Real time estimate of available PV Power

Hardware
1

Last week I had a solar PV system installed using commercial off the shelf components from Studer. It is a hybrid system with grid tie and storage and I would like to better automate load management. I have Home Assistant monitoring the power from the grid, and I will soon add power monitoring coming from the inverter. What I would like to have is an estimate of available PV power from the panels. The PV system has a web interface that lets me see the power sent from the panels to the charge controller, but it doesn’t tell me how much more the panels would produce if I added more load.

I was thinking that I could add a very small panel with a resistive load and monitor the voltage to estimate the available PV power. Of course the resistive power curve will be different from an MPPT curve, but it could probably be estimated closely enough by passing the voltage readings to a look up table, or a formula, or a combination of the two. This sounds like something that has already been tried. Does anyone have any experience with this, or seen any related articles?

2

Doesn’t the fact the system is grid tied negate this issue? The load is going to be the grid when the pv system is exporting isn’t it. Might be useful in a off grid setup. Can’t say I seen this mentioned much. Perhaps it’s just my ignorance.

3

My utility gives two options:

  1. Export all PV generated energy
  2. Self consume all generated PV energy
    I have chosen to consume all generated PV energy. When the grid goes down, being able to better manage the load would make the usage of the PV generation more efficient.
4

So you system never exports? That’s how option 2 reads. Doesn’t really sound like a hybrid system.

Unless you mean it stops exporting only when the grid goes down? A hybrid system, at least to me, means that your inverter is grid connected and able to export. When the grid goes down, it switches to island mode and keeps your house running, but export is shut off for grid works safety.

If it never exports then the battery(storage) will still be a load. When the battery is full is when you would want your extra load.

You might find your answer looking at information for off grid setups and load efficiency or something.

5

Its Hybrid in that it automatically take energy from the grid when there isn’t enough PV, or the batteries are getting low. The inverter is connected to the grid, and has the capability to export, but is set to not export energy. If the grid goes down, it disconnects from it and keeps the house energized on PV and or battery.

“You might find your answer looking at information for off grid setups and load efficiency or something.” That sounds like a good idea. I will check what off gridders are doing.

6

Probably worth chatting to the manufacturer of the inverter, to see if they any tweaks for a export limited setup.

Simplest thing I can think of, would be to run an automation…

If it’s summer and before ~11am and the battery is 80%… Run the air con

Sounds like you are going to be curtailing in some scenarios.

Do they give you significantly better tarrifs for not exporting?

7

The manufacturer does have a configuration for not exporting and that is setup. I haven’t gotten the full details yet for the tariffs yet, but I think they charge the regular tariff if you have solar and don’t export. But I have read that if you are on the nonexport tariff and you do export, that you are charged the regular rate on what you export. If you are on the export only tariff, then your PV system is connected to a circuit and meter that are independent of the house.

I have some automations that look at sun elevation, current weather (sunny, partly cloudy, cloudy, foggy, or rainy), and the amount of power coming from the grid. Its working pretty well, but I would like something better and that doesn’t rely on external web based information like sun elevation and weather.

This automation turns the water heater on in partly cloudy weather, and there is a similar one for turning it off.

alias: >-
  Sunny Period Load Unshedding (Water Heater) (Elevation > 34 Degrees and Partly
  Cloudy)
description: >-
  If EDP grid power falls below 100 Watts in the sunny  every day period, Turn
  water heater back on.
trigger:
  - platform: time_pattern
    minutes: /9
condition:
  - condition: numeric_state
    entity_id: sun.sun
    attribute: elevation
    above: '34'
  - condition: state
    state: partlycloudy
    entity_id: weather.home
  - type: is_power
    condition: device
    device_id: 6b9e428c79b0ee247c45bd1771e2e868
    entity_id: sensor.shelly_em_channel_1_power
    domain: sensor
    below: 100
action:
  - type: turn_on
    device_id: 7fc8c9c152088485333f31fa95ef0b70
    entity_id: switch.tz3000_ew3ldmgx_ts011f_70b98efe_on_off
    domain: switch
mode: single
8

I wish I could read the battery state of charge, but there doesn’t seem to be an HA integration for Studer inverters. There is an OpenHab integration for Studer. I will be looking into that to see if I can use that to communicate with my PV system, and if there is a way to get OpenHab to communicate with HA.

9

Slight aside, but have a look at solcast.

Ive found using forecasting to be far more efficient than real time data when doing automations.

Eg a forecast of “im going to generate 3 kWh in the next hour” is more useful than “i am currnetly generating 3000W” or “I generated 3kWh in the last hour”

I use the solcast API for this — i think theres an integration on HACS somewhere, but mine is still setup using rest sensors.

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