system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:What are Tesla's "Battery Farms" and how do they work?
gpt
Australia has a problem.  The ways that they generate electricity are fairly constant from moment to moment, but the demand for electricity is not. 

While they have lots of resources and abilities to generate electricity, demands are far too spiky.  Meaning, during the hottest times of the day everyone is turning on their AC.  That uses up LOTS of electricity.  Most of South Austrians generation is done through wind power and that's a fairly constant generation, even overnight.  

So while on average demand is meeting supply, there's a problem of timing. Basically, there's lots of electricity at night time, when no one wants it and not enough at noon when everyone needs it.  This causes blackouts, and that's bad.

The solution here is to store the electricity for use later.  Generate it all day and store it in batteries so that they can draw down during the hot times. That is a battery farm.

It's really just a very large amount of batteries all in one place. Tesla recently has been building the world's largest battery factory (called the Gigafactory).  Batteries, funny enough, are one of the things in this world that we basically can't make enough of.  Batteries are in VERY high demand for everything from laptops, and cell phones, to electric cars.  

So using them for something like this battery factory was previously kind of a nonoption.  It simply took so many that it would be too expensive.  So electric utilities would look at other solutions like importing electricity from other districts or turning to non-renewable sources that can be easily turned on and off (like a coal plant).

Tesla's very large factory has recently started pumping out batteries and that is what's allowing Tesla to do things like sell battery storage products to the home consumer market (the Tesla power wall), sell inexpensive electric cars (like the Model 3) and do battery farm projects like this.