What a retrofit costs
A retrofit means adding a battery to solar panels already installed, instead of buying both at once. Every source agrees a retrofit costs more, for labor, wiring and sometimes a new inverter, which turns battery power into house current. None puts a number on how much more. EnergySage, a marketplace that collects installer quotes, says a retrofit means you "will pay extra for labor, wiring, and in some cases, equipment." No such figure appears in any source, so none is invented here.
The 2 ways to wire it in
There are 2 ways to wire a retrofit. An alternating current coupled system adds a second inverter beside the existing one. EnergySage calls it cheaper upfront and less efficient, since the power converts twice. A direct current coupled system replaces the solar inverter with one hybrid inverter for both, costing more upfront but running more efficiently. EnergySage says it fits best when the existing inverter is already 5 to 10 years old and due for replacement anyway.
The price, and the credit that is gone
A 13.5 kilowatt hour battery, the size EnergySage tracks for its 2026 average, cost 15,647 dollars installed before incentives, the price before a retrofit adds more. The credit that used to soften that price is gone too. The One Big Beautiful Bill Act, the law passed in 2025, ended the federal tax credit that had cut 30% off a new solar system and a battery alike. Sales still climbed. Homeowners installed 673 megawatts of storage nationwide in the first quarter of 2026, a BloombergNEF analysis found, after a fourth quarter of 2025 that was already a record.
Where installations concentrate
California, which has rewarded pairing storage with solar since 2023, accounted for around three quarters of the nationwide total in both 2024 and 2025.
Canary Media states that California accounted for around three quarters of the total, in both 2024 and 2025. 75 is that fraction written as a number. The rest of the country figure is 100 minus that share, arithmetic done for this draft, not a number Canary Media itself states.
Show the numbers
| California | 75 |
| Rest of the country | 25 |
More than 50% of new California solar installations were paired with storage by April 2024, up from just over 20% in October 2023, per the Energy Information Administration, a 2 year old figure that explains why a household that bought solar alone before the shift now faces the retrofit decision a newer buyer skips.
The rebate that does not punish waiting
Hawaii is the one place, in practice a utility territory, that solved this directly. Hawaiian Electric runs Bring Your Own Device Plus, paying a household to let the utility draw on part of its battery during a set window each day. It pays 400 dollars for every kilowatt of battery capacity committed, with no stated maximum, and a low or moderate income household gets another 400 dollars per kilowatt on top, again with no maximum.
The third bar is the first 2 added together, arithmetic done for this draft, not a figure Hawaiian Electric states as a single number. The rate applies whether the battery was committed with new solar or added to solar installed earlier.
Show the numbers
| Every household | 400 |
| Low or moderate income, added | 400 |
| Low or moderate income, total | 800 |
The program accepts both a battery bought with new solar and one added to solar already installed, so a household that waited pays nothing extra to join. In the worked example Hawaiian Electric publishes, a household with a 15 kilowatt hour battery that commits 5 kilowatts of it for a 2 hour window each day gets a one time payment of 2,000 dollars, plus an average export credit of about 52 dollars a month that the utility says changes with the billing rate and the island a customer lives on. Joining requires an advanced meter and a 5 year agreement.
Bring Your Own Device Plus replaced an earlier program called Battery Bonus, now closed to new participants. It is the clearest rule found that treats a household adding storage after the panels the same as one that bought everything at once.