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The easiest solution would be to modify the sketch in a way such it doesn't transmit the high or low values .. just set a minimum and maximum value the measurement must have, and if the current measurement doesn't fall into the interval just discard it instead of sending it ....

It would appear that your readings read accurately until the generated power goes below about 2 W, and then they get spuriously high until it cuts off. The same when it first starts up. So I don't think thresholding the values will work, since it thinks it is measuring about 70 W just before it powers off. For the start up, you could have the sketch just wait a certain amount of time before transmitting any data, say 1 - 5 minutes after it powers up, so you know it will have enough power to give accurate measurements. The evening drop off is a bit harder to manage. You could have a thresholding function that says if the measured power is below a certain amount, say 3 or 4 W, to output a zero, and after a certain number of zeros, stop all output and wait for the long sleep of night. In the morning, as soon as it wakes up , the first output it does is zero, so the two connected points (last point the day before to the first point in the morning) will not integrate to any energy for the night. Then it waits the proper amount of time before putting out the first real power measurement.

Someone else who knows the Atmega328 might be able to suggest some method to measure the Vcc and be able to tell it to output zero if that is below some value. That would be another way to do it that might be more accurate.

Dan

A suggestion: use the d.c. voltage you're already measuring and only send data when it is above an acceptable threshold - enough to run the regulator that's feeding your emonTx. For good measure add some delay on a rising voltage but shut down immediately on a falling voltage. You might need to allow a margin so that there's enough voltage left to measure accurately and do an orderly shut-down before it falls over.

i used succesfully dc voltage threshold just below inverter threshold. this works most of the time with PV. there is a problem anyhow if the last transmissions does not go through as you can not quarantee that the last transmission does not collide in 868mhz network.

anyhow one of the recent (this spring) releases of emoncms introduced a problem you described that emoncms does show a line between two more or less arbitrary points on some screens (e.g. weekly view) and then when zoomed in it shows accurate values.

I think I'll try Robert's solution and insert an if statement that switches off data transmission when the solar voltage is <12V.

It looks like the problem appears when the input voltage is lower than 8,5V, then the power supply of the circuit stops working correct.The 3,3V supply is not the problem but the 5V supply for the current monitoring is it. It consisting of a 7812 and a 7805 connected in series plus a 1N4001 diode, so it is able to handle up to 40V input from the solar cell but needs at minimum 8,5V input to give correct 5V output.

After installing a modified script that only sends data when the solar voltage is greater than 12V it looks better. The only problem is that the actual power for AC and DC side are frozen, so they will count for the kwhd values.

That is a "feature" of emoncms. It joins the dots. To get around that, you need to send a manufactured final value of zero in the process of shutting down, and a manufactured first value of zero as you start up before sending true readings again.

Ok when I dismount it next time, I'll try to insert something like this to ensure that I always get a clear 0 value in the time the voltage is below 12V from evening to morning and don't have to transmit and store 0's all the night:

if (actual_voltage >12V) send_values ();

else

{ if (old_voltage!=0)

  { old_voltage=0;

    actual_voltage=0;  // also set all other values to 0 before transmitting them, voltage is only the example.

    send_values ();

  }

   else old_voltage=0;

}

I know that the syntax isn't correct, this is only for a better understanding of the script!

And you need to make sure you send a zero first when waking up - I don't think what you have above will necessarily do that. The easiest place for that will be in setup( ) of course.