Residential Solar Estimator — Rooftop Production and Battery Storage | SolarTI83
solarTI-83

Residential solar estimator

GuideHow much energy will my solar panels actually make?Where the kWh number on your solar quote comes from — sun position, irradiance, roof orientation, shade, panel temperature, and inverter clipping — and how to tell whether it’s real.18 min readRead the guide →GuideWhy west-facing solar panels fall further behind east-facing ones in north Florida than near PhoenixIn north Florida a west-facing roof plane gets about 5% less sunlight a year than an east-facing one and 11% less in summer; near Phoenix the gap is about 1%.8 min readRead the guide →GuideWhen homes use electricity: hourly load by heating fuel and climateHow heating fuel, floor area and climate shape a home’s hourly electricity use, and why solar sized to a year’s use supplies only 33% to 50% of it directly.9 min readRead the guide →

How the estimate works

Search for your address. If the search can only find the street, or the address lands away from the building it finds, the tool asks you to click your house on the map. The tool reads that roof from Google's Solar API: the pitch and direction of each roof plane, how much sunlight each part of the roof receives, and the building outline. It lays out panels on every plane and starts with enough of them, on the sunniest planes, to make about as much electricity in a year as the home uses; you can add or remove panels plane by plane. Satellite shows the layout over the aerial image, and 3D model shows the house with its panels.

Savings and payback

The savings section works out the electricity bill hour by hour three ways: with no solar, with the panels you placed, and with the battery if you added one. It starts from your state's 2025 average price from the U.S. Energy Information Administration, or the plan of the utility that serves your county, with presets for the two or three largest utilities in each state and how each credits solar sent to the grid, and you can type in your own price, time-of-use prices and what your utility pays for solar sent to the grid. Cost starts at the national average of $3.36 per watt (SEIA) and $1,074 per kWh of battery. Over 25 years, prices rise 3.2% a year and the panels lose 0.5% a year; the result is the payback year, the 25-year gain and the yearly return, paid in cash or with a loan.

Hourly production

The yearly total comes from the sunlight on the panels you placed, after a flat 14% system loss (the PVWatts default). That total is spread over the 8,760 hours of a typical year using the Typical Meteorological Year for the site from NREL's National Solar Radiation Database (NSRDB), which is compiled from decades of satellite-derived measurements.

Home electricity use

The building load uses NREL ResStock (2024) hourly profiles for single-family homes in the same state, starting from that state's most common home. You can change the heat fuel, air conditioning and home size, enter your own annual kWh, or upload an hourly usage CSV such as a utility Green Button download.

Battery storage

Turn on the battery section to add a Tesla Powerwall 3, Enphase IQ Battery 5P or SolarEdge Home Battery using datasheet values, or enter your own capacity, power and round-trip efficiency. The battery charges only from solar surplus and discharges only to the home's load, hour by hour through the year. The readouts give self-sufficiency, grid import, the share of solar used on site and full cycles per year, each against the same home with no battery, and a note says whether the battery is undersized or oversized for a typical day's surplus.