A recent twitter conversation started by the incisive Suzy Waldman highlighted the hope many energy-conscious folks have that some form of economical large scale storage technology will soon be deployed to start enabling variable renewable energy to effectively meet demand – much like dispatchable capacity already does.
If this were possible, with consideration of scale of materials and energy required to construct all this storage, then it would be great to see, especially if the life cycle analysis indicated nice low emissions per kilowatt hour (kWh) of supplied electricity.
However there are a few undeniable considerations against it being adopted at a significant scale, at least in the form envisaged by optimistic variable renewable proponents.
The limitations on net energy return on investment have been patiently fleshed out. The actual prohibitive scales of land area or physical amounts of refined metals and chemicals have also been estimated. Another factor which I suspect hasn’t occurred to many, if not most, proponents is a simple matter of economics.
As explained by FERC:
Pumped storage projects move water between two reservoirs located at different elevations (i.e., an upper and lower reservoir) to store energy and generate electricity. Generally, when electricity demand is low (e.g., at night), excess electric generation capacity is used to pump water from the lower reservoir to the upper reservoir. When electricity demand is high, the stored water is released from the upper reservoir to the lower reservoir through a turbine to generate electricity.
Electricity can be thought of as an homogeneous good, and storing excess when demand is low – and thus its cost is low – so that it can be sold later when demand – and the price – is high is the economical way to operate a pumped hydro storage facility. Further, these daily periods of low and high demand are effectively set in stone, which is exactly how an operator of an industrial facility would prefer them.
Pumped storage projects are also capable of providing a range of ancillary services to support the integration of renewable resources and the reliable and efficient functioning of the electric grid.
Which seems at odds with the previous logic, which of course it is, while also being technically true. An energy storage installation could buy oversupplied summer sunlight in the hours around lunchtime and sell it back around dinner time. Or it could buy oversupplied wind generation… whenever that happens to be, with a view to selling it at the next peak demand time. It is “also capable of providing a range of ancillary services to support the integration of renewable resources” but doing so rapidly erodes the economics of operating the storage.
So when economical storage is proposed as the large-scale answer to the shortcomings of variable renewable energy, what autocratic mechanism do proponents support for ensuring that dispatchable sources such as coal, CCGT (combined cycle gas turbine) and nuclear power are excluded from supplying it more economically?
Remember, too, that it’s the excess summer sunshine which is destined for storage. In this envisioned storage-balanced renewables grid, substantial overbuild is unavoidable.
To make it work, wind farms such as Rokkasho-Futamata feature co-sited battery installations for load levelling and reserve capacity. As the case study states:
The Japan Wind Development Company’s 51 MW Rokkasho-Futamata Wind Farm project was integrally developed with energy storage capacity of 34 MW, using NGK Insulators’ sodium-sulfur (NaS) batteries for load leveling, enabling the storage of low cost off-peak wind power for sale/ distribution during peak demand times.
A similar capability is seen for some pre-commercial concentrating solar thermal projects, where molten salt stores solar energy as heat. The cost of doing this is already apparent in such proposals as Alinta‘s pilot project.
It would be interesting indeed to see the re-evaluated economics of variable renewable energy projects if such load levelling integrated storage became standard.