watt if
a guided energy checkup for your home

Find it · Trace it · Price it

What if your roof
paid the bill?

Search for your home, trace your usable roof on the satellite map, and enter your monthly electricity bill. We combine local tariffs and equipment prices with NASA POWER annual solar-resource data for the searched location. Roof direction and shading stay adjustable assumptions.

Search your address, then zoom in until you can see your roof.
Pre-filled roof, bill, and complete report.
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Click Trace roof, then click the corners of your roof on the map. Skip it and we'll size from your bill instead.

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Saved only in this browser. No account, analytics, or watt if database. Address, map, and sunlight requests use external services. What is saved and sent?

usage— system— saves— payback— 10-year result—
01

Your roof

What fits up there, and what it would generate

Recommended system — panels — kW sized to your usage
Usable roof traced — m²
Physical roof maximum — × 550 W
Maximum roof capacity — kW
Sun at your location — h/day
Proposed panels on the map

Approximate placement only — final spacing, orientation and obstructions require a site survey.

  • — kWh generated per month
  • Sun data: regional average

02

Your bill, covered

Usage, energy flows, and what solar saves each month

Monthly usage — kWh
Energy offset —% of usage
Bill offset —% of bill
You save about — / month
Solar install (est.) — Solar only
Pays for itself in — years
Solar generated —
Used directly by home —
Exported to grid —
Imported from grid —
Energy offset —
Bill offset —
Your home
—
Typical home
—

03

Backup power

What stays on when the grid goes down

Include in the financial model Solar only

The backup recommendation is shown below but excluded from installation cost, payback, and the ten-year chart.

Keep these running
Load to carry — W
Energy needed — kWh
Battery to buy — kWh
Inverter — kW

04

Ten years, two paths

Stay grid-only, or add the selected system

Stay on the grid Install solar
Cumulative ten-year cost: staying on the grid versus installing solar

Refine the estimate — shading, roof direction, tariffs, prices

Tariffs, sunshine, and prices are regional averages — your utility bill and installer quotes are the real source of truth. This report is a planning estimate, not financial advice.

Field notes

The fine print,
in plain English.

What comes from satellite data, what you control, and where this estimate stops.

Estimate, not quote

Use watt if to compare scenarios. A site survey and installer quote set the final design.

01 How exact is the sunlight estimate?

NASA POWER supplies a location-level annual sunlight average—not a scan of your roof. Direction, pitch, shade, trees, chimneys, and other obstructions remain assumptions you can adjust under Refine the estimate.

02 What if the live sun lookup fails?

The checkup uses the selected city’s regional average instead. The source line under Your roof always tells you whether live location data or the fallback is active.

03 Why is the recommendation smaller than the roof maximum?

They answer different questions. The recommendation matches the monthly use inferred from your bill. The roof maximum only says what could physically fit by area. A large roof does not automatically justify a large system.

04 Why can energy offset and bill offset differ?

Energy offset compares total solar generation with total use. Bill offset values electricity differently: power used directly avoids the full retail rate, while exported power may earn less. Reaching 100% energy offset therefore does not guarantee a zero bill.

05 Are the blue rectangles an installation plan?

No. They are a scale-approximate concept for the proposed panel count. An installer still needs to check pitch, setbacks, structure, shade, obstructions, and local code.

06 Is the backup battery included in the economics?

Only when you choose Solar + backup battery. That mode adds one recommended battery allowance to installation cost, payback, and the ten-year chart. It does not assume extra bill savings from daily trading or a replacement within ten years.

07 What is saved, and what is sent?

Saved on this device: your bill, selected region, roof outline, map view, proposed system, backup choices, and estimate assumptions. They live in this browser’s local storage so the checkup survives a reload. The city, bill, and map view also sit in the URL fragment so a bookmark can restore them. Start over removes the saved checkup and clears that fragment.

Sent only when needed: the address text you search goes directly to OpenStreetMap’s Nominatim service; the selected latitude and longitude go to NASA POWER; and the map area you view requests imagery tiles from Esri. The site host, Google Fonts, and unpkg receive ordinary web requests needed to deliver the page and may retain routine connection logs under their own policies.

Not sent by watt if: your bill, traced roof polygon, report results, appliance choices, and refinements are not submitted to a watt if server. watt if has no account system, analytics, or server-side checkup database.

Nominatim policy NASA POWER API Esri privacy Google Fonts privacy