Commercial Solar Calculator
Found on your monthly electricity bill
System Size Estimate
This is a sizing estimate, not a price or a quote. It assumes standard 400W modules, a typical system derate, and regional average sun hours. Actual system size depends on your load profile, roof structure and orientation, shading, available area, interconnection limits, and utility rate schedule. Installed cost varies widely by site and cannot be estimated from system size alone. For real numbers, send us a utility bill and our energy team will build a project-specific assessment.
Request a Solar AssessmentHow to Size a Commercial Solar System
The size of a commercial solar system comes down to three inputs: your monthly electricity consumption in kilowatt-hours, the percentage of that consumption you want solar to cover, and the peak sun hours available at your location. The estimator above handles the calculation, including a standard derate for inverter losses, temperature, soiling, and wiring.
Most commercial systems are sized to offset 75 to 90 percent of a facility's usage rather than 100 percent. A full offset often requires more roof or ground area than is practical, and keeping a grid connection preserves reliability and simplifies net metering. The U.S. Department of Energy's commercial solar resources provide additional guidance on sizing, interconnection, and incentive eligibility.
| Region | Peak Sun Hours | States | Impact on System Size |
|---|---|---|---|
| Southwest | 6.0 hrs | AZ, NV, NM, CA desert | Smallest system needed for a given output |
| South / Mountain West | 5.5 hrs | TX, CO, UT, KS | Excellent solar resource |
| Southeast | 5.0 hrs | FL, GA, SC, TN, AL | Good solar resource year-round |
| Midwest / Mid-Atlantic | 4.5 hrs | IL, OH, VA, NC, MO | Moderate resource |
| Northeast | 4.0 hrs | NY, PA, MA, CT, WI | Larger system needed for the same output |
| Pacific Northwest | 3.5 hrs | WA, OR | Lowest resource, system size increases accordingly |
What Determines the Cost of a Commercial Solar Project
Commercial solar does not have a list price, and system size alone is not enough to estimate one. Two facilities with identical kilowatt ratings can price very differently depending on how the system has to be built and interconnected. That is why FSG prices every project after an engineering review rather than publishing a per-watt figure.
The variables that move commercial solar cost the most:
| Cost Driver | Why It Matters |
|---|---|
| Mounting type | Ballasted flat roof, attached roof, ground mount, and carport structures carry very different structural and labor scopes. |
| Roof condition and age | A roof nearing end of life may need replacement or reinforcement before panels go on it. |
| Electrical infrastructure | Switchgear capacity, panel upgrades, conduit runs, and distance to the point of interconnection. |
| Interconnection and utility requirements | Study fees, protection equipment, and utility-mandated upgrades vary by territory and can be significant. |
| Permitting and jurisdiction | Local AHJ requirements, structural engineering, and inspection timelines differ market to market. |
| Equipment selection | Module and inverter choice, monitoring, and whether domestic content sourcing is required for incentive eligibility. |
| Storage and controls | Adding battery storage or demand management changes both scope and economics. |
| Site logistics | Crane access, occupied-facility work, phasing, and after-hours labor requirements. |
FSG's process is to review your utility bills and site conditions first, then produce a single project-specific model that includes engineering scope, production estimates, and the incentives your business actually qualifies for. Send us a bill and we can run a pre-qualification check quickly.
Federal Incentives for Commercial Solar
Federal incentives materially affect commercial solar returns, but the value depends on your entity type, tax appetite, project structure, and location. The percentages below reflect the federal framework. The dollar value of any of them is specific to your project and tax position, and should be modeled with your CPA alongside a real proposal.
| Incentive | Value | How It Works | Notes |
|---|---|---|---|
| Federal ITC -- Base | 30% | Direct dollar-for-dollar federal tax credit | Available to eligible commercial systems |
| ITC -- Domestic Content Adder | +10% | Additional credit for compliant domestic content | Requires eligible US-manufactured components |
| ITC -- Energy Community Bonus | +10% | Additional credit for qualifying Energy Community locations | Check eligibility at Treasury.gov |
| MACRS Depreciation | 5-year schedule | Accelerated depreciation instead of a 39-year schedule | The depreciable basis is reduced by half the ITC value. Benefit depends on your tax rate and bonus depreciation position. |
| State and Utility Incentives | Varies | State tax credits, REC programs, utility rebates, tax exemptions | Check your state at DSIREUSA.org |
Eligibility rules, adders, and procurement timing requirements have changed repeatedly in recent years. Current guidance is published by the IRS. Confirm current deadlines and eligibility with FSG's energy team and your tax advisor before making a procurement decision.
Frequently Asked Questions
Want real numbers for your facility?
FSG designs and installs commercial solar for businesses, industrial facilities, and multi-site national accounts nationwide. Send us a utility bill and our energy team will build a project-specific assessment covering system design, production, and the incentives your business actually qualifies for.