Next Steps
The final design hurdle is developing the piston seal. The GPM uses a stationary seal system mounted halfway down the main shaft. The seal must have low friction along the moving piston but must also hold against a pressure differential of ~500 psi and accommodate small piston diameter variation. In planning is a 2-m seal test to identify the optimum sealing material, followed by a full-scale 30-m test at full pressure and maximum piston speed. The seal development is a solvable problem; it may even involve using an off-the-shelf product.
The piston seal is the last preliminary design milestone for the GPM. The next step is to build the proposed demonstration plant. It is for these tests that the Series B round financing is being sought.
Gravity Power holds the promise of reasonably priced, easily sited, and insignificant-environmental-impact bulk energy storage. I predict that the GPM will soon be a critical part of grid of the future, both in the U.S. and other countries.