Introduction

Solar PV too The amount of solar photovoltaic power generation was very small in 2004 when this page was created. Solar PV is, similarly to wind generation, variable. There is, of course, no solar power at night and the amount of solar power being generated during the day varies with cloud cover. Many of the points on this page in relation to wind power also apply to solar power.

One of the main objections to wind farms is that they produce a varying amount of electricity. This variability of supply in the electricity grid means that there must be other power generators, such as batteries or natural gas fired power stations, capable of coming on line at short notice if unacceptable fluctuations in voltages or even brown-outs or black-outs are to be avoided. Keeping generators in reserve requires capital expenditure and continuing running and maintenance costs.

Australia, especially southern Australia, is short of water. Desalination of seawater is a possible additional supply. However, it is still fairly expensive (about Aust$1.10/kL) and requires a lot of electricity.

The main aim of this page is to point out that one, at least partial, answer to the two problems above, the variability of the amount of power generated by wind farms and Australia's shortage of water, could be a careful marriage of the two technologies. Electricity can not be cheaply stored, but water can.

Use surplus electricity from wind farms to desalinate sea water. When there is a falling amount of surplus electricity, reduce the number of desalination units running. The water produced when the wind farms are in full production can be stored relatively cheaply until it is required.

Units

For the sake of consistancy, I will try to use kilolitres (kL, 1kL=1m³), megalitres (ML), days, kilowatts (kW), megawatts (MW), kilowatt-hours (kWh) and megawatt-hours (MWh) as far as possible on this page. The main unit of currency will be the Australian dollar.

Costs

Extracted from Water Technology.

Western Australia has set up a sea-water desalination plant at Kwinana, about 25km south of Perth. The initial daily capacity of the plant is 140ML with a designed expansion to 250ML/day. The total project cost was Aus$387m, annual running costs under $20m, and the anticipated water cost has been estimated at $1.17/kL. (Electricity for this desalination plant - which has an overall 24MW requirement and a production demand of 4.0kWh/kL to 6.0kWh/kL - comes from the new 80MW Emu Downs Wind Farm, 30km east of Cervantes.)

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Electricity requirement for desalination

Electrical consumption figures from Californian Coastal Commission for the desalination of seawater. (I converted the US figures to metric and calculated the cost figures. Note that these costs are for electricity only, other heat is required for multi-stage-flash and multiple-effect-distillation.)

Method	kWh/kL	Cost Aust$/kL
Multistage Flash (MSF)	2.8-5.7	$0.20-$0.40
Multiple Effect Distillation (MED)	2-4	$0.14-$0.28
Vapour Compression (VC)	8-12	$0.56-$0.84
Single Pass Reverse Osmosis (RO)	4.7-9	$0.33-$0.63
Double Pass RO	5.3-10	$0.37-$0.70

Cost is based on Aust$0.07/kWh and includes only electrical consumption, does not consider capital or maintenance costs.

For MSF about 21kWh/kL additional thermal energy is required, and for MED, an additional 18kWh/kL.

Aust$60-70/MWh (Aust$0.06-0.07/kWh) is a typical wholesale price for green electricity (about Aust$0.03-0.04/kWh for fossil fuel electricity). The differential is connected to a 'Renewable Energy Certificate' which is currently about Aust$0.03/kWh. Information from Pacific Hydro

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Where would you do it?

The obvious places to use this technique first would be where there is both a desperate shortage of water and an abundance of wind. The Eyre Peninsula of South Australia and the south-western corner of Western Australia come to mind.

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A large desalinator in SAs upper Spencer Gulf?

In early 2007 it seemed likely that a large (44GL of fresh water per year, for comparison, Adelaide uses 120GL/year) seawater desalination facility would be built in the upper Spencer Gulf of South Australia, with the aim of supplying the expansion of the Olympic Dam copper, uranium and gold mine.

The mine expansion didn't happen and the desalination plant was not built.

Some environmental implications of this are discussed below.

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Environmental considerations

The salt that is removed from the water that goes into any desalinator must be disposed of in an environmentally responsible way.

Seawater at 35 000mg/L salt will be used to feed the proposed Spencer Gulf desalinator and the waste water from the desalinator will be around 65 000mg/L. If this is simply released back into the sea it would be significanly more dense than normal seawater and so would lie on the bottom. Much sea life is unable to handle salinities significanly higher than normal, and could easily be killed.

If, as seems likely, a seawater desalination facility with a capacity of around 44GL/year of desalinated water is built in the northern Spencer Gulf, the brine outflow must not be released back into the Gulf. Seawater circulation in northern Spencer Gulf is slow and limited, evaporation in the warmer half of the year is high, so salinities in this area are significantly above those of the open ocean. Environment SA's newsletter #3 on the Spencer Gulf Marine Plan indicated that the salinity in Northern Spencer Gulf rises as high as 47 000mg/L. No desalination waste water should be released into upper Spencer Gulf. The only responsible and economically viable way of disposing of it seems to be by pumping it into evaporation basins for the commercial harvesting of salt.

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Where is wind desalination in use?

There are at least two wind-powered reverse osmosis systems in use in Spain: at Fuerteventura Island and at Gran Canaria Island. See Economic analysis of wind-powered desalination (A 222kb PDF document by Garcia-Rodriguez, Romero-Ternero, Gomez-Camacho. Unfortunately this document is not easy to draw any useful information from.)

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Power consumption controlled to match generation

Unlike fossil fuelled and large-scale hydro power stations, that can be regulated to suit demand, most environmentally friendly forms of generation produce power when it is available; for example, when the sun shines or when the wind blows. This is a problem when the power grid has been operated to suit a power-on-demand model, but there are alternatives. It is quite possible to imagine a power supply system designed to use power partly at the whim of the consumer, but also based on the availability of power.

Several energy demanding processes that could be regulated based on power availability include:

1. Water desalination
2. Water heating (for home heating and/or household consumption;
3. Slush ice production for home cooling;
4. Recharging of electric cars;

The technology for controlling suitably equipped electrical appliances by a signal propagated through the grid already exists. It can be used for jobs such as meter reading.

I'd like to express appreciation to Gary A Tulie, Henrik Bindner, and Lars Henrik Nielsen, for some of the ideas in this section.

I have treated this subject in more detail in Sustainable Electricity.

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Related pages

Update, November 2019 This page was written in 2004. Things have changed. I have written another page on much the same subject: Renewable energy and desalination.

While Southern China is well watered, northern China has water supply problems. A China Daily article (link no longer valid) told how seawater desalination in China is to increase to around 150ML/day by 2005 and then to around 400ML/day by 2010. As of 2005 China desalinates around 40ML/day of seawater. The same article quotes Abdulhamid Al Mansour, president of the International Desalination Association (IDA), as saying that 100 million people worldwide rely on water from seawater desalination.

There is an Australiasian Desalination Association. You can email the CEO of the ADA at roya.sheikholeslami@ausdesal.org

Australian Water Services, which is part of Degremont, an international water treatment specialist, has a remarkably poorly organised and not very informative Internet site at AWS. You can email them at aws@aws.aust.com. Degremont has the contract for the proposed 45GL/year Perth seawater desalination plant.

On my pages related topics include: Sustainable electricity, which discusses various ways of matching electricity demand to electricity generation and Eyre Peninsula water supply, South Australia.

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Some conversions

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