Stunning success of home battery boom will slash rooftop solar exports, and reshape the grid – again

New analysis of the stunning boom in household battery installs – courtesy of the federal government’s newly launched rebate scheme – suggests that it could lead to an another unexpected reshape of the grid’s power supply.

Australia’s leadership in the uptake of rooftop solar and the huge amounts of exports to the grid has already created one remarkable change in the shape of the grid, including the emergence of the “solar duck” curve, with profound implications on coal generation and the future of so-called “baseload power.”

But new analysis from Green Energy Markets points to the virtual elimination of solar exports in many homes, thanks to the unexpectedly high uptake of household batteries, and because bigger batteries are now being installed as a result of the modular nature of new battery systems, as well as labour cost savings.

More than 1,000 battery storage systems a day have been installed since the Cheaper Home Batteries Program began on July 1 – the equivalent of a Hornsdale battery every two weeks.

And the battery sizes are bigger than expected – 17 kWh instead of the 10-12 kWh that had been forecast. GEM expects the average size of home battery systems to quickly rise to 25 kWh.

“In my view the scale of what we are seeing in terms of battery installations completely transforms the game for the role that rooftop solar can play in decarbonising our grid,” says Green Energy Markets’ Tristan Edis, the author of the report that was commissioned by the Australian Conservation Foundation and the Smart Energy Council.

“At present, a typical household with a 6.6 kilowatt solar system will export a substantial majority of the solar system’s output to the grid – 70% to 80% is common,” Edis writes.

“However, as the charts (above) illustrate, these solar exports largely disappear for a household with a 25 kWh battery system in place along with an electric vehicle and no gas appliances,” Edis says.

“The uptake of household batteries, along with electrification, will mean a large proportion of household solar generation is soaked up in satisfying increased household electricity demand and charging up batteries.”

This, in turn, has an impact on the overall power system, resulting in less “ramping” of thermal plants (because there is less variation in the output of rooftop solar), and less curtailment of large scale wind and solar plants.

GEM notes, however, that this does depend on some sensible reform of network prices that would encourage households to export power when the need is great, and even allow for low cost imports when the overall power demand is low.

GEM also calls for greater uniformity and stability in network tariff structures across the country to allow technology suppliers to develop products that can help households to better utilise their home battery capacity to benefit the wider electricity system and other consumers.

“In addition, changing regulations to allow households to join virtual power plant operators that are independent from their choice of electricity retailer (as is the case for large electricity consumers) will assist in providing enhanced choice and competition for consumers,” GEM writes.

“That means they will be more likely to enrol their battery in a VPP so it can be better utilised.”

The push to bigger battery installations has been driven by the fact that the cost per kWh is significantly reduced as the system gets bigger.

This is now easy to do because of the modular “stacks” that most battery packs are delivered in, meaning there are significant labour savings. Added to this, the rebate is available to a household only once, so the incentive is there to make the system as big as possible.

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