FYI: 129 MWh would be about 1300 42U-style racks for batteries alone.
Source: there's a guy in socal (Jehu Garcia) building a reclaimed peaker 1 MWh pack in about 10 racks from used batteries and equipment (50 kW 480VAC inverter) on the cheap in order to store energy off-peak (plus possibly charge using solar) and use it at peak supplemented by grid power. This is how manufacturing and other heavy industry / large electrical consumers can save money right now in US day-of-use billed grid systems.
Jehu Garcia's Youtube videos are definitely worth checking out, the guy is doing cool things with 18650 lithium ion cells. He converted a VW bus into an electric vehicle. My main takeaway after watching his videos and others in the same vein is that lithium ion battery packs are the gasoline of the 21st century.
You can build 18650 packs for electric bikes, scooters, boats etc... or build your own Power Wall type home electric energy storage.
The costs of these cells coming out of China have gotten down to $1 each in some cases of excess inventory...
Indeed. I hadn't actually reviewed ebay for electronics things for a couple of years, because any of the products I used to see there were significantly more expensive than anything I could get from aliexpress. It looks like, at least in this instance, that has turned around. I could even see individual 18650 cells for $1.
Wouldn't some kind of gravity-based storage be cheaper/safer? Just lift some huge weights with excess energy, lock it in place, and then let gravity pull it down to reclaim it.
Australian Synchrotron is already using three giant flywheels as an UPS, here is a short presentation. I am sure that you will be able to find enough information to determine if doing this would be feasible on a commercial scale.
There are a few experimental installations of these around. I don't believe they are viable for larger scale storage, but fit smaller scale they seem competitive.
Source: there's a guy in socal (Jehu Garcia) building a reclaimed peaker 1 MWh pack in about 10 racks from used batteries and equipment (50 kW 480VAC inverter) on the cheap in order to store energy off-peak (plus possibly charge using solar) and use it at peak supplemented by grid power. This is how manufacturing and other heavy industry / large electrical consumers can save money right now in US day-of-use billed grid systems.