Understanding true-up billing
First, the monthly bill. Where does this $12 come from? It turns out PG&E charges E-6 (TOU) customers a “meter charge” of approximately $0.25 per day. E6 and E-1 both also have a “minimum charge” of approximately $0.15 per day; they don’t explain what this means, but if my reverse engineering of my bills is correct, for NEM customers it’s essentially a placeholder for your usage before they know what your usage is. These fees added together and multiplied by the number of days in a billing cycle yield the approximately $12 amount that I was billed for each month (billing cycles ranged from 28 to 32 days, so the monthly bill ranged from $11.22 to $12.83, with the most common bill being $12.02 for a 30-day billing cycle).
Second, the usage charges. These are not simple (since they involve both the tiering and TOU calculations), but they are actually decently explained on the monthly NEM statement itself, and with one nitpicky exception
8, they’re the same as what you had before you added NEM, and the true-up calculation doesn’t affect them.
Third, the cumulative usage charge. This one is completely straightforward: add the usage charges for the current true-up period, to date. Each NEM statement shows the current cumulative charge (this amount) and the amount by which it changed (the month’s usage charge), and you can verify that the current cumulative balance is equal to the previous month’s balance plus/minus the current month’s usage charge/credit. However, as mentioned above, this amount will swing one direction and then correct due to seasonal variation,
Fourth, the true-up amount. This is a simple calculation if you know where it comes from, but PG&E doesn’t explain it, so I had to reverse engineer it, learning to understand the daily meter and minimum charges. What it boils down to is that the $0.15 “minimum charge” is not a real charge once the true-up period is over, but a provisional placeholder: you pay this with each month’s $12 bill, but at the end of the year, when your real usage is known, you get back the provisional amount and pay the real amount. At the end of the year, you take your usage charge/credit, and add the meter charge ($0.25 per day or about $7.50 per monthly bill or $92.33 in a full year
9), and that’s what you owe for the year. Except you’ve already paid that meter charge, plus you’ve paid the “minimum” usage charge as a provisional placeholder. So subtract the provisional usage charge ($0.15 per day or about $4.50 per monthly bill or $53.96 in a full year), and you have the amount that’s unpaid, that you must still pay in order to True Up. So, your first 11 bills are for 30-ish days of meter charges and minimum charges, totaling about $12; your 12th bill is for 30-ish days of meter charges, minus 335-ish days of minimum charges, plus your cumulative usage charge for the whole year. In my case, actual usage at the end of the year was $60.22, of which $46.27 had already been paid monthly as that “minimum” charge, so what I’d call the actual true-up component was $13.95; add in $8.07 in meter fees (32 days at $0.25/day) for the final billing period and we have what PG&E calls my true-up bill of $22.02.¹