Snowy Hydro gets a boost, but ‘seawater hydro’ could help South Australia

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The Conversation

Cultana, South Australia: scene of the nation’s next big hydro scheme? Roger Dargaville, Author provided

Cultana, South Australia: scene of the nation’s next big hydro scheme? Roger Dargaville, Author provided

The federal government has announced a A$2 billion plan to expand the iconic Snowy Hydro scheme. It will carry out a feasibility study into the idea of adding “pumped hydro” storage capacity, which it says could power up to 500,000 homes. The Conversation

Hydro is one of the oldest and most mature electricity generation technologies. And pumped hydro storage – in which water is pumped uphill for later use, rather than simply flowing downriver through a hydro power station – is the dominant form of energy storage globally.

But there are limitations to how much freshwater hydro can be accessed, so it’s worth looking at what alternate approaches are available. One promising prospect is to use seawater instead of rivers. This tactic could potentially help South Australia resolve its highly publicised energy problems.

Hydro basics

The principle behind conventional hydro power is straightforward: rainwater runoff feeds a river, which is dammed to create a large reservoir of water. This is then gradually released through pipes to a turbine at the foot of the dam, thus converting the gravitational potential energy into electricity. The water then flows on downriver.

Hydro power is fossil-free and also “dispatchable” – it can be turned on or off at will (provided there is water in the dam). This gives it a significant advantage over wind turbines and solar photovoltaic (PV) panels, which produce power only when the wind blows or the sun shines.

Hydro thus makes an ideal partner for wind and solar PV, as it can adjust its output in response to changes in output from these non-dispatchable renewables.

Pump it up

Pumped hydro energy storage (PHES) is very similar to conventional hydro power but differs in that rather than being a generator, it’s more accurate to describe it as a battery.

Normally done at smaller scales than conventional hydro, PHES uses excess electricity from the grid (such as during periods of low demand and/or high generation) to pump water uphill from a lower reservoir to a higher one.

Later, this water is released back downhill through the turbine, returning the electricity to the grid when it is most needed – typically during the evening peak. It is this approach that is being considered in the Snowy Hydro 2.0 project.

Pumped hydro storage thus helps to “smooth out” peaks in demand by effectively transferring excess electricity from periods of low demand to periods of high demand. It has a “round trip” efficiency of ~80%, which is comparable to that of batteries.

PHES is the most common form of grid-connected energy storage in the world, accounting for around 97% of the total. It is often built in partnership with “baseload” power generators such as coal and nuclear plants, to help them vary their output to cope with peaks and troughs in demand.

Australia already has three PHES facilities – at Tumut 3 in the Snowy Hydro Scheme, at Shoalhaven in New South Wales, and at Wivenhoe Dam on the Brisbane River in Queensland.

South Australia is arguably the place that is most in need of grid-scale energy storage. Unfortunately, South Australia lacks the rainfall, rivers and mountains to run a conventional hydro system, with or without storage.

However, there is a way to use this technology without rivers and mountains: by using the ocean as the lower reservoir, and building an artificial upper one.

The upper reservoir doesn’t need a river to feed it fresh water; it just needs to be significantly higher than the ocean (that is, there should be a steep slope on or near the coastline, up which the seawater can be pumped). Using seawater also avoids the need to divert freshwater resources into a large reservoir, where a significant amount would be lost through evaporation.

Testing the technology

So far, only one seawater PHES installation has been built anywhere in the world – on the island of Okinawa, Japan. It came online in 1999 and was decommissioned in 2016, after Okinawa’s power requirements changed. Seventeen years for a first-of-its-kind project is a significant success. However, the Okinawa project was combined with a coal-fired power station, so linking this technology with intermittent renewables has never been trialled anywhere.

So could this technology help to ease South Australia’s energy crisis? The Melbourne Energy Institute (MEI) report on Pumped Hydro Opportunities identifies several potential seawater PHES locations in South Australia. This includes a very promising site at the northern end of the Spencer Gulf, with significant elevation close to the coast and close to high-capacity transmission lines.

The Department of Defence manages this land, and discussions are ongoing as to how the project might be designed to not interfere with the department’s operations on the site. A win–win development is the primary design aim.

The MEI study suggests that PHES could be delivered at around A$250 per kWh of storage. This compares well with utility-scale lithium ion battery storage, which currently costs of the order of A$800 per kWh, although recent announcements on Twitter from Elon Musk suggest this might be coming down towards A$500 per kWh.

The Spencer Gulf site has the potential to provide at least 100 megawatts of dispatchable generation, effectively making the wind and solar generation in South Australia significantly more reliable.

The Australian Renewable Energy Agency (ARENA) will help fund a feasibility study into the technology, working with partners Energy Australia, Arup and MEI. If the facility is ultimately built, it could become a key element in SA’s bid to avoid future power blackouts.

Source: The Conversation. Reproduced with permission.  

  • George Darroch

    This site and proposal are very promising. I hope it is expedited – there’s no reason it needs to take years for shovels to hit the ground.

  • Eb

    So if it does cost $250/kWh, then the 600MWh, 100MW EnergyAustralia proposal will cost ~$150m to build. My quick estimate is that it will earn less than $10m per year, so no one will finance the project. Though I’ll wait for the ‘Knowledge Sharing’ from the $450k feasibility study before betting this seawater pumped hydro project won’t happen soon:

    • Miles Harding

      We have to stop thinking of the elements individually. Without this sort of ‘loss maker’, the whole system fails.

      • Jonathan Prendergast

        Which suggests there is lots of value created that the pumped hydro does not capture, as it’s only revenue stream is energy arbitrage.

        • Miles Harding

          And only large scale energy at that.
          This makes smaller scale energy storage, such as batteries and even cars, which will have bigger batteries than houses, important players in this mix.

          Perhaps the biggest value is in the mindset created by this move.

    • Ian

      Is it a fiction that a 100% renewables grid of such a size as South Australia’s, needs days or weeks of storage? It’s power requirement is about 1GW. 1 day of no primary generation is 24GWH. If primary generation is reduced by 50% then 24GWH would last 2 days. At 10% shortfall this would last 10 days. A little PHES such as proposed won’t last 1/2hr if primary generation sources fail. You wonder how much energy security this will actually buy.

      If there is never or hardly ever a time when both wind and solar fail completely then overcapacity of these installations will serve as insurance against prolonged windless cloudy days. An overcapacity of 20% will ensure full generating capacity when these resources drop to 83%. Load shedding could similarly compensate for reduced resource times. Large and reliable interconnectors could spread the risk of a prolonged shortfalls. Whilst all these storage systems are expensive, their use should be mostly restricted to daily generation/load matching.

      Gas is a difficult standby energy source whether this is biogas or fossil. You need roughly 10GJ gas for 1MWH electricity. For our standby storage of 24GWH you’d need 240TJ of gas. What size tanks for this ? 4500tonnes of LNG (about 2 Olympic swimming pools volume of refrigerated/compressed natural gas or 6.3 million m3 of gas.

  • Miles Harding

    Ahh, Jay can out-trump Malcom.

    With this sort of thinking and some more wind and solar, the shiny new gas plant will hardly ever be needed.

  • Miles Harding

    Ahh, Jay can out-trump Malcom.

    With this sort of thinking and some more wind and solar, the shiny new gas plant will hardly ever be needed.

  • Pixilico
    • Tim Forcey

      Thanks for that link!

      • Pixilico

        You’re welcome! If there’s a will, there’s a way! 😉

  • Brunel

    It is not a recent announcement. Musk tweeted “$250/kWh for large scale deployments” on 1 May 2015 UTC.

  • Malcolm M

    For all the excitement about pumped storage using seawater, it carries a lot of financial uncertainty about long term maintenance costs. Unless the sea is needed as the lower storage, is it not better to use fresh water ? The cost of a small desalination plant, sufficient to replace evaporation, would probably pay for itself through lower maintenance costs of the turbines, penstocks, and membranes for the upper storage.

    • Rod

      I watched a doco on Netflix the other day “Islands of the future” which had an Island (can’t remember the name, Greek or Maldives) Population 20,000
      Anyway, this island did just that. Seawater -> desal -> top tank -> turbines.
      Drinking water was a problem for this Island. All wind power except for emergencies. Replaced diesel generation.
      I’m sure seawater would be problematic.

  • Ian Mclaughlin

    Just to make it clear all that is proposed is a feasibility study! So $2 billion means nothing, a figure out of his— well you know.