Going to all desalination


Perth has just experienced its second driest winter in 150 years of reliable rainfall records.  Streamflow into dams has been negligible.  You might think this would engender some panic in the city, but it hasn’t.  Rationing of water is fairly modest given the circumstances.  Households will only be permitted to turn on sprinklers once per week until Christmas.  Hand watering is unrestricted.

The reason for the lack of panic is that the reality of climate change has been long recognised by policy makers and governments in Western Australia.  In the years 1911-1975 the average annual streamflow into Perth dams was 360 GL.  From 1975-2009 the average was 160 GL and this year it has been nearly zero.  Perth has come to rely mostly on artesian water from acquifers a thousand meters beneath the sandy plain that the city sits on, and desalination.  The first desalination plant has been running at its capacity of 45 GL per year since its completion in 2006 and the second plant will deliver another 50 GL per year from 2011 (hence the absence of panic).  The later plant has approval for expansion to 100 GL.  Since the streams are delivering less and the acquifer is being pumped out at an unsustainable rate, Perth will inevitably go to an all desalination model of water use (or largely desalination).  

And why not?  Desalination is not so expensive in the full scheme of things.  The capital cost of desalination plant per person in Perth is about $1600 per person (average water useage of 300 L per person per day and capital costs of $15 million per GL).  The Government is thinking of spending about $500 per person on a new football stadium.  The total cost of producing desalinated water, including the costs off-setting CO2 output is less than $2.50 per kL.  I will be happy if Perth goes to an all desalination model and charges users the full cost of producing water.  Perth is growing faster than any other major city in Australia, but there is no more concern about running out of water than running out of electricity (which actually is a worry).

The other day I was lucky enough to be seated next to Dr Jim Gill on a flight from Melbourne to Perth.  Dr Gill, who is now the Chancellor of Curtin University, was formerly the head of the Water Corporation in WA for 15 years until 2008.  He is a terrifically interesting person who has an expert knowledge of desalination having presided over the building of Australia’s first major desalination plant.  I have been collecting vignettes which show how little energy is used in the desalination of water and Jim Gill told me the following one.  In Perth the average increase in the temperature of shower water in its journey from the water main to the shower head is 20C.  The electricity used to desalinate water is only enough to heat the water about 3.5C.   So, for shower water that is desalinated and then heated in an electric hot water heater, the desalination accounts for only about 14% of the energy used.  My mental calculation is that desalination corresponds to a 5C increase in the water temperature, but Dr Gill was adamant that it is 3.5C, and he has a PhD in engineering from Cambridge and has actually built a desalination plant, so I believe him.

13 Responses to "Going to all desalination"
  1. From Sustainable Energy – without the hot air, real life desalination has an electricity cost of 8 kWh per m3, so the temperature rise corresponding to the desalination cost is ((8 kWh) / (1000 litres)) / (4.2 ((kJ / kelvin) / litre)) = 7 kelvin. So you were right, according to another person from Cambridge!  [If you were to use a heat pump to deliver your temperature rise, instead of a resistive heater, you would get a different answer]

  2. A couple of issues here.
    First of all you don’t measure “climate change” by the amount of water that flows into dams. Water consumption for irrigation purposes is not related with climate, so that number is not relevant to the discussion. If you want to check “climate change” look at the average rainfall, which has not changed in Perth or anywhere in Australia in the last 100 years.
    Second, it rains more in Perth than in Melbourne (believe it or not: 790mm/yr in Perth vs 650mm/yr in Melbourne. Since the desal plant in Melbourne is going to supply the most expensive water in Australia, using the most energy to get it, and given the fact that a construction of a single dam would generate water at ZERO energy cost and (at most) 1/5th of the per kiloliter cost, the claim that going all desal is something advisable is absolutely nonsensical.
    Third, and perhaps most troubling, is the calculation used to prove that the energy cost of the water that comes from the desal plant is very small. Well, I have some news for you, 8kWh/1000 litres is a huge energy cost and not all of this water is going to end up in showers. That’s a bad comparison. The comparison that has to be made is between ZERO energy (dam) and 8kWh/1000 plus the energy cost to pump all that water from Wonthaggi uphill to the dams. The whole project seems to be designed to throw money down the drain, and succeeded beautifully in doing so.
    A suggestion for this government, always keen on wasting money. Why don’t we put electric heaters in the dams themselves to supply Melbourne with warm water so we can dispense our home heaters? That is the equivalent of using desal were there is plenty of water available that being thrown to the sea anyway.

  3. Zappi, the point is not so much whether using desal is a better option than dams, is that it’s perfectly feasible to supply all of our coastal cities’ water from desal at an affordable economic and environmental cost.
    At a rough calculation, you could make enough fresh water for Melbourne’s entire water supply using 300 MW continuously.
    That’s in the context of Victoria’s baseload demand of 5000MW or so.  Indeed, the Portland aluminium smelter uses 720 MW continuously on its own.

  4. Robert, you have a good point. It is feasible, I have no doubts about that. Is it however economically sound? Or worse, is it environmentally reasonable?
    Your numbers say that 300MW(continuous) would supply Melbourne with desalinated water. Ok. you are trading half an aluminium smelter for… water that is already available for collection and is happily running into the bay! Let’s look at the numbers again, from another perspective:
    300MW continuous would cost $525m/yr at current domestic rates. After the increase of 50% that we will pay in a couple of months this would be worth $750m/yr. Is it reasonable to waste energy like that? It would be enough energy to lit up Melbourne with EXTRA 1 million high power sodium lamps, to make our city it visible from the outer space. Is it reasonable?
    The Portland smelter manufactures 350,000 tons of aluminium per year, which is worth almost 1 billion dollars, generating employment, exports and tax revenue. There is a net benefit from such an enterprise and, even better, is funded by private money.
    The desalination plant is simply wasting lots of energy at a huge capital expense, courtesy of the dumb taxpayer, to replace a dam that the government is too coward to push forward. How can such a huge waste be considered economically or environmentally sound?

  5. Zappi
    You are presenting a good example of the exaggeration in many arguments against desalination.  By your argument 300 MW continuous of electrical power is worth $750 million per annum.  Which means the 720 MW used by the Portland smelter (Robert’s figure) is worth about $1.8 billion, which is 80% more than the smelter’s aluminium is worth, by your reckoning.

  6. Sam,
    I presented the numbers to offer the readers a real feel of the magnitudes we are talking about. I clearly stated “at current domestic rates”.
    Of course Aluminium smelters don’t pay domestic rates, being among the biggest consumers of electricity in the planet. And incidentally the biggest cost in the manufacture of aluminium is electricity itself.
    Appears to me that a new category of big electricity consumers is arising in Australia: desalination plants in places where there is plenty of available water.
    Want a valid comparison? Put electrical heaters on the Cardinia reservoir and bring the temperature of the water up by 3.5°C. Alternatively you can do something useful with the energy, like turning Melbourne every night into a gigantic Xmas tree with 1 million 400W sodium lamps easily visible from the moon with the naked eye. And if you want you can even sell the electricity to consumers at the retail price I mentioned before.
    And let’s not even mention the billions of tons of carbon that this project will add to the atmosphere year after year.
    What a humongous waste of money and energy! What a mockery of reason!

  7. Most of the cost of providing electricity at “current domestic rates” is the cost of building and maintaining the grid, and supplying peaking power.
    Neither of these is at issue with desal.

  8. Quoting from a Bureau of Meterology presentation dated 2008:

    “Victoria’s mean autumn rainfall has decreased over the past 100 years reflecting a delayed autumn break in rainfall. Spring rainfall has tended to increase. The delay of the autumn break has become pronounced over the last 20 years and is responsible for a severe reduction in riverflows across Victoria.”

    This is taking place within a context of high variability of annual Victorian rainfall where the 50s, 60s, and 70s had exceptionally high annual rainfalls. (Talking of average annual rainfalls in Victoria is not very useful apparently.)

    If one believes that climate change will lead to further issues with replenishing our current water supply or that the rainfall we used to regard as “normal” is no longer valid then building another dam under such circumstances is also perhaps wasteful of taxpayers’ money.

    With a desal plant we are paying for a certainty of supply. Whether that price is too high depends on the context and the probability of ongoing issues with replenishing our water supply via rainfall catchments.

  9. The real waste of energy here is not desal but hot showers.  How crazy to heat water up by 20 degrees C so it can warm your skin for a second and then disappear down the drain.
    That is not to say that I enjoy cold showers, but is there no feasible way to recover the waste heat?

  10. Dave, in short, no.
    The temperature difference between a hot shower and the environment is too small for the heat to be efficiently recaptured.

  11. yes.
    It’s remarkable that anyone would think that an electric hot water heater is an appropriate technology in this day and age. They are very much going the way of the dinosaur.

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