Ethan BrooksBy Ethan Brooks

Updated November 2026

A whole house off-grid solar system powers every circuit in your home without a utility connection. In this guide, you will learn how to total your daily energy use, size the panels, battery bank and inverter, and wire the pieces together safely. The method below works for most single-family homes, though the final design should be checked by a licensed electrician or solar installer.

Step 1: Calculate Your Daily Energy Use

Start with your utility bills. Divide the total kilowatt-hours used over the last 12 months by 365 to get an average daily load. If you have no bills, list every appliance, multiply its wattage by the hours it runs per day, and add the results. A refrigerator that draws 150 watts and runs 24 hours uses about 3.6 kWh per day, though compressors cycle, so actual use is often lower.

Shopping for one? See our guide: 7 Best Off Grid Solar Systems for House Options Compared (2026).

Add a 20 to 25 percent margin for inefficiency and future loads. Most homes end up between 10 and 30 kWh per day, depending on heating, cooking and water heating fuel.

Step 2: Size the Battery Bank and Solar Array

Next, decide how many days of backup you need without sun. Multiply your daily load by the number of autonomy days, then divide by the usable battery capacity (often 80 to 90 percent of nameplate for lithium, about 50 percent for lead-acid). That gives your required battery kWh.

For the array, divide your daily load by the peak sun hours at your site (commonly 4 to 6 in much of the US), then divide again by roughly 0.75 to cover system losses. A home using 15 kWh per day in a 5-hour sun location needs about 4 kW of panels.

Choose the Inverter Size

The inverter must handle your highest combined simultaneous load, not your daily total. Add the running wattage of the appliances you expect to run together, then add surge capacity for motors such as well pumps and air conditioners. Many whole-home designs use a split-phase 120/240 V inverter rated in the 8 to 12 kW range.

Step 3: Build the Parts List and Wiring Plan

A complete system needs these components, in this order from the array to the house:

  1. Solar modules, mounted on a ground or roof rack with proper tilt.
  2. Combiner box with fuses or breakers for each string.
  3. Charge controller (MPPT type sized to array voltage and current).
  4. Battery bank with its own overcurrent protection and disconnect.
  5. Off-grid inverter/charger with transfer capability.
  6. Main service panel, grounding electrode system and surge protection.

For a clear view of how these connect, compare your plan against a Wiring Diagram for Off-Grid Solar System: A Step-by-Step Guide before purchasing wire and conduit.

Design Input How to Find It Typical Result
Daily load Annual kWh divided by 365 10 to 30 kWh
Battery capacity Daily load times autonomy days, divided by usable percent Varies by backup goal
Array size Daily load divided by sun hours and 0.75 4 to 10 kW
Inverter size Highest simultaneous load plus surge 8 to 12 kW

Common Mistakes to Avoid

  • Sizing the inverter from daily kWh instead of peak simultaneous wattage.
  • Ignoring winter sun hours, which can be less than half of summer.
  • Skipping a backup generator for long cloudy stretches or heavy electric heating.
  • Mixing battery chemistries or undersized battery cables.
  • Forgetting that a permit and inspection may be required in your area.

A clamp-on power meter lets you measure real appliance loads before sizing, which is more reliable than nameplate figures. View on Amazon

A digital multimeter is essential for checking voltages during commissioning and troubleshooting. View on Amazon

FAQ

How many solar panels does a whole house off-grid system need?

Most homes need between 4 and 10 kW of panels, depending on daily energy use and local sun hours. Divide your daily kWh by your site’s peak sun hours and add about 25 percent for losses.

Can an off-grid system power electric heat and central air?

It can, but these loads are large and often require a bigger array, battery bank and inverter. Many owners pair the system with a propane or diesel backup generator for winter.

Do I need a professional to install a whole house system?

Many jurisdictions require a licensed electrician to connect to the main panel and may require permits. Consult a qualified professional before installation, especially for battery and high-voltage work.

Conclusion

A whole house off-grid solar system is built from three numbers: daily energy use, battery autonomy and peak simultaneous load. Work through the sizing steps, build a complete parts list, and verify the design with a professional. Careful planning at this stage prevents costly changes after installation.

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Ethan Brooks

About Ethan Brooks

Ethan Brooks 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.