When it comes to energy production, the modern world has a glut of potential sources. Storing the energy we produce, however, has long been an issue that plagues the utility industry and limits the effective implementation of many renewable energy solutions. The inability to store energy means we could produce a glut of power during off-peak hours, and still face an energy-crunch during peak times.

The problem may not be one we face for much longer. Advances in advanced battery technology and innovative systems are already making an impact on our ability to store energy in both front-of-the-meter and behind-the-meter applications. Here are the energy-storage solutions already available in 2016—and those on the horizon.

Pumped Hydro

An old stand-by for front-of-the-meter use, pumped hydro accounts for up to 99 percent of the world’s energy storage, although some feel the system is approaching obsolescence. Water is pumped from low to high elevations during off-peak hours and stored until needed, at which point is it released. Gravity takes over, using the water to power turbines.

Lead-Acid and Deep-Cycle Batteries

The oldest type of rechargeable batteries for large-scale energy storage, lead-acid batteries bathe plates of lead and lead oxide in an electrolyte solution to release short bursts of energy. The next generation of lead-acid batteries, deep-cycle batteries, use thicker plates of lead and require less maintenance. Both generations can be used on- and off-grid.

Lithium-Ion Batteries

In 2015, Tesla Motors announced the Powerwall, a stackable, rechargeable lithium-ion battery capable of storing energy from solar or wind. Available for both commercial, residential, and utility use, Powerwall batteries can either make stored energy available for building use, discharge it back into the grid during peak demand, or keep it in reserve as an emergency backup.

Tesla isn’t the only automobile company exploring the potential of rechargeable batteries. Nissan has announced plans to make the power packs from its LEAF electric cars do double duty as home energy storage devices, envisioning a future of mobile energy storage.

Flow Batteries

Unlike Tesla and Nissan’s lithium-ion batteries, flow batteries are generally used only in large, stationary application. A membrane held between two electrodes separates two tanks of liquid. When pumped through the membrane, chemicals in the liquid interact with the electrodes to produce energy.

Compressed Air Energy Storage

Compressed air energy storage, or CAES, pressurizes air into large tanks. When needed to produce energy, the air is heated and released to turn turbines. One of the largest CAES facilities in the world, Utah’s Intermountain Energy Storage Project, stores compressed air in four enormous subterranean salt caves.

Power-to-Gas

Power-to-gas systems convert excess renewable energy into hydrogen gas, which can then be stored in tanks for months before use.

Flywheel Energy Storage

Flywheel energy storage systems store rotational energy in a large mass, or rotor, that spins in a near-frictionless container. The rotor turns a turbine-like device when energy needs to be accessed. Drawing energy slows the rotor, which is then brought back up to speed using an electric motor.