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Converting Utility Bill $$$ to Kilowatt-Hours

Here in northern California, it’s tricky to convert dollars to kilowatt-hours, because our utility, PG&E, has tiers, where every customer receives some cheap electricity, but, as his/her usage climbs, jumps to more and more expensive rates.

There’s a PG&E webpage that does a fine job showing how the different tiers combine to make-up a monthly bill:

NOTE: PG&E periodically removes this page from their site. If the link above is not working, it’s still useful to review the example below. Because the page is periodically disabled, the rates I’m showing below will be out of date.

The user is asked to select the season, enter the zip code, and indicate if the home is just electricity, or electricity and gas. (These selects are because PG&E provides different quantities of cheap electricity, depending on season, climate zone, and whether the home uses electricity for heating as well.)

Let’s say our typical summer electrical bill is $185, we live in 94920, and our home has both gas and electric service. We enter the information, and then drag the slider to the right, until it shows $185, which we’re told equals 744 kilowatt-hours.

Lots of numbers seemed to be changing as we moved the slider, so we can slide it back and forth a few times, to note again what changed on the screen. It starts to make sense – as we move the slider from the left, indicating a higher and higher bill, we see the cheap electricity buckets used-up, one after another.

And the opposite also holds true: we can see that IF we reduce our bill by 10 or 20 or 50%, it’s the expensive electricity that gets removed from our bill, not the cheap electricity, or even the average of all the tiers.

We’ve probably noticed these tiers on our electricity bill as well:

In a perfect world, we would purchase enough panels to replace our entire electrical bill. But money’s tight, and 13-cent electricity is pretty cheap, and perhaps not worth replacing with solar. And the portion of our roof facing south may not be large enough to handle a system designed to eliminate our entire bill. So, as a compromise, we’ll calculate how much solar we need to replace just our tier 3 and tier 4 kilowatt-hours. (Yes, the rates displayed on this PG&E page are out of date!) Then, maybe we’ll get a second quote, to see how much it costs to replace all of our PG&E electricity.

Determining the expensive kilowatts is easy. Look at the slide-bar again. Tier 2 maxes out at 293 kWh, so 744 – 293 = 451 kilowatt-hours of expensive electricity per month.

Multiply this number by 12 to determine the annual consumption:

451 x 12 months = 5,412 kilowatt-hours of expensive electricity per year.

Note: Electrical bills bounce up and down, so selecting one bill and multiplying it by 12 is not that accurate. Alternatively, with one phone call, PG&E will read you your last 12 months’ electrical usage — in dollars and kilowatt-hours. Just call 800-743-5000, and make the selections to get to a live person.

Converting Kilowatt-Hours to Panels