Spa town? South Australia’s hot water systems set to soak in the solar


Subscribing to off-peak hot water used to mean heating your water at night when electricity prices were at their lowest. Today, with rooftop solar pouring into homes and overflowing into the grid when the sun is highest, the cheap-energy tide has been turned. A new trial announced this weekend by the Australian Renewable Energy Agency (ARENA) and Solahart will take active control of 2,400 residential hot water systems in renewables-endowed South Australia, to help balance the grid, but also to bring lower electricity bills to homes with and without rooftop solar.

The trial is supported by both the Australian Federal Government (through ARENA) and the South Australian Government, each of which is contributing $1.98 million to the $9.9 million Active Hot Water Control project conducted by Rheem through its renewable energy brand Solahart.

Participating homes will be kitted out with Solahart PowerStore, a solar-smart, grid-interactive electric water heater, integrated with a home energy management system, with the aim of demonstrating a low-cost, scalable way for hot water systems to provide demand management services.

The Solahart PowerStore system typically works in tandem with a property’s rooftop solar system, using solar energy surplus to the household’s immediate needs to gradually heat water, rather than allowing that excess to flow to the grid. Solahart describes it as being like a battery: it stores energy — but it’s more affordable.

For homes without solar, it will likely be reconfigured to tap into times of cheapest grid energy supply — that is, when the grid is flooded with solar-generated energy.

The new off-peak water heating makes clever use of solar energy.

Image: Solahart

“As more of Australia’s electricity comes from solar, we need to increasingly shift more of our energy consumption to daylight hours when solar PV is generating,” said ARENA CEO Darren Miller.

Being able to coordinate surplus energy supply with high residential loads such as the heating of water is one way of managing abundance to help both the grid and consumers.

In preparation for this summer, South Australia, which already has one in three households living under rooftop solar, rushed in emergency measures that would allow state distribution network provider (DNSP) SA Power to switch off large swaths of rooftop generation if the influx of energy became too much for the grid to handle. 

The steamy times of day

Hot water systems have traditionally been significant users of electricity in the early mornings and evenings, when the largest proportion of people are showering pre or post work, washing dishes and setting a load of laundry in motion. Helping householders to choose to switch when they heat their water and use other appliances at peak solar times is a more rewarding way to balance the system than enforced shutdowns.

The Active Hot Water Control project will trial various incentives to find out what motivates different customers — those with and without solar on the roof, and across socioeconomic groups — to participate in demand response.

As part of the project, Solahart will establish a virtual power plant (VPP) that aggregates the electrical load of hot water heaters among participants, curbs electricity use at peak times, participates in electricity price arbitrage, and provides network services to the grid.

Learnings from the project are likely to have countrywide application. “By aggregating and optimising the energy use of hot water systems and other household appliances, VPPs could play a major role in managing system stability and reducing power bills for customers,” Miller said.

Distributing the solar love

Rheem CEO, Chris Taylor added that South Australians are leaders in the adoption and use of renewable energy solutions, and that this project and the technology used are unique in enabling residents of the state to participate “in the renewables boom whether or not they are able to invest in solar PV”.

Australia saw 7 GW of new combined — large and small scale, wind and solar — renewable generation installed in 2020, an 11% increase on 2019, the previous record year which had already clocked up 6.3 GW of new green energy capacity.

The continuing passion for rooftop PV is expected to triple the country’s small-scale solar capacity by 2030, with an additional 24 GW predicted to be installed over the coming 10 years.

“This project will help South Australia to get the most out of this boom and maximise the use of renewables in the grid, reducing pressure on the electricity system,” said Federal Minister for Energy and Emissions Reduction Angus Taylor in a statement on Saturday.

ARENA elaborated on the potential benefits of Rheem’s trial, saying on its online project page that it will:

  • alleviate power quality issues such as voltage rise
  • increase network hosting capacity of distributed energy resources
  • improve overall rooftop PV asset optimisation and use in both households and the distribution network

The Active Hot Water Control project is also anticipated to create new jobs at Rheem Australia, and support local installer employment in the residential enablement phase.


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