Putting a DC wattmeter between solar panel and MPPT controller possible?

[Jordi]

Just a check here.

Since the MPPT controller just varies the circuit resistance to allow the panel delivering at its maximum power point (best combination of Voltage and Current), placing a DC wattmeter (with external battery) between panel and controller should not negatively influence the effect of the MPPT, right? The wattmeter would just act like copper cables, right?

Thanks for your answer.

 

[FilterGuy]

The wattmeter would just act like copper cables, right?

Yes, A wattmeter could be set up to measure the PV wattage without significant impact on the function of the MPPT.

To determine the wattage, a wattmeter is going to look at 2 things:
1) Voltage
2) Current.

The voltage can be detected with a very high impedance sensor across the PV inputs and will have no measurable impact on the function of the MPPT.

The current will be detected in one of two ways. 1) A Hall effect sensor or 2) a Shunt in series with the PV lines.
The hall effect sensor will have no measurable impact on the function of the MPPT.
A shunt is a very low-value resistor so it is not quite going to act like copper cables. This will have a slightly larger but still negligible effect on the function of the MPPT but since the resistance is low, the impact on the function of the MPPT will be small.

However, the question is this: What Watt Meter will function properly? Since the PV voltage will vary from 0 to Voc during normal operation,
it is not a very reliable source for powering the meter. Consequently, to work properly at the beginning and end of the day, the wattmeter needs to be powered from a separate source than the PV. Do you have a Watt Meter in mind?

 

[sunshine_eggo]

Just a check here.

Since the MPPT controller just varies the circuit resistance to allow the panel delivering at its maximum power point (best combination of Voltage and Current), placing a DC wattmeter (with external battery) between panel and controller should not negatively influence the effect of the MPPT, right? The wattmeter would just act like copper cables, right?

Thanks for your answer.

It doesn't really work like that. It's a DC-DC converter. It starts applying a load (charging the battery) and then finds the maximum charge power it can. That depends on what the input does.

Agree with @FilterGuy. No harm in doing it. You may be challenged to find a wattmeter that will survive full series Voc, and you have correctly identified that you need to power it with a separate source. IIRC, the ones you see Will using are typically limited to 60V.

Does your MPPT not report PV input parameters?

 

[Jordi]

Thank you very much for your answers and clarification.

The panel arrangement is 2S 16VDC 100W panels with a max. 6,25A current. Therefore I found this nice PZEM015 for it.

The plan is to put the wattmeter between the panels and the grid tied inverter. The setup has no battery; all production goes directly into the grid tied inverter and thus the grid. Goal is to have a measurement of output from panels to monitor and evaluate several parameters over time.

The wattmeter can work without shunt for currents between 0 to 10 A and so I aim to use it. I also ordered the shunt for other possible projects in the future (eg. use the panels in 2P for which max current becomes 12,5A).

The meter will be externally powered with some rechargeable batteries (AA or 18650) so during the night it also stays on and doesn't loose the watt count. I still have to test the meter myself, If the watt count does not reset (which I think is the case) then maybe I will rethink the external battery concept. The meter may consume up to 1W, so the small batteries mentioned would be drained in a matter of weeks.

As this project advances, I will post photos. Ordered stuff the first of October and still waiting.

 

[Rednecktek]

I have one of the RC watt meters between my panel and the controller for my driveway lights. Works just fine for giving me an idea what my system is getting to its PWM controller which doesn't tell me anything other than charging/not charging and battery SOC (low/med/full)