The low-carbon grids require more storage, and new technologies are successfully scaling it.

FREMONT, CA: For a future in which wind and solar power control new power plants and eventually replace other electricity sources, long-term energy storage holds great promise. Wind and solar generate power sometimes, so they need a backup technology to help address the gaps. Moreover, if they want to extend them out for several hours, the lithium-ion batteries that provide 99 percent of today's new storage power are very costly.

The issue is, there is no winner to play that long-term position. They have been following the contestants here at Greentech Media for years, ranging from quixotic defiers of physics laws to understated, scientifically minded strivers. The composition of this roster has varied according to the rate of bankruptcies and new acquisitions.

Due to two related patterns, it is finally beginning to shift. First, in the U.S. and other developed nations, wind and solar are now competing very successfully for power. In areas with high concentrations of wind and solar farms, the abundance of these tools generates its push for long-term storage. Remote or island grids, where renewables-plus-storage already outperform imported diesel fuel in price, is an especially attractive market.

Pumped hydro

A gravity-based system physically transfers water from a low reservoir to a high reservoir, from which the water goes to produce electricity when required. It dates from way long before the early days of lithium-ion and still offers about 95 percent of U.S. grid storage.

Once installed, these devices boast low storage costs and store vast quantities of energy relative to even the world's largest battery. The issue is that modern pumped-hydro storage facilities are exceedingly difficult to develop, owing to the permitting consequences of extensive water-based infrastructure and recent difficulties in implementing major construction projects in general.

Liquid air

Highview Power no longer considers itself a startup. This U.K.-based firm has changed from operating pilots to building large-scale plants after 15 years of improving its technology.

The air cools down by the company's system and stores it in pressurized above-ground tanks. The compression equipment and power producers in mature industries emerge from established supply chains. For grid storage, the technical breakthrough is using them.