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.