Posted on 01/04/2019
When monitoring your inverter, it can be useful to know whatsome expected readings might be so you know if your system is functioning aswell as it should be. To do this you’ll need to know how much solar (in Watts[W] or kilowatts [kW]) you have installed on your roof – otherwise known asyour solar array size.
There are two main power productions of interest:
Instantaneous Power in Watts or Kilowatts is often one ofthe main displays shown on your solar PV inverter. This, as suggested is thepower that the system is producing this instant. This figure is great tounderstand when best to power on appliances around the house to take advantageof the available power.
Daily Output Power in Kilowatt hours (kWh). This is arunning total of how much power has been produced that day and can be used tocompare with your power consumption as noted on your power bill.
Instantaneous Power
First we should look at what the available “average sunlight” should do for a solar system. This graph shows the expected output on an average day for a north facing, unshaded solar panel system.
While this is a fairly broad generalisation, it is fairlytypical of what you could expect to see at an initial glance what a solar systemmight produce. For instance, on an average sunny day at 10am in summer anaverage 5kW solar system would likely be producing up towards 3.5 to 4kW but inwinter you might only expect between 2 and 3kW.
Cloud cover also has a fairly drastic effect on the outputof solar panels.
On a sunny day you should see a nice smooth curved output like the above graph:
In cloudy weather things will look a little different
It is very likely that in very cloudy times a 5kW solarsystem could produce less than 1kW.
If you like the look of these graphs, check out our blog on Monitoring Options.
Daily Output Power
Most brands of solar PV inverter will give you a display ofDaily kWh or Energy Today or something similar. Consult your inverter manual ifnecessary. This is the amount of power generated by your system since itstarted in the morning.
There are again many factors to take into account toaccurately predict how much power your solar system should make each day. Butthere is also a VERY simple formula to give you a rough idea.
Daily Average Production = Solar Array Size x 4
Yes, that’s it! So a 5kW solar system should on averageproduce around 20kWh per day. You will likely see much more power producedduring great solar days in summer, probably up to 30kWh and much less powerproduced during a cloudy winter day maybe lower than 10kWh. But over the yearit should average out to around 20kWh. You don’t need to be out there with apen writing all this down, but if you would like to do an occasional check justbefore dark, check the daily total. Divide by 4 and you should have a numberpretty close to the size of your solar array.
If you feel that your system is performing poorly, the next step would be to consider cleaning your solar panels. If that doesn’t fix the issue, it would be a good idea to give your solar installer a call to discuss what else can be done. See our article on how to tell if your system is working correctly.
