Pumped Hydro
The Silent Giant of Energy Storage
Brief housekeeping
This is the first week I’ve done this letter from a proper publishing platform. I had been holding off moving it from a simple email as I wanted to keep an informal feel. On balance I’ve decided that benefits around ease of sharing, insights, GDPR compliance and, let’s be honest, formatting, outweighed any drawbacks. I’ll still endeavour to keep the tone casual and can pretty much promise that typos will persist. In the name of continually striving for better answers, I very much welcome feedback or alternative views on anything covered. And, please do share with anyone who you think might find these valuable. (If you are receiving this from someone else, you can subscribe using the big blue button below. Obviously.)
Climate action, like so much else, is driven by narrative, pushing where people focus and what is top of mind and influencing capital flows. Some areas get disproportional air time relative to their (near term) climate impact. (Longer term readers will have noticed more than a few notes on CDR and nuclear fusion.) Older or simpler technologies with big impact get overlooked, e.g. fat, straight pipes, from last week’s Notes. This is probably nowhere more true than in the sphere of energy storage. Batteries get a huge amount of focus, as do new mechanical storage methods like Energy Vault. And yet >90% of today’s energy storage capacity comes from a hundred-year old technology - pumped hydro. For anyone not familiar, pumped hydro involves using excess electricity at times of oversupply to pump water from a lower reservoir to a higher reservoir, and then releasing back through a turbine to generate electricity when it is needed, with similar round trip efficiency as batteries (around 80%). Like so:
Source: www.hydropower.org
Part of the reason that pumped hydro gets less attention is that it requires quite specific topography and there is generally an impression that most of the best spots have been taken. This is probably especially true where there is a process of environmental permitting and public comment, such as… not China, where State Grid just commissioned the world’s largest pumped hydro project (at 3.6GW around x10 bigger than the biggest battery system).
This topographical restriction on growth does see pumped hydro overtaken by batteries in terms of new storage additions over the coming years, but the IEA still expects pumped hydro to account for 42% of capacity additions over the next five years, with the International Hydropower Association estimating 50% growth in pumped storage capacity by 2030 to about 240GW. The IHA has a fun interactive map of all of the projects, existing and planned / under construction. Again, China.
Source: IEA
There seems to be scant innovation around traditional pumped hydro storage, but one company, RheEnergise, is taking an interesting approach. They’ve developed a system that uses an ecologically benign liquid that is x2.5 as dense as water, allowing the projects to be commensurately smaller and lower differences between upper and lower reservoirs.
Ripple Effect: Pumped-hydro electricity storage
Pumped hydro has been around for >100 years. Has historically been used to absorb excess energy from coal or nuclear (firm, inflexible generation) at times of low demand. Now more being looked at in relation to adding storage to renewables projects.
Principle challenges are around siting:
needs to have min 300m, or ideally 600m elevation (or “head”) between upper and lower reservoirs
needs to not conflict with critical natural habitats or cultural heritage sites
has to be able to access the water without impacting other uses
no severe visual effects
able to access transmission lines
Permitting is always subject to a period of public comment. This is where many projects come unstuck and favours investing significant time and care with the initial site selection, anticipating any areas of objection.
Closed-loop pumped hydro projects usually provide about 8-10 hours of electricity. [This compares with 4-6 hrs for utility scale battery storage.] So, whilst they can store the energy more or less indefinitely (excepting some evaporation losses), the total capacity will struggle to cover big lulls in generation.
There are about 150 projects operating globally - 42 in US. Japan has pumped hydro equivalent to 20% of grid capacity.
There are some specific opportunity to repurpose waste water currently being squandered, e.g. a water treatment plant that dumps >1m litres of water into the desert every day where it just evaporates.
Regarding water usage, whilst there is an initial investment of water to fill the reservoirs, the ongoing usage is relatively minimal, just offsetting the evaporation. This is especially vs thermal generation (e.g. coal plant). Take example of a project in Wyoming, where the utility had water rights for 20,000 acre-ft already reserved for a coal plant that never got built, and only needed to allocate 4,200 acre-ft for the pumped hydro project. [The relative capacity of each was not shared.]