Thirsty work: is clean power the answer to clean water security?
Energy Blog, 18 December 2019
Sebastian Reid proposes the coupling of renewable energy with desalination as a win-win solution for both developers and governments.
Over decades of investigation, the search for extra-terrestrial life has been based on a single principle; follow the water. Up to 60% of the human body is literally water, so life without liquid water seems as yet inconceivable.
Back on Earth, water is not hard to find – two-thirds of the planet covered by it. Yet London, Tokyo and Barcelona are some of the many cities expected to experience clean water shortages from 2025. Earlier this year, Indonesia announced it would move its capital from Jakarta, as the rapid depletion of the city’s groundwater resources is causing it to sink, displacing 10 million people. In 2017 and 2018 Cape Town suffered a severe shortage, with water levels dropping to 15% of dam capacity. Currently only 0.5% of the Earth’s water is fresh and accessible, and this resource, once thought plentiful, is being exhausted due to inefficient use of water resources combined with urbanisation and overconsumption.
Agriculture, in particular, has been put once again under the spotlight. 70% of all water demand derives from agriculture alone; a single beef burger has a water footprint of 2,000 litres, and 50 billion beef burgers are eaten each year in the US alone. To put it into perspective, a whopping 100 trillion litres of water per year are used to meet the burger needs of just 4% of the world’s population. Surely savings must be made.
Whilst management of water demand must improve, something can also be done on the supply side. Over 97% of the world’s water reserve is stored in our oceans, but in each kilogram of this water sits around 35 grams of dissolved salts which render this precious commodity unusable, a fact which leads us of course to desalination.
An age old technology
Desalination is frequently referred to as the silver bullet which will solve all our water problems. The technical process itself is very well established and has been practiced for millenia. Aristotle himself was something of an expert. After World War II, we mastered desalination on a large scale with multiple methods, roughly grouped into membrane-based (reverse osmosis) and thermal-based. These days the city of Melbourne in Australia retrieves one third of its clean water consumption from the Wonthaggi Desalination Plant, and on the other side of the word 100 million gallons of seawater are desalinated each day at the Lewis Carlsbad Desalination Plant on the California coast.
Like renewables, desalination plants require a large capital investment before they can generate any revenues, but where they differ is in the operational cost. The cost of the desalination process is high regardless of which one of the two technical methods you use. Reverse osmosis requires water to be exposed to high pressure as it is forced through filtering membranes. Thermal processes require constant heat to mimic nature’s process of evaporation and condensation in rainfall. Both processes are highly energy intensive and therefore significantly costly. A single cubic meter of desalinated water typically has an energy requirement of 4 kWh (compared to 0.4 kWh for recycling the same amount of freshwater).
In many parts of the world the cost of this energy is a secondary problem, as people who live in areas without access to clean water tend not to have access to a well-established energy system capable of delivering this power. California and Australia are exceptions, but large parts of sub-Saharan Africa face the dual challenge of an undeveloped electricity and water grid.
So how do we solve this?
One possible answer may be to couple desalination plants with renewables in a decentralized electricity system. Desalination plants in arid or windy areas may benefit from the ability to generate solar or wind electricity locally and by being directly wired to the generation equipment they eliminate unnecessary grid costs. With electricity costs accounting for 50% of the cost of operating a plant the overall levelized cost of water (LCW) could be reduced by up to 20%.
Marrying renewable energy with desalination plants can be a win win for both parties. The renewable energy asset has a steady long term revenue matching the lifespan of both assets and the desalination plant obtains a high proportion of their electricity at a price significantly lower than what the grid can offer. Combine both assets under the same SPV or in a HoldCo and you could optimise the offtake revenues stream with a single external offtake contract in the stable water market. Electricity is consumed by the desalination plant, which delivers clean water to a creditworthy party (Government or utility) at a fixed price throughout its lifespan.
If you are lucky enough to have access to a grid connection, there may be an additional revenue stream available playing the local electricity spot market. If the desalination plant can secure a fixed price for the supply of grid electricity on demand (let’s say 50 USD/MWh), whenever power prices rise above 50 USD/MWh the renewable energy asset could sell directly to the grid, benefiting from this price arbitrage, whilst the desalination plant continues to operate with electricity from the local utility, securing the constant clean water output.
As climate change disrupts weather patterns it will become increasingly difficult to predict the change in water reserves in our reservoirs. Desalination plants are not a silver bullet, but they can help to provide water security for future generations with a steady and predictable output.
For project financiers and investors, coupling renewable energy with desalination means securing a long-term stable offtake agreement for the renewable power, whilst significantly reducing the overall cost of desalination. If this combination can meet the clean water demands of society, we may not need to turn to the depths of space to find water. Perhaps Elon Musk’s dream of becoming a multi-planet species can wait a bit longer after all.