Part 1 of a series on what I learned by accident when I started paying attention to my electricity bill.
It started with a dishwasher.
Earlier this year, I switched my Ameren Missouri service over to a rate plan called Ultimate Saver. The pitch was straightforward: pay less for electricity if you can shift your usage away from peak hours. I’m not particularly frugal, but I’m curious about systems, and the structure of the plan was interesting enough that I wanted to understand it.
What I didn’t expect was that trying to figure out when to run my dishwasher would pull me into a rabbit hole about how the entire North American power grid works, and into a slowly unfolding crisis that I think most people don’t realize is happening.
This is the first of four posts about what I found. It starts small, with my own electric bill, and gets progressively bigger from there. By the end of the series I’ll be writing about why the AI data center boom is colliding with physical reality, and what that means for everyone who pays an electric bill.
But first, the dishwasher.
The plan that made me think
Ultimate Saver has two parts that work independently of each other, which took me a while to untangle.
The first part is time-of-use energy pricing. On weekdays, electricity costs more during two on-peak windows, 6 to 8 AM and 6 to 8 PM, and less during all the off-peak hours in between and around them. Weekends are entirely off-peak. So far, so simple: don’t run the dryer during dinner on a Tuesday.
The second part is a demand charge. This one is weirder. Once a month, Ameren looks at every single hour of my electricity use between 6 AM and 10 PM, every day of the month, weekends included, and finds the one hour where I drew the most power. Whatever that peak hour was, in kilowatts, gets multiplied by a per-kW rate and added to my bill. One bad hour can dominate the demand charge for the entire month.
When I first read this, I thought it was a gimmick. After spending some time with it, I think it might be one of the more honest pricing structures a utility has ever offered me.
Here’s why. The cost of providing electricity isn’t really about how much energy you use over a month. It’s about how much capacity the grid has to maintain to serve you when you need it. A house that uses 1,000 kilowatt-hours spread evenly across a month is much cheaper to serve than a house that uses the same 1,000 kilowatt-hours but spikes hard for a few hours every evening. The first house lets the utility size its infrastructure to a steady average; the second house forces the utility to build for the peak and let that capacity sit idle most of the time.
A demand charge takes that hidden reality and makes it visible. The price signal it sends is, basically: please don’t all hit the grid at once.
Figuring out my own house
Once I understood the structure, I started thinking about my own appliances. The big draws in a house like mine are the air conditioner, the electric dryer, the dishwasher (especially the heated dry cycle), the oven, and to a lesser extent things like the microwave.
The AC was the puzzle to start with, because in summer it runs almost constantly. But here’s the thing about my thermostat: it’s set to 74°F during the day and drops to 70°F at 10 PM, when we go to bed. That means the AC’s most intense work, the pulldown from 74 to 70, happens right at 10 PM, the exact moment the demand-tracking window ends. The AC’s biggest single hour of the day falls outside the window that gets billed.
So my real demand exposure during cooling season is the AC holding 74°F somewhere in the late afternoon, plus whatever else I happen to run on top of it. The pulldown is free.
This made everything else simpler. If the AC’s contribution to demand is roughly fixed during the day, then the question becomes: what else am I stacking on top of it, and when?
The dryer and the dishwasher, it turns out, are completely flexible. Nobody cares whether the dishwasher runs at 8 PM or 11 PM. Nobody cares whether the dryer finishes at 7 PM or 1 AM. These are appliances we treat as “run them whenever,” but their actual draw is significant. The dishwasher’s heated dry cycle and the dryer’s heating element are both heavy loads. Running them on top of an AC that’s already working hard in the late afternoon is exactly the kind of stacking that sets a new monthly demand peak.
So I started running them after 10 PM. The dishwasher gets loaded throughout the evening and I just start it on my way to bed. The dryer is less convenient but still workable.
It’s not a dramatic lifestyle change. It’s a small habit shift. But it removes both appliances from demand tracking entirely, and it captures the off-peak energy rate, which is a fraction of the on-peak rate. Two benefits for one decision.
The question that broke the dam
After a few weeks of this, a question started bothering me.
Why 10 PM?
The number is so specific. Not midnight, not 9 PM, not the time the sun sets. 10 PM, every day, weekends included. It’s the same number that ends the demand window and roughly the same time the on-peak energy pricing ends on weekdays. Ameren clearly chose it for a reason. But what reason?
The easy answer is “that’s when people go to bed.” But that’s not really an answer. Lots of people don’t go to bed at 10 PM. And anyway, why would a utility care exactly when its individual customers go to bed? Utilities don’t bill at the individual scale; they think in aggregate.
The real answer, I started to suspect, had to do with the grid itself.
So I went looking.
What I found when I looked at the actual data
Ameren Missouri is part of a regional grid operator called MISO, the Midcontinent Independent System Operator. MISO coordinates electricity across 15 states and one Canadian province, from Minnesota down to Louisiana. They publish real-time operational data on their public website: how much electricity is being generated, where it’s coming from, how it’s flowing between regions, what the forecast looks like for tomorrow.
I pulled their load curve for a normal weekday this spring. The shape of it is striking. Demand bottoms out around 4 AM at roughly 58,000 megawatts across the entire MISO footprint. It starts climbing around 6 AM as people wake up, grows steadily through the morning and afternoon, peaks around 6 to 7 PM at about 88,000 megawatts, and then, here’s the part that mattered to me, drops fast.
By 8 PM, load is down 3,000 megawatts from peak. By 9 PM, it’s down 6,000. By 10 PM, it’s down 10,000. By 11 PM, it’s down 14,500 megawatts from the evening peak.
Between 6 PM and 10 PM, the grid sheds roughly the equivalent of an entire nuclear fleet’s worth of demand. By the time the demand-charge window closes at 10 PM, the grid has genuinely entered a different operating regime. Expensive natural gas peaker plants that had to fire up to meet the evening peak can throttle back. Cheaper baseload generation, nuclear, coal, wind, handles the overnight load comfortably. The system is no longer stressed.
That’s why 10 PM. It’s not about when I go to bed. It’s about when the grid as a whole stops needing to scramble. The number maps to physics, not to convenience.
When I saw that, really saw it, in the actual hourly data, something shifted for me. The rate plan stopped feeling like a marketing structure and started feeling like a window into a real system. My dishwasher decision was a tiny instance of a much larger problem the grid is constantly solving.
And the closer I looked at that larger problem, the more interesting it got. And the more concerning.
Where this is going
I want to tell you what I found, because I think most people have no idea how much is changing right now in the systems that quietly power their lives.
Over the next three Sundays, I’ll be posting the rest of this series.
Next week, I’ll write about what MISO actually does. How a continental-scale power grid manages itself in real time, what the 2003 Northeast Blackout taught us about how this can fail, and why every appliance you own is connected to a machine spanning half a continent that has to stay in perfect synchronization, every second of every day.
The week after, I’ll get into what I now think is the most important undercovered story in the country: the collision between the AI data center boom and the physical infrastructure that has to power it. The companies building these data centers are starting to give up on the public grid entirely, with consequences that will eventually show up on your electric bill, whether you’ve heard about any of this or not.
And in the final post, I’ll bring it back to where this started. What all of this means for someone like me, an ordinary Ameren customer running a dishwasher at 10 PM, and what we can actually do about it.
I didn’t expect to spend this much time thinking about my electricity. But the more I understand about the system on the other side of my wall outlet, the more I think it’s one of the most important things I’ve ever paid attention to.
The dishwasher was just the beginning.
Next Sunday: The Grid Behind the Grid. What MISO actually does all day, and why the lights have to go out exactly as often as they do (which is more often than you think).
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