Thus far, batteries haven't taken over grids around the world. Due to the sheer expense of batteries, large installations have generally been government mandated or heavily subsidized. In South Australia, though, Tesla's giant 100MW/129MWh battery has seen a lot of success—not by selling power to meet general demand but by providing so-called "frequency response services." And a company called Restore has just partnered with Tesla to replicate that success for itself in Belgium.

In South Australia, Tesla Powerpacks are charged by the energy from a nearby wind farm, and the battery installation dispatches electricity to the grid when grid frequency suddenly drops. Grid frequency—a measure of current that must be held constant for the grid to work properly—is vitally important to the functioning of any grid system.

In Europe, for example, a recent power dispute between Serbia and Kosovo led average frequency on the Continental Europe Power System to drop to 49.996Hz instead of the required 50Hz, which resulted in oven and microwave clocks everywhere across Europe being six minutes slow after just a month of these conditions.

Grid operators will generally pay a premium for frequency response services, which are often provided by natural gas plants or other generators that can reliably ramp up and begin sending power to the grid in minutes' time. But in South Australia, Tesla's battery has been valuable in that it's able to nearly instantaneously send power to the grid as soon as frequency fluctuates. Compared to other spinning generators that might compete with the battery, it's very fast.

That has allowed Tesla's battery to take advantage of frequency response pricing, which has piqued the interest of investors. And according to a recent presentation by some McKinsey analysts, the battery has been able to cut South Australia's frequency-maintaining costs by up to 90 percent. In addition, the battery has taken over nearly 55 percent of the Frequency Control Ancillary Services (FCAS) market on that grid, according to McKinsey.

The Terhills, Belgium, installation, which Tesla teased on Monday in a tweet, is considerably smaller than the Australia installation, but it's meant to do largely the same job. In an email to Ars, Tesla said this latest installation is made up of 140 Tesla Powerpacks that can provide 18.2MW of power or store 21.7MWh of energy. In addition to putting power on the grid when frequency is low, the battery installation also charges by absorbing power when there's too much energy on the grid.

According to The Energyst, however, the new battery isn't going to replace any big generators on the grid in Belgium. In fact, Restore's business will also use these batteries to help other types of generators ramp up to deliver power to the grid for a longer period of time, if power is needed for a full hour or more, according to an October press release.

Restore plans to replicate the model in the UK as well, on a smaller scale. Though it's not exactly taking generators off the grid, Restore is helping to make the case for economic battery installations. And as the battery market gets bigger, more competitive, and more experienced, the hope is that prices for batteries will come down far enough to justify them on a larger scale.

Listing image by Tesla