Graham FisherBy Graham Fisher

Updated November 2026

An off grid solar power system design PDF is a documented plan that lists your loads, sizes your panels, batteries, charge controller and inverter, and shows how everything connects. Working through the steps below, you will end up with a set of numbers and a wiring outline you can print, mark up and hand to an installer or electrician. Treat the output as a planning document, not a stamped engineering drawing.

Step 1: Calculate Your Daily Energy Use

Start with a load list. For every appliance, record its wattage, how many hours per day it runs and its daily watt-hours (watts multiplied by hours). A 60 W refrigerator that runs about 10 hours per day in real terms uses roughly 600 Wh, though compressor appliances often cycle, so check the rated consumption on the label or in the manual if you can. Add everything up and then add 20 to 25 percent for inverter losses and future needs. That total is your design load in watt-hours per day.

Shopping for one? See our guide: 6 Best DIY Solar Power System Kit Options for Off-Grid Homes (2026).

Step 2: Size the Battery Bank and Inverter

Battery capacity depends on how many days of autonomy you want, meaning how long the system can run with no sun. Multiply daily watt-hours by the number of autonomy days, then divide by the usable depth of discharge (commonly 50 percent for lead-acid, higher for lithium iron phosphate). Divide that result by the nominal battery voltage to get amp-hours. For the inverter, add up the running watts of loads you expect to use at the same time, then choose a continuous rating at least 25 percent above that sum, and check the surge rating for motors.

Step 3: Size the Array and Charge Controller

Divide your daily watt-hours by the peak sun hours for your location during your worst month. If you need 2,000 Wh per day and your worst month averages 4 peak sun hours, you need about 500 W of panels, and you should add a margin for system losses, often around 25 percent, which brings the figure to roughly 625 W. The charge controller must handle the array’s short-circuit current at your battery voltage, with a safety margin. Use an MPPT controller when the array voltage is well above battery voltage.

Step 4: Draw the Wiring Diagram and Assemble the PDF

Sketch the layout: panels to combiner or disconnect, controller, battery bank with fusing, inverter, and the AC distribution panel. Include wire gauges calculated from current and run length, with voltage drop kept under about 3 percent on DC runs. Put your load list, calculations, component specs and diagram into one document and export it as a PDF. For a worked example of the wiring layout, see Off Grid Solar Power System Wiring Diagram PDF: Step-by-Step Guide.

Checklist for your design file

  1. Load list with watts, hours and daily watt-hours
  2. Autonomy days, depth of discharge and battery bank amp-hours
  3. Peak sun hours used and array wattage with losses included
  4. Controller, inverter and fuse ratings with the calculations shown
  5. Wire gauge and voltage drop figures for each run
  6. Single-line wiring diagram with disconnects and grounding

Common mistakes

  • Sizing from nameplate watts instead of measured or rated daily energy use.
  • Using annual average sun hours rather than the worst winter month.
  • Ignoring surge loads from well pumps, compressors and power tools.
  • Forgetting that lead-acid batteries lose capacity fast below 50 percent discharge.
  • Undersizing DC wire, which causes voltage drop and heat at the battery terminals.

If you want ready-made math instead of building it by hand, Solar Off-Grid System Design Calculation PDF: A Step-by-Step Guide walks through the same process with more worked numbers. For a quicker first pass, the Off-Grid Solar Power System Calculator: How to Size Your Setup Step-by-Step method is useful.

  • Clamp meter helps you measure real current draw from appliances so your load list reflects actual use rather than guesses. View on Amazon
  • Kill-A-Watt style watt meter plugs between the wall and an appliance to log watt-hours per day, which is the most useful number in your design. View on Amazon
  • Digital multimeter lets you verify open-circuit voltage, charge voltage and voltage drop during installation. View on Amazon

FAQ

Do I need an engineer to make an off grid solar design PDF?

Not for a personal planning document, but a licensed electrician or engineer should review the final design for permitting and safety. Many jurisdictions require inspection of DC and AC work.

How many peak sun hours should I use?

Use the lowest monthly average for your site, usually winter, so the system still works in the worst season. Solar resource maps from government sources list these values by location.

Should the design file include a battery bank size?

Yes. The battery bank is where autonomy, depth of discharge and voltage all come together, so it should be documented with its calculation shown.

Conclusion

A good off grid design PDF turns your daily energy use into a clear list of panels, batteries, controller and inverter sizes with wiring to match. Build it step by step, keep the calculations visible, and review the final plan with a qualified professional before installing anything.

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Graham Fisher

About Graham Fisher

Graham Fisher is part of our editorial team and reviews and edits our DIY solar power systems guides, checking product details against manufacturer specifications and owner feedback.