# No energy to graph for s solar export output - explained

I have just setup a Iotawatt and really impressed.
I just have one issue I can’t work out - I can graph my solar export, but energy shows 0.
I have CTs on each of the 3 phases feeding my house usage, and 3 CTs on my solar output wiring.
I eventually worked out how to get a solar export output that didn’t show 0 - " SolarEstExport = (Solar_pA + Solar_pB + Solar_pC - HouseUse_pA - HouseUse_pB - HouseUse_pC) max 0"
And that seems to work and the power graph looks good. But when I tick energy it is just 0.
I have some other outputs that add up some circuits and they seem to work fine, with the main difference being that I am not using the Max function for those - is this somehow the issue?

I think I know what’s going on, but only if my assumptions about your setup are correct.

You say you have three-phase residential power, and that you have a PV system with a three phase inverter. I am assuming by the formula you say is working to plot export power that the inverter output connects to the incoming mains on the supply side of the mains CTs, such that the inverter output doesn’t drive the mains negative.

In that scenario, the solar CTs measure the PV production directly as a positive value, and the mains CTs measure your absolute consumption as a positive value.

So when you plot that export function as power, it is a flat zero line until the sun comes up and the PV output exceeds usage. At that time you start to see the line climb to indicate the net export power. You could upload a screenshot of that to validate this assumption.

Now energy is an entirely different matter. Power is the net Watts for each given interval, which in a daily plot is typically 120 seconds, or two minutes. Energy is the cumulative kWh from the time you first started the IoTaWatt until the particular interval. So if you have used more energy than you produced since you installed the IoTaWatt, your formula will yield a negative number which becomes zero with the “max 0” function.

There is a discussion of the problem in this post Tracking separate solar Feed In Tariff

Probably the easiest way to get an accounting of daily export is to setup a PVoutput account and upload the data to it. The export numbers will then be at 5 minute resolution and daily totals should be accurate. You can also use another external database like influxDB or Emoncms to get finer granularity.

Thanks, yes you have it right. And I guess that makes sense. What you are saying is that Outputs are only ever calculated when monitored on the status page or graphed, they don’t log along the way like a input does.
I have already done PVoutput and that is fine, I was trying to get the graphs off the device directly to work. I am also working on setting up EmonCMS.