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| 07/06/16

Hydro dams and compressed air cheapest energy storage options


A pair of relatively simple existing technologies has come out top in a fresh analysis comparing the costs of energy storage options that could be attached to wind and solar electricity generation to improve their cost-competiveness with non-intermittent rivals.

Wind and solar industries have mushroomed globally in recent years with the help of government-driven incentives and as manufacturing costs have plummeted. The installed bases of both have grown at roughly 30 percent annually over the past three decades, and offer an attractive installation speed and flexibility compared to traditional power plant construction. However, both technologies still only supply a small percentage of global electricity generation, and so do not yet substantially contribute to climate change mitigation.

The key barrier is their fluctuating supply of energy over time due to changes in weather, seasons and daylight hours. For these two renewable resources to be able to compete with fossil fuels, hydroelectric and nuclear power, which can provide ‘always on’ electricity, some form of energy storage technology will have to be developed that is both low-carbon to manufacture and, crucially, low cost.

Up to now, a range of studies have looked at the feasibility of particular storage technology options for specific locations and contexts of use, but comparing costs on a common scale that can be applied anywhere has been challenging. This is because some options are expensive on the power side of things (such as pumped-hydro generation equipment like turbines)—in other words how to get the energy back out once stored—but cheap on the energy storage side of things (the reservoir, as expensive as it is, is cheaper than other storage options), or vice versa, while no single technology is cheap for both the power and the energy side of the problem.

But last month, a trio of energy systems researchers published a paper in Nature Climate Change describing how they devised a new conceptual approach, in essence a set of equations that values from different storage options can be plugged into, in order to compare the various technology choices in terms of cost on a common scale.

Using the method, they compared nine different options, including pumped-storage hydro (PHS – in which water stored in a reservoir is released through turbines to produce electricity), compressed air energy storage (CAES – in which air is compressed and stored under pressure, then later heated and expanded in a turbine that drives a generator), and a range of batteries (lead-acid, nickel-cadmium, sodium-sulphur, lithium-ion, zinc-bromine, vanadium-redox, and flow batteries). They were compared on the basis of how much revenue and cost they added to hypothetical utility-scale renewable energy providers: a well performing solar farm, a well performing wind farm, and a pair of poorly performing wind and solar sites, in order to explore varying price dynamics and varying generation performance.

They concluded that PHS and CAES, technologies that exist today, did add value to wind and solar energy in some locations and for the lower end of cost estimates. PHS significantly out-performed lead-acid batteries for example. Nevertheless, they also concluded that further cost reductions in the technologies would still be needed to reach widespread profitability.

Hydrogen as an energy storage medium was not investigated however, as there currently are limited data on costs available.


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Pumped-storage hydro and compressed-air storage have come out top in a cost comparison of energy storage options

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