"Battery storage is the future of our national energy market, and the eyes of the world will be following our leadership in this space," he said. The declaration by Elon Musk that coal doesn't have a long-term future has rankled politicians. Credit:ABC The project is intended to sustain 100 megawatts of power and store 129 megawatt hours, which could power about 30,000 homes according to Tesla. That was more than three times as powerful as the world's next-largest such battery, Mr Musk said on Friday. The billionaire entrepreneur, who first expressed interest in the project over Twitter in March, promised to stick by his pledge to have the system installed and operating within 100 days from signing a contract "or it is free". "That's what we said publicly, that's what we're going to do," Mr Musk said.

The project, slated for completion by December, will harness the existing Hornsdale Wind Farm to charge the mega-battery while the wind is blowing and discharge power when it is most needed. South Australian Premier Jay Weatherill (right) with Treasurer and Energy Minister Tom Koutsantonis. Credit:AAP "It's a fundamental efficiency improvement to the power grid, and it's really quite necessary and quite obvious considering a renewable energy future," Mr Musk said. Romain Desrousseaux, deputy chief executive of Neoen, said the project would demonstrate "large-scale battery storage is both possible and now commercially viable" and can provide "dependable, distributable power". South Australia's electricity troubles, including numerous blackouts, have become a politically contentious issue between the state and federal governments, amid debate about the capacity of renewable energy.

A freak storm in September destroyed transmission lines, triggering backup systems. A key interstate connector with Victoria was ultimately tripped "off" due to automatic safety precautions. But early responses from Energy Minister Josh Frydenberg and other commentators pinned some of the blame on the state's reliance on renewables. In a final report, the Australian Energy Market Operator said a higher reliance on "non-synchronous" forms of energy such as wind and solar meant the power grid was "experiencing more periods with low inertia and low available fault levels", and was more susceptible in times of crisis. "AEMO is working with industry on ways to use the capability of these new types of power generation to build resilience to extreme events," the report noted. Loading Tesla, which had become the most valuable carmaker in the US, has seen its share value fall by 20 per cent since June 22, losing $US12 billion ($15.8 billion) in market capitalisation.