Energy independence tool

Become your own power utility

Off-grid solar and batteries, or a utility connection? Tell us a few things about your place and we’ll compare what each costs over 20 years, and when going off-grid makes sense.

About your place

Sets how much sun your panels get, especially in the cloudiest month.
On your bill. A typical Big Island home uses 400–700 kWh. Not sure? $1 of bill is about 2 kWh.
Compare keeping your connection with cutting the cord.
A generator that runs a few days a year lets you buy far fewer panels and batteries.
How many sunless days the batteries alone should carry you.
Local market uses island prices for panels, batteries and inverters bought locally, with you or a handy friend installing. Licensed installer covers a contractor doing the whole job.
Prices and assumptions (edit to match your quotes)

Planning estimates for the Big Island in late 2026, not quotes. Check local listings or get two or three bids before you decide. Sun-hour figures are approximate; check your address with NREL’s PVWatts calculator.

What each choice costs over 20 years

Running total, including upfront costs, bills, fuel, upkeep and battery replacement

When off-grid makes sense

  • You’re far from the grid. If a new line would cost more than a solar-and-battery system, off-grid usually wins on day one.
  • Your use is modest and steady. Efficient homes under about 600 kWh a month need smaller, cheaper systems.
  • You’re on the sunny side. Kona, Kohala and Kaʻū panels make 30–40% more in winter than panels in Hilo or Puna.
  • You value staying powered. Off-grid homes kept their lights on while storms like Hurricane Lala cut power to a fifth of the island.

When to keep the utility tie

  • You’re already connected and use a lot of power: a grid-tied system with a battery often gives you most of the savings and backup for less money.
  • You live in a cloudy spot and don’t want a generator: off-grid then needs a lot of extra panels and batteries.
  • You plan to add big loads such as two EVs or central air.
  • Check the rules first: county building and electrical permits apply either way, and some lenders and insurers ask about off-grid homes.

How this works

Off-grid systems are sized for the cloudiest month, not the average: panels = daily use ÷ (December sun hours × 78% system efficiency), less 15% with a generator or plus 20% without one. Batteries = daily use × backup days ÷ 92% round-trip efficiency. The grid-tied option sizes panels to about 90% of your yearly use and adds one 13.5 kWh battery; it assumes the solar covers 80% of the power you buy and that exports earn little under today’s Smart DER rules. Costs are added up over 20 years, with utility rates rising each year, batteries and inverters replaced once around year 12, and the Hawaiʻi renewable energy tax credit (35%, up to $5,000 for a home system). The federal homeowner solar credit ended for systems installed after 2025. Default rates come from Hawaiʻi Electric Light’s October 2026 residential bill. Equipment prices default to local-market prices with owner installation; switch to licensed-installer prices above. Results are estimates to start a conversation, not financial advice.