The world’s top market for rooftop solar is looking for new ways to add distributed PV to its electricity system by fine-tuning its interplay with the power grid. 

This year, utilities in the Australian states South Australia and Victoria will roll out a "flexible exports" pilot. The AUD $4.8 million (USD $3.7 million) project, which will cover 600 customers across the two states, will allow rooftop solar customers to vary their exports to the network in alignment with available grid capacity, instead of being restrained by fixed export limits. 

“The hosting capacity of the grid is dynamic,” Daniel Chung, home and business application engineer at SMA Australia, the inverter company and one of the project partners, explained in an email. “It depends on the instantaneous, local electricity generation and demand.”

Flexible exports would allow distributed energy resource penetration to be increased to levels closer to the hosting capacity of the grid, he said. “It allows more PV generation when there is a lot of demand for it and curtailment when there is little demand.”

Planners believe this will not only allow existing customers to discharge more solar onto the system but also make it possible to add new distributed PV arrays, even though grid hosting capacity is reaching its limits. 

“At the moment, earlier PV systems can export full power to the grid, whereas new connections are increasingly confined to lower static export limitations, which lowers the value proposition from feed-in tariffs,” Chung said. 

In advance of the 12-month pilot, SA Power Networks and Victoria-based AusNet Services have worked with the inverter manufacturers Fronius, SMA and SolarEdge, and energy management software company SwitchDin, to adapt solar systems for flexible exports.

“The project will establish a new connection standard for enabling flexible export limits for solar PV systems, then develop and test the end-to-end technical capability,” Paul Roberts, manager of corporate affairs at SA Power Networks, said in an email. 

The capability will be built into Australian products from Fronius and SMA, and will be enabled in other inverter brands through SwitchDin’s Droplet distributed energy resource controllers, he said. 

The project, which kicked off in mid-2020 with almost AUD $2.1 million (USD $1.6 million) in funding from the Australian Renewable Energy Agency, has already led to the development of an inverter interoperability guide that could be adopted across Australia, Chung said. 

Smart inverters for solar-saturated grids

Australia is a vanguard market for managing the influx of high-volume solar penetration on distribution grids. But it’s not alone in attempting to use the capabilities of smart inverters to manage the supply of customer-generated power. 

In the United States, similar challenges have emerged in Hawaii, with its separate island grids hosting the highest per-capita rooftop solar numbers in the country. This can cause voltage and power flow disruptions on certain circuits. State regulators and utilities have turned to new solar regulations that limit power export, while also tapping smart inverter capabilities for more active management

California, the state with the most rooftop solar by volume, is also testing how smart inverters can balance local grids via autonomous or utility-linked control settings. State regulators and utilities are in the midst of implementing rules that could allow more solar to be interconnected if it can modulate its output to avoid overloading circuits during times of peak production.

Arizona, another solar-heavy state, is testing both utility-controlled and automated solar inverter controls to solve the same challenges. 

In Australia, flexible exports will be the latest in an array of measures that SA Power Networks is introducing to deal with rampant rooftop solar growth in its distribution region. 

Last year, the company implemented measures to disconnect systems remotely if needed during periods of peak solar generation. SA Power Networks has also upgraded 140 major substations and introduced a “solar sponge” tariff to encourage consumption of PV generation. 

More than 35 percent of South Australian residential and business premises have PV systems, and as of mid-2020, they added up to in excess of 1.5 gigawatts of capacity. This makes rooftop solar “by far the state’s largest generator,” Roberts said. 

“The number of systems installed and the average size of those systems continue to increase year-on-year, adding capacity at a rate of more than 300 megawatts” annually, he commented.

What is happening in South Australia could soon spread to other parts of the country. 

According to a March 2020 bulletin from the Reserve Bank of Australia, in 2019 Australians spent AUD $3.5 billion (USD $2.7 billion) on small-scale generation systems including solar heating and rooftop PV. 

This generation is now equivalent to around 20 percent of the total capacity on Australia’s National Electricity Market, it said.

“We are now reaching the limit of our capacity to host rooftop solar in some areas without major network upgrades, with the most immediate consequence being increasingly widespread overvoltage issues in residential areas at times of high solar output and low demand,” Roberts said.

“Flexible exports will enable solar customers in South Australia and Victoria to continue to feed more energy into the grid.  This means more customers will benefit from rooftop solar, with higher exports, less energy wasted, greater reliability and a more stable electricity supply.”