Energy

Sea-bed 'air batteries' offer cheaper long-term energy storage

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BaroMar says its undersea compressed energy storage system creates an air battery cheaper than any other for long-duration storage
BaroMar
BaroMar says its undersea compressed energy storage system creates an air battery cheaper than any other for long-duration storage
BaroMar
Energy is recovered through a turbo expander/generator at a targeted 70% round-trip efficiency
BaroMar
Cages full of heavy rocks pin these cheap concrete/steel tanks to the sea floor
BaroMar
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Israeli company BaroMar is preparing to test a clever new angle on grid-level energy storage, which it says will be the cheapest way to stabilize renewable grids over longer time scales. This innovative system lets water do the work.

The zero-carbon energy grid of the future looks remarkably complex. Solar, wind and other renewable energy sources will all contribute power when they can – but this won't match up with demand, so energy storage and release measures will be critical. And these will be needed for a range of different time scales. Some will need to smooth out daily peaks and troughs. Others will operate between days and weeks, filling in when overcast weather makes for a couple of days of poor solar output.

And then there's long-duration storage, which will attempt to stash electrons for the winter, when there'll be a seasonal lull in solar generation that wind might not make up. That's the area BaroMar wishes to address with its interesting take on compressed air energy storage (CAES).

CAES involves using excess energy to run compressors, typically pumping air into large, rigid tanks where it can be stored at high pressures, then released through some kind of turbine that can drive a generator to recover the energy. It's already quite a cost-effective energy storage option – but BaroMar says it can beat traditional systems over long-duration energy storage using an amusingly low-tech solution.

Cages full of heavy rocks pin these cheap concrete/steel tanks to the sea floor
BaroMar

Basically, the company's plants will be stationed near coastlines with access to deep water. And instead of large high-pressure tanks, BaroMar uses the pressure of the water column to store compressed air in much cheaper enclosures.

We're talking a series of big, cheap, dumb, concrete and steel tanks with cages full of rocks on top of them, to keep them submerged at between 200-700-meter (650-2,300-ft) depths. These tanks have a number of water-permeable valves around them and start out completely full of seawater. The compressor and generator systems live close by on dry land, and when there's excess energy to be soaked up, the compressor feeds ambient air down to these tanks through long hoses at 20-70 bar (290-1,015 psi), depending on the depth.

The compressed air forces water out of the tanks – but since the hydrostatic pressure of the external water equalises against the internal air pressure, the tanks don't need to be anywhere near as strong or expensive as land-based tanks that need to hold high-pressure internal air against regular atmospheric pressure on the outside.

When it's time to recoup the energy, the system allow air to run back up the hose into a thermal recovery system, followed by a turbo-expander that drives a generator. At the other end, water rushes back into the tank, ready to be displaced again when the compressor is running.

According to engineering consultancy Jacobs, which has been appointed to design a pilot project in Cyprus, the target is a round-trip efficiency around 70% – about the same as the world's largest CAES plant (a 100-MW, 400 MW/h installation in Zhangjiakou, northern China), and a very high efficiency compared to traditional compressed air systems. This underwater pilot will, of course, be much more modest, storing just 4 MWh.

Energy is recovered through a turbo expander/generator at a targeted 70% round-trip efficiency
BaroMar

BaroMar claims it should beat competing long-duration energy storage (LDES) options on cost, thanks to its long-lasting, very low-cost tanks and low-to-zero underwater maintenance costs. Running a 100 MW/1 GWh installation 350 days per year for 20 years, BaroMar says it can deliver a Levelized Cost of Storage (LCoS) of US$100 per MWh, as compared to "other LDES technologies" which, it claims, come in closer to $131/MWh.

Of course, there are challenges with anything that's designed to operate for 20 years under the sea. Jacobs, tasked with actually designing the thing to a standard that can be built, hints at the hurdles ahead. "This project requires extensive geophysical, geotechnical and bathymetric surveying, investigation, feasibility studying and permitting for tank installation at deep depths for onshore mechanical and electrical equipment needs," said Jacobs Vice President Fiachra Ó Cléirigh in a press release.

Still, the cost-effective and scalable solutions are going to win in the new renewable grids – and if BaroMar's idea does what the company claims, it'll be relevant to plenty of locations, since cities are so often close to the coast. We look forward to hearing more about this project.

Source: BaroMar and Jacobs via CleanTechnica

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12 comments
Cymon Curcumin
Proposals for this sort of concept have been floating (😁) around for decades. Maybe this time it will work but who knows.
TechGazer
I'm skeptical about the 70% efficiency claim. Compression heats the air, which would transfer to the water (which would be cold, deep down), unrecoverable. Adding a thermal transfer/storage component shouldn't be too expensive, but I'm not sure how much energy loss would be prevented. I suppose the losses won't be as bad if it's just used for short-term load-leveling, but they're proposing it for long-term storage.
Karmudjun
Nice Article Loz. The air/water displacement with "ballast cages" above sounds like an Engineering triumph, but the sea water inlets worry me. How many years of this cycle before the tanks need to be cleaned out of accumulated oceanic detritus? Besides, the air pumps would induce heating of the displaced water wouldn't it, and then there is increased sea temperature gradient (milli-degrees at first, but what impact on global warming? Not so sure on the Engineering triumph!
Magnetron
I am sceptical about the amount of carbon needed to build this system, especially using concrete tanks, relative to how much it would save in the long run. I hope I’m wrong, but we can all build systems that use zillions more carbon to build than they save just to make the governments look good. Think of the heavy-oil burning ships to seismically survey the seabeds onwards up until project completion. Using solar and wind power to lift rocks to store power is most likely better and can use recycled infrastructure.
mikewax
ballast tanks. i'll bet the guy who thought of it is a submariner.
Dcisfun
The subs and divers needed to deal with this and for regular maintenance are also factored in? I think the accumulation of silt has been neglected here and will have an impact on the movement of said compressor over time even to the point of adding wear and tear from scraping the surface away.

I want more info on fixing up the inevitable leaks from hoses and moving parts from the bottom of the seas to the surface and over land. The path from that device will have to be off limits or buried increasing costs

Falaniko
Rather than going to the expense of pumping air down to great depths couldn't you use the surplus electricity and electrolysis to creat the gases institute, while simultaneously using the water column to pressurise it.
The hydrogen could be separated for its normal use.
And the chlorinated oxygen could be used to drive turbines to assist in creating more electrolysis or peak load electricity demands as required.
SteveMc
Just a thought; what would the potential gain be if the tanks could raise from the sea/lake bed, utilising the atmospheric pressure differential as it raises? The very reason scuba divers have to exhale as they slowly ascend from a mere 20-30m depth, avoiding ruptured lungs from the air expansion over that distance.
windykites
Apart from storing electricity, is enough energy being generated by wind and solar, or is there still an energy gap?
byrneheart
These tanks could be filled with fresh water that pumps out to on land, raised storage and returns to the tank when or is generated. No need for corrosive saltwater inlets and outlets.