Energy

Renewable Energy and Desalination

Desalinating brackish groundwater can help boost agricultural production and provide clean water to remote communities. However, the energy required for desalination can represent a significant portion of the total costs, not including the expenses related to brine disposal. When powered by fossil fuels, desalination also produces significant greenhouse gas emissions.

The intermittent nature of variable renewable energy sources poses a challenge for certain desalination technologies, particularly reverse osmosis (RO), which requires a continuous and stable energy supply to operate effectively. To address this issue, several strategies can be employed.

• One solution is to oversize the desalination plant and use water storage, so the plant can produce sufficient desalinated water during daylight hours when solar PV is available. However, this approach can result in higher desalination plant capital and operating costs.
• Another strategy is a hybrid renewable energy and battery storage system. Batteries can store excess energy generated during periods of high wind or sunlight, which can then be utilized when renewable sources are insufficient. This approach helps mitigate the variability of renewable energy and provides a steady supply for the desalination plant.
• Alternatively, diesel generators can serve as backup power, but they rely on fossil fuels, resulting in higher operational costs and greenhouse gas emissions.

As a result, the potential use of stand-alone renewable energy hybrid systems – comprising solar photovoltaic (PV) panels, wind turbines, battery storage, and diesel generators for backup power has been examined.

What regions were assessed?

A detailed optimisation analysis of hybrid energy systems has been conducted across the Perth Basin, Carnarvon Basin, West Canning in the Canning Basin, the Alluvial Fan region in East Pilbara, the Karratha Hinterland region in West Pilbara, and selected palaeovalley regions such as Murchison. Additionally, specific locations associated with remote communities were included in the analysis.

What assessment was based on?

The Bureau of Meteorology Atmospheric high-resolution Regional Reanalysis for Australia (BARRA) data from 1990 to 2019 were used to develop solar PV and wind farm outputs in 12 km grids across the selected groundwater regions and remote communities. The results of this optimisation were the optimal photovoltaic, wind turbine, battery storage and diesel generator capacities required to meet the desalination electricity demand. The optimised systems were then selected at reliability levels of 60% up to 99.9% in 10% increments to minimise levelised cost of electricity (LCOE) and maximise supply reliability.

Least-Cost Renewable Energy

The results show that a hybrid system combining solar PV, wind turbines, battery storage, and diesel generators for backup can supply a constant 100 kW load with greater than 99% reliability across the modelled locations in WA.

The locations with the lowest LCOEs are the Carnarvon Basins, the Karratha Hinterland in the West Pilbara, West Canning in the Canning Basin, and the northern parts of the Murchison Palaeovalleys. The highest LCOEs are found in remote communities in the northern parts of WA and the southwestern parts of the Perth Basin.

The study also revealed that the LCOE increases substantially at reliability levels of over 90%. This increase is due to the need for larger amounts of battery storage and/or the operation of the diesel generator to maintain a consistent electricity supply to run 24 hours a day.

When comparing renewable energy hybrid systems to diesel-only generators, the study found that the hybrid systems are generally the most cost-effective. The LCOE for the renewable hybrid systems, at a reliability level of 99%, ranges from $0.11$/kWh to $0.40/kWh. In contrast, diesel-only systems with the same mode of operation have an LCOE ranging from $0.45/kWh to $0.74/kWh, depending on fuel costs.

The study also examined the impact of LCOE on the energy cost of desalinating water, which varies depending on the salinity of the water. Sites with higher salinity levels (greater than 14,000 mg/L total dissolved solids) face energy costs that are up to three times higher than those with low salinity levels (less than 3,000 mg/L total dissolved solids).

For sites with a mean LCOE at a reliability level of 90%, the cost of desalinated water ranges from $0.15/kL to $0.45/kL, depending on the salinity level.

Conclusions

Hybrid renewable energy systems, combining solar, wind, battery storage, and diesel backup generators, offer a cost-effective and sustainable solution for powering off-grid desalination plants in Western Australia.

Site selection for renewable energy generation is critical. The most affordable hybrid systems can cost less than a third of the most expensive systems, depending on local renewable resource conditions. Diesel-only systems were found to be more expensive than all hybrid renewable energy options, reinforcing the practicality of hybrid systems. As renewable energy and storage technologies improve and reduce their capital cost, the cost of hybrid systems is expected to decrease further, making off-grid projects even more economical.

Salinity levels of the feed water play a crucial role in desalination costs, as higher levels of salinity require more energy to desalinate. Energy consumption for desalination is about three times higher at high-salinity sites compared to low-salinity sites. Selecting sites with lower salinity can reduce energy use and costs, while also minimising the amount of brine, which is costly to treat.