Improving SA solar investment returns

Worried about investing thousands of dollars on solar panels only to receive poor returns from the grid? Engineering researchers at Flinders University have analyzed the best solar energy setup for residential households in South Australia to achieve maximum return on investment.

The new study compared the size of rooftop solar panels and battery energy storage systems (BESS’s) for houses connected to the grid by considering Flat and time-of-use (TOU) electricity tariffs to demonstrate which setup should be used to reach the minimum cost of electricity (COE).

The modeling published in Energies considered electricity grid constraints, daily supply charges, degradation of PV and BESS equipment, real electricity load consumption of a typical household in SA, and the current market prices of new components.

Dr. Amin Mahmoudi, Lecturer in Electrical Engineering at Flinders University, says the modeling shows a 6 or 9kW PV solar system with battery storage configured to make returns from a TOU-Flat (TOU for buying electricity and Flat for selling) tariffs will result in the highest financial return on investment.

“Our study found the TOU-Flat option for the PV-BESS configuration achieves the lowest COE compared to any other options. The optimal capacities of rooftop PV and BESS are obtained as 9 kW and 6 kWh, respectively, for the household with this TOU-Flat option. The payback period for the investment of this system is 6 years.”

“Significant growth has been observed in the number of home battery installations in Australian houses over the past 5 years. According to national reports, 22,661 energy storage systems with a total capacity of 233 MWh were installed in Australia in 2019. A total of 73,000 home battery installations have been reported since 2015 so this suggests that 8% of Australian houses with a rooftop PV have also installed battery solar systems despite the cost.”

Under the current TOU system, the electricity price changes two or three times throughout the day and is most expensive at peak periods, so the optimal capacity of PV solar and battery storage needs to be selected according to those import and export costs to obtain the highest economic returns for households.

The researchers analyzed all four tariff options based on buying and selling electricity prices: Flat-Flat, Flat-TOU, TOU-Flat, and TOU-TOU.


Table 3 lists the electricity prices of flat and TOU rates for purchasing and selling electricity. The TOU rates of electricity are changed in three time periods for residential customers in SA. The off-peak period is between 11:00 p.m. and 8:00 a.m., the shoulder period is between 8:00 a.m. and 6:00 p.m., and the peak period is from 6:00 p.m. to 11:00 p.m.

“The data takes into consideration the unit size of solar panels, lifetime durability, and cost of components with the average lifetime of rooftop solar considered to be 25 years. The pricing data was incorporated based on retail market prices in SA,” says Rahmat Khezri, a Flinders University engineering researcher.

“Using the recommended TOU-Flat tariff option, South Australian’s purchase electricity by TOU rates and sells the PV’s extra power under flat rate. The financial return on the PV-BESS system was about 2.62 ¢/kWh lower than that of the PV only system without a storage battery. The annual imported electricity from the grid (AIEG) of the PV only system was almost half of the normal case and two times higher than that of the PV–BESS system. The annual BESS degradation was obtained as 1.46%; hence, the battery lifetime was about 13 years.”


Optimal Sizing of Rooftop PV and Battery Storage for Grid-Connected Houses Considering Flat and Time-of-Use Electricity Rates is published by Iflah Javeed. Rahmat Khezri, Amin Mahmoudi, Amirmehdi Yazdani and G. M. Shafiullah in journal Energies with DOI: https://

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College of Science and Engineering Sustainability