Image the scene. It’s a beautiful summer’s day and the sun is strong. You’re lying on the beach, enjoying a drink, and decide to check your Solar Analytics app to see how much your 15kW solar system at home is generating – it should be at almost 100% output. You know the AC and a few other things are on, but that’s usually only 5kW. So the other 10kW should be going straight to the grid, earning you lovely feed-in credit!
But you’re surprised to find out that only 5kW is going to the grid. Why? Where are those last five kilowatts?
The answer is export limiting, also known as export control.
First, the good news. If your system is on a 5kW inverter (even if you have 6.6kW or more of panels), you very likely have no export limit. So you can ignore everything below, if you so desire.
But if your inverter (note this always applies to inverter size, not solar system size) is larger than 5kW, you may be export limited.
The basic premises is to avoid power cuts – as backwards as that may sound. You see, if every solar panel started generating MWs of power and exporting it all to the grid, the grid may struggle. After all, it was built decades ago to cope with dispatchable coal-fired stations, not variable renewable energy! If the grid was suddenly flooded with power, it could damage the equipment, cause it to fail, and cause a brownout or blackout.
Until the grid is upgraded (hurry up AEMO!) the “solution” is to limit the amount of free clean power the grid can receive.
This export limit varies by region, and the quality of the grid in your area. Regional/rural areas tend to have lower export limits, for example. Your 20kW system could have no export limit (i.e. able to export the full 20kW), perhaps only up to 5kW (common for single-phase supplies), or worst-case situation, 0kW a.k.a. zero export. This is where the expertise of your solar retailer comes in.
Note that this only applies to energy you’re not consuming. If you’re using 5kW, exporting 5kW, and “wasting” 5kW, but decide to turn on an 8kW AC unit, you’re now using 13kW, exporting 2kW, and wasting none.
This export limit can be achieved in a couple ways. Many inverters, especially top-of-the-market ones such as Fronius, provide smart meters that can provide the export control function. If you decide to go with a cheaper inverter, you may have to purchase a seperate export control board.
At GI Energy, we don’t like the hassle, so we only provide market-leading solar systems that include quality panels, inverters, and smart meters.
And the excess energy…?
You might be wondering “what happens to the energy that is generated but not used or transferred back into the grid (or stored in a battery)?” The simple answer is nothing. The slightly less simple answer is it is converted into heat and dissipated into the air – much like the sunlight itself would do. And don’t worry, it won’t damage your panels.
Another related concept is network protection. This is for larger systems; combined inverter capacities over 30kW. Technically it’s 30kVA, but for this simple explanation we can consider 30kW = 30kVA.