You installed solar. Your panels are working — the app confirms it, the production numbers look right. And your electric bill is still higher than you expected, especially in the evening.
This isn't a malfunction, and it isn't a sign you got a bad install. It's a timing mismatch that has a name in the utility industry, and once you see it, your bill stops being a mystery.
Run your own numbers first. The Solar Math Worksheet is one fillable page: your rate structure, TOU spread, battery sizing goal, incentive stack, and payback estimate — the math this site keeps telling you to do, in order. Download the free PDF. No email required.
The Quick Answer
Your solar panels make most of their electricity in the middle of the day. You use most of your electricity in the early evening — cooking dinner, running AC or heat, charging an EV, turning on lights as the sun goes down. By 7 PM, your panels have largely stopped producing, but your household hasn't stopped consuming. If your utility charges more for electricity during those exact evening hours, you're buying expensive grid power at the worst possible time, regardless of how much free solar you made six hours earlier.
That's the whole problem in one sentence. The rest of this is about why utilities price it that way, and why that pricing structure specifically targets the hours right after your panels clock out.
What "Time-of-Use" Rates Actually Mean
Most utilities used to charge one flat rate no matter when you used electricity — a kilowatt-hour at 2 PM cost the same as a kilowatt-hour at 9 PM. That's changing. A growing number of utilities now use time-of-use (TOU) pricing, which charges different rates depending on the hour of day.
The logic isn't arbitrary. The grid is under the most strain when everyone is drawing power at once — typically when people get home from work, start cooking, and run climate control simultaneously. Utilities price electricity higher during that window to reflect what it actually costs them to deliver power at peak demand, and to nudge people toward using less of it then.
A simplified version of a typical residential TOU schedule looks something like this:
| Window | Typical hours | Relative price | |---|---|---| | Off-peak | Late night to mid-morning | Lowest | | Mid-peak | Midday to late afternoon | Moderate | | Peak | Roughly 4 PM – 9 PM | Highest — often 2–4x off-peak |
The exact hours and multipliers vary by utility and state, but the shape is consistent almost everywhere TOU rates exist: a multi-hour peak window that starts in the late afternoon and runs through the early evening.
Look at that peak window again. Then look at when your solar panels stop producing.
The 7 PM Problem
Solar production follows the sun, not your schedule. It ramps up through the morning, peaks around solar noon, and tapers off through the afternoon — dropping sharply as the sun gets low, faster in winter, a bit later in summer. By 6 or 7 PM in most of the country, your panels are producing a small fraction of their midday output, if anything at all.
Your household's demand does the opposite. It's lowest while everyone's at work or school, and it climbs sharply starting in the late afternoon, right through dinner and into the evening — exactly the hours your panels are winding down.
Lay those two curves on top of each other and you get a gap shaped like a duck's back — utilities actually call this the duck curve at the grid level, because the chart looks like one. At the household level, that gap is your 7 PM bill spike: you're drawing the most grid power at the exact hours your utility charges the most for it, and your solar system — which may have produced more electricity than you used that day, in total — isn't there to cover it.
This is the core mismatch. It's not that your system is undersized. It's that solar production and TOU peak pricing are timed almost perfectly against each other.
Why This Catches Solar Homeowners Off Guard Specifically
If you installed solar expecting it to flatten your bill the way it would have a few years ago, here's what changed.
Under older net metering structures, exporting your excess midday solar to the grid earned you a credit worth close to the retail rate — meaning the cheap power you didn't use at noon could offset the expensive power you bought at 7 PM, dollar for dollar, more or less. The math worked because the price was the same whether the kilowatt-hour moved in the morning or the evening.
That's not how most current programs work. Many utilities — California's net billing tariff is the most-cited example — now compensate exported solar at a rate tied to wholesale or time-based value, which is typically much lower during the hours your panels are actually exporting (the sunny midday hours when the grid has plenty of supply). Meanwhile, the power you buy back at 7 PM is priced at peak. You're selling low and buying high, on the same meter, most days.
This is why a correctly sized system — one that produces as much or more than your home uses annually — can still leave you with a frustratingly high bill. Annual production was never the problem. Hourly timing is.
What Actually Fixes This
More panels don't fix a timing problem. Adding panels increases how much cheap midday electricity you generate and have to sell at a low export rate — it does nothing for the hours after your panels stop producing, which is where the expensive part of your bill is coming from.
The fix is storing the power instead of exporting it: capture the solar you make at noon, hold it, and use it yourself during the peak pricing window instead of buying grid power at the highest rate of the day. That's the entire job of a home battery — not backup power for outages (though it does that too), but shifting your own cheap solar from the hours you don't need it to the hours you do.
That doesn't mean a battery is automatically the right move for every solar homeowner. Cost, payback timeline, your specific TOU rate spread, and how much of your usage actually falls in the peak window all change the math — sometimes significantly. That's a big enough decision to deserve its own breakdown rather than a few paragraphs at the end of this one.
→ We cover sizing, real payback math, and what to actually look for when shopping in our home battery buyer's guide — read that next if the 7 PM spike sounds like your bill.