How I run a solar CAD offline workflow on every array
The job that taught me this was a 24-panel install on a barn roof in 2023. The site sat two fields off the road with no mobile signal and no broadband. I opened my cloud design tool to check the string sizing against the inverter, and it asked me to sign in. I could not. I paced the roof, guessed, and fixed the stringing that evening at the kitchen table. Since then every array I design runs through a solar CAD offline workflow that lives on my laptop, opens with no login, and works on a scaffold with the signal bars at zero. This is that workflow, roof survey to hand-off. If you want to follow along, download the offline editor and open a blank roof while you read.
Why solar CAD offline software has to run fully local
Most of my design work happens in the worst place for a connection. On the roof itself, in a loft, or in a plant room next to the inverter. A tool that phones home on every save is dead weight up there. That is the core reason solar CAD offline software has to run fully local: the drawing needs to be where the modules go, not where the router reaches.
There is a numbers angle too. A PV array is a yield calculation before it is a drawing. Tilt, azimuth, shading and string voltage all move the annual output, and I sanity-check my layouts against NREL's System Advisor Model for PV yield so the panel count on the roof matches the energy I promised the client. The electrical side is documented against real rules: in Europe the array design reference is IEC 62548 photovoltaic array design requirements, and a clean single-line diagram is what an inspector or a DNO reviewer actually reads.
The last reason is ownership. When a design lives only in someone else's cloud, you rent access to your own work. I watched an installer lose three years of layouts in 2024 when his subscription lapsed and the export button greyed out. My rule since then is blunt: the file sits on my disk, in an open format, and it opens with no account. That is the whole point of a solar CAD offline setup, and it is why I stopped trusting a login to be there when I am standing on a roof.
How I design a PV array step by step
My solar CAD offline process runs in four passes, so nothing gets missed between the roof and the hand-off.
Pass one: roof survey and module layout
I draw the roof plane to scale first, with ridge, eaves, hips and any obstructions. Then I lay modules in rows against the real setbacks, because most jurisdictions want a clear path to the ridge for firefighters. A standard 400 W module is roughly 1.76 by 1.13 metres, so on a plain pitched roof I can fit the array and read the leftover margin in seconds. On a barn roof I placed 24 modules and still held a 400 mm ridge setback. The way how solar installers in Houston lay out a roof handles obstruction spacing matches how I work here.
Pass two: stringing and the MPPT window
Every module row gets assigned to a string, and every string has to land inside the inverter's MPPT voltage window across the local temperature range. This is the pass that stops warranty calls. I keep the cold-morning open-circuit voltage under the inverter's ceiling and the warm-afternoon operating voltage above its floor. Getting this on the drawing, not in my head, is what saves the callback. You can open a blank array on your laptop and test a stringing option before you commit a single clamp.
Pass three: the photovoltaic single-line
A layout proves the modules fit. A single-line proves the electrics work. I draw modules to strings, strings to a combiner or straight to the inverter, then the AC side to the board, with isolators, fusing and the rapid-shutdown boundary marked. This is the sheet the DNO and the inspector sign against, and it shares the same logic as the battery installation diagram workflow when storage is added later.
Pass four: export and hand-off
I export to DXF and PDF. DXF because it is the open format every other CAD tool reads, PDF because that is what the client, the inspector and the scaffolder want. Both export locally in under a second. No render queue, no upload, no waiting on a connection that is not there.
A real job: 6.4 kWp on a pitched terrace
In April 2025 I designed a 6.4 kWp system on a south-facing terrace roof: 16 modules at 400 W, split into two strings of eight on a dual-MPPT inverter. The roof had a chimney two-thirds up the slope that killed the obvious single-block layout.
I drew the roof plane first, dropped the chimney with its real footprint, and split the array into two clean rectangles around it. Because the layout carried the exact module dimensions, I could show the homeowner why 16 panels fit and 18 did not, without an argument. Then I strung it: eight modules per MPPT held the cold-start voltage about 12 percent under the inverter ceiling, with headroom for a -10 degree morning. The single-line showed a 20 A AC isolator, the rapid-shutdown line, and the tie-in to a spare way on the board.
The whole design took roughly 40 minutes in one solar CAD offline session, with no connection the entire time. That replaced what used to be an evening of redrawing after the site visit. The commissioning engineer signed off on the first visit because the string map on the drawing matched the array on the roof exactly. Crews elsewhere land the same result with the same habit, which is why the New York solar installer workflow also strings the array before it draws the roof.
Solar CAD offline versus PVsyst, AutoCAD and SketchUp
I want to be fair here, because these are all capable tools and I have used every one.
PVsyst is the reference for yield simulation, and nothing beats it for a detailed loss diagram, but it is a simulation package, not a drafting tool, and its annual licence runs into the hundreds of EUR. AutoCAD reads DXF natively and draws anything, yet Autodesk lists its subscription near 2,000 EUR a year as of 2026, which is hard to justify for a solo installer producing layouts and single-lines. SketchUp is excellent for 3D roof massing and shading studies, but a string map and an AC single-line are not where a 3D modeller shines.
Where a focused solar CAD offline tool wins is the combination in one file: the roof layout, the stringing, the photovoltaic single-line, and DXF plus PDF export, with no login and no monthly bill. The Diaz Editor licence is a one-time €197 lifetime purchase with 3 seats, and the AI features sit in a separate optional monthly subscription that starts at 9 EUR rather than being forced into the base price. You can read the one-time lifetime licence in full before deciding.
None of this makes the big packages bad. If you live in PVsyst for simulation, stay there and draw the install alongside it. But if your day is roofs, strings and single-lines, and you design on site where the signal dies, a dedicated offline tool earns its place inside a week.
FAQ
What is a solar CAD offline tool?
It is design software that produces PV drawings and runs entirely on your own machine, with no cloud dependency. In practice it gives you three outputs from one file: a scaled roof layout showing module rows and setbacks, a string map assigning modules to MPPT inputs, and a single-line diagram for the electrical review. Together they prove the array fits the roof, stays inside the inverter window, and is safe to connect.
Do I need internet to design solar panels offline?
No, and that is the point. The editor, the symbol library and the export engine all run locally on your laptop. I have designed full arrays on scaffolds and in lofts with no signal since 2023. The file saves to your own disk, so the drawing is available exactly where the modules go, not only where the router reaches.
Which file formats should a solar drawing use?
DXF and PDF cover almost every case. DXF is the open interchange format that AutoCAD, BricsCAD, QCAD and FreeCAD all read, so nobody is locked out of your work. PDF is what inspectors, DNOs and clients expect for sign-off. Keeping a DXF master and exporting PDFs on demand gives you one source of truth and no format arguments later.
How long does a domestic array design take?
For a standard pitched-roof system I budget under an hour, including the roof layout, the string map and the single-line. My last 6.4 kWp job took about 40 minutes with the full string assignment. The saving comes from reusable blocks: once a module, a string tag or an isolator carries its own rating, you place it rather than redraw it every time.
Is a one-time licence really cheaper than subscription solar software?
Over any real horizon, yes. A drafting subscription near 2,000 EUR a year keeps charging whether you design one array or a hundred. A one-time lifetime licence at €197 is a single payment you own outright, with 3 seats for a small crew. For a solo installer or a two-van firm doing steady domestic work, the break-even against an annual subscription arrives inside the first few months.
Where to start
If your array designs still live on a phone photo and a mental note, the fix is not a bigger tool, it is a focused one that opens without a login and produces an inspector-ready single-line. I built my whole solar CAD offline workflow around drawing the roof first, assigning strings second, and exporting to DXF and PDF locally. It cut an evening of redrawing down to 40 minutes on a real 6.4 kWp job, and the reusable blocks are the part that pays you back on every roof. Start with a blank canvas, draw one array you already know, and see how it feels. When it clicks, put the editor on your work laptop and design your next system the way a commissioning engineer wants to read it, on the scaffold, with the signal at zero.