Best Solar Panel Calculators of 2026: 6 Free Tools Compared

Updated October 2026 by Wolf River Electric. One of the six calculators below is ours, and we say so where it appears.

How We Compared

We did not run one address through every tool. Instead, we read each tool’s own pages in October 2026 and recorded what it asks for and what it models. Where a tool’s site doesn’t say, the table says “Not stated.” Tools change, so check the tool itself before you rely on a feature.

One of these calculators is ours. We kept it out of the table so we aren’t grading our own work, and we describe it separately below.

Comparison Table

PVWatts: Best for a Production Number

PVWatts is the free solar production model from the National Laboratory of the Rockies. That’s the U.S. Department of Energy lab called the National Renewable Energy Laboratory (NREL) until DOE renamed it on Dec 1, 2025. The calculator is at pvwatts.nlr.gov.

You enter a location (a street address, ZIP code or latitude and longitude), then system size, module type, array type, tilt, direction and system losses. Losses are split into categories such as soiling, shading, snow and wiring, so you can raise the shading number for a roof with trees. PVWatts uses typical-year weather data from the National Solar Radiation Database to estimate how much electricity the system will make.

What it doesn’t do: price the system, apply incentives or size a battery. It values the power at a simple flat electricity rate instead of modeling your bill. Use it to check the production number another calculator gives you. SolarReviews has said its own calculator uses PVWatts for production.

Google Project Sunroof: Best for a Roof-by-Roof Look

Project Sunroof is Google’s solar tool at sunroof.withgoogle.com. You enter your address, and you can add your typical electric bill to tailor the result. Google says it uses aerial imagery from Google Earth to model the roof, then accounts for roof direction, shade from trees and nearby buildings, and local weather to estimate sunlight and savings. It can also connect you with local solar providers.

Not every roof is mapped. EnergySage noted in December 2022 that Sunroof’s changelog hadn’t been updated since 2018 and that its data may be out of date because incentives have changed. Google said in 2016 that Sunroof processed about 1,000 state and local incentives, so check whether the savings figure reflects 2026 rules, including the end of the 30% homeowner credit.

EnergySage: Best for Local Prices

EnergySage’s solar calculator asks for your address, property type and average monthly electric bill, then has you drag a pin onto your roof. The address step says it is powered by Google Project Sunroof. EnergySage says the estimate is based on your roof, your bill and actual offers in your area, and that it checks roof size and orientation, shading, electricity rates, rebates and incentives, and market prices.

EnergySage says its service is completely free to use; installers pay a fee to join its marketplace. The step after the estimate is getting quotes from its pre-screened installers. The calculator form itself asks for no name, email or phone number.

Omni Calculator: Best for Doing the Math Yourself

Omni Calculator’s solar panel calculator is fully manual. You enter yearly electricity use, sun hours per day, the share of your bill you want to cover and an environmental factor for losses. A second part takes your roof area, panel size and panel wattage. It returns the array size, number of panels and roof area needed.

The page shows its formulas, starting with array output = yearly use divided by (365 times sun hours per day). There’s no address lookup, roof imagery, price or incentive math. Shade is up to you: Omni says to leave shaded or unusable roof areas out. It’s a good way to see how the math works before you trust any other tool.

SolarReviews: Best for Battery Options

The SolarReviews calculator starts with your ZIP code and utility, then roof direction and pitch from dropdowns. There’s no street address or satellite view. Results include the number of panels (it assumes 400-watt panels), recommended system size, payback period, 25-year savings, savings from incentives, and local price ranges for the system and a battery.

You can choose cash or a loan, and pick a battery approach: store extra daytime solar, cover overnight use, back up selected appliances during an outage, or skip the battery. At its September 2021 launch, SolarReviews said the tool was free, needed no personal information and used PVWatts for production. A “Continue To See Prices” button leads to its installer network. The page still refers to the federal solar tax credit, so check that the incentive line doesn’t assume a credit you can no longer get.

Wolf River Electric Calculator: For Midwest Homes (Ours)

Disclosure: this one is ours. The Wolf River Electric solar calculator is a quick estimate for homes in Minnesota, Wisconsin, Iowa, Illinois, North Dakota and South Dakota. You’ll see an estimate range, and we can follow up with an exact design.

The calculator page also lists the price per watt from our own 2026 contracts and works through sample math for Minnesota, Wisconsin and Iowa homes, so you can see where the numbers come from. If you want an answer without talking to an installer, start with PVWatts or Omni. If you live in our area and want to know what your roof would cost, use ours.

Best Project Sunroof Alternatives

People look for an alternative when Sunroof hasn’t mapped their roof or its numbers look out of date. Pick by what you need:

• Production only: PVWatts. You enter the roof details yourself, so it works for any address, mapped or not.
• Savings with local prices: EnergySage. It uses Sunroof data where it has it, and EnergySage says it assumes solar covers 100% of your bill when Sunroof hasn’t mapped the roof.
• No street address: SolarReviews works from your ZIP code and utility.
• Your own math: Omni shows every formula.
• A Midwest home: our calculator, with an exact design to follow if you want one.

Why Results Differ

Calculators can disagree on the same house for a few reasons:

• Production. Each tool decides how much sun your roof gets. Sunroof models the roof from imagery. PVWatts and SolarReviews rely on the tilt and direction you enter. Omni uses the sun hours you type in.
• Price per watt. EnergySage uses offers from its marketplace. SolarReviews uses a local median or a price you set. The gap adds up fast: on a 10 kW system, EnergySage’s Minnesota average of $3.24 per watt comes to $32,400, while the middle half of our 2026 Minnesota contracts ran $27,000 to $31,500.
• Electricity rates. Savings depend on what your power costs. EnergySage pulls rates from Arcadia, then falls back to NREL rates or state averages. PVWatts uses one flat rate.
• Incentives. A tool that still subtracts the 30% homeowner credit understates the cost of a 2026 purchase. On a $29,300 system, that’s $8,790 in savings that no longer exists. The credit ended for systems installed after Dec 31, 2025.
• Panel size. SolarReviews assumes 400-watt panels. A different panel changes the panel count, not the kW you need.

When two results don’t match, compare the system size first. If the sizes are close, the difference is price or incentives.

FAQ

What is the best free solar calculator?

It depends on the question. PVWatts is best for production, EnergySage for local prices, SolarReviews for battery options and Omni for doing the math yourself. For a Midwest home, our calculator gives an estimate range, and we can follow up with an exact design.

Is PVWatts still run by NREL?

It’s the same lab under a new name. The U.S. Department of Energy renamed NREL the National Laboratory of the Rockies on Dec 1, 2025, and the calculator is at pvwatts.nlr.gov.

What is a good alternative to Google Project Sunroof?

PVWatts for production, EnergySage for prices, and SolarReviews if you’d rather not enter a street address.

Why do solar calculators give different answers?

They use different production models, prices per watt, electricity rates and incentive rules. Compare system size first, then price per watt.

Do solar calculators include the tax credit?

Some still refer to the 30% federal credit. The homeowner credit ended for systems installed after Dec 31, 2025, so a 2026 purchase shouldn’t include it. A prepaid lease can still pass along savings from the business credit. Our solar tax credit guide explains what changed.

Which solar calculators don’t ask for a phone number?

PVWatts and Omni ask for no contact information on their pages. SolarReviews said at launch that its calculator needs no personal information. EnergySage’s calculator form asks for an address and your bill, not a phone number.

Want a number for your own roof? Try the Wolf River Electric solar calculator or request a free quote for an exact design.

Sources: National Laboratory of the Rockies (PVWatts calculator and PVWatts overview, July 2025; System Advisor Model help); U.S. Department of Energy (NREL renaming, Dec 1, 2025); Google (Project Sunroof launch post, Aug 2015; Google Sustainability, Dec 2016); EnergySage (solar calculator; partner savings model; how we make money; Project Sunroof overview, Dec 2022; Minnesota price data, Oct 2026); Omni Calculator (solar panel calculator; mission page); SolarReviews (solar calculator; launch release, Sept 2021); IRS (Residential Clean Energy Credit); Wolf River Electric contract data (June to October 2026).