Time-of-Use Rates and Solar: When You Use Power Is Money

On a flat electricity rate, a kilowatt-hour costs the same at noon as it does at eight in the evening, so solar savings collapse to a single number: how much energy your panels produce over the year. Move to a time-of-use rate and that clean picture shatters. Suddenly the same kilowatt-hour is cheap in the middle of the day and expensive in the early evening, and your savings depend not just on how much you generate but on when you generate it and when you use it. For a growing share of homeowners this timing isn’t a footnote — it’s most of the math, and it catches people off guard because many utilities now place solar customers on time-of-use plans by default the moment their system goes live. If you’re going to be billed by the clock, you need to understand where the money actually hides on it.

The day splits into price windows

A time-of-use plan carves the day into pricing periods — typically an expensive peak window, a cheap off-peak window, and sometimes a mid-tier band in between. The peak window is deliberately placed where the grid is most strained, and across most of the country that now means the late afternoon and evening, roughly four to nine in the evening. That’s when people come home, when cooling and cooking loads stack on top of each other, and, crucially, when solar generation across the whole region is fading with the sun. The utility isn’t picking those hours arbitrarily; it’s pricing the moments when it has to work hardest and buy the most expensive power to keep the lights on. Understanding that logic tells you something important before you look at a single number: the expensive window is expensive precisely because that’s when supply is tight and demand is high, and it’s going to sit stubbornly in the evening no matter what your panels are doing.

The gap between peak and off-peak is not a rounding error. As a planning assumption, peak prices commonly run two to three times the off-peak rate, and in some territories the spread is wider still. That multiplier is the entire game. On a flat rate, shifting a load from evening to midday changes nothing, because every hour costs the same. On a time-of-use rate, every kilowatt-hour you can pull out of the peak window — or generate during it — is worth far more than a kilowatt-hour moved around during the cheap hours. The savings live in the spread, and the size of that spread determines how much attention the whole question deserves for your particular household.

Period (typical shape)	When	Relative price
Peak	Late afternoon to mid-evening	Highest
Off-peak	Overnight and mid-day	Lowest
Mid-peak	Shoulder hours	In between

The exact windows and multipliers are set by your utility and vary from one territory to the next, sometimes dramatically, and they can also shift by season — summer peak windows are often longer and pricier than winter ones because that’s when air conditioning drives demand. So the first move on any time-of-use plan, before you optimize anything, is to read your own rate schedule rather than assume the shape in that table applies to you. Two homeowners served by different utilities can be on plans that look superficially similar but reward completely different behavior, and only your actual schedule tells you which hours to defend and which to ignore. Everything that follows about adapting to a time-of-use plan is downstream of knowing your specific windows and your specific spread, because a mild spread barely rewards any effort while a steep one rewards it enormously.

A detail that surprises people is that they often don’t choose to be on a time-of-use plan at all — they’re placed on one automatically the moment their solar system is interconnected. Many utilities have made time-of-use the default, and sometimes the only, rate available to customers with rooftop solar, on the reasoning that solar owners both produce and consume on schedules the utility would like to price by the hour. So the first thing to check isn’t how to optimize your plan but whether you even have a choice of plans, because in some territories a flat rate simply isn’t on the menu once you go solar, while in others you can compare a time-of-use schedule against a flat one and pick whichever suits your usage. It’s also worth knowing that the windows and multipliers frequently shift by season and sometimes by day of the week — a summer peak window may be longer and pricier than the winter one, and weekends often carry a gentler shape than weekdays, because demand on the grid genuinely differs across those periods. All of which means the rate schedule you need to read is your own, in full, including its seasonal variants, rather than a single representative snapshot. The plan you’re on and the plan that would serve you best aren’t always the same, and finding out which is which is the groundwork for everything else.

Reading the schedule itself is worth doing carefully, because the details that decide your savings are exactly the ones a summary glosses over. Find the tariff sheet for your specific rate — utilities publish these — and look for three things: the precise clock hours that define each period, the price attached to each period, and any seasonal split that changes those hours or prices through the year. Pay attention to where the peak window begins and ends, because an hour of difference at the edges can matter a great deal for a household whose big loads cluster around dinnertime. Note whether weekends and holidays follow a different, gentler schedule, since many plans exempt them from peak pricing entirely. And check whether the plan layers time-of-use pricing on top of a tiered structure that also charges more as your total monthly usage climbs, because the two mechanisms can stack in ways that reward both shifting load and reducing it. None of this takes long once you know what you’re looking for, and it converts the vague sense that “peak is expensive” into the concrete map you need to actually respond to it.

Why a south-facing array and an evening peak pull against each other

Here is the tension at the heart of solar on a time-of-use plan. A standard south-facing array produces most heavily around midday and tapers through the afternoon, going quiet by evening. On many modern time-of-use schedules, midday is now off-peak — the cheap window — precisely because so much solar floods the grid during those hours and pushes the regional cost of power down. So your panels tend to generate their biggest surplus exactly when exported energy is worth the least, while your household’s most expensive hours arrive after the sun is down and the panels have already stopped. The production and the high prices miss each other, and a naive expectation that “I generate a lot, so I’ll save a lot” runs straight into the reality that generation and value are landing in different parts of the day.

Whether that midday surplus even earns you anything close to the peak rate depends entirely on your utility’s export structure, and this is where the distinction between two arrangements becomes more decisive than your panel count. Under traditional net metering, exports bank at the retail rate for the time they’re sent, so midday exports credit at the low midday price and you carry those credits forward to offset expensive evening imports — the grid effectively acts as a free battery that stores your cheap daytime energy and returns it at whatever the evening costs. Under a net-billing structure, by contrast, exports are often valued at something closer to a wholesale rate while the power you import still costs full retail, which means sending energy to the grid at midday and buying it back at the evening peak becomes a losing trade rather than a wash. Our comparison of net billing and net metering explains why that difference can matter more to your bottom line than how many panels you install, and our look at what utilities actually pay for the power you send back covers the export-rate mechanics that decide how much your surplus is really worth.

The upshot is a trap that surprises people: on a time-of-use plan, your total annual production can look perfectly healthy on paper while your savings quietly underperform, because the production is landing in the wrong price windows and, under the wrong export structure, isn’t being credited at anything like the value you’re paying for it in the evening. A homeowner who read only the total-kWh figure would conclude the system is working exactly as promised, while the bill tells a more disappointing story. This is why judging a solar system on a time-of-use plan by its annual generation alone is a mistake. What matters is how much of that generation offsets expensive peak consumption versus how much of it exports cheaply at midday, and that ratio depends on the shape of your production, the shape of your usage, and the export rules stitching the two together.

The reason midday value has collapsed in so many places has a name among grid operators: the shape of regional demand over a day now dips in the middle, when solar across the whole area is pouring power onto the grid, and then spikes sharply in the early evening as that solar fades and households ramp up. When a region has a lot of solar, the middle of the day is the moment of least scarcity and therefore least value, and the evening ramp is the moment of most scarcity and most value — which is exactly why time-of-use schedules have migrated their expensive windows into the evening and pushed midday into the cheap tier. Understanding this reframes the whole tension: your south-facing array isn’t underperforming or badly designed when its midday surplus earns little, it’s producing abundantly at precisely the hour the grid least needs more supply. The mismatch is a policy and market response to solar’s own success, not a fault in your system. That framing matters because it tells you where the fix lives. You can’t change the fact that the sun is overhead at midday and the peak is in the evening, but you can change how much of your production lands in the valuable hours and how much of your consumption you drag out of the expensive ones — and those two levers, not the raw quantity of sunlight, are what a time-of-use plan actually rewards.

The practical consequence is a metric worth watching that isn’t your total production at all: how much of your consumption during the peak window you cover with your own energy, whether that’s live production tilted into the late afternoon or stored energy discharged from a battery. A system that generates a huge annual total but meets none of its evening peak with its own power is leaving most of the time-of-use value on the table, while a more modest system that reliably covers the expensive hours captures it. That reframing is the whole reason total kilowatt-hours is the wrong scorecard on a time-of-use plan. The right question is always what share of your peak-hour spending your system displaces, and every design choice that follows — where the panels point, when you run your loads, whether you add storage — is ultimately in service of raising that single number.

Bending production and usage toward the money

The fix for the timing mismatch isn’t to avoid solar on a time-of-use plan — it’s to align your production and your consumption with the price map, and three levers do most of that work. The first is where you point the panels. A due-south array maximizes total annual energy, but a west-facing array shifts production later into the afternoon, dragging more of it toward the front edge of the peak window. Under a steep time-of-use spread, that later production can be worth more per kilowatt-hour even though there’s slightly less of it in total — one of the rare cases where the financially optimal orientation is not the one that generates the most energy. Our breakdown of south-facing versus east-west layouts walks through exactly when tilting the array westward pays for itself, and the answer hinges on how steep your particular spread is: a mild spread doesn’t justify giving up annual production, while a steep one can.

The second lever is your own consumption, which is the half of the peak-rate problem homeowners most often neglect. A large share of household load is schedulable if you decide to schedule it. Running the dishwasher and the laundry at midday when your panels are supplying the house, pre-cooling the home before the peak window opens so the air conditioner coasts through the expensive hours, and timing EV charging to the overnight off-peak block all pull spending out of the costly window and into the cheap or self-supplied ones. On a flat rate none of this does a thing; on a time-of-use rate every load you move is a direct saving. The more flexible load you can push into daylight, where your own production covers it, or into the overnight hours, where the grid is cheapest, the smaller your exposure to peak pricing becomes — and the beauty of it is that this lever costs nothing but attention and a few timer settings.

The third and most complete lever is storage. A home battery soaks up your midday surplus — the very production that would otherwise export at the cheap rate or, under net billing, at a wholesale pittance — and discharges it during the evening peak, letting you sidestep the most expensive grid hours entirely. This is time-of-use arbitrage, and it’s the mechanism that makes battery economics far stronger on a time-of-use or net-billing plan than they ever were under old-style net metering, where the grid already played the role of a free battery and left storage with little to arbitrage. The wider your peak-to-off-peak spread, the more each daily charge-and-discharge cycle is worth, and the faster a battery earns its keep. The solar battery calculator helps you size storage against your evening load and the length of your peak window, so you’re buying enough capacity to cover the expensive hours without overpaying for capacity you’ll never cycle. Because everything here depends on your utility’s specific windows, price multipliers, and export rules, time-of-use savings resist rules of thumb more than almost any other part of solar economics — a homeowner on a mild spread with midday-heavy usage might barely notice the plan, while a homeowner on a steep spread with a big evening load, a west-facing array, and a battery can see dramatically better returns from the identical hardware.

A rough illustration shows why the levers are worth pulling together rather than one at a time. Assume a steep spread where peak power costs three times the off-peak rate, and suppose you can move or supply 10 kWh of evening consumption every day — pre-cooling the house, shifting the laundry, and letting a battery cover the rest of the evening peak. Every one of those kilowatt-hours you keep out of the peak window is worth three times what it would have cost you off-peak, so the daily saving is the full peak-to-off-peak gap on all 10 kWh, repeated 365 times a year. Tilt a share of the array westward on top of that, and more of your own production lands during the front of the peak window, shrinking what you need to shift in the first place. The levers compound: orientation reduces the peak load you’re exposed to, behavior shaves it further at no cost, and storage mops up whatever’s left. The numbers here are illustrative and hinge entirely on your real spread and your real evening load — a mild spread would make the same effort barely worth the bother — which is the whole point of modeling your own schedule rather than trusting a generic figure. Pull your utility’s actual windows and prices, map your own daily usage against them, and run the payback with those inputs in the solar ROI calculator rather than assuming a flat blended rate. On a time-of-use plan, when you make and use your power isn’t a detail attached to the savings math. It is the savings math.