Battery storage · Oʻahu
A home battery stores daytime solar for the evening and keeps the circuits you choose running when Hawaiian Electric's grid goes down. Alternate Energy Hawaii, a Pearl City contractor since 1993 and a Tesla Premier Installer, designs and installs battery storage for new and existing solar across Oʻahu, sized to your loads and HECO's program rules.
How it works
A battery does three jobs, and most Oʻahu systems are set up to do more than one. Deciding which job matters most is the first step in sizing it.
1
The battery keeps a share of its charge in reserve. When the grid fails, a backup gateway disconnects your home and the battery powers the circuits you chose, such as the refrigerator, lights, Wi-Fi and a medical device.
2
Panels produce most at midday, when your house often needs the least. A battery stores that surplus for the evening. Hawaiian Electric's 2024–2026 export rates on Oʻahu credit 13.5¢/kWh in the daytime and 32.9¢/kWh in the 5–9 p.m. peak (Hawaiian Electric).
3
Under BYOD Plus, a new battery sends part of its stored energy to the grid during a two-hour window you pick each day, for an upfront incentive and bill credits. Your home is served first (Hawaiian Electric).
Hawaiian Electric programs
Every new rooftop system on Oʻahu joins one of Hawaiian Electric's programs, and all Smart Renewable Energy participants need an advanced meter (Hawaiian Electric).
| Program | Battery | What the battery does |
|---|---|---|
| Smart Renewable Energy Export | Optional | Shifts daytime solar into the evening, when exports earn 32.9¢/kWh on Oʻahu versus 13.5¢ during the day (rates). |
| Smart Renewable Energy Non-Export | Needed to use surplus | Nothing may be exported, so solar is used as it's produced or stored for later (program page). Without a battery, surplus midday power is wasted. |
| BYOD Plus | Required | Pays $400 per kW committed upfront, plus $400 per kW for qualifying low- to moderate-income customers. You commit at least 1 kW for a daily 2-hour window, under a 5-year agreement (BYOD Plus). |
| NEM Plus | Optional | For existing NEM customers: add panels, a battery or both without changing your NEM agreement; the added system can't export (NEM Plus). |
| NEM Plus Limited Export | Required | Must include a battery enrolled in a grid-services program such as BYOD Plus. Total solar can't exceed twice the new battery's size (NEM Plus Limited Export). |
Hawaiian Electric's own example: a 15 kWh battery committing 5 kW for 2 hours earns a one-time $2,000 and about $52 a month in bill credits. Customers on NEM or NEM Plus get the upfront incentive but no monthly BYOD Plus credits (BYOD Plus). Our BYOD Plus guide walks through enrollment.
Equipment
Tesla promoted AEI to Premier Installer in December 2023 (announcement), and we also install Enphase storage. The two take different approaches.
13.5 kWh
High power from one unit, including larger appliances. More on Tesla Powerwall on Oʻahu.
Source: Tesla datasheet, Tesla system design
5.0 kWh
A natural fit for homes already on Enphase microinverters, or for starting small and adding capacity later.
Source: Enphase
Sizing
Size a battery on two numbers: power (kW), how much it can run at once, and energy (kWh), how long it can run. We start with your Hawaiian Electric bills and a walk-through of the loads you care about.
1
Outage backup, evening self-consumption, BYOD Plus or a mix.
2
A refrigerator, lights, Wi-Fi and outlets need far less than central AC, an electric water heater or a range.
3
Continuous output (kW) has to cover everything on those circuits at once, plus motor start-up surges.
4
Divide usable kWh by the average draw: 13.5 kWh feeding circuits that average 1 kW lasts about 13 hours before solar starts recharging it.
5
A 5 kW BYOD Plus commitment for 2 hours sends up to 10 kWh a day to the grid after your house is served (Hawaiian Electric), so size for that on top of your backup reserve.
Costs depend on the number of units, backup equipment and electrical work. See what a solar battery costs in Hawaiʻi.
Existing solar
Usually, yes. Tesla says Powerwall 3 can be added to existing solar and works with all major inverter brands (Tesla), and Enphase's IQ Battery is AC-coupled, so it doesn't need to replace your inverter (Enphase). Your Hawaiian Electric agreement decides the design:
Add a battery under NEM Plus (no export), or under NEM Plus Limited Export, which requires BYOD Plus or another grid-services program (Hawaiian Electric).
CGS, CSS, CGS Plus and Smart Export customers can add storage of any size, but any added capacity is limited to 1 kW (Hawaiian Electric).
You can't move into BYOD Plus with your existing battery; the program requires a new battery (Hawaiian Electric).
Each change goes through Hawaiian Electric as an amendment to your existing agreement, which we prepare and submit. If the roof is near the end of its life, re-roof before more equipment goes on; an older electrical panel may need an upgrade.
Outages
Utilities require grid-connected systems to disconnect from the grid during a power failure, so line workers aren't hurt (U.S. Department of Energy). That's why solar without a battery doesn't keep your lights on in an outage.
With a battery and backup gateway, the system separates from the grid and keeps your backed-up circuits running. Tesla's gateway provides an "automatic disconnect for seamless backup" (Tesla datasheet). During daylight, the panels keep recharging the battery while the grid is down, so a multi-day outage becomes a daily cycle instead of a countdown.
Whole-home or selected circuits? Whole-home backup needs enough power to start every large load, which can mean several batteries. Most Oʻahu homes back up a selected-loads panel and leave central AC and the water heater off it.
Before a storm
Powerwall's Storm Watch charges the battery to full when a severe weather watch or warning is issued for your area. Grid charging has to be enabled for it to work (Tesla).
Our storm preparedness guide covers what to check before hurricane season.
Compare
| Solar only | Solar + battery | |
|---|---|---|
| Upfront cost | Lower; fewer components | Higher; battery, gateway and backup wiring |
| Midday surplus | Exported for SRE credits (13.5¢/kWh daytime on Oʻahu) | Stored for your evening use or exported at the evening-peak rate (32.9¢/kWh) |
| Evenings | You buy grid power | The battery covers part or all of it |
| Grid outage | System shuts off | Backed-up circuits stay on; solar recharges by day |
| HECO incentives | Export credits only | Can add BYOD Plus: $400/kW upfront (+$400/kW LMI) and monthly credits |
| NEM owners adding capacity | NEM Plus (no export) | NEM Plus or NEM Plus Limited Export |
| Best fit | High daytime use, tighter budget | Evening-heavy use, outage concerns, BYOD Plus |
Export rates: Hawaiian Electric SRE Export 2024–2026 (source); programs: BYOD Plus, NEM Plus. Going solar-only for now? Ask us to design it battery-ready, with an inverter and layout that make adding storage later straightforward. See home solar on Oʻahu.
Protection
10 years for Powerwall 3 (Tesla); a 15-year limited warranty up to 6,000 cycles for the Enphase IQ Battery 5P (Enphase).
Coverage for the installation itself is written into your proposal.
Our own employees install the system, so the same local team handles monitoring questions and maintenance afterward.
Joining BYOD Plus? It's a 5-year agreement: leaving early means repaying a prorated part of the upfront incentive (Hawaiian Electric).
Incentives
Ended
Batteries of at least 3 kWh qualified for the 30% credit from 2023, but it isn't available for property placed in service after December 31, 2025 (IRS).
Capped
Act 24 (2026) puts a $40 million annual cap on the credit; systems placed in service before May 21, 2026 are exempt (TIR 2026-02). The guidance doesn't address batteries specifically. See our 2026 tax credit guide.
Open
A utility incentive, not a tax credit: $400 per kW committed, plus $400 per kW for qualifying LMI households (Hawaiian Electric).
Every household's tax situation is different; check yours with a tax professional.
FAQ
It depends on the battery's usable energy and what's connected. A 13.5 kWh Powerwall 3 running circuits that average 1 kW lasts about 13 hours; adding central AC shortens that sharply. With solar, the battery recharges each sunny day while the grid is down, so we size it around your essential circuits rather than a fixed number of hours.
Usually. Powerwall 3 can be added to existing solar with any major inverter brand, and Enphase batteries are AC-coupled. Your Hawaiian Electric agreement shapes the design: NEM customers use NEM Plus or NEM Plus Limited Export, and older programs can add storage with added capacity limited to 1 kW. We prepare and submit the amendment.
BYOD Plus pays $400 per kW committed, once, plus another $400 per kW for qualifying low- to moderate-income households. Most participants also get monthly bill credits; NEM and NEM Plus customers don't. Hawaiian Electric's example is $2,000 upfront and about $52 a month for a 5 kW commitment. It requires a new battery, an advanced meter and a 5-year agreement.
BYOD Plus dispatches only during the 2-hour daily window you choose, and the battery serves your home before exporting anything. Outside that window the battery follows your own settings, including its backup reserve, and Powerwall's Storm Watch charges the battery to full ahead of severe weather warnings when grid charging is on. We set the reserve and window together with you.
The 30% federal credit no longer applies: the IRS says it isn't available for property placed in service after December 31, 2025. Hawaiʻi's state credit has a $40 million annual cap from 2026 under Act 24, and the state's guidance doesn't address batteries specifically. Ask a tax professional; BYOD Plus is a separate utility incentive that's still available.
Powerwall 3 gives 13.5 kWh and 11.5 kW from one unit with a built-in solar inverter and a 10-year warranty. Enphase's IQ Battery 5P is a 5 kWh modular unit with a 15-year limited warranty that pairs naturally with Enphase microinverters. The right pick depends on your existing equipment, the loads you back up and your budget.
Free evaluation
Send us your recent Hawaiian Electric bills and tell us what you want the battery to do. We'll review your usage, your existing solar and HECO agreement, your panel and roof. Then we'll recommend a battery size, backup circuits and program, with a written proposal.
Running a business? See commercial solar and storage.