SoCal Edison Billing

I just saw a “preview” of my bill for next month, and it is about $900. However, since I have solar panels installed, Socal Edison (SCE) effectively bills me once a year. Each month, I only get billed for basic charge, whatever that is, and it is only $0.031/day. That usually comes out to about $1/month. However, SCE is tracking my actual usage, calculating the cost, but deferring the actual billing. Since SCE screwed me on the original system install (limited system size), I never generate enough power to cover usage. If I look at my Tesla app, my solar system generates a maximum of ~22 kW each day. I am also unsure what that is measuring: is it the panel output, inverter output, AC or DC power? In any case, SCE adds my power usage and solar generation to get a net usage number, and that is applied to the tiered rates. Currently, tier 1 is $0.23/kWh, tier 2, is $0.29/kWh, and tier 3 is $0.39/kWh.

Earlier, I said SCE screwed me on the installation. Part of the reason I installed solar panels on my house is my Tesla EV. For some reason, SCE placed an upper limit on system size based on last 12 month’s usage. I believe we were using about 500+ kWh per month, or a rough average of 20 kWh/day. Well, my Tesla has a 72 kWh battery and gets about 3.3 miles/kWh. If I drive 100 miles round trip to work, that is about 30 kWh, which is greater than our base electricity usage without the EV. If I did not get solar panels and charged daily at home, that would put me at tier 3 every month, and it would cost me marginally $0.39/kWh to charge the car. Luckily, I ended up charging mostly at work and occasionally use a Supercharger.

So fast forward to this year. Since I paid about $800 last year, $900 this year sounds reasonable. There were some very hot days last Fall, and due to the pandemic, our family just hung out at home most of the time. What I am still confused about is reconciling power generation numbers. Last month’s bill from SCE says generation was 304 kWh. I went to the Tesla app and downloaded data for the same dates and got 516 kWh generated. Again, I do not know what each company is measuring. Hopefully, SCE’s number is measured at the meter so power in = power out. Unfortunately, solar panels generate DC so each system requires an inverter to convert DC to AC. I cannot remember what the conversion factor is. I know there is a √2 somewhere… pretty sad for someone with two electrical engineering degrees. 🥵