People have used moving water to create energy for thousands of years. Today, pumped hydro is the most common form of grid-connected energy storage in the world.
This technology is in the spotlight because it pairs so well with solar and wind renewable energy. During the day, when solar panels and wind farms may be generating their highest level of energy, people don’t need really need much electricity. Unless it is stored somewhere the energy is lost.
Pumped hydro can cheaply and easily store the excess energy, releasing it again at night when demand rises.
Here’s how it all works:
How it works
Put as simply as possible, it involves pumping water to a reservoir at the top of a hill when energy is in plentiful supply, then letting it flow back down through a turbine to generate electricity when demand increases.
Like all storage systems, you get less energy out than you put in – in this case, generally around 80% of the original input – because you lose energy to friction in the pipes and turbine as well as in the generator. For comparison, lithium ion batteries are around 90-95% efficient, while hydrogen energy storage is less than 50% efficient
The benefit is we can store a lot of energy at the top of the hill and keep it there in a reservoir until we need the energy back again. Then it can be released through the pipes (this is called “penstock”) to generate electricity. This means pumped hydro can create a lot of additional electricity when demand is high (for example, during a heatwave).
The disadvantage of pumped hydro is you need to have two reservoirs separated by a significant elevation difference (more than 200m is typically required, more than 300m is ideal). So it doesn’t work where you don’t have hills. However, research has identified 22,000 potential sites in Australia.
Pumped hydro is traditionally paired with relatively inflexible coal or nuclear power stations, using under-utilised electricity when demand is low (weekends and nighttime), then providing additional generation when demand increases during the day and into the evening.
With the rapid increase in deployment of wind and solar, pumped hydro is again gaining interest. This is because the output of wind and solar plant is subject to the variability in the weather. For example, solar power plants generate the most electricity in the middle of the day, while demand for electricity is often highest in the evening. The wind might die down for hours or even days, then suddenly blow a gale. Pumped hydro can play a key role in smoothing out this variability.
If the electricity being produced by wind and solar plant is greater than demand, then the energy has to be curtailed (and is lost), unless we have a way to store it. Using this excess power to pump water up hill means the solar or wind energy is not wasted and the water can be held in reservoirs until demand rises in the evening.
There are lots of different kinds of energy storage technologies, each with their own advantages and disadvantages. For large-scale grid-connected systems where many hours of storage are required, pumped hydro is the most economically viable option.
Prime Minister Malcolm Turnbull’s plan for a A$2 billion upgrade and expansion of the Snowy Mountains Hydroelectric Scheme, announced last week, will be an impressive engineering achievement. Snowy Hydro 2.0 will increase the scheme’s capacity by 50%.
Meeting this extra capacity will depend entirely on the natural water supply available in the Snowy Mountains. But the current environmental conditions of these mountains, and the Australian Alps where they are located, are compromising both water delivery and water quality.
The only way to maintain water flow is to control the threats that are actively degrading the high country catchments. These include introduced animals, wetland loss, and climate change.
Restoration and management
The remarkable Snowy Hydro Scheme was developed over 25 years from the 1940s. During this period the NSW Soil Conservation Service and later NSW National Parks effectively managed soil and restored areas damaged by grazing.
Conservation efforts focused on looking after topsoil, stabilising wetlands, and restoring vegetation after decades of grazing. This ensured good amounts of high-quality water for both hydro power and irrigation downstream.
More recent efforts have focused on the impacts of building the original Snowy scheme. This includes restoring areas cleared for roads and construction sites, and areas where rock and soil from blasting and cutting were dumped.
Threats to mountain catchments
The Australian Alps are the nation’s water towers. They provide water for growing food and hydroelectricity, but face several threats.
Across the Alps, despite well-informed and committed control programs, feral horses, pigs and deer are destroying wetlands, degrading streamside vegetation, and causing moisture-holding peat soils and stream channels to erode. This leads to more evaporation, more rapid runoff and erosion, less water flow, and lower water quality.
There is currently no effective response to this damage. We estimate that more than 35% of the high mountains’ wetlands have been affected, and the problem is getting worse.
The Alps are also recognised as extremely vulnerable to climate change. Climate models suggest that alpine areas that currently receive at least 60 days of snow cover will shrink by 18-60% by 2020.
Temperatures in the alps are already increasing by 0.4℃ per decade, an increase of 1.79℃ since records began. Climate change projections for the Australian Alps indicate the hottest summer days will be around 5°C warmer in 2100, minimum temperatures will rise by 3-6℃, and precipitation (rain and snow) will decrease by up to 20%, with less falling as snow. These changes are already putting pressure on iconic mountain ecosystems including the peatlands, snowgum woodlands and alpine ash forests.
The Australian Alps are also likely to experience more extreme events such as heatwaves, storms, fires and severe frosts. All of these affect high mountain ecosystems, making the environment more vulnerable to disturbances such as more fires, weeds and disease outbreaks.
For example, the root-rot fungus, Phytophora cambivora, recently appeared in the alps. The fungus killed large areas of shrubs following unusually warm springtime soil temperatures.
New weeds are an additional concern for the alps as these may compromise the existing plant communities and their ability to deliver services such as water. Alpine peat soils, which build up over thousands of years, can also burn in drought.
Reliable water depends on functioning ecosystems
A stable water supply from the Alps is crucial for energy and food production. This relies on intact vegetation.
Back in the 1950s, it became clear to the researchers at the Soil Conservation Service that hard-hooved animals, in this case domestic cattle, were severely damaging the alpine catchments.
The success of the original Snowy scheme depended on removing cattle from alpine areas, controlling soil erosion that resulted from prior grazing and hydro works, and carrying out extensive revegetation works across the whole of the nearby mountain ranges.
However, land managers to this day are still controlling a legacy of disturbance and weed invasions from both the Snowy scheme itself and years of previous grazing. Snowy 2.0 must consider these lessons from the past, and work to improve mountain catchments.
Alpine plants and animals often live close to their environmental tolerances, meaning they are not necessarily able to cope with change. For some species, climate change is likely to exceed these thresholds. Vegetation communities will change as current populations decline and colonisers from different species move in to occupy the gaps, including invasive species.
Feral horses make it even more difficult for native species to respond to a changing climate, by exacerbating environmental degradation and impacts on water.
Part of the solution is restoring and re-vegetating degraded high country landscapes. For example, restoring snowgum communities, which were severely affected by burning and grazing, may lead to increases in the amount of water trapped as drifting fog.
But climate change will demand new research and management partnerships to find species that will survive well into the future and to develop adaptation pathways to respond to uncertain conditions.
This will be a new and different world. We are currently ill-prepared to maintain high-quality water yield in the future, to predict the impacts of climate change, or to effectively protect our alps for future generations.
But we are confident these questions can be answered with adequate investment in the environmental infrastructure needed to underpin the engineering. We estimate that between A$5 million and A$7 million per year is needed to research and develop new management structures. You could see this investment as royalties returned to the system that provides the water and power.
Turnbull’s plan may deliver more power, but only if the environment is carefully managed. Otherwise Snowy Hydro 2.0 may be left high and dry.
In its latest move on energy policy, the Turnbull government has unveiled a plan to boost generation from the Snowy Hydro scheme by 50%.
The government says the expansion, which it has labelled the Snowy Mountains Scheme 2.0, would add 2,000 megawatts of renewable energy to the National Electricity Market. This would be enough to power 500,000 homes.
Claiming the upgrading would be an “electricity game-changer”, Prime Minister Malcolm Turnbull said that in one hour it would be able to produce 20 times the 100 megawatt-hours expected from the battery proposed this week by the South Australian government, but would deliver it constantly for almost a week.
Turnbull flew to the Snowy early Thursday to formally announce the plan. The commonwealth is a minority shareholder in the Snowy Hydro, with a 13% stake. New South Wales and Victoria have 58% and 29% stakes respectively.
The government, through the Australian Renewable Energy Agency (ARENA), would examine several sites that could support large-scale pumped hydroelectric energy storage in the area, Turnbull said.
Energy Minister Josh Frydenberg said the cost would run into “billions of dollars”. It is being suggested it would be around A$2 billion. Frydenberg avoided being tied down on when it would be completed.
He said three new tunnels were being looked at, stretching 27 kilometres for the pumped hydro-facility. It would not involve new dams, but connect existing reservoirs and recycle water.
The plan had the potential to ensure there would be the needed renewable energy supply for those on the east coast at times of peak demand, Frydenberg said.
Tony Wood, energy program director at the Grattan Institute, cautioned that the plan would involve technical and economic issues, including whether it could make money, and to what extent it could contribute to solving the short-term power crisis.
“This isn’t some sort of magic panacea,” Wood told the ABC. Some hard-headed thinking was needed on what it would do and how it would work.
Turnbull said: “The unprecedented expansion will help make renewables reliable, filling in holes caused by intermittent supply and generator outages.
“It will enable greater energy efficiency and help stabilise electricity supply into the future,” he said – adding that this would ultimately mean cheaper power prices.
He said successive governments at all levels had failed to put in place the needed storage to ensure reliable supply.
“We are making energy storage infrastructure a critical priority to ensure better integration of wind and solar into the energy market and more efficient use of conventional power.”
Turnbull said an “all-of-the-above” approach, including hydro, solar, coal and gas, was critical to future energy supplies.
Snowy Hydro already provided back-up energy to NSW and Victoria and could extend to South Australia when expanded, he said. The expansion would have no impact on the supply of irrigation water to NSW, South Australia and Queensland.
The feasibility study for the expansion is expected to be completed before the end of this year, with construction starting soon after, he said.