Energy Vault (NYSE: NRGV) has licensed six additional EVx gravity energy storage systems in China after starting construction of the world’s first facility near Shanghai.

After trying, then giving up on, battery technology (which is not exactly eco friendly), Energy Vault is designing and building facilities that essentially recreate the physics of the most popular form of energy storage – pumped hydro – but with giant movable blocks.

The design goes like this: Energy Vault installations use excess renewable energy at low times to lift massive composite blocks. Then, when the energy is once again needed on the grid, the blocks are lowered and the potential energy is turned to kinetic energy from the dropping blocks. That lowering then spins generators that supply electricity to the grid. The company believes it will be able to achieve a respectable round-trip efficiency (RTE) of over 80% with its current design.

Like many other projects, the devil is in the details – and there is growing skepticism. There is almost no solid technical details being released by the company. Many have questioned how the designs will achieve the astounding 80% efficiency when the gold standard of pumped hydro can’t usually achieve that rate. There’s no information on how the motors work or just about all the details that would be required to figure out if the claims are even remotely feasible.

Many are claiming this all smells like another Forbes 30 under 30 scam wrapped in greenwashing. Adding to the skepticism, there’s a new securities fraud investigation about Energy Vault relating to stock price manipulation. The stock has dropped almost 75% since it was introduced. This could spell bad news for the company, and China isn’t known for being lenient to scammers.