Solar Backstop Mechanisms - The what and the why
A Solar Backstop Mechanism is a way for electricity system operators to reduce or switch off rooftop solar generation. This blog looks at why this is important, how it works, and what happens when it gets used.
If you just want some quick advice on what you should keep in mind, jump down to our checklist!
Why are these backstop mechanisms being introduced?
To understand the “why”, we also need to understand the “who”, and there are two key players here:
- the Australian Energy Market Operator, who is responsible for keeping the National Electricity Market working; and
- Distribution Network Service Providers, who maintain the poles, wires and transformer boxes that allow electricity to flow from generators to consumers. Depending on where you are geographically, this varies - it could be Ausgrid, Essential Energy, Ausnet, Energex, among others.
The Australian Energy Market Operator (AEMO)
The market operator cares about balancing supply and demand, and doing this at the lowest cost possible. The electricity system is not a battery - generators don’t pool energy in which consumers then consume when they switch on a toaster. Instead, when that toaster switches on, somewhere there is a generator that starts working a little bit harder to meet that additional demand. This is why we build big interconnected electricity grids across state borders - more consumers and generators makes it easier to balance everything. The odds are, when you turn your toaster on in the morning, someone else’s toaster has just switched off, so the overall demand that generators need to meet is nice and smooth.
Lucky for AEMO, total generation from rooftop solar is not too hard to predict. As a cloud passes over your house, it moves away from someone else’s, kind of like the toaster example. We combine consumer demand and rooftop solar into a measurement called “operational demand” - the demand that big generators need to meet. On very sunny days, particularly in spring when air conditioning isn’t required, we can see “minimum demand events”, which signify such low operational demand that AEMO can’t keep big generators spinning.
Yippee! That means we get to switch off coal and gas, right? Not quite. Lots of rooftop solar inverters are grid-following, which means they follow what the grid is doing, and if there is a disturbance, they tend to switch off in case there is a fault. This makes it very scary to run a grid on purely rooftop solar (right now, at least - grid-forming technologies and applications are developing!). Additionally, it can take hours to restart a coal generator, meaning that shutting them off isn’t a valid option if we’re likely to need them again soon. This means AEMO often tries to keep a certain amount of spinning machines running at any one time, but those machines need to be feeding load, and if there isn’t demand for them to supply, they can’t run. This is one reason why AEMO might need to reduce rooftop solar outputs for brief periods of time.
AEMO also needs to consider trips (also known as contingency events). Just like household circuit breakers can trip sometimes (sometimes for good safety reasons, and sometimes seemingly for no reason at all), the big transmission interconnectors that form the backbone of the electricity market can also trip. This can be particularly dangerous if one region is feeding a lot of power to another. For example, imagine it’s hot in Queensland (imagine?) and the aircons are cranking, with a tonne of energy flowing up from the southern states. Then, the NSW-QLD interconnector trips, leaving QLD to meet demand on its own, and NSW with a bunch of energy that has nowhere to go. This would be a situation where being able to rapidly reduce solar output in NSW would be critical to preventing bigger problems and allow NSW to re-stabilise into a supply-demand balance, while the interconnector problem gets resolved.
Distribution Network Service Providers (DNSPs)
DNSPs are the poles-and-wires people who you probably know from the faults & emergencies phone number on your electricity bills or the plaques they stick on their powerline poles. We’ll call them Networks (capitalised) here when referring to the businesses, in contrast to referring to the physical network infrastructure. In the past, their job was pretty simple - power comes in from the high-voltage transmission system, and they install poles and wires that carry it out to houses, stepping the voltage down to safer levels as they go, similar to running high pressure pipes for the long distances, but dropping the pressure down before delivering it to houses. There is one assumption which hasn’t held up particularly well - that power is only going to come in from the high voltage end of the system! Rooftop solar flips this on its head - now, we have generators connected to the low voltage network, and if the power they supply can’t be consumed locally, it has to flow backwards through transformers and substations - something that the distribution networks weren’t really designed for.
This was fine while a minority of households had rooftop solar, but with more solar being installed, problems arise. Not many people are at home using power at midday, but that’s when solar production peaks, so you can have entire suburbs acting as net-generators. In fact, you can have all of the suburbs acting as net generators, but getting that power back to industrial zones and other large loads is challenging. Even if DNSPs build up the physical infrastructure to better handle this powerflow, it becomes a lot like the trip scenario described above, which AEMO has to manage. If something goes wrong or the network doesn’t have capacity to offload excess power, rooftop solar needs to be turned down, or off, to prevent bigger issues.
How does it work?
The implementation in Australia’s electricity market is that Networks are responsible for managing solar backstop. If AEMO needs to engage a backstop, they do so via controls that the Networks are expected to have in place.
Connecting any new generation to a distribution network, such as solar panels or batteries, requires connection approval, so this allows the Networks to manage and enforce requirements such as solar backstop compliance. When adding a new inverter, the connection application will now require an inverter from a list of complying options to be used. Solar installers will complete the pre-approval for connection, and then proceed with installation of the hardware.
The way the Networks talk to inverters (or other devices which can control the inverters) is via a communication protocol called the Common Smart Inverter Profile Australia (CSIP-Aus), where a server operated by the Network tell inverters them how much power they can export to the grid at any given time*.
Therefore, the hardware needs to be connected to the internet so that it can receive solar backstop signals as needed, and if it loses internet connection (for example, if you change your WiFi password), then it must default to an export limit of 0kW. If you don’t have consumption monitoring installed and connected to your inverter, then it will completely shut off all production when it loses connection to the internet, so consumption monitoring should be seen as a must-have for backstop-enabled installations.
What happens when the backstop is used?
There are a few kinds of signals that can be sent via the CSIP-Aus interface as part of the backstop mechanism, and we won’t go into detail here, but there are three kinds of outcomes that are worth understanding:
- Switch off: Pretty simple - all inverters need to switch off and stop producing. Loads within the house will be forced to draw from the grid.
- Zero export: For systems that have consumption monitoring (can measure power flows to/from the grid), limit generation to meet loads behind the meter only. Don’t export out to the grid. Installations that can’t measure power to/from the grid will have to switch off entirely.
- Reduce export: Reduce exports to the grid to below a limit. House loads are still met first, and some power can also be exported, but solar may still be turned down to obey the export limit. This isn’t really part of the critical backstop mechanisms being rolled out, but it is a capability that the CSIP-Aus interface allows for, and many Networks are moving towards Dynamic Connection Agreements, which will use these signals instead of static export limits, to allow greater exports when the network can handle them, and only reducing exports when the network reaches its limits.
*There are still a few other older mechanisms in place that achieve similar outcomes, but we won’t go through those here. All networks are moving towards a CSIP-Aus approach.
Conclusion
So, are solar panels still worthwhile? Yes, and not just because we install solar panels and batteries! The backstop mechanism is a safety system to allow more solar to be installed into the grid at the distribution level, which empowers homes to reduce their own energy costs. It is also a key part of transitioning the electricity grid to renewable energy. If we are serious about running the grid on solar, batteries and wind, we need these technologies to actively participate in energy markets, and respond to electricity system needs, just like big generators have always done. It’s a critical maturing of this technology. We don’t expect the backstop mechanism to be used unnecessarily, and consumer watchdogs and regulators will certainly keep an eye on it too.
This does introduce more complexity, which in some cases may increase the cost of solar and battery systems, but it has been a long time coming. Reposit Power demonstrated our first solar curtailment technology back in 2018, with the knowledge that this would be critical in the future of the energy transition, and it’s a key part of why we can offer a comprehensive No Bill guarantee in a turbulent time for the energy system and energy consumers. It’s not all about us, either - we’re keen to see what other business models emerge as consumer energy technologies become a major part of the energy system!
Quick Advice for navigating solar backstop
- Backstop mechanisms are in place in SA, VIC and partially in QLD. They are coming to NSW & ACT next year.
- It will not be applied to any existing installations, unless you make significant changes/upgrades/repairs.
- Make sure to install consumption monitoring with new inverters - this allows your solar to continue meeting your house loads even when the backstop requires it not to export. Without consumption monitoring, all backstop signals will result in a total shut-off of the inverter*.
- Your backstop-enabled inverter needs to be internet connected, or it will not work effectively. Consider requesting a hard-wired LAN connection or 4G connectivity, so that WiFi password changes don’t reduce your solar generation!
- Solar backstop allows the grid to host more renewable solar power. It’s a good thing for the energy transition!
- Consider a Reposit No Bill system, and let us handle the tech, the complexity and the risk, while you get a guarantee of No Bills!
*It is possible that some inverter manufacturers may implement a very “dumb” management of the backstop mechanism, and shut-off inverters entirely even when consumption monitoring is installed.
Marlon is an Operations Engineer. Reposit Power is a an Australian energy technology company that helps households completely remove their energy costs, and applies technology to guarantee those costs won't come back.
