Water use by the Australian renewable energy sector

Biomass is seen as a renewable energy resource as crops can repeatedly be grown as long as the inputs of seed, arable land, water, sunlight and nutrients are available. There are three main forms of biomass used in Australia:

• Conventional biomass – vegetable and animal derived materials such as sugar cane waste, wood chips and animal waste products like manure. These materials are burnt to produce heat which will drive turbines to generate electricity. Although this process releases greenhouse gasses, they are reabsorbed when the next crop is grown. The Australian Sugar Industry produces around 429 MW of electricity from sugarcane waste. Half of this electricity is used to power sugarcane operations and the other half is exported to the national electricity grid.
• Biogas – produced by the anerobic digestion of animal and plants waste. This gas, which is predominantly methane, is used in a similar manner to natural gas to produce power. The Nowra Bioenergy facility which will produce methane from the digestion of food waste and cow manure will produce 2.2 MW of power.
• Biofuels – predominantly ethanol produced by the fermentation and distillation of sugar and starch crops or biodiesel produced from vegetable oils and animal fats. Most of the ethanol in E10 fuel in NSW is produced from the fermentation and distillation of starch left over from flour production.

Compared with other renewable energy sources, biomass is a very water intensive energy source. The bulk of water abstraction in Australia (around 70%) is used for agriculture. Water use for growing crops can be high, for example sugarcane requires 60-70 tons of water to produce a ton of sugarcane. This however will produce multiple products, including sugar and molasses as well as bagasse (sugar cane waste). The bagasse which was traditionally a waste product can then be used to generate power.

Soybeans have been considered as a source of biomass for electricity generation, particularly in the US, however 79 kL of water is required to produce 1 kL of biodiesel. There is also the issue that if crops are grown specifically for biofuels then that same arable land cannot be used for food production. Global water consumption for the production of biomass has been projected to increase to 125,000 GL. Instead, biomass as an energy source is most sustainable when it is the waste products that have no further use that are used as the fuel source.

Solar

Solar produces over 40% of Australia’s renewable energy with rooftop solar being the dominate source (63%) of the total solar photovoltaic market. Solar hot water is also a major contributor to the renewable energy market in Australia, saving users 80% of the costs of heating water. Solar does not consume water during electricity production as energy is produced by the generation of direct current via the photovoltaic effect. Solar panels require a modest 75L per MWh for cleaning, making them one of the least water intensive energy sources available.

Additionally, solar panels can be used to stop evaporation of surface water sources and become a water-negative renewable energy source through the use of floating solar panels. There are a range of aids added to dams and other surface water sources, such as baffles and chemical monolayers, that stop evaporation which can cause up to 50% of the total volume of the reservoir to be lost. Floating solar panels can be used to not only stop evaporation but also generate electricity at the same time.

Wind

Wind is another renewable energy source that does not usee water for power generation. Wind power is generated by the direct turning of turbines by wind – no water is required for this process. Even in the largest turbines, most inverters, transformers and generators will use air instead of water cooling. Water use on wind farms is predominantly for the maintenance of access tracks and the supply of potable water for onsite staff. Even when the entire lifecycle of the wind farms are taken into consideration, the total water use is only 640 L/MWh, making wind power the least water intensive power generation systems.

The Emu Downs wind farm, north of Perth in Western Australia, is a 79 MW onshore wind facility that produces 250 GWh of power annually. The power generated from this wind farm is fed into the grid and used to offset the power required by the Perth Seawater Desalination Plant (180 GWh/year) which produces 140 ML/day of drinking water for Perth residents.

Hydroelectricity

Hydroelectricity uses the natural flow of water through turbines to generate electricity. The main hydroelectric power stations in Australia are the Snowy Mountains Scheme (consisting of 8 power stations and 16 major dams) and those operated by Hydro Tasmania (30 power stations and 15 dams). Although hydroelectricity projects can have environmental downsides due to the change of natural streamflows and the flooding of reservoirs, the dams essentially act as large storage batteries and allow power to be switched on (released through turbines to generate power) on demand.

The main water use for hydroelectricity comes from evaporation from the dams as the production of energy from hydroelectricity itself does not remove any water from the stream. The Gordon-Pedder dam, operated by Hydro Tasmania, is the largest constructed water storage catchment in Australia. With an area of 272 km² (assuming air temperature of 15 degrees Celsius and wind speed of 15 km/hr) this basin loses almost 3 ML/day to evaporation.

Hydroelectricity also relies on rainfall to keep the dams full to maintain power availability. If rainfall cannot maintain dam levels then water will need to be pumped to the dams to refill them (pumped hydroelectricity). Generally water will be pumped during off peak periods for economic considerations. The Snowy Hydro Scheme relies on pumped hydro to maintain dam levels. Water is pumped to upper dams when the demand for power is low. However, if the pumps pumping water uphill are powered by fossil fuels like coal and not surplus renewable energy, then the water use of the hydro scheme will increase in line with thermoelectric power generation.

Moerk Water are experts in renewable energy powered water treatment. Contact Moerk Water today for advice on how best to sustainably produce water in your industry.