Well, this 80% efficiency is what they are targeting not what the system will do.
The test system Energy Vault build in a MUCH smaller form factor had a round-trip efficency of 75%
The EVx ™ system is projected to achieve an impressive round-trip efficiency exceeding 80%. Source
Only time will tell if they can reach 80% with a bigger system or at all. If they actually manage this it would be a decent alternative to Hydrodams in areas where these are just not possible since it would be a similar round-trip efficency.
Pumped storage systems have a round-trip efficiency of about 80%, which is competitive with battery storage. Source
In my opinion these systems are inferior to fly wheel energy storage (can reach up to 90% round trip efficency
Source) but might still be an option depending on price.
Fly wheels are pretty cool too, it could be that this is just easier to build and maintain though. I imagine the primary considerations are around how cheap it is to produce and whether it holds enough energy to make it worthwhile.
What about friction within the pulley?
Again, they state over 80% efficiency in the article. So, that’s your answer.
Well, this 80% efficiency is what they are targeting not what the system will do. The test system Energy Vault build in a MUCH smaller form factor had a round-trip efficency of 75%
Only time will tell if they can reach 80% with a bigger system or at all. If they actually manage this it would be a decent alternative to Hydrodams in areas where these are just not possible since it would be a similar round-trip efficency.
In my opinion these systems are inferior to fly wheel energy storage (can reach up to 90% round trip efficency Source) but might still be an option depending on price.
Fly wheels are pretty cool too, it could be that this is just easier to build and maintain though. I imagine the primary considerations are around how cheap it is to produce and whether it holds enough energy to make it worthwhile.