The four hours between 5pm and 9pm cost Hawaii homeowners more than the other twenty combined. Here is how the rate structure works and what you can do about it.
$0.329 per kilowatt-hour. That is what Hawaiian Electric charges Oahu homeowners for every unit of electricity consumed between 5pm and 9pm under its Smart Export (SRE) rate schedule. During the daytime, that same kilowatt-hour costs $0.135. The difference is not a rounding error — it is a 2.4x multiplier, and it is the single most important number in Hawaii residential energy economics right now.
If you have solar panels, a battery, an electric vehicle, or even just a dishwasher with a delay-start button, HECO's time-of-use rate structure should be shaping every energy decision you make. Most homeowners we talk to know their rates are high. Far fewer understand that when they use electricity matters as much as how much they use.
For decades, HECO charged a flat per-kilowatt-hour rate. You used electricity, you paid the same amount whether it was noon or midnight. That model worked when the grid ran on oil and demand was the only variable. It stopped working when rooftop solar changed the supply curve.
Hawaii now generates so much solar electricity during midday hours that HECO routinely curtails renewable production — essentially telling solar farms and rooftop systems to stop exporting because the grid cannot absorb any more. According to HECO's own curtailment data, Oahu curtailed over 400 GWh of renewable energy in 2025. That is clean electricity thrown away because there was nowhere to put it.
Then the sun sets. Between 5pm and 9pm, solar production drops to zero while demand surges. Families come home from work. Air conditioning runs hard as houses trapped afternoon heat. Ovens, dryers, televisions, EV chargers — everything switches on at once. HECO fires up its most expensive peaking generators to cover the gap, burning imported oil at costs that dwarf midday solar.
Time-of-use pricing is HECO's attempt to align what electricity costs the grid with what customers pay. Cheap power when supply is abundant, expensive power when the grid is strained. The economics are rational. The question for homeowners is how to respond.
HECO divides each day into three pricing periods. These apply across all islands served by Hawaiian Electric, though the per-kWh rates differ by service territory.
| Period | Hours | Grid Condition | Oahu Rate |
|---|---|---|---|
| Daytime | 9:00 AM – 5:00 PM | Solar surplus, low demand | $0.135/kWh |
| Peak | 5:00 PM – 9:00 PM | Solar gone, demand spike | $0.329/kWh |
| Overnight | 9:00 PM – 9:00 AM | Low demand, baseload generation | $0.189/kWh |
The daytime rate is the bargain. Solar panels are flooding the grid, HECO has more supply than it needs, and electricity is priced accordingly. The overnight rate falls in between — demand is low, but generation costs are moderate because the grid is running on conventional baseload. The peak window is where HECO makes its money and where homeowners get punished.
Oahu gets the most attention, but HECO's TOU structure extends to Hawaii Island and Maui County, each with its own rate schedule reflecting local generation costs and grid conditions. The pattern is consistent across all three: daytime is cheap, peak is expensive, overnight falls in between.
| Island | Daytime (9a–5p) | Peak (5p–9p) | Overnight (9p–9a) | Peak-to-Day Ratio |
|---|---|---|---|---|
| Oahu | $0.135 | $0.329 | $0.189 | 2.44x |
| Hawaii Island | $0.117 | $0.289 | $0.168 | 2.47x |
| Maui County | $0.142 | $0.341 | $0.198 | 2.40x |
Maui County residents pay the highest peak rate at $0.341/kWh, a reality shaped partly by the smaller grid's limited generation diversity and the rebuilding costs still rippling through Maui Electric's infrastructure. Hawaii Island's rates are the lowest of the three, reflecting its geothermal baseload from Puna Geothermal Venture, which provides roughly 25% of the Big Island's electricity and runs around the clock regardless of sun.
Regardless of island, the takeaway is the same: the 5pm-to-9pm window costs roughly 2.4 times as much as daytime. That ratio is the fulcrum of every solar-plus-battery financial calculation in the state.
Four hours. That is all it takes to account for the largest chunk of many households' monthly HECO bills. A family running a central AC system, cooking dinner, doing laundry, and charging devices between 5pm and 9pm can easily consume 15–20 kWh during that window. At $0.329/kWh on Oahu, that is $5 to $6.50 every single evening — $150 to $200 per month just from peak-hour usage.
The reason the peak rate is so high is not arbitrary. HECO's peaking generators — the oil-fired units that ramp up when solar disappears — are the most expensive assets on the grid. They burn imported petroleum, they run inefficiently because they cycle on and off daily, and they require staffing and maintenance disproportionate to their operating hours. Those costs get concentrated into the peak window because that is when they run.
There is also a policy dimension. The Hawaii Public Utilities Commission has signaled repeatedly that it wants to discourage peak consumption as part of the state's 100% renewable energy mandate by 2045. Higher peak rates are a demand-reduction tool as much as a cost-recovery mechanism. HECO is telling homeowners, in the clearest language available: shift your usage or pay for the privilege of not doing so.
This is where the economics get interesting. A home battery system — a Tesla Powerwall 3, an Enphase IQ 5P, a Franklin WH — does something no behavioral change can match: it turns cheap daytime solar into peak-rate revenue.
The math is not complicated. Your solar panels generate excess electricity during the day when it is worth $0.135/kWh. Without a battery, that surplus goes to the grid at the daytime export rate. With a battery, you store it. Then between 5pm and 9pm, you either use that stored energy (avoiding a $0.329/kWh purchase from HECO) or export it to the grid at the peak rate. Either way, every kilowatt-hour your battery shifts from daytime to peak is worth an additional $0.194 — the spread between the two windows.
A typical Powerwall 3 with 13.5 kWh of usable capacity can shift roughly 12 kWh per cycle from daytime to peak, accounting for round-trip efficiency losses. That is $2.33 in daily arbitrage value, or about $70 per month. Over a year, roughly $850 in peak-rate savings from a single battery — and that is before counting HECO's BYOD+ program incentives, which add $400/kW upfront and monthly performance payments.
In our assessment, battery storage has moved from an optional upgrade to the centerpiece of any financially rational solar installation in Hawaii. The TOU spread alone justifies the investment; the backup power and BYOD+ payments are gravy.
A family in Mililani Mauka contacted us in late 2025. They had a 9.2 kW solar system installed in 2021 under the old NEM program, no battery. Their HECO bill had crept back up to $185/month despite the panels. They could not figure out why.
The answer was in the peak window. Their solar system produced plenty during the day — enough to export 18–22 kWh daily to the grid. But by 5pm, production dropped to near zero and the family's heaviest usage was just beginning. Two teenagers streaming and gaming, a central AC unit fighting afternoon heat trapped in the house, dinner prep, and an EV that had been plugged in automatically at 4pm. They were buying 16–18 kWh nightly at peak rates while their daytime exports earned a fraction of that cost.
We added a Powerwall 3 and reprogrammed their EV charger to start at 10am instead of 4pm, drawing from solar production while they were at work. The results showed up on their first full billing cycle.
| Before (Solar Only) | After (Solar + Battery + EV Shift) | |
|---|---|---|
| Monthly HECO bill | $185 | $24 |
| Peak-hour grid purchases | ~510 kWh/mo | ~45 kWh/mo |
| Peak-hour exports | 0 kWh | ~180 kWh/mo |
| Monthly savings vs. previous | — | $161 |
That $161/month swing came from two changes: storing daytime solar instead of exporting it cheap, and shifting EV charging out of the peak window. The battery paid for itself in under three years when combined with BYOD+ incentives and the federal ITC on storage.
One of the underappreciated features of HECO's Smart Renewable Export (SRE) program is its rate lock. When you enroll, your export compensation rates — the $0.135 daytime, $0.329 peak, and $0.189 overnight on Oahu — are locked for seven years from your interconnection date.
That matters more than most people realize. HECO adjusts its retail rates frequently based on fuel costs, infrastructure spending, and PUC rate cases. The general direction over the past decade has been up. But SRE participants are insulated from changes to their export compensation for nearly a decade. If retail rates climb (likely) while your export rates hold steady, the value of peak exports relative to your avoided purchases shifts. If HECO raises peak retail rates above $0.329, your battery's value actually increases because you are avoiding a more expensive purchase while exporting at a locked rate.
The rate lock is effectively a hedge against rising electricity costs, and it is one of the strongest arguments for enrolling in SRE sooner rather than later. Use our HECO program navigator to see which program fits your situation.
Electric vehicles are the biggest new load most Hawaii households have ever added. A typical EV consuming 30 kWh per 100 miles, driven 12,000 miles per year, needs about 3,600 kWh annually — roughly equivalent to adding a second household to your meter.
When you charge that vehicle matters enormously under TOU pricing. Charging during peak hours at $0.329/kWh costs about $99/month for an average driver. Charging during the daytime solar window at $0.135/kWh drops that to $41/month. That is $700 a year saved by changing nothing except the time on a charging timer.
For homeowners with rooftop solar, the optimal strategy is straightforward: charge the EV during midday when your panels are producing surplus. If you work from home, plug in at 9am and let the car soak up solar all day. If you commute, a Level 2 charger with a programmable timer can start at 9am and finish well before 5pm. The EV becomes a second battery — one that stores cheap daytime energy you would otherwise export at $0.135/kWh and displaces peak-rate grid purchases you would make after work.
For households with both a home battery and an EV, the choreography gets more precise. The battery's job is to cover the 5pm–9pm peak window. The EV's job is to absorb excess solar during the day. Neither should draw from the grid during peak hours if the system is sized and programmed correctly.
Homeowners who enrolled in HECO's original Net Energy Metering (NEM) program before it closed to new applicants got a flat credit rate — roughly equivalent to the full retail rate — for every kilowatt-hour exported, regardless of time of day. No peak premium, but no daytime discount either. A simpler deal that rewarded total production over timing.
Under NEM, a solar-only system (no battery) made strong financial sense because daytime exports earned full retail credit. Under SRE's TOU structure, those same daytime exports earn $0.135/kWh while the homeowner buys evening power at $0.329. The gap is the entire reason batteries went from optional to near-mandatory in Hawaii's solar economics.
If you are currently on NEM, do not switch. The rate is grandfathered and almost certainly more favorable for a solar-only system than SRE. If you are installing a new system in 2026, SRE with battery storage is the path forward, and the TOU structure actually rewards you more generously at peak than the old flat rate did — you just need the battery to capture that value. Our solar calculator models both scenarios to show you the comparison.
The 5pm–9pm peak window is the only rate period that most homeowners need to obsess over. Everything else follows from that focus.
If you have solar but no battery, the battery addition should be at the top of your priority list. The TOU spread makes it a 3–4 year payback investment before incentives, and the 30% federal ITC on standalone storage (available through 2032) plus HECO's BYOD+ payments compress that further. We have run the numbers on hundreds of Oahu retrofit installations, and the return is consistently strong — especially for households with EV charging or central AC pulling heavy evening loads.
If you are starting from scratch, install solar and battery together. The economics of solar-only under SRE are weaker than they were under NEM, and the incremental cost of adding a battery during the initial installation is significantly lower than retrofitting one later. A 10 kW solar system with a Powerwall 3 on a single-story home in Ewa Beach or Kapolei, where roofs tend to have clear southern exposure and minimal shading, is close to an ideal configuration for TOU optimization.
If you do not have solar at all, start by understanding your peak-hour consumption. Pull up your HECO bill, check the TOU breakdown, and calculate what you spend between 5pm and 9pm each month. For many households in neighborhoods like Hawaii Kai, Kailua, and Kaneohe, peak-hour charges alone exceed $100/month. That is the number a solar-plus-battery system is designed to eliminate.
Regardless of where you are in the process, talk to a local installer who understands HECO's rate structure and can model TOU savings specific to your household. The generic national solar calculators do not account for Hawaii's unique rate windows, and the difference between a system designed for TOU optimization and one designed for maximum production is often the difference between a good investment and a great one.
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