‘Intelligent control’ the key to grid-friendly solar
IN February this year, South Australia announced a plan for a 50,000-home, 250 megawatt (MW) capacity ‘virtual power plant’, with 650 MWh of battery storage. The plan is based on the idea of intelligent grid management, with signals relayed by communications servers integrating the flow of energy from dispersed rooftop solar panels to the grid, and to and from household batteries.
But how feasible is it to coordinate so many separate solar–battery systems so that they function as a single, reliable power supply feeding into the grid?
Results from a much smaller, year-long trial in Queensland – which recently wrapped up after a year of close monitoring by CSIRO energy researchers – show that such distributed networks are not only feasible but may be key to ensuring the future stability of the national grid.
Is there such a thing as too much solar?
The Virtual Power Station 2.0 (VPS2) trial, funded through the Federal Government’s ARENA program, was based in a new housing development south of Brisbane. The new suburb of Yarrabilba, developed by Lendlease, has attracted a 6 Star (the highest rating) Green Star Communities rating from the Green Building Council of Australia and includes a fast charger for electric vehicles.
Many Yarrabilba residents have elected to install solar panels on their homes to reduce their power bills.
It sounds like a wonderful thing. But here’s the paradox. As more and more homeowners opt for rooftop solar – and we lead the world in the rate of uptake of this technology – the more unstable the local grid can become.
That’s because Australia’s power distribution systems were historically designed to flow one-way, from generator to customer. In this conventional grid, voltage is centrally controlled to flow smoothly within a specific range.
But when that conventional grid encounters a high density of solar panels along the way – all pumping power into the grid in the middle of a sunny day, then winding back when clouds appear, and switching off at night – the result is fluctuating and high voltages and frequencies, and an unstable power supply.
Not surprisingly, some network providers have put a limit on the size of solar systems allowed to be installed in areas with existing high-densities of rooftop solar. In a worst-case scenario, rooftop solar may be banned altogether.
That’s why Yarrabilba has been so important. By creating a ‘virtual power station’ across a small grid catchment, CSIRO researchers have shown that rooftop solar and a stable grid can co-exist.
The key is web-based intelligent control algorithms designed by CSIRO which help smooth the flow of electricity in the grid.
A ‘happier’ grid reduces the need for restrictions on new photovoltaic cells and for costly network upgrades and, perhaps most importantly, cuts the cost of power for local residents.
All parties on board
The Yarrabilba trial involved 67 homes – 27 of which had rooftop solar panels and five of which had storage batteries with advanced inverters that act as intelligent control systems.
Chris Knight, from CSIRO Energy in Newcastle, is the VPS2 project manager. He says the trial is unique in being designed to benefit two key parties involved in the electricity market, both distribution networks and consumers.
Knight adds that the key enabling technology in the trial was the new generation of intelligent inverters that automatically monitor and control the flow of electricity between solar panels, batteries, home appliances and the grid. (Inverters traditionally convert the DC electrical current from solar panels to the 230 V AC current supplied to our homes by the grid.)
It is this new inverter technology, combined with the similar capability of many new appliances – such as air conditioners, pool pumps and hot water systems – to be remotely controlled by the network through the voluntary Demand Response Enabling Device (DRED) initiative that is the game-changer, according to Knight.
DRED-enabled appliances can be remotely switched on or off or turned down during electricity peak hours in response to signals from the power company, usually in exchange for power discounts.
“With those two bits of technology, we showed that you can improve power quality and remove instability in the local grid. That’s essentially what VPS was about – improving power quality for the distribution network and enabling consumers to continue benefiting from rooftop solar power.”
Trial participants more energy-smart
Knight says another spinoff of the trial is that it made participants more keenly aware of the way they used energy and of just how much energy their appliances used – both on and in standby mode.
Yarrabilba resident and trial participant, Adrian has a family of four, including a 7-year-old and 4-year-old.
Apart from having the air conditioning running frequently, Adrian says the family uses the washing machine once or twice a day, as well as running the dishwasher daily.
When he joined the CSIRO trial, Adrian’s home already had solar panels and inverter, and CSIRO supplied a battery. For Adrian, the energy savings associated with the battery were an eye-opener.
“With the first bill, we couldn’t believe it – we saved 60 per cent on our power costs. As soon as we got the battery, we went from feeding $80–90 into grid from the solar panels to cutting our power bills.”
Apart from the savings from storing solar energy in the battery, the family have become more aware of how to avoid using big appliances during peak periods and making use of daytime solar or off-peak electricity. The washing machine and dishwasher are run during the day, and the clothes drier is rarely used.
Another Yarrabilba resident and trial participant, Jim, is a semi-retired broadcast engineer who drives a Nissan Leaf electric car (EV) and has a lifetime fascination for new technology.
“The game-changer for us was the battery,” he says. “Although we were generating power in the daytime, it was going back to the grid. We were getting 6c per kWh in feed-in tariff and having to pay 32c per kWh to buy power back from the grid.”
The distributed-energy future
It’s hard not to overstate the importance of research such as this for Australia. Brian Spak, who leads CSIRO’s Grids and Renewable Integration program says: “To date, no regulator or network in the world has effectively navigated the transition from a model centred on large, remote power plants to one that relies heavily on distributed energy.
“The strong economics of distributed energy in Australia today put us at the forefront of this evolution, and so we are faced with the challenge – and opportunity – of redesigning the electricity sector before most of the rest of the world.
“Australian science and technology, in distributed energy and associated control methods, really can lead the world.”