Solar panels in Hilo, HI

Roofs in Hilo get about 1,510 hours of usable sunlight a year — more than 51% of the cities we've measured. Here's what that means in cost, savings and payback, using real rooftop data rather than a national average.

Check your specific roof in Hilo → City averages are a starting point; your own roof's size, pitch and shading change the answer a lot.

What a typical Hilo solar system costs

A 22-panel system (8.8 kW) is about right for an average Hilo home using 10,800 kWh a year. It would produce roughly 11,295 kWh annually and offset 100% of that usage.

How we worked this out for Hilo

Every number on this page comes from these seven steps. Nothing is a national average — the sunlight figure is measured from Hilo rooftops.

Step 6 matters more than it looks. Only 33% of what a system this size produces in Hilo is used the moment it is generated; the other 7,515 kWh is exported and credited one-for-one under net metering. Because exports here are credited at or near retail, that split changes the payback very little — 3.7 years against the 3.8 we show. In places where exports pay a fraction of retail the same split moves payback by years, which is why we model it explicitly rather than assuming.

Assumptions: 400W panels, 15% system losses (inverter, wiring, heat, soiling), $2.85/W installed, 10,800 kWh typical annual household use, 42.1¢/kWh electricity. Change any of those and every figure above moves — which is exactly why a single national "solar costs X" number is misleading.

Notice that payback barely improves as systems get bigger, and eventually gets worse. That's because you can only save money on electricity you were going to buy anyway. Once a system covers your usage, extra panels mostly generate exports at a much lower rate.

Why Hilo gets 1,510 sun hours

That figure comes from Google's analysis of real rooftops across Hilo — it already accounts for shading from trees, chimneys and neighbouring buildings, which is why it's lower than the raw "hours of daylight" figures you'll see elsewhere. An unusually open, unshaded roof in Hilo reaches about 1,636 hours, roughly 8% better than typical.

The numbers behind this page

When Hilo actually produces

Annual totals hide the thing that catches people out: 29% of Hilo's yearly sunlight arrives in May–July, and just 20% across November–January.

Output is unusually steady — only about 1.5× between Jun and Dec. Hilo is close enough to the equator that seasonal variation is mild, which makes sizing a system considerably more predictable.

The annual total is measured from Google's rooftop imagery. Its split across months is calculated from solar geometry at Hilo's latitude, not separately measured, so treat the monthly figures as the shape of a typical year rather than a forecast.

How Hilo compares to the other 788 cities

What actually stands out about Hilo:

• Roof space is the binding constraint. A typical Hilo roof fits about 33 panels and a typical home needs 22 — so there is little room to oversize. If you add an EV or heat pump later, plan the array for it now.
• Dimmer than the rest of Hawaii. Hilo roofs get 7% less usable sunlight than the typical Hawaii city we've measured — statewide averages will overstate what you can expect here.
• Expensive electricity works in your favour. At 42.1¢/kWh, Hawaii is among the priciest places to buy power — which is exactly what makes generating your own pay back faster.
• Older imagery. Google's aerial capture of Hilo dates from 2013. Tree growth and new construction since then are not reflected.

Cities with almost the same sunlight

These are the closest matches to Hilo's 1,510 usable sun hours from other states and provinces. Same sunlight, different electricity prices — which is usually what decides whether solar is worth it.

Nearby cities

See all of Hawaii → statewide sunlight, rates, incentives and every city we've measured.

Hilo solar questions

Worth reading before you buy

Estimates only, generated 2026-08-22 from Google Solar API rooftop samples and average Hawaii electricity rates. Not a quote and not financial advice. Your roof, usage, utility plan and local incentives will change these numbers — get real quotes before buying.