An interview with William Ertler by Jacinta Agostinelli
In late 2021, honours student William Ertler, and another student from Australian National University, conducted research into a community battery for Yea. One of the findings led William to realise that shifting domestic electric hot water heating to solar hours can reduce the battery capacity required for 100% self-consumption of residential PV by over 80%, and reduce energy costs to households on high solar generation days. In effect the hot water is acting like a battery.
What is load-shifting?
The electricity system requires generation and demand to be perfectly matched at all times. Historically, electricity system operators would rely on generators to change their output in response to changes in demand for electricity. Unlike traditional fossil fuel powered generation, the majority of renewable energy generation is dependent on the availability of sun or wind, which does not always align with periods of peak electricity use. This can cause issues if renewable energy is not available when demand is high.
To minimise the amount of renewable generation that needs to be constructed, and provide the lowest cost electricity, consumers can change the time at which they use energy to best match the availability of renewable energy resources. This is known as demand-side management, or load shifting, where consumers change the time at which they use electricity to best match available generation.
Load shifting requires a flexible load. Something like household lighting is an inflexible load, as it needs to be switched on at exactly the time it is needed. Other household electricity uses such as heating or a dishwasher are flexible loads as you could heat you house in the afternoon prior to coming home, or run the dishwasher overnight if you don’t need clean dishes until the next morning.
Load shifting is becoming an increasingly important part of the energy transition with a higher proportion of variable renewable generation in the system and greater loads with electric vehicles and the continued electrification of home appliances. In my research I focussed on shifting hot water load to midday when the most solar energy is available.
Have the peak and off-peak usage times and charges changed recently?
Yes, as of September 2021. A two-part electricity tariff has a period of cheaper off-peak prices and a period with more expensive peak prices. Historically the off-peak period occurred overnight, meaning solar generation occurred during the peak pricing period. Now a new two-part tariff is available with the peak period only occurring from 3-9pm, and off-peak at all other times. This means maximum solar generation now coincides with off-peak prices. This will encourage the use of rooftop PV generation and enables off-peak loads to be shifted to midday for no increased cost. It is important to note that peak and off-peak periods may still differ depending on each resident’s current electricity contract and residents should still do their own research to see if this new peak and off-peak structure is best for them.
What was the case study you undertook that involved the town of Yea? Why did you use Yea?
In late 2021 another ANU student and I completed a report on community batteries in Yea. One of the key findings from this work was that there was a peak in electricity demand at 1am (Figure 1). This peak is caused by electric hot water heaters operating on a timer to access off-peak electricity prices. Given that Yea exports solar energy on more the 50% of days annually, this presented an opportunity to shift the water heating load to midday to soak up excess solar energy.
While extensive research has been conducted exploring the benefits of load-shifting, how this strategy interacts with community batteries is not as well understood. As 2030Yea has expressed interested in a community battery, the town provided a great case study to explore how load-shifting of hot water heating would impact the sizing and operation of a community battery.
How would load-shifting benefit a resident in Yea? Are there any disadvantages?
For a typical Yea resident with solar PV installed they can use more of their own solar generation by load-shifting. This means that rather than sending excess solar generation back to the grid or storing it in a battery, it can be stored as heat in a hot water cylinder. Depending on the electricity plan they are on, and the solar feed in tariff they receive, residents may see savings on their electricity bill. There are risks associated with load-shifting, such as interruptions to hot water supply or increased costs. This depends on the exact circumstances of each household. Further research is required to provide accurate advice on whether to implement load-shifting for hot water systems.
What if I don’t have solar installed?
I only accessed aggregated data for electricity consumption in Yea, so my analysis did not differentiate between households with and without solar installed. Further research using smart meter data from individual households would be required to answer this with confidence. However, I can say that without solar installed, households would not see any financial benefits from load shifting under conventional electricity contracts. Households without solar could still lower their emissions by heating hot water during the day as typically this is when more renewable energy is generated. They would also be able to utilise more electricity that is generated locally from solar within Yea.
If I have a heat-pump and/or other energy efficient devices, would the benefits associated with load-shifting still be significant?
While I was not able to explore this in my research, more energy efficient homes would still see benefits from load-shifting. As more efficient appliances use less electricity, the maximum savings from load-shifting will be less. However this could mean there is more excess solar energy available for other uses such as charging an electric vehicle.
How do I change my hot water system to heat during the day?
It is best to contact your installer to determine the configuration of your current system and if this can be changed without negatively impacting performance. Changing the operation of hot water systems may not be suitable for all homes depending on the type of hot water cylinder installed and the needs of each household. Financial implications may also differ depending on the current electricity plan of each household.
How does load-shifting benefit a community?
Community wide load-shifting of hot water systems would mean that in effect, Yea would have a community battery which stores energy thermally. If there was widespread shifting of hot water heating to midday, then a much larger proportion of local solar generation would be used. This means less electricity from the grid would need to be imported into Yea.
To achieve the goal of 100% renewable energy by 2030 Yea will need to decrease the use of grid electricity, which still utilises coal-fired generation, and use more locally generated electricity from rooftop solar. By shifting hot water loads to midday, more locally generated solar will be used in Yea, increasing the proportion of renewable energy used.
Did your study consider aspects of energy injustice in relation to load-shifting?
As I only accessed aggregate data for the entire Yea community, I was unable to compare the impacts across different groups in the community. The impacts of load-shifting on groups such as renters and those with less control over their energy systems must be considered before implementation occurs.