Solar Choice recently received a comment from a visitor to our site asking about whether distributed battery storage systems – using Reposit Power‘s battery management technology – could be used to restart the grid in the event of a blackout. We reached out to Reposit for a response, and they came back to us with the article below.
We note that while Reposit Power is unequivocally an innovation leader in the distributed energy space, the issues discussed here could be addressed with other technologies as well. It is highly likely the 100% renewable grid of the future will rely on Reposit-enabled ‘virtual power plants’ alongside conventional and other distributed power plants for restarting the grid in the event of a blackout.
Restarting the grid after a blackout
In September 2016, South Australia experienced a state-wide blackout following severe storms. After elements of critical infrastructure were affected, the grid shutdown to protect itself from further damage. While large-scale blackouts are rare, the market operator, Australian Energy Market Operator (AEMO), has protocols and contracts with third parties to get the grid operational again. This is known as system restart ancillary services (SRAS) or blackstart and is provided by AEMO.
Counterintuitively, electricity generators require electricity before they can generate – it’s the old chicken and egg problem. To resolve this, some generators are paired with small diesel generators that can be started with compressed air. These small generators can provide enough energy to get a bigger generator producing electricity. Once a bigger generator is back online AEMO conducts a very complicated dance to bring the whole system back.
As we saw in South Australia, these small diesel generators are often unreliable. After two failed to start in South Australia, the grid was eventually brought online slowly from Victorian interconnectors.
The question is, could Reposit-controlled batteries blackstart the grid instead? The simple answer is yes, but there a few things that need to happen before this can happen:
- anti-islanding protection would need to be disabled;
- a high-density battery community near generators would need to be established;
- coordination with the local distribution network service provider (DNSP) is needed; and
- the batteries would need to be signalled to dispatch.
Solar and battery inverters are prevented from sending power to the grid in a blackout. This is known as anti-islanding. Anti-Islanding Protection is an important safety feature built into all grid connect inverters by law. It’s for the safety of the workers fixing the electricity grid and grid hardware.
For Reposit to start the electricity grid, anti-islanding protection would need to be disabled.
High density battery community
Reposit customers are part of a virtual power station. Solar panels and battery storage at hundreds of Reposit properties across the country are linked together and dispatch excess stored energy into the electricity system to stabilise it.
When a blackout occurs, sections of grid are isolated from one another. To blackstart the grid, Reposit houses would need to be near each other and produce enough energy to not only power their area, but also a generator.
As seen in the image above, households can’t dispatch energy straight to the generator. Houses between the last house in the area and the generator will take some of that energy. The further the houses are from the generator; the more energy is needed. To blackstart, a community of Reposit batteries close to a generator would be needed.
Coordination by DNSP
Before a generator can be restarted, coordination is needed from the local distribution network service provider (DNSP) – the company that operates the distribution grid in that area. The local DNSP would need to create a path for the network of Reposit-controlled batteries to dispatch to. The DNSP would need to close breakers and control the transmission connections and flow of energy from batteries trying to start the generator.
Reposit signals batteries to dispatch their excess power via an internet connection. If there is no path to get the signal through, it is impossible to tell the batteries to dispatch. 4G communication networks would still need to be operational, or household internet routers would need to be on the battery circuit for Reposit-controlled batteries to dispatch in a blackout.
Batteries and blackstart
If anti-islanding protection was disabled, there was a high-density battery community near generators, coordination from DNSP, and internet connection to signal the batteries to dispatch, Reposit-controlled batteries could provide and perform a blackstart.
As we saw in September, SRAS services aren’t always reliable. South Australia tried to power up the grid from these small diesel generators, but two failed, and ultimately the South Australian grid was restarted from a transmission line in Victoria. Reposit-controlled batteries pose another option for providing this service.
Each year tens of millions of dollars are paid by AEMO to buy SRAS from generators. If Reposit battery communities could provide this service, it would be provided at a much lower cost. This would see everyone’s bills lowered and Reposit customers earn additional GridCredits for providing this essential service to the grid.
- Could distributed battery systems ‘blackstart’ the grid? - 17 May, 2017
Out of interest, In a Reposit controlled battery storage installation can Reposit (via some internet connection disable the anti islanding function of the battery or PV inverter. If not by what means can the anti is landing function be by passed or over ridden.
Hi Patrick – we’ve reached out to Reposit for a response and they’ve told us that they’re working on it. Hopefully they will get a response to you by tomorrow. In the meantime, perhaps someone else with a bit more insight into this sort of thing will have a response for you.
For what it’s worth, we do know that some ‘gateway’ solutions like Reposit’s Reposit Box function over 3G networks as opposed to WiFi – and perhaps these could theoretically be used as a ‘trigger’ to signal inverters to switch back on when the time is right.
Further to my previous comment, response from Reposit below:
“No, we cannot disable the anti-islanding. That is specified in AS4777 and so would require a standards change.
If that were to occur then the inverter would allow us to command an export of power into a dead grid connection.”
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