The grid was designed well before the rise of renewable energy, and the two sometimes struggle to get along. But a trial in NSW and Victoria is looking at how rooftop solar and home energy storage can improve the stability and reliability of electricity supply.
For reliable supply, power has to be kept within a tight voltage and quality range. Solar and batteries can create power quality problems for the network if they are not managed well.
The Networks Renewed trial is the work of the Institute of Sustainable Futures at the University of Technology Sydney, and more than 150 electricity customers will be recruited to take part.
Institute of Sustainable Futures research director Chris Dunstan expects the majority of sample households will already have solar installed. The trial is primarily focused on inverters but funding has been put aside to provide a rebate for installation of batteries for some of the applications, but not all.
Inverters installed in residential solar systems are generally set to maximum power point tracking mode, to maximise the amount of kilowatt hours the inverter produces, whether that’s to the grid or for self-consumption.
That’s OK, Dunstan says, unless there are challenges on the grid such as a leading or lagging power factor, where there is too little or too much voltage in the grid.
“If instead we can use the inverters to take the energy from the solar panels or the batteries and use that to deliver a mix of real and reactive power to address the power factor problems, you can address the voltage problems on the grid,” he says.
“That means the inverter is helping the grid rather than potentially contributing to problems that may exist on the grid already.”
In other words, the best solution in some circumstances may be that an inverter does not export electricity to the grid.
“In doing so it may facilitate more output of solar and more installation of solar because it’s helping to address the problems that are on the grid.”
Balance of power
When households provide this reactive power to the grid, which is real power they have forgone, they should naturally be compensated for adding value to the grid, Dunstan says.
“We need not just a different mode for operating the smart inverters but we also need a different business model to ensure there is a win-win outcome for the consumers as well as the networks.”
It’s not necessarily about maximising self-consumption but rather the type of power fed into the grid and the timing. Dunstan hopes the research will help the case for installing more solar without networks having to invest in extra infrastructure to accommodate that, by ensuring better management of the PV output.
Networks face a problem of delivering voltage within a range, which is a struggle over long feeders because the voltage tends to be higher closer to a transformer and lower further down the line as it nears the last customer.
“But if you have a situation where you are starting to put PV into the grid, if you put that PV in at the end of the feeder then that can help address voltage problems,” Dunstan says. “That’s a good thing.”
On the other hand, PV that feeds in nearer the transformer end, where the voltage is already high, may not be accepted. In that case, the inverter will read a high voltage and not dispatch until the voltage drops below a threshold.
Solar systems spread around a grid, particularly with batteries, can provide for a more balanced voltage along feeders.
“As a network business you need to design your system to accommodate for times of high demand and low demand; of high solar input and of low solar input,” he says.
“If instead of simply injecting normal power back into the grid the inverters are set up to supply reactive power to offset the poor power factor that’s being created [by use of air-conditioning motors, as an example] … then you can accommodate greater demand and more solar on the grid.”
It takes teamwork
The institute is partnering with electricity network businesses Essential Energy in NSW and United Energy in Victoria, storage software start-up Reposit Power, solar technology provider SMA Australia, the Australian Photovoltaic Institute and the NSW and Victorian governments.
Essential Energy will recruit households in the NSW demonstration and United Energy will recruit households in Victoria. A pilot scale trial of about 30-40 houses is expected to be complete by mid-2017, and a market scale trial of up to about 150-200 houses by mid-2018.
The Australian Renewable Energy Agency is providing $1.87 million in funding for the trial.