Whose problem is it when residential solar becomes so popular in some suburbs that the peaks and troughs of energy demand start to look like the Swiss Alps? Homeowners with PV systems who are paying lower bills won’t complain, and those without solar won’t notice any difference. The rare few who have installed behind-the-meter batteries will be happy, but they’ll also still be a long way from paying off their investment, most likely.
The folk who run the local network, however, will be biting their nails as greater levels of unused solar flow into the grid during the day. Those electrons are worth money.
United Energy, which serves eastern and southern Melbourne, saw the opportunity for using community batteries to temper swings in midday exports in Black Rock and Highett, suburbs where PV penetration is high. If storage assets could be mounted up power poles, they could be set to work lopping peaks in daytime supply as residential solar systems exported most of what they generated, assuming most people are at work.
“Peak lopping works in both directions,” says Michael Jansen, managing director of Power Technology Engineered Solutions. “It’s not only peak load lopping, it’s actually more often peak generation lopping. In the middle of the day we typically have what the utilities call reverse power flow – more generation than load – and it overloads the transformer, typically.”
Power Tech’s winning bid provides United’s network support by soaking up some of that daytime generation, using it to reduce some of the evening peak load and controlling voltage along the way, says Jansen.
As the energy system transitions to clean but unpredictable sources of generation, energy storage is a mandatory part of system design. There is no argument about that. But Jansen tells EcoGeneration the project in Melbourne’s Bayside region has illustrated to him that shared energy storage assets are a better solution than individually owned ones.
“I believe that for a community, a community central battery is more efficient than a group of home batteries,” he says.
Seat of power
The project uses two 85kWh Kokam batteries, “robust but expensive” technology that can do without air-conditioning and survive up a post, thus meeting United’s requirements for near-silence and minimal visual impact. “No-one anywhere in the world has put 85kWh on a pole,” Jansen says. “It is immensely condensed, the way we’ve structured it.”
Peak-lopping was the focus of the application at the start but most of the time the batteries are used for aggregated market services, he says, including energy arbitrage and price cap trading.
“We have extended the software with our distributed energy resource control system to aggregate the systems and be able to dispatch them based on a frequency signal or a price signal – even if we would have a large number [of identical or similar community storage assets].”
The batteries are performing as expected in terms of power, energy, temperature and functionality. “However, we haven’t seen the summer yet. The moment of truth when it comes to network constraints during hotter weather is still to come,” says Jansen, whose company also worked on AusNet’s 18-home Mooroolbark residential community minigrid trial.
Community vs home batteries
Are community batteries substitutes for home batteries? “Because these assets are bigger than home batteries we can put more sophisticated functionality in there,” Jansen says, in particular the mix of network functionality and market services in one system. “We can work with less losses with higher dynamics because the systems are bigger and you can put a bit more sophistication in them than home batteries.
“For a community, a central battery is more efficient than a group of home batteries.”
The systems are meant to pay for themselves over 10 years but revenue from providing market services will shorten that. The project should have a positive effect on energy bills but only United Energy would be able to say how much.
The power of pole-mounted community storage will become more obvious when there is a fleet of “maybe 50 or so” units, Jansen says. “It makes a lot of sense not only for a network but also for communities.”