How to go almost completely off-grid with solar plus flow battery storage

Redflow Executive Chairman and CEO Simon Hackett shows off the ZCell. Pic: Redflow.

Redflow non-executive director Simon Hackett shows off the ZCell. Pic: Redflow.

By Jason Deign

PV-plus-storage could allow homes in Australia to cover more than 99% of annual power consumption from solar, the experience of one household indicates.

Adrian Shand’s home in Glenlyon, Victoria, is expected to need only around 30 hours of petrol genset-based generation a year to supplement the power provided by a solar-plus-storage system, Shand told Energy Storage Report.

That means around 99.7% of annual energy consumption is provided by a combination of 21 260W Tindo solar panels, delivering up to 5.2kW, and two 3kW, 10kWh Redflow ZCell flow batteries installed in March this year.

The flow battery storage can keep Shand’s house running for up to two days with no recharge, and can go from zero to full charge in just four hours under sunny conditions.

The property, a stone cottage surrounded by forest northeast of Daylesford, central Victoria, has no mains electricity supply and had previously been powered by a genset and some solar with lead-acid battery storage. 

A steady power supply

“When we bought the place, it had quite an old OutBack solar system,” said Shand, a sound technician who relies on a steady power supply to work from home. “They had 1.5[kW] installed in panels and a 3kW inverter.”

The Shands had set aside a budget to improve the off-grid electricity supply and spent AUD$56,000 on a new PV and storage setup, including a Victron MultiPlus 48/5000/70 inverter/charger, installed by Off-Grid Energy Australia.

The ZCell zinc-bromine flow battery chemistry offered a better “bang for buck” than competing lithium-ion products, said Shand. “The most important thing was the claims of no degradation,” he said.

“They have warrantied 10 years at 10kWh, and to be honest the expected life is double that. But the warranty says in 10 years minus one day you shall see 10kWh of capacity to both charge and discharge. That’s what attracted me.”

Another significant factor in ZCell’s favour was that the materials in the flow battery are naturally fire-retarding, which is potentially important in a bush-fire area like the one where the Shand household is located. 

A fan of new technology

Finally, said Shand: “I’m a fan of new technology and I liked the idea that this was in its infancy.”

That final point ended up becoming a complication when Redflow ran into technical problems with its residential ZCell product.

Shand said he went through three software updates and product recall before operating glitches were fully ironed out. Despite this, the purchase made financial sense. Getting a grid connection would have cost around $200,000.

This could have potentially been reduced if both of Shand’s neighbours shared the grid link, but even at a third of the price it would still have been cheaper to go with the solar-plus-battery setup.

Plus, staying off grid means Shand avoids having to pay power bills which he said might average $1,000 a quarter and could easily be up to $1,600. 

A PV-plus-ZCell setup

Based on even the lower of these estimates, a PV-plus-ZCell setup like Shand’s on a grid-connected property would have a payback time of just over 15 years, even allowing for backup genset running costs of $300 a year.

And that is assuming electricity prices do not go higher in the future, as seems likely to be the case. “This part of the world is in an energy-cost crisis,” said Shand.

“The average cost of electricity has quadrupled in the last five years and doesn’t seem in any capacity heading downwards.”

The economics of solar plus storage would likely be even better in other parts of Australia, since Glenlyon, in the central highlands of Victoria, has one of the lowest direct normal irradiation rates in the country.

Around the year, the location gets an average of about 4.5 hours of “perfect sunlight” a day, which translates to 28kWh a day in the summer, 20kWh in spring and autumn and 13kWh in the winter, said Shand. 

Enough sunlight to recharge batteries

Even in overcast conditions, there is usually enough sunlight to partially or completely recharge the batteries during the day, he said.

With the initial teething problems largely ironed out, Shand said he was pleased with his decision to go with a largely untested residential energy storage brand and concept.

With Redflow, he said, “I have direct contact with the CEO. I don’t think Elon Musk was ever going to call me if I was kicking around at Tesla’s.”

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