Calculations

Megawatt hours (MWh) of backup potential: Seen in “CA VPP Impact“ section.

Calculation:

Total CA VPP MWh backup potential = (SCE homes + PG&E homes) * avg kWh contribution per PG&E home during 3hr events to date

Why: We use 3hr events because historically the VPP is pretty tapped at the end of 3hrs which indicates an exhausted max capacity. We apply PG&E data to SCE homes to get a whole state estimate because the program is so big and we don’t expect much behavior variance in the network.

Discharge rate in kilowatts (MWh): Seen on the graph mapping discharge rate on the half hour during events.

Calculation: We print the 1st number a few minutes into the event and the last number a few minutes before the end

Why: We want to track the discharge rate for every half hour segment in an event. The VPP network takes a few minutes to spin up and wind down, so we omit the super low numbers that only represent a few minutes of the first and last half hours for a more accurate picture.

Megawatt hours (MWh) contribution per event, per home and to date: This is all the energy the VPP has discharged in total based on half hour averages.

Calculations:

PG&E VPP MWh contribution hour 1 = (((discharge rate hr0 + discharge rate hr.5)/2)+((discharge rate hr.5 + discharge rate hr1)/2))/2

PG&E VPP MWh contribution hour 2 = (((discharge rate hr1 + discharge rate hr1.5)/2)+((discharge rate hr1.5 + discharge rate hr2)/2))/2

PG&E VPP MWh contribution hour 3 = (((discharge rate hr2 + discharge rate hr2.5)/2)+((discharge rate hr2.5 + discharge rate hr3)/2))/2

Total PG&E VPP MWh contribution per event = Hour 1 + Hour 2 + Hour 3 (if applicable)

Avg PG&E kWh contribution per home = event total contribution / PG&E participating homes

Avg SCE kWh contribution per home estimate = avg PG&E per home contribution per event * SCE participating homes in each event

Total CA VPP MWh contribution = total PG&E MWh contribution to date + total SCE MWh contribution to date

Why: It’s worth noting, this does not yet say “total MWh sent to the grid”. We want to show this number, but we’re still digging to figure out if the VPP discharge rate is 100% to the grid or if it includes energy going to VPP participant homes too. Here is the “why” for the above calculations. We apply averages from the PG&E program to the whole state because we have the best data on PG&E and the program is large. We average the half hour discharge rates to calculate the contribution by hour because it’s the fastest way to get in the ballpark (range).

Total revenue made by customers: Not shown yet, but it’s what Tesla customers have made by selling clean power to the grid.

Calculation:

Total revenue generated by CA VPP customers = ((SCE total kWh contribution + PG&E total kWh contribution) * $2 program pay per kWh)* % adjustment down to capture fringe cases where customers export to the grid on a regular basis

Why: This number really matters because it drastically improves the financial case for owning a Tesla solar system with Powerwalls. It also proves that there is real money to be made by working together as a distributed network of owners, imagine this on a national and global scale.

Disclaimer: Lastbulb is not affiliated with Tesla. We use information made available to customers in the app to make estimates about the growth and impact of the program. We do this to bring clarity to an under appreciated ecosystem of energy products that offer a better way to live.