Calculating spare/potential PV capacity

[mrgrumpy83]

Right now, my system will cap solar production to whatever the maximum export rate is set to + house load is (on sunny days, when there's enough generation etc) once the battery is full. Currently this is after about 9.30am.

I'm wondering though, if there's a way to work out what the potential available solar power is at any one time. For instance, if I'm exporting 5kW, house load is 1kW and the battery is full, then the solar will be producing 6kW. If I turn on a large load (say, ducted aircon), then the solar will ramp up to match the load, where it can. Sunny at midday I will max out the capacity of the 10kW inverter.

What I'm wanting to do is be intelligent about loads - but with the option to keep maximum exports as part of this.
In my example above, there would be 4kW of excess capacity - realised when turning on a load that draws 4kW. Is there any way using the sensors available to calculate what the PV could be producing if there was a load to match it? I want to use the resulting figure to enable additional loads.

Eg -
Available Capacity = Solar potential - export - house load
(to a maximum of inverter capacity).

Single Phase, 10kW.
14.5kW panels.

[AndyFlysJabs]

OK, so Im not an elec eng just an electronics tech so it may be that I don't get this fully accurate, but as I understand it the system only measures and pulls what is needed at any point in time from the solar panels. In the case where what is needed is close to what is able to be produced then the MPPT in the inverter will kick in and match the PV impedance to the inverter impedance so that we get the most possible power transferred from the circumstances faced.

As such the system knows what is needed but never what the maximum potential is available at any point in time is, if the load was there to support the supply potential. In the old days your inverter simply ran flat out and you were always able to assume that exports at any point in time was what was available for increased load (self consumption) should you feel the need to kick something else on inside your house.

So how do you know what extra capability you have at any point in time to enable more effective automation and use of potential available:-

1. you can estimate using solar PV forecasting to get what the 3rd party providers who are in the know feel that you should be seeing at your place. HA comes with one out of the box, but depending on where you are in the world the data provided might be good...or not so much. For me, in Australia it wasn't great and I went with a local provider Solcast who has a free offering for enthusiasts, but I get the impression that better results are available as you start to pay for the service. For example on my house I have North East and West facing arrays, Solcast for free will only allow only 1 array in a house, if paid service then I can more accurately model what I have. I have a dirty big mountain (hill anywhere else in the world) to my west and I don't know if their model takes it into account, curtailing expected outputs as the sun dips behind the hill or not..... anyway, they offer a whole bunch of estimates like this:-

these sensors are useful in determining in automation if you do or don't do something. That is, subtract your house load (actual) from the estimated power production now fand youll get an idea of what extra may be available.

Alternatively, instead of deciding if you can or cant turn something on, change mindset, turn it On and then measure what you see to determine if you should immediately turn it back off... that is, if you turn something on and then measure power usage from Grid you'll quickly see if your extra load has caused you to be importing or exporting, if wanting to run the additional load for free and you can see you are importing then turn off, set some time frame to wait and then repeat....

Remember that depending on what it is that your turning on and off it may be that the OEM has preferred times we should stick with, for example if the Aircon is turned on then don't immediately turn off until 1 minute later to allow X to occur (just an example, more modern controls do all this in their own controllers for us) , alternatively if turning off then don't turn on for Y minutes so that the compressor is not trying to start from 0rpm with a pressure head already in place. I generally don't start and stop air cons more frequently than 5 minutes apart, in fact if using this I will rather than turn hard on and off rather set the mode from say cooling to dry or fan only in order to reduce the impact to less (dry) or minimal (for fan only) . A split aircon running in fan only mode draws generally less than 60w, in dry mode maybe a few hundred W, in cooling on initial turn on maybe 2-3kw. Generally in HA you have access to all the modes and fan speeds etc in order to pick your load required. When turning Hard On and Off the process is long and noisy as the head folds up and hides vanes etc, a mode change can be made with the head showing no real change in running speed or noise beyond that you might already be exposed to as it automatically tracks a setpoint temp.

Hope these ideas help

Andy