Off-Grid and On-Grid Solar System: How to Plan, Size and Wire One

By Mason Hollis

An off-grid and on-grid solar system differs mainly in whether it connects to the utility. This guide walks you through the core differences, how to size each part of the system, and how to choose a configuration that matches your loads. By the end, you will be able to estimate your daily energy use, calculate the panel, battery and inverter capacity you need, and understand the wiring decisions that come with each design.

What Separates Off-Grid From On-Grid Solar

An on-grid system, sometimes called grid-tied, uses solar panels and a grid-tie inverter that synchronizes with the utility’s AC supply. Excess power flows back to the grid, and when the sun is down you draw from the utility as usual. An off-grid system has no utility connection. It relies on panels, a charge controller, a battery bank and an off-grid inverter to supply every watt you use. A hybrid setup combines both, using batteries and a hybrid inverter so the system can run on solar, battery or grid power as conditions allow.

Shopping for one? See our guide: 7 Best DIY Solar Power System Kit Options for Off-Grid Beginners (2026).

For a broader comparison of these categories, see Off-Grid, Backup and Hybrid Solar Systems: How They Differ. The short version is that grid-tied systems are simpler and cheaper to maintain because they carry no battery bank, while off-grid systems demand more careful sizing because every kilowatt-hour has to be stored or generated on site.

Comparing the Two Designs

Step 1: Calculate Your Daily Energy Use

Every sizing decision starts with your load. List each appliance, its power draw in watts and the number of hours it runs per day. Multiply watts by hours to get watt-hours, then add everything up. A refrigerator might draw 150 watts for an average of 8 hours a day, which is 1,200 Wh. LED lights totaling 100 watts running 5 hours add 500 Wh.

Your utility bill shows monthly kilowatt-hours. Divide that by 30 for a rough daily figure, then compare it with your appliance tally. Add a 20 to 30 percent margin for inverter losses, wiring losses and future additions.

Tools and Data You Will Need

• A plug-in watt meter to measure real appliance draw
• Your last 12 months of utility bills
• A spreadsheet or notepad for the load list
• Manufacturer nameplates showing voltage and wattage

Step 2: Size the Battery Bank for Off-Grid Use

For an off-grid and on-grid solar system with batteries, the battery bank is the most important sizing decision. Multiply your daily watt-hours by the number of days of autonomy you want, which is how long the system should run without sun. Then divide by the usable depth of discharge. For lithium iron phosphate (LiFePO4) batteries, manufacturers often specify around 80 to 90 percent usable capacity. For lead-acid, 50 percent is a common conservative figure.

Example: 4,000 Wh per day, two days of autonomy, 80 percent depth of discharge. That is 8,000 Wh divided by 0.8, or 10,000 Wh of nominal battery capacity. At a 48V bank, that is about 208 Ah. For battery chemistry comparisons, see 5 Best LiFePO4 Batteries for RV Compared for Off-Grid Camping (2026).

Step 3: Size the Solar Array

Divide your daily energy need by the peak sun hours at your location, then add a loss factor. Peak sun hours are the equivalent hours per day at 1,000 W/m². Many US locations fall between 4 and 6 hours depending on season and latitude. Use a conservative winter value if the system must run year-round.

Example: 4,000 Wh per day, 4 peak sun hours, 0.75 system efficiency. 4,000 divided by 4 gives 1,000 W, divided by 0.75 gives about 1,333 W of panels. A 1,400 W array would cover that. For the full method, see How to Size Solar Panels for a DIY System.

Step 4: Choose the Inverter

The inverter must handle your peak simultaneous load, not just your daily total. Add the wattage of everything that might run at once, then add a margin of about 25 percent. Motor loads like well pumps or air conditioners need a surge rating two to three times their running watts. Check the guidance in How to Size an Inverter for a DIY Solar System for surge calculations.

For grid-tied systems, the inverter is sized to the array output, usually with a DC-to-AC ratio between 1.1 and 1.3. For off-grid systems, it is sized to the peak household load.

Step 5: Plan the Wiring and Protection

Off-grid systems usually run 12V, 24V or 48V DC on the battery side. Higher voltage reduces current and wire size. Grid-tied systems operate at higher DC voltages on the array side, so string sizing must respect the inverter’s maximum input voltage, especially in cold weather when panel voltage rises.

1. Draw a single-line diagram showing panels, combiner, charge controller or inverter, battery, disconnects and loads.
2. Size DC cable for voltage drop under 3 percent on the battery side and under 2 percent on the array side.
3. Install fuses or breakers at the battery, at each string and at each load branch.
4. Add a disconnect at every point where power can enter or leave the system.
5. Ground the array and metal enclosures per the National Electrical Code (NEC) for your jurisdiction.

For a checklist covering voltage and protection details, see DIY Solar System Design Checklist: Voltages, Protection and Expansion. An overview of component roles is in DIY Solar System Components: What Each Part Does.

Step 6: Consider a Hybrid Path

Many homeowners start grid-tied and later add batteries, moving toward an off-grid and on-grid solar system with backup. This requires a hybrid inverter or a battery-ready grid-tie inverter, plus a battery bank and a transfer or backup circuit. Plan the panel array and inverter capacity for the future setup from day one, so you do not have to replace the inverter later.

Common Mistakes

• Sizing the battery without accounting for depth of discharge, leading to shorter life than expected.
• Ignoring winter peak sun hours, so the system fails in the months you most need it.
• Using undersized DC wire, causing voltage drop and heat at connections.
• Connecting a grid-tie inverter to a battery bank, which the inverter may not support.
• Skipping a load audit and guessing at consumption, which leads to undersized arrays.
• Forgetting that a grid-tied inverter shuts off during a grid outage unless it is paired with a backup-capable system.

Tips for a Smoother Build

• Monitor battery state of charge and daily production with a battery monitor or inverter display.
• Leave room in the electrical panel and combiner box for future circuits.
• Check local permitting and utility interconnection rules before buying equipment.
• Keep a written record of every wire size, fuse rating and torque setting for future troubleshooting.

Recommended gear

• Victron SmartShunt 500A is a battery monitor that tracks state of charge, current and time remaining, which helps you verify your autonomy assumptions. View on Amazon
• Kill A Watt P3 P4400 is a plug-in power meter that measures real appliance wattage and daily kilowatt-hours for your load list. View on Amazon
• Renogy 20A MPPT charge controller is a maximum power point tracking controller suited to small off-grid arrays, with adjustable battery profiles for different chemistries. View on Amazon

FAQ

Can I switch an on-grid system to off-grid later?

Yes, but you need batteries, an off-grid or hybrid inverter, and a transfer arrangement. The panels can often stay, though the grid-tie inverter usually must be replaced or supplemented.

Do on-grid systems work during a power outage?

Standard grid-tied systems shut down during outages for worker safety. Only systems with battery backup and an islanding-capable inverter continue producing power.

How many days of autonomy should I plan for?

Many off-grid designers use one to three days. More autonomy means a larger battery bank, so choose based on how reliable your sun and backup generator access are.

Is LiFePO4 better than lead-acid for off-grid?

LiFePO4 offers higher usable capacity, longer cycle life and lower weight. Lead-acid is lower in initial complexity but needs more capacity and maintenance for the same usable energy.

What peak sun hours should I use?

Use local data from a source such as NREL’s PVWatts calculator, and base your design on the lowest month if the system must run year-round.

Do I need a permit for a DIY solar system?

Requirements vary by city, county and utility. Grid-tied systems almost always require utility interconnection approval. Consult your local building department and a licensed electrician for code compliance.

Can I use a grid-tie inverter with batteries?

Generally no, unless the inverter is specifically designed for battery integration. Check the manufacturer’s specifications before connecting batteries.

Conclusion

An off-grid and on-grid solar system choice comes down to whether you need power during outages and how much storage you can afford in maintenance and capacity. Start with an accurate load audit, then size batteries, panels and the inverter in that order. Keep wiring conservative, verify your design against local code, and consult a licensed electrician for any connection to your home electrical service.

About Mason Hollis

Mason puts together our diy solar power systems guides, digging through specifications, manufacturer details and owner reviews so you don't have to.