> Adding a market participant with the motive and means to buy when the price is low and sell when the price is high reduces the price volatility.

Anecdotally, I've heard from people who work in business related to the australian energy market that it is sometimes profitable to push the electricity system in a direction that increases imbalances of supply & demand (i.e. increase the volatility of the actual system -- not merely the price) in order to maximise profit of an individual market participant.

That's not clear. California briefly had total deregulation with a power auction ever half hour, and volatility increased so much that there were blackouts. Expecting markets to produce stability is naive. Markets don't typically converge on some equilibrium, they oscillate around it.

This is true, and one of the reasons the Telsa battery was able to make so much profit was because it took the peaks off the very high peak prices that other market participants were happy to allow to occur before.

There is a market regulator that stops most of the worst of the manipulation that happened with Enron, but it is an imperfect system.

Large parts of Australia are on a single market, but with separate quasi-state based pricing sections. South Australia had a difficult market, with large amounts of renewable power (mostly wind and roof-top solar) and a single interconnector to coal-fired stations in another state.

That left it very vulnerable to price spikes, especially at ~17:30 during summer when people would get home from office and turn on their air-conditioners. That would case huge price spikes.

The big battery is able to supply enough to get over much of that peak load spike, and an additional gas generation peaker plant along with even more geographically diverse renewables has fixed the rest of that problem. There is a second interstate interconnect being built too.