Free Solar Design Software: 2026 Reality Check

The catch with every “free” solar design tool is that the free part is real, but the workflow it serves is narrow. SAM is free because it is a research-grade financial model that the National Renewable Energy Laboratory (NREL) maintains for the industry. PVWatts is free because it is a quick yield estimator that NREL publishes for pre-feasibility studies. OpenSolar is free because the company collects 0.8 to 1.5 percent on every financed deal routed through their finance partners. The right question for an installer is not “is there a free tool” but “for which jobs is the free tool actually enough, and at what point does the cost of working around the gaps exceed the cost of a real platform.” This guide is a working answer from a design bench that runs all of them on real projects.

Direct answer. Free solar design software works for three jobs: research-grade financial modeling (SAM by NREL), pre-feasibility yield estimates under 10 kW (PVWatts by NREL), and zero-upfront residential sales with a transaction-fee model (OpenSolar). It does not work for permit-ready package generation, bankable C&I yield reports, or NEC 2023 single-line diagrams. For installers above 10 kW per project who need a real platform without a transaction fee, the SurgePV free trial covers two to three real projects end to end with no credit card required.

What “Free” Actually Costs

Free tools are not free. The cost shifts from a subscription line item to time, transaction fees, or design quality. For an installer doing real volume, the question is always which of those three costs is cheapest, and the answer changes with the project size and the deal mix.

The three free-tool cost models

There are exactly three ways free solar design software stays free in 2026.

1. Government-funded research tools (SAM, PVWatts) are free because NREL pays the engineering bill from federal research funding. The tools are not built for installer workflow; they are built for academic modeling and pre-feasibility.
2. Transaction-fee tools (OpenSolar) are free at the seat but charge a percentage on every financed deal. The cost scales with volume.
3. Trial tools (SurgePV, Aurora’s limited demo, others) are free for a window. The cost is the migration risk if the team commits to a platform that does not actually fit.

Each of these has a real use case and a real ceiling. The reality test below covers all three.

What free tools cannot do

Across every free tool in the US market, there are four jobs that cannot be done well without a paid platform.

SAM (NREL) for Research

The System Advisor Model is NREL’s research-grade techno-economic platform. It is the tool academic researchers, finance modelers, and policy analysts use to compare PV technologies, storage configurations, and financing structures. It is not a design tool.

What SAM does well

SAM ships a detailed financial model with cash flow, tax credit handling, PPA structures, and debt service modeling. The PV performance model is hourly and accepts custom weather files. For an analyst modeling a hypothetical 50 MW project to compare two ITC scenarios, SAM is the right tool.

What SAM does not do

SAM does not generate a layout. It does not output a stamped drawing. It does not produce a customer-facing proposal. It does not have an AHJ library. The Windows-only installer is a friction point for any team running on Mac or cloud. For an installer trying to ship a permit package, SAM is not the right shelf.

PVWatts for Pre-Feasibility

PVWatts is NREL’s hosted pre-feasibility calculator. A user plugs in a location, a system size, a tilt, an azimuth, and a derate factor, and the tool returns an estimated annual energy production. It is the right tool for a one-sentence answer (“a 6 kW system in Phoenix at 20 degrees tilt produces about 10,500 kWh per year”).

What PVWatts does well

PVWatts is fast, accessible from a browser without an account, and grounded in NREL’s TMY3 weather database. For an installer doing a phone-call sanity check on a residential lead, PVWatts is the right tool. According to NREL’s 2024 US PV benchmark, PVWatts is the most-cited pre-feasibility tool in US distributed PV studies.

What PVWatts does not do

PVWatts does not handle shading from trees or adjacent buildings. It does not account for module-level mismatch losses, soiling patterns, or detailed wire-loss modeling. It does not generate a drawing, a proposal, or an SLD. For any system above 10 kW or any project with meaningful shade, PVWatts is not enough.

OpenSolar Free Tier

OpenSolar is the only credible free design and proposal platform for residential installers in 2026. The seat is free; the cost is the 0.8 to 1.5 percent transaction fee on financed deals routed through OpenSolar’s finance partners.

What OpenSolar’s free tier ships

The free OpenSolar seat ships satellite roof capture, an AI design helper, an hour-banded shading model, a built-in residential proposal, and a customer-facing portal. For an installer under five financed deals per month, this is a genuinely viable free workflow.

Where the free tier breaks

The hour-banded shading model is not module-level. OpenSolar does not generate an NEC SLD. The AHJ preset library is limited compared to Aurora. And the transaction fee scales with deal volume; at twenty financed deals per month at a $25,000 average ticket, the “free” tier costs $48,000 to $90,000 per year. For the full picture, see our OpenSolar alternatives review.

SurgePV Free Trial as the Practical Alternative

For an installer who needs a real platform but does not want to commit a $1,299 per seat annual budget before testing the workflow, the SurgePV free trial is the practical answer. The trial covers two to three real projects end to end, including AI 3D roof design, 8,760-hour shadow analysis, the NEC 2023 SLD, and a customer-facing proposal. There is no credit card required.

What the SurgePV trial covers

The trial tier ships every feature on the standard plan. A residential installer can run a complete satellite-to-proposal motion on two or three live projects, including the proposal sent to a real homeowner, before committing to a subscription. For a C&I designer, the trial covers the 8,760-hour simulation, the layout DXF export, and the SLD on a small commercial project.

Why this beats every other free option

PVWatts and SAM are free for research but not for installer workflow. OpenSolar is free at the seat but charges per deal. The SurgePV trial is free at the seat for the trial window, with no per-deal cut and no feature gating. The downside is the trial is time-bounded; for an installer who needs ongoing free capability, OpenSolar or a hybrid (PVWatts for sanity checks, SurgePV trial for permit-ready projects) is the right path. You can book a SurgePV demo or start the trial directly. For pricing if the team converts, see SurgePV pricing.

When Free Is Enough vs When It Is Not

The honest answer is that free works for a specific job profile, and an installer who knows the profile can stay free for years. Outside that profile, the cost of working around the gaps exceeds the cost of a paid platform.

When free is enough

A small residential installer doing under five financed deals per month, all under 10 kW, in a single state with a familiar AHJ, can run OpenSolar’s free tier plus PVWatts for sanity checks and a manual NEC SLD drawn in a free CAD tool. The transaction fees stay under $2,250 per year. The team does not need a paid platform.

A researcher, policy analyst, or finance modeler can run SAM for techno-economic comparison and PVWatts for pre-feasibility yield checks. Neither tool charges anything, and both are accepted in academic and policy work. For more context, see our PVsyst glossary entry on where SAM sits relative to bankable yield platforms.

When free is not enough

Above 10 kW per project, PVWatts loses fidelity and a paid 8,760-hour simulation is required. Above five financed deals per month, OpenSolar’s transaction fee exceeds the cost of a paid SurgePV or Aurora seat. For any permit office that requires a stamped NEC SLD, the free workflow stops at the layout step. For any C&I or utility-scale project with an IE review, PVWatts is not bankable, and SAM is not the format IEs ask for. See our bankability glossary entry and P50 entry for what underwriting actually requires.

For a broader read on the paid platform landscape, see our review of solar design software and best solar design software. For the residential-specific picture, our Aurora Solar alternatives and OpenSolar alternatives reviews cover the upgrade path. For C&I, see HelioScope alternatives and commercial solar design software.

How Heaven Designs Helps

We are a working solar design bench. We ship permit-ready residential and C&I packages on behalf of installers who run free tools, paid tools, or a hybrid. The reason the breakdown above is granular is that we route real projects through SAM, PVWatts, OpenSolar’s free tier, and paid platforms like SurgePV every week, and the gaps show up in time-to-permit not in marketing copy.

For an installer who currently runs OpenSolar free and is hitting the transaction-fee ceiling, we typically recommend running the next three permit-ready projects through the SurgePV trial in parallel and comparing the proposal close rates. The Heaven Designs permit design, rooftop detailed engineering design, and 3D pre-design services are platform-agnostic, which means we can build the package on whichever tool the installer prefers. If the installer also runs a CRM like QuickEstimate on the sales side, we coordinate the hand-off so the design and the finance numbers match.

According to SEIA market data, US residential financing penetration reached 78 percent of new installs in 2025. That number makes the OpenSolar transaction-fee math relevant to every installer, not just high-volume ones. According to IEA PVPS research, free pre-feasibility tools (PVWatts and equivalents in other markets) handle roughly 60 percent of small residential lead-screening across major PV markets, but only 8 percent of project-level design ships through them. The split between pre-feasibility and execution is real.

To talk through a specific project profile and whether the free workflow is enough, contact us with a project sample.

Frequently Asked Questions

Is there a truly free solar design software in 2026?

SAM (NREL) and PVWatts (NREL) are genuinely free for research and pre-feasibility, paid for by federal research funding. OpenSolar is free at the seat but charges 0.8 to 1.5 percent on financed deals. The SurgePV free trial is free for two to three projects with no credit card. None of these is free for permit-ready package delivery at meaningful volume.

Can I use PVWatts for a permit submission?

No. PVWatts is a pre-feasibility tool. It does not generate a layout, a drawing, an SLD, or a proposal. Most permit offices require a stamped SLD and a layout drawing, neither of which PVWatts produces. PVWatts is the right tool for an initial sanity-check yield estimate on a small residential lead.

Is OpenSolar’s free tier actually free?

The seat is free. The transaction fee on financed deals is 0.8 to 1.5 percent of the deal value. At a $25,000 average residential ticket and twenty financed deals per month, the “free” tier costs $48,000 to $90,000 per year, which is well above any paid subscription on the market.

What is the catch with the SurgePV free trial?

The trial is time-bounded. The team can run two to three real projects end to end at full feature parity with the paid standard tier, but the trial is not an ongoing free seat. For installers who need ongoing free capability, the right answer is OpenSolar’s free tier or a hybrid stack.

Is SAM (NREL) good for installers?

No. SAM is built for researchers, policy analysts, and finance modelers. It does not generate layouts, drawings, proposals, or SLDs. For an installer trying to ship a permit package, SAM is not the right tool.

Which free tool produces NEC single-line diagrams?

None. PVWatts and SAM do not produce drawings. OpenSolar does not include an NEC SLD generator. For a permit office that requires a stamped SLD, the installer will need a paid platform (SurgePV, Aurora top tier) or an external design partner. See our review of AI solar design software for the SLD-side picture.

Can I use free tools for a C&I project above 100 kW?

No. PVWatts is not bankable, OpenSolar’s hour-banded shading is not C&I-grade, and SAM does not produce the layout or report format an IE expects. For C&I above 100 kW, the right tools are HelioScope, PVsyst, or SurgePV. See our HelioScope alternatives and PVsyst alternatives reviews.

Where does Heaven Designs fit in the free-tool picture?

Heaven Designs is a working solar design bench. We ship permit-ready packages on whichever platform the installer runs, including free-tier OpenSolar workflows paired with our external SLD and structural callouts. We do not sell software. We help installers decide whether the free workflow is enough for their specific volume and project mix, and we ship the design when it is not.