Hawaii Solar Calculator

Enter your island and monthly bill — get system size, production, 30% ITC + 35% Hawaii state credit, and payback period. Hawaii has the fastest solar payback in the US.

Your Hawaii home

Average monthly electric bill?

Your island / utility?

System size?

Add battery storage??

Roof orientation?

Hawaii solar analysis — 4 kW system

$4,480 after incentives (was $12,800)

Recommended system size2.8 kW

Annual production (5.8 PSH)6,774 kWh/yr

Annual kWh usage4,683 kWh/yr

Bill offset100%

Annual savings (at $0.41/kWh)$1,920.00/yr

Gross system cost$12,800

Federal ITC (30%)-$3,840.00

HI state credit (35%, max $5,000)-$4,480.00

Net cost after all credits$4,480

Payback period2.3 yrs

25-year net savings$43,520

🌴 Hawaii has the highest electricity rates in the US ($0.39-0.43/kWh). This drives 5-8 year paybacks — fastest in the nation. HI property tax exemption also applies.

⚠️ New Hawaii grid-tied systems typically use the Self-Supply program (no net metering). Battery storage is strongly recommended to avoid curtailing excess solar generation.

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How to Use This Calculator

Enter your bill and select your island

Start with your average monthly electric bill. Hawaii electricity rates are the highest in the US — Oahu (HECO) at $0.41/kWh, Maui (MECO) at $0.43/kWh, Big Island (HELCO) at $0.39/kWh, and Kauai (KIUC) at $0.42/kWh. These rates are 3-4× the mainland average, which is why Hawaii has some of the fastest solar payback periods in the nation.

System size and battery decision

Hawaii homes typically use less electricity than mainland homes — no heating season and moderate cooling needs. Common sizes: 3-5 kW for condos and smaller homes; 6-10 kW for larger homes; 10+ kW for Big Island off-grid or high-usage homes. Battery storage is strongly recommended for new Hawaii installations because most utilities now use the Self-Supply program rather than traditional net metering — excess solar not stored or self-consumed is essentially wasted.

Read the incentives

Hawaii stacks two major tax credits: the federal 30% ITC plus Hawaii's 35% state credit (up to $5,000). On a $20,000 system, you get $6,000 from the federal ITC and $5,000 from the state (the cap), bringing net cost to $9,000. The property tax exemption also applies — solar doesn't increase your Hawaii property tax assessment.

The Formula

Annual kWh = Monthly Bill × 12 ÷ Island Rate Recommended kW = Annual kWh ÷ (Island PSH × 365 × 0.80 × 1000) Annual Production = System kW × 1000 × Island PSH × 365 × 0.80 × Roof Factor ÷ 1000 Gross Cost = System kW × 1000 × $3.20/W (HI premium) Federal ITC = Gross Cost × 30% HI State Credit = min(Gross Cost × 35%, $5,000) Net Cost = Gross Cost - Federal ITC - HI State Credit Payback = Net Cost ÷ Annual Savings 25-year Savings = (Annual Savings × 25) - Net Cost

Hawaii's $3.20/W installed cost is higher than the mainland average due to shipping costs for equipment, higher labor costs, and permitting. Despite this premium, the exceptional $0.40+ electricity rates mean payback periods of 5-8 years — among the fastest in the US. The 35% state credit (capped at $5,000 per system) is one of the most generous state credits in the country.

Example

The Nakamuras — Maui home, 8 kW system

The Nakamuras have a $345/month MECO bill on Maui ($0.43/kWh). They want an 8 kW south-facing system without battery. They owe state and federal income tax to use the credits.

Monthly bill$345/mo (MECO, Maui)

Rate$0.43/kWh — highest in US

System size8 kW

PSH5.7 (Maui)

Result

Annual production~13,300 kWh/yr

Annual savings~$4,140/yr

Gross system cost$25,600

Federal ITC (30%)-$7,680

HI state credit (35%)-$5,000 (capped)

Net cost$12,920

Payback~3.1 years

25-year savings~$90,600

A 3.1-year payback is exceptional by any measure. Hawaii's $0.43/kWh Maui rate means every kWh generated is worth more than 3× what it would be in the average US state. The Nakamuras' 25-year net savings of $90,600 represent a compelling financial case — even accounting for Hawaii's higher installation costs.

FAQ

Why does Hawaii have the highest electricity rates in the US? ▼

Hawaii's electricity costs are high for three reasons: (1) Fuel transportation — Hawaii historically burned imported oil to generate electricity, and shipping fuel across the Pacific is expensive. (2) Island isolation — each island has its own grid with no mainland interconnection, so there's no ability to buy cheap power from neighbors. (3) Small scale — smaller grids have less economy of scale. Renewable energy, particularly solar, has been aggressively deployed to reduce oil dependence — Hawaii has one of the highest solar penetration rates per capita in the US.

What is Hawaii's 35% solar tax credit? ▼

Hawaii offers a personal income tax credit equal to 35% of the installed cost of a solar water heating or solar PV system, capped at $5,000 per system (or $2,250 for single-family solar water heaters). To claim the maximum $5,000 PV credit, your system must cost at least $14,286. The credit is claimed on Form N-342 with your Hawaii state tax return. It is non-refundable but carries forward 5 years. It stacks directly with the 30% federal ITC.

What is the GEMS green energy loan in Hawaii? ▼

GEMS (Green Energy Money Saver) is Hawaii's on-bill financing program for solar and energy efficiency upgrades. Key features: loan amount up to $10,000 per household; interest rates of 4.5-6%; repaid through your utility bill in small monthly increments; no home equity required; available to renters with landlord approval. GEMS allows lower-income Hawaii residents who can't afford upfront solar costs to access solar savings. Contact Hawaii Green Infrastructure Authority (HGIA) for current program details.

Does Hawaii still have net metering? ▼

Traditional net metering (NEM) in Hawaii was closed to new customers in 2015. The primary program for new grid-tied solar customers is now Self-Supply — you must use or store solar on-site; excess energy is not exported or credited. This makes battery storage essential for new Hawaii solar installations. Customers who installed before 2015 may still have legacy NEM agreements. HECO and MECO have introduced Customer Grid Supply programs with limited export credits for some customers.

Is going off-grid a good option in Hawaii? ▼

Off-grid solar is more viable in Hawaii than almost anywhere in the US because of the combination of high electricity rates and good sunshine year-round. The Big Island in particular has a strong off-grid community, partly because grid extension to rural properties is extremely expensive. A well-designed 10 kW system with a 20-30 kWh battery bank can reliably power most Hawaii homes. The loss of net metering under Self-Supply has also made the economics of a larger off-grid system more competitive with grid-tied.

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