Bill to system size

This calculator is not live yet

Turning a bill into a system size needs two inputs we do not yet have a sourced value for: a current residential rate for your utility, and a modelled production figure for your location. We are not going to ship a calculator with invented constants, so this page explains the arithmetic instead and is not listed in search.

The arithmetic, so you can do it yourself

  1. Take your annual kilowatt-hours from twelve months of bills. Do not start from the dollar amount — rates, fixed charges and tiers vary, so the same bill means different consumption at different utilities.
  2. Multiply by 1.15. Under Florida PSC Rule 25-6.065 a net-metered system must not be expected to produce more than 115% of your annual consumption. That is your production ceiling.
  3. Divide by the specific yield for your location — the kilowatt-hours a single kilowatt of installed capacity produces in a year, given your roof orientation and shading. That gives system size in kilowatts.

Step three is the one we cannot fill in yet. It comes from a production model, and we take ours from NREL PVWatts. When we have ingested those figures, this page becomes a working calculator and appears in search.

What you can do today

Our estimator already applies steps one and two, so it will tell you your production ceiling in kilowatt-hours from your own usage. It stops short of converting to kilowatts, for the same reason this page does.

Sources

What each source supports on this page, and when we last verified it. Every source we use, with its freshness policy, is listed in the source register.

  1. Florida Administrative Code Rule 25-6.065, Interconnection and Metering of Customer-Owned Renewable Generation

    Florida Public Service Commission

    Net-metering eligibility, interconnection tiers and system-sizing limits for customers of Florida investor-owned utilities.

    Verified August 16, 2026

  2. PVWatts® Calculator v8 API

    National Renewable Energy Laboratory

    Modelled annual AC energy production for a given location, tilt, azimuth and loss assumption.

    Verified August 17, 2026 · Production values not yet ingested in this environment. See scripts/ingest-solar-resource.ts. NREL became the National Laboratory of the Rockies and retired nrel.gov on 29 May 2026; this API now lives on developer.nlr.gov, per https://developer.nlr.gov/docs/nlr-domain-transition/. The organisation name is kept as "National Renewable Energy Laboratory" because that is how the PVWatts model is cited in the literature.

  3. Helio41 estimate methodology, version 0.1

    Helio41

    How Helio41 sizes an indicative system, what it models, and what it deliberately does not claim.

    Verified August 16, 2026

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