Have you wanted to put on a big solar system or add more panels to your existing system, only to be told that your local electricity network operator won’t allow it? Or do you have a solar system that stops exporting to the grid once your excess solar reaches a limit? This increasing practice is called “export limiting”.
How export limiting works
Export limiting is determined by your local electricity network operator and involves using additional hardware to throttle the inverter output if certain solar export limits are reached, typically around 5kW. The network companies have been progressively introducing this rule for several years for a variety of reasons, including to reduce the effect of too much solar entering the network on strong solar production days (impacting electricity quality, creating surges, affecting transformers etc).
For example, if you have a 10kW PV system and there is no energy consumption during the day, you could technically generate and export up to 10kW. However with export limiting, the inverter will throttle the export at 5kW maximum. Any solar energy that your system has produced on top of that, will be wasted by the inverter or the export limiting device, typically as heat.
The latest state to introduce limiting is South Australia where a State-wide rule came into effect on December 1st 2017, limiting single phase solar systems to 5kW. A good synopsis of their ruling can be found here.
The impact of export limiting
Export limiting severely impacts the data that you can see from your solar system, making it nearly impossible to know how your system is performing.
Firstly, if your solar inverter provides monitoring, the inverter will only report what is produced (limited to 5kW), not what could have or should have been produced. This under-reporting means that you cannot tell if your solar is performing as it should, or if there is something wrong.
Secondly, it’s impossible to find out how much energy is lost each day due to export limiting, which affects how concerned you need to be about it.
Finding your lost energy
The only way to find out how much energy is being lost is to accurately measure your expected energy production and your actual energy production and compare them using sophisticated algorithms and deep solar knowledge.
For Solar Analytics users, your software measures your data in two main ways:
Like inverter monitors, Solar Analytics measures the output of the inverter, but it is extremely accurately (+/-0.5%) and constant (every 30 seconds).
Additionally, Solar Analytics measures solar radiation, temperature and other factors using BOM and satellite data. This allows Solar Analytics to accurately predict what your solar system should have generated on any given day.
By comparing the actual to the expected generation, Solar Analytics finds that lost energy and displays it on your dashboard.
In the following example, the Solar Analytics user has a 15kW system that has been export limited at 10kW. You can see that there is a maximum of 10kW of excess solar being exported to the grid, on top of that already being used onsite (consumption). If the consumption increases, the system is allowed to produce more solar while still not exceeding the 10kW export limit.:
You can clearly see the solar production curve mirror the consumption pattern, once the site reaches the 10kW threshold.
What you get from this information
Fault notification: you may learn that you are losing more energy than can be explained by the export limitation each day and therefore you more than likely have a fault with your system that can be fixed quickly.
Impetus for change: you may learn that you are losing 30% to 40% each day to export limiting and it’s worth doing something about it, like shifting the bulk of your electricity usage (load shifting) to the time of day you have maximum solar production or considering battery storage.
Peace of Mind: you may find out that you are only losing 5 to 10% of solar generation each day to limiting and it’s no big deal.
Right now there’s not much that can be done about export limiting rules, but the good news is that if limiting affects you, your Solar Analytics monitoring can mitigate some of the issues it can cause.