Measuring electricity sold

I’m planning my IoTaWatt install and figuring out where to put what CTs. One item I want to measure has me stumped: how do I measure how much electricity I am selling from my solar panels?

Below is one of my distribution panels. The 30A breaker on the left is marked as “solar panels”. (All the other breakers on the right are circuits in the house; the one in the middle is the main breaker for that distribution block).

This is another distribution panel. I’m fairly sure this is where the electricity enters the whole distribution system, specifically the thick black wires on the left in the back. The box in the center is marked as having something to do with buying and selling electricity, but I don’t know what. I suspect it’s the controller that decides when to buy and when to sell.

The sensors that you can see are for the existing energy monitoring system. Unfortunately they’re not labeled in any way that helps me figure out what they are for. I do find it interesting that for both the solar breaker and the main input there are sensors on both sides of the breaker. I have no idea why, though.

There’s also a home battery in the mix, but I have no idea where it’s connected to the system. It charges from the grid and discharges into the house.

Where should I put sensors to measure how much electricity I’m buying and how much I’m selling?

When you are generating more energy than you are using, you have a surplus, and when you are generating less than you are using, you have a deficit. Ordinarily, you would export (sell) any surplus and import (buy) to make up a deficit.

You have a battery, so you can alternatively charge the battery with any excess, and draw from the battery to make up any deficit.

With the battery you can also import (buy) energy when the price is low, storing it in your battery. You can also export (sell) energy from your battery when the price is high.

Regardless of how or when you buy and sell, I believe the energy must be imported or exported through the mains. Presumably you have a meter that records the amount bought or sold at the different rates.

So keeping track of what you buy and sell is simply a matter of measuring import and export using a pair of CTs on the two mains. ioTaWatt can do that easily.

So all I need to do is measure the solar output and the mains?

That’s the way it looks to me.

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