Power is gradually returning to South Australia after wild storms blew across the state last night, but some areas could be offline for days.

The storm - associated with heavy rain, lightning, and severe winds - damaged transmission lines that carry electricity from power generators to people, causing a state-wide blackout.

South Australian premier Jay Weatherill told ABC radio, “the system operated as it was meant to operate”.

However senator Nick Xenophon, in calling for an independent inquiry, said “there are key questions that need to be asked”. He has also questioned whether more gas-power stations would have prevented the power failure. Deputy prime minister Barnaby Joyce pointed the finger squarely at the state’s reliance on renewable energy.

So, what did cause South Australia’s blackout?

Was it because of wind or wind turbines?

Dylan McConnell, Research fellow, Melbourne Energy Institute, University of Melbourne

It has everything to do with wind - because that’s what blew over the transmission lines. But it has nothing to do with South Australia’s wind turbines. Transmission lines are large power lines that take electricity from generators to the smaller distribution lines that bring power to our homes.

South Australia’s energy generation mix is mixture of wind, gas and some solar, and as of this year, zero coal. The state is connected to the rest of eastern Australia’s electricity market through two inter-connectors, one of which is down for service.

Where the transmission lines, managed by ElectraNet, came down is south of Port Augusta. In May this year South Australia closed its last coal-power station at the port. If those coal-power stations were still operating, they still would have dropped offline and seen the cascading failure that tripped the generations. Having those thermal generators there wouldn’t have helped at all.

A lot of generation capacity was lost because of the transmission failure. Because of that there was a voltage drop, which triggered safety protection measures that tripped the Haywood inter-connector that connects South Australia with Victoria. This could have happened in any state or with any generation technology.

Roger Dargaville, Deputy Director, Energy Research Institute, University of Melbourne

These kinds of failures in the National Energy Market (NEM) which covers the five eastern states) are extremely rare. The NEM experiences a range of extreme weather on a regular occurrence and a vast majority of the time copes well.

The system contains multiple levels of redundancy and safety mechanisms, however it is impractical if not impossible to build any complex system that is completely 100% reliable. Providing additional redundancy to insure against such events would be extremely costly, and would still not completely guarantee against further extreme events.

That being said, as we find out more about the incident it may become apparent that there are weaknesses in the grid that need addressing. However it is hard to imagine how the high penetration of renewable energy in the state could be implicated in this incident.

Just under 1,000 megawatts of wind power was dispatching onto the grid at the time of the blackout with another 400 megawatts from gas plant and 300 megawatts supply from the Victorian inter-connector making up the total. Had either of the brown coal generators still been in operation the system would not have been any more resilient to this event.

AEMO , Author provided

Why is South Australia vulnerable?

Hugh Saddler, Honorary Associate Professor, Centre for Climate Economics and Policy, Australian National University

Wide-area blackouts like that in South Australia this week are rare, but by no means unknown. For example, between 1998 and 2012 there were no less than six major blackouts in the US, each affecting many more consumers for much longer than the South Australia blackout.

In each case damage caused by extreme weather was the primary cause, exacerbated in some cases by poor management of the unfolding event. Whether that was also the case in South Australia will undoubtedly emerge from the investigations not the event.

Regardless of that, as a generalisation the electricity supply system in South Australia is at higher risk of blackouts occurring than other areas with mature electricity grids such as Europe or North America, Victoria, New South Wales and south east Queensland. This is a simple consequence of geography and population density, not of the quality of the grid per se.

In western Europe if one transmission line is knocked out, as appears to have happened in South Australia, the dense network of nearby transmission lines is usually able to supply demand by alternative pathways without any over-loading.

By contrast, the National Electricity Market grid as a whole is widely-recognised as being amongst the most the most spread-out or “skinny” interconnected electricity grids in the world. This means that there is a much lower density of alternative transmission pathways for electricity to flow, in the event of a failure on one major line.

The consequence is that the few alternative transmission routes are more likely to become over-loaded, and then tripped out, by the automatic protection systems designed to prevent further and more severe damage to the grid as a whole.

South Australia, being at the extreme end of the grid, and north Queensland at the other end, each have a relatively small share of total NEM demand for electricity, and are particularly vulnerable. Generation on one side of the failure event is cut off from customers on the other side of the failure, and customers are blacked out. On this occasion there appears to have been plenty from windfarms operating at the time.

Of course, if there were more alternative transmission lines available, the blackout may have been avoided. Equally obviously, however, transmission lines are very expensive. Whether such redundancy should exist comes down to how much electricity consumers would be prepared to pay to further reduce the risk of another supply disruption as rare, though very severe, as occurred on Wednesday.

Have the states been reckless with renewables?

Nicky Ison, Senior Research Consultant, Institute for Sustainable Futures, University of Technology Sydney

Prime minister Malcolm Turnbull has also questioned the role of renewables, stating “a number of the state Labor governments have over the years set priorities and renewable targets that are extremely aggressive, extremely unrealistic, and have paid little or no attention to energy security”.

This statement comes a day after federal government officials admitted that there is no modelling on how Australia will meet its Paris climate change targets.

Amid a national climate and energy policy vacuum at the federal level almost all state governments across Australia (not just the Labor states - New South Wales has committed to developing an Advanced Energy Strategy) are developing strategies about how to deal with the challenges facing our energy system.

These challenges include how to:

Replace Australia’s ageing power generation fleet, Facilitate growing consumer demand for new energy technologies and services such as solar and batteries, Maintain system reliability and security within a 21st century energy paradigm and Meet Australia’s climate change targets which is a moral, economic and soon to be legal imperative.

Renewable energy technologies are actually a key part of the solution. Numerous studies from many organisations have demonstrated that Australia can have 100% renewable electricity generation.

Indeed, increasing decentralised energy solutions such as solar with battery storage and micro-grids would likely increase the resilience and energy security of South Australia’s very stringy electricity network.

This is what New York has done. In the aftermath of Hurricane Sandy in 2012 which saw millions of people without power, they have launched an energy reform process to increase their energy security and disaster preparedness through micro grids and similar solutions that happen to also be low carbon. That’s what I call a win-win.

Instead of blaming states for taking action, hopefully Turnbull’s statement today will mean that we see Australia’s federal 2020 Renewable Energy Target extended and expanded to a scale that is commensurate with meeting the challenges we face.

Was it climate change?

Andrew King, Climate extremes research fellow, University of Melbourne

The role of climate change in the storm that hit South Australia yesterday is unclear. With these types of storm systems it is much harder to see the human fingerprint than it is for heatwaves for example.

For intense rainfall events like yesterday’s you need two main ingredients: a lot of moisture in the atmosphere and a trigger, such as a deep low pressure system. We know that climate change is increasing the amount of moisture in the air, but the human influence on the frequency of the triggers is far less clear.

In general the storms that track across southern Australia are moving southwards with climate change. For very intense storms like the one that hit South Australia yesterday we don’t have enough data to make a definitive statement on how they’re changing in this region.

We can’t say that climate change was to blame for this storm without a full analysis of the event.