OSMOTIC ENERGY STORAGE
Most renewable energy is intermittent - wind doesn't always blow and the sun isn't always shining.
The gap in the intermittent supply of renewable energy to the continuous demand of energy is one of the biggest hurdles towards transitioning to a clean energy infrastructure.
What Are The Options?
When energy storage is mentioned, lithium batteries, flywheels, heat energy storage, or pumped hydro may come to mind. To date, pumped hydro energy storage accounts for over 96% of the worlds grid-connected energy storage systems in terms of rated power output. Whereas lithium batteries are less than 1%.
 DOE Global energy storage database
Pumped Hydro Popularity is Rising
but there are only so many hills
Over the past 35 years, an average of 4 new pumped hydro plants have been commissioned each year. The demand for pumped-storage is expected to grow, but suitable locations for large reservoirs in mountains and hills are shrinking. Fortunately, an alternative technology that can fit the role of pumped hydro is being developed by Pani Energy, Osmotic Energy Storage (OES).
The key difference between OES and pumped hydro technology is that OES is geographically unconstrained. Pumped hydro requires significant elevation difference between its two reservoirs to store an equivalent potential energy (per unit of water) to OES technology. With OES, we replace the mountain-top reservoirs of pumped hydro with semi-permeable membranes used in the desalination industry.
A Salty Solution
Osmotic Energy Storage (OES) can be understood as a comparison to pumped storage hydroelectric generation. Pumped hydro operates on the principle of gravitational potential energy, storing water in reservoirs at an elevation difference, OES stores energy based on chemical potential energy, the concentration difference between two reservoirs or tanks. This allows the energy storage facility to be closer to cities for improved reliability and reduction in transmission line expenses.
Furthermore, OES has the potential to convert waste-heat to stored energy. For example, low-grade waste heat from thermal power plants or industrial processes can be used to separate fresh water from salt water using distillation, creating the chemical energy potential required for OES electricity generation.
How Good Is It?
OES can have roundtrip efficiencies in the range of 30-70% and leveled costs of 0.10-0.60 $/kWh
For comparison, toxic lead batteries have efficiencies of 77-86% but cost around 0.7-1.7 $/kWh.
Where Do We Start?
An expected $4 trillion of electrical infrastructure upgrades in the next 20 years will require an energy storage technology. The initial target markets for OES are medium scale services, with several applications, including: continuity of renewable energy in places like Germany; powering remote systems in places like Hawaii, Caribbean; assisting with electric infrastructure upgrades for developing countries with growing electricity demands like India and Brazil.