire building, was about $130. The building receives a feed-in tariff of 7.2c/kWh from its electricity retailer.

SwitchDin billing software will split the cost between units by consumption.

The target is for 80% self-sufficiency and students are each expected to save $35 a month on their electricity bills. The $120,000 system was paid for with a grant from the City of Sydney of $80,000, on the condition Stucco raise half that amount again.

Solaray won the tender and “really liked the design”, Sturmberg says, which included 30kW of solar and 40kW of storage.

Plugged in

Average daily use for the building is 80kWh, or 2kWh for each resident – well below the average, although that’s mostly to do with the meagre offering of modern conveniences. “It’s not a high-tech version of low-carbon living,” Sturmberg admits. “It’s just absenteeism.”

The wall of 36 Enphase batteries is the largest installation of the 1.2kWh storage units in the world, and installers took just 11 minutes to plug the 20kg units into place. Trina Honey panels with Enphase microinverters were used.

Sturmberg calls up the Enphase Enlighten software on his laptop to show solar generation, battery storage levels and consumption by 15-minute increments. It’s been overcast, so the chart shows a “pretty underwhelming kind of day,” he says.

He flips back in time to the previous day, which shows a typical hump shape for solar generation peaking at noon, with morning and evening peaks for consumption. The batteries lasted to 1am that day, and Sturmberg goes back a few weeks to call up days where stored energy lasted into the first peak of the following day. “I find this stuff super interesting,” he says.

The Enlighten platform’s other strength is troubleshooting, where a local installer or Enphase technician on the other side of the world can access the system online and isolate issues down to individual panel or battery level.

The simple graphic representation of energy supply and demand cuts through with the gang at Stucco. “It’s perfect for us,” says King. “You can change your behaviour. Without it you’re guessing, really.”