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Building an off grid solar system for backup power

By the Plain Prepper editors. Updated 2026-10-14.

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Quick answer

An off grid solar system has four parts: panels, a charge controller, a battery bank and an inverter, sized so the battery covers your daily use and the panels refill it. The Department of Energy describes battery-backed solar homes switching to an islanded mode within seconds when the grid fails. Start from your daily watt-hours, add the inverter's own idle draw, size the battery to cover that with margin, and add panels until a sunny day refills it. All-in-one inverters like the EG4 6000XP combine the controller, charger and inverter in one box.

The four parts

• Panels make DC power from sunlight. DOE says silicon modules are expected to last 25 years or more while keeping over 80% of their original output.
• Charge controller manages how panels charge the battery. Modern MPPT controllers are often built into all-in-one inverters. The EG4 6000XP has two MPPT inputs and up to 8,000 W of usable solar.
• Battery bank stores energy for night and cloudy days. A 12.8 V, 100 Ah LiFePO4 battery holds 1,280 Wh. A 12 V, 100 Ah AGM gives about 600 Wh if you stop at 50%, as Renogy advises.
• Inverter converts DC to the AC your home uses. DOE calls it one of the most important pieces of equipment in a solar system.

Why off-grid design matters in an outage

DOE's Solar and Resilience Basics describes the goal. When a substation fails, residential PV systems with battery storage detect the loss of grid power and switch to an islanded mode within seconds to keep the power on. DOE's inverter basics adds the catch: systems rely on advanced inverters to run without the grid only if they are designed to. A plain grid-tied array with no battery and no backup-capable inverter may not supply your home during a blackout. If backup is the point, design for islanding from day one.

A simple sizing method

1. Daily use. List what must run and for how long. For example: a fridge's compressor time, lights, a router and phone charging. Add up watt-hours per day.
2. Add inverter idle draw. The EG4 6000XP lists about 50 W idling on battery, which is about 1,200 Wh over 24 hours. Small systems often lose a big share to this.
3. Size the battery. Cover at least one day of use plus margin for cloudy days. Remember usable capacity: about 100% of a LiFePO4's rating, about 50% of an AGM's.
4. Size the panels. Panels rarely deliver their rating. Jackery's numbers show it: a 200 W panel refilling a 1,070 Wh station in 7.5 hours averages about 143 W, roughly 71% of rating, on a good day. Add panels until a typical sunny day refills your daily use.
5. Size the inverter. Continuous watts must cover everything on at once, and surge must cover motor starts.

Worked example

Say your essentials use 2,400 Wh a day, and the inverter idles at 50 W, adding 1,200 Wh. Your daily need is 3,600 Wh. A 48 V inverter like the EG4 6000XP needs a 48 V bank. Four 12.8 V, 100 Ah LiFePO4 batteries in series make 51.2 V and 5,120 Wh, about 1.4 days of that need. A second string in parallel adds a real cloudy-day buffer. At about 143 W effective per 200 W panel, refilling 3,600 Wh in 7.5 hours of good sun takes about 3,600 divided by (143 x 7.5), or roughly 3.4 panels. So plan on four 200 W panels, more for winter. These are illustrations. Your site, season and loads set the real numbers.

Code, safety and getting help

Off-grid systems carry high DC voltage and big battery currents. The EG4 6000XP accepts up to 480 V DC from panels. LiTime lists 100 A continuous discharge from a single 100 Ah battery. Use the fusing, breakers and disconnects the manuals call for, keep battery banks within their charge temperature limits, and have a licensed electrician design or inspect anything tied to your home's wiring. Permits are common for permanent systems.

What to look for when you buy

Questions people ask

What do I need for an off grid solar system?

Panels, a charge controller, a battery bank and an inverter, plus wiring, fuses and disconnects. All-in-one inverters combine the controller and inverter.

How many solar panels do I need to run a house off grid?

Divide your daily watt-hours by each panel's real output over a sunny day. Jackery's figures imply about 143 W average from a 200 W panel, so 3,600 Wh a day needs about four 200 W panels.

Will my solar panels work when the power goes out?

Only with batteries and an inverter designed to island. DOE describes battery-backed systems switching to islanded mode within seconds of a grid failure.

How long do off grid solar batteries last?

LiTime rates its LiFePO4 at 4,000 cycles at full discharge. Renogy rates its AGM at 500 cycles at 50% discharge.

Sources

• Solar and Resilience Basics, U.S. Department of Energy
• Solar Integration: Inverters and Grid Services Basics, U.S. Department of Energy
• Solar Photovoltaic Cell Basics, U.S. Department of Energy
• EG4 6000XP Off-Grid Inverter Specification Sheet v1.2.1, EG4 Electronics
• LiTime 12V 100Ah LiFePO4 Lithium Battery (specifications), LiTime
• Deep Cycle AGM Battery 12 Volt 100Ah, Renogy
• Jackery Solar Generator 1000 v2, Jackery

Sources checked 2026-10-14.