Solar System Energized!


June 3rd, 2023, PSE (Puget Sound Energy), our power utility, energized our solar system and house batteries.

On May 25th, we had 44 photovoltaic (PV) panels feeding two SolarEdge inverters installed producing 15.5 kW. That's a lot of energy. The house draws a mere 2.3 kW at this moment, the batteries and Tesla are topped off, so 13.2 kW is going back to the grid, earning credits towards our power this winter. The system includes two Tesla PowerWall batteries with a capacity of 13.5 kWh each and a Tesla car charger (plugged into my Model Y with a capacity of 81 kWh). 

I learned so much during this process, that I had to write articles to share with my geeky friends, so here is the first!

Why did we have to wait to have the system on?

Before this system was installed, we had a single direction meter from PSE. This means that the meter was measuring the flow of power in either direction as consumption. If we had turned on the system, the utility would have charged us for the 13.2kW flowing out instead of the 2.3 kW that would have been flowing in without the system. So, the $$$ means it was not worth turning on. However, when the batteries or Tesla are charging, the flow would have been very different, and it might have been profitable to turn the system on. The money is not the real reason to keep the system off. 

The real reason is backflow into the grid. When there's a power outage and the grid is off, the utility needs to ensure that these residential power systems and batteries do not feed power into the disabled grid. There are 7200V lines at the street hooked up to a transformer that converts it to our 240V line to the house (where it's again transformed to 120V lines within the home for normal residential appliances). When the grid is down, technicians will be working on those 7200V lines to fix the issue. Their lives depend on the lines staying off. Our street transformer, however, is bi-directional and will feed the power we supply from our solar panels and batteries into those 7200V lines. So, the utility ensures that all these new systems will stop feeding power into the grid when the grid goes out.

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