New competition for energy storage and demand response schemes?

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By Michael LoCascio

Reverse osmosis (RO) plants – even with the best energy recovery systems – use about 2.7 kWh/m³ (in addition to energy used in pretreatment) of product water, all of which is derived from electricity. Although flow rates – and hence total energy use – varies considerably from plant to plant, all but the smallest systems for hotels and other site-specific applications use prodigious amounts of energy. 

For example, the Carlsbad 50 mgd desal (190,000 m³/day) plant uses 513,000 kWh/day (an average power of 21 MW). It is for this reason that RO plants are often collocated with power plants and because the warm saline water exiting the power plant requires less energy to remove salt and shared infrastructure reduces capital costs.

Although most people are aware of desalination's primary objective of producing potable water from saline or brackish seawater and inland sources, it's less well-known that reverse osmosis desalination facilities act as a form of spinning reserve – albeit one that modulates demand instead of electricity supply – that can actually stabilize the grid. This is possible because, unlike energy, there is inexpensive and extensive water storage infrastructure in the form of aquifers and reservoirs.

In a discussion a few months back with Poseidon, a developer of RO plants in the U.S., it was mentioned that its facilities pay a "ridiculously low rate for power" because they agree with utilities to modulate its pumps (and hence water output) as a function of grid demand. When more power is needed – even on short intervals – the desal plant throttles back on production, and conversely, makes more freshwater when demand is slack. 

In short, continued rapid deployment of RO desalination plants may serve as a new source of competition with some of the other nascent energy storage and demand response schemes under consideration. Furthermore, although desal plants are often derided as energy hogs by detractors, they may, ironically, help support the deployment of intermittent renewables like solar and wind.

Michael LoCascio is a senior analyst for Lux Research, which provides strategic advice and on-going intelligence for emerging technologies. For more information, visit the Lux Research site.

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