Using the information captured by a net meter can tell us something about the output of the solar system, but doesn't have all the information needed to calculate the actual output of the solar system.
I’ve attached a chart from the LPEA SmartHub website for my house using the Net Meter Analysis chart. What this chart shows is what LPEA calls Generation, Consumption and Net.
The Generation number (-10.17 kWh) is when your meter is ‘spinning backwards’ and your solar system is producing more energy than the house is consuming at that moment.
Consumption (5.74 kWh) is the opposite; when your house is consuming more than the system is producing at that moment and you are receiving energy from LPEA. For example all your usage at night will be part of this number.
The Net is just Generation minus Consumption (10.17-5.74 = 4.43 kWh). In the attached chart, my solar system produced 4.43 kWh more than I consumed on September 16, 2017.
In order to determine how much electricity my solar system produced on this day, there is a number missing. That number is how much electricity was consumed during the day while the solar system was producing power. This number is not on the LPEA charts and they have no way of capturing this information without a separate smart meter that measures only the output of the solar system. For example, when my solar system is producing power and my refrigerator turns on, part of the electricity from the solar system will be consumed directly by my refrigerator and will not pass through the net meter. How much energy is consumed instantaneously in this way is not captured by LPEA.