Mason HollisBy Mason Hollis

Updated November 2026

A renogy off-grid solar system is a set of matched components, usually panels, a charge controller, batteries and an inverter, that together power a home or cabin without a utility connection. In this guide you will learn how to calculate your daily energy use, size each component, and wire the system in the correct order so it runs safely. The math is simple once you break it into steps, and the same method works for almost any battery-based DIY build.

Step 1: Calculate Your Daily Energy Load

Every sizing decision starts with how many watt-hours you use per day. List every appliance you plan to run, its wattage, and how many hours per day it operates. Multiply watts by hours to get watt-hours (Wh), then add the totals.

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

For example, a 60 W LED light running 5 hours uses 300 Wh. A 40 W refrigerator that runs about 10 hours a day (compressors cycle, so the average is lower than the nameplate) uses roughly 400 Wh. Add a laptop at 50 W for 4 hours (200 Wh) and a 100 W water pump for 1 hour (100 Wh), and your daily load is about 1,000 Wh.

Check nameplate ratings on each appliance. For refrigerators, many owners find the real average draw is well below the label figure, but measuring with a plug-in watt meter for a day gives the most reliable number.

Add a Safety Margin

Add 20 to 30 percent to your daily load to cover cloudy days, appliance aging and future additions. A 1,000 Wh load becomes about 1,250 Wh of design energy.

Step 2: Size the Battery Bank

Battery capacity determines how long your system runs without sun. Two factors matter: days of autonomy (how many days you want to run on stored energy alone) and depth of discharge (DoD), the percentage of capacity you can safely use.

The formula is:

Battery capacity (Wh) = Daily load × Days of autonomy ÷ DoD

Using our 1,250 Wh design load, one day of autonomy, and a lithium iron phosphate (LiFePO4) battery at 80 percent DoD:

1,250 × 1 ÷ 0.80 = 1,562 Wh, so a 12 V, 100 Ah battery (1,280 Wh nominal) is slightly short. A 12 V, 150 Ah battery (about 1,920 Wh) fits better.

Lead-acid batteries (AGM or flooded) typically allow 50 percent DoD for long life, so the same load would require roughly double the nominal capacity. This is one reason lithium is popular for compact renogy off grid solar system builds. Manufacturers’ published cycle-life figures vary, so check the spec sheet for your specific battery.

Series and Parallel Wiring for Batteries

Batteries connected in parallel add amp-hours but keep voltage the same. Batteries in series add voltage. Most small cabin systems use a 12 V bank, and larger systems move to 24 V or 48 V to reduce current and wire size. Use identical batteries (same model, age and state of charge) when paralleling.

Step 3: Size the Solar Array

Your panels must replace the energy you use each day, plus losses. Use peak sun hours for your location, which you can find in NREL’s solar resource maps or a local weather service table. A typical value for much of the US is 4 to 5 peak sun hours per day, but winter values in northern states can drop to 2 to 3.

Array watts = Daily load (Wh) ÷ (Peak sun hours × System efficiency)

System efficiency usually falls between 0.70 and 0.80 once you account for wiring, charge controller and battery losses.

Example: 1,250 Wh ÷ (4 × 0.75) = about 417 W. Round up to 500 W of panels to cover winter months and provide margin.

Choosing Panel Configuration

Match your panel string voltage to the charge controller’s maximum PV input voltage. Series wiring raises voltage and reduces current, which is useful for longer wire runs. Parallel wiring keeps voltage low. Stay within the controller’s stated limits, because exceeding maximum open-circuit voltage will destroy the unit.

Step 4: Select the Charge Controller

The charge controller regulates battery charging from the array. Two common types exist:

  • PWM (pulse width modulation): lower cost, works best when panel voltage closely matches battery voltage.
  • MPPT (maximum power point tracking): captures more energy when panel voltage is higher than battery voltage, typically 10 to 30 percent more harvest in cold or partly cloudy conditions.

Size the controller current with this formula: Controller amps = Array watts ÷ Battery voltage × 1.25. For 500 W on a 12 V system: 500 ÷ 12 × 1.25 ≈ 52 A. A 60 A MPPT controller is a reasonable choice.

Step 5: Size the Inverter

The inverter converts battery DC to 120 V AC. Its continuous rating must exceed the sum of simultaneous loads, and it must handle surge current from motors and compressors.

  • Add the wattage of loads you expect to run at the same time.
  • Multiply by 1.25 for headroom.
  • Check surge rating: refrigerators and well pumps often need 2 to 3 times running watts at startup.

For 1,500 W of simultaneous loads with a 1,000 W well pump, a 2,000 W pure sine wave inverter is a sensible starting point. Pure sine wave output is the safer choice for motors and electronics.

Step 6: Plan Wire Sizing and Fusing

Undersized wire causes voltage drop and heat. Keep voltage drop under 3 percent for DC circuits between panels and controller, and under 2 percent for battery cables. Use the NEC ampacity tables and a voltage drop calculator as your reference. Install a fuse or breaker within 7 inches of each battery positive terminal, and fuse every string and load circuit.

Step 7: Wire the System in the Correct Order

Follow this sequence to avoid damaging components:

  1. Mount panels and run conduit to the controller location.
  2. Mount the battery bank in a ventilated space, and connect batteries to each other first.
  3. Connect the charge controller to the battery bank with fused cables. Confirm the controller powers up and reads battery voltage.
  4. Connect the panels to the controller last, after disconnecting the array from the sun or covering it.
  5. Connect the inverter to the battery bank with fused cables, then connect AC loads.

Always disconnect in reverse order. Working with battery banks carries real risk of arc flash and shock. If you are unsure about any step, consult a licensed electrician.

Grounding and Code Compliance

Ground the system to a driven earth ground rod, and bond the frame of each panel and the controller. Local codes and the National Electrical Code (NEC) apply to off-grid installations in most jurisdictions, so check permit requirements before installing.

Example Component Summary

Component Sizing Basis Example Value
Daily load Sum of appliance Wh + 25% 1,250 Wh
Battery bank Load × autonomy ÷ DoD 12 V, 150 Ah LiFePO4
Solar array Load ÷ (sun hours × efficiency) 500 W
Charge controller Array W ÷ battery V × 1.25 60 A MPPT
Inverter Simultaneous loads × 1.25, plus surge 2,000 W pure sine

Common Mistakes

  • Sizing from appliance nameplate ratings instead of measured run time.
  • Ignoring winter sun hours, which leaves systems short exactly when they are needed.
  • Mixing old and new batteries in one bank.
  • Connecting panels to the controller before the battery, which can cause the controller to fault.
  • Undersizing wire and skipping fuses.
  • Forgetting that inverters draw standby power, which can drain small batteries overnight.

Tips for a Reliable Build

  • Track real energy use with a battery monitor shunt for the first month and adjust.
  • Leave room in the battery bank for future expansion by choosing a controller and inverter with headroom.
  • Keep the battery compartment cool, since heat shortens battery life.
  • Read the manufacturer manuals for voltage limits and charging profiles before connecting anything.

A battery monitor with a shunt shows real amp-hour use and state of charge, which is the fastest way to validate your sizing. Search for Victron Energy SmartShunt and compare display options. View on Amazon

An MPPT charge controller with a Bluetooth or display interface makes it easier to confirm array input and battery charging stages. View on Amazon

A plug-in watt meter lets you measure real appliance draw over 24 hours, which removes guesswork from your daily load figure. View on Amazon

FAQ

How much solar do I need for a renogy off-grid solar system?

It depends on your daily energy use and local sun hours. Divide daily watt-hours by peak sun hours and system efficiency (about 0.75). A home using 1,000 Wh per day in a 4-hour sun region needs roughly 350 to 400 W of panels, and many builders round up for winter.

Is lithium or lead-acid better for an off-grid battery bank?

Lithium iron phosphate generally offers higher usable capacity, lighter weight and longer cycle life, but costs more upfront. Lead-acid is familiar and tolerant of certain charging conditions, though it needs a larger bank for the same usable energy. Choose based on budget, space and how often you cycle the batteries.

Can I run a refrigerator on a small off-grid system?

Yes, a modern efficient refrigerator can run on a properly sized system. Measure its real daily consumption, because compressor cycling makes the average much lower than the label rating. Include its surge current when choosing the inverter.

Do I need an MPPT or PWM charge controller?

MPPT is generally recommended for systems where panel voltage is well above battery voltage, or where cold weather and partial shade are common. PWM can work for very small, simple setups with matched voltages.

How long do off-grid batteries last?

Lifespan depends on chemistry, depth of discharge, temperature and charging practice. Check the cycle-life rating the manufacturer publishes for your battery, and keep discharge within its recommended range.

Can I expand my system later?

Yes, if you plan for it. Choose a charge controller and inverter with spare capacity, use a battery bank that can be paralleled with identical units, and size wiring for the future array.

Do I need a permit for an off-grid solar installation?

Many jurisdictions require permits for electrical work, even off-grid. Check with your local building department. Consult a licensed electrician or solar installer for code-compliant wiring and grounding.

Conclusion

Building a renogy off-grid solar system comes down to four numbers: daily load, battery capacity, array wattage and inverter size. Work through each formula with measured data rather than estimates, and add a safety margin for weather and growth. Wire the components in the correct order, fuse everything, and verify performance with a battery monitor. When the math and wiring are right, the system will run reliably for years.

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Mason Hollis

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.