Overview
On a backfed PV installation (that is, an installation where excess solar production is fed back through a breaker on the main distribution panel to the utility) it is relatively easy to see the net import and export of power. The CTs installed on the main utility feeds are in effect net CTs, as they see power imported from and exported to the utility. Any register created using those CTs will thus change polarity when production exceeds consumption, and change back when consumption exceeds production. For instructions on displaying the net import/export values for a backfed system, see this article.
However, a line side tap PV installation (where the solar is tapped between the main utility feed CTs and the utility meter itself) only tracks the consumption of the main distribution panel by default. A register using the main utility feed CTs will only see the consumption associated with that panel, regardless of how much production is being fed back to the utility. In this case, a comparison between the main utility CTs ("Grid" register) and the production CTs ("Solar" register) can show how much power is being imported or exported.
Prerequisites
- Valid login credentials are needed to apply these changes.
Instructions
Step 1: Navigate to Setup → Other settings, then Installation to the left.
Step 2: In addition to the Grid and Solar registers, add two formula registers as shown:
- Net In =
min($"Solar" - $"Grid",0) - Net Out =
max($"Solar" - $"Grid",0)
Note that this assumes two registers, one named "Grid" which tracks only consumption on the main distribution panel, and one name "Solar" which tracks total solar production. If needed multiple registers can be combined. Note the spelling and capitalization must match exactly.
- A new register will not contain any historical data. There is no way to backfill historical data into a new register.
Step 3: Add two new virtual registers: "Net.Usage" and "Net.Generation". Note the spelling and capitalization must match exactly.
Step 4: Set "Net.Usage" to equal "Net In" and "Net.Generation" to equal "Net Out". When done, they should look like this:
Step 5: Save and Reboot.
Data can be viewed on the main graph page by selecting the "Net" view.
The images below show a comparison between the default "total used/total generated" graph and the new "net used/net sold" graph.
Additional Resources