How do I size an off-grid solar system?

Start by calculating your total daily energy consumption in kWh — list every appliance, its wattage, and daily run hours. Divide that by your location's peak sun hours to get the solar array size in kW. Add 20–25% for inverter losses and wiring inefficiency. For battery storage, multiply your daily usage by the number of backup days you want, then divide by your usable depth of discharge (80–90% for lithium, 50% for lead-acid). The calculator above automates all of these steps.

How many days of battery backup do I need for off-grid?

Most off-grid designers recommend 2–3 days of autonomy — the battery capacity to run the home with no solar input. In high-sun climates with reliable weather, 1.5 days may suffice. In cloudy regions or where the system must power critical loads year-round, 3–5 days is safer. The tradeoff is cost: each day of autonomy adds significant battery bank expense.

What size inverter do I need for an off-grid system?

Your inverter must handle the peak simultaneous load of all appliances that could run at once. Add up the running watts of your largest concurrent loads, then apply a 25% safety margin. Inverters are also rated for short surge capacity (2–3× running watts) to start motors in pumps, refrigerators, and air conditioners. A common off-grid home needs a 3,000–6,000W inverter.

What is the difference between 12V, 24V, and 48V battery systems?

12V systems suit small setups (cabins, RVs) under ~1,000W. 24V handles medium loads up to ~3,000W with lower wire losses. 48V is the standard for whole-home off-grid systems — it reduces current by 4× compared to 12V for the same power, allowing thinner cables and higher efficiency. Most quality inverter-chargers above 3kW operate at 48V.

Can I go completely off-grid with solar panels?

Yes, but it requires careful system sizing and a backup plan for extended low-sun periods. A generator or wind turbine as a secondary charger dramatically improves reliability. Pure solar off-grid works best in high-sun climates with conservative energy usage. In northern latitudes or heavily wooded sites, winter solar production may drop 60–70%, requiring a larger battery bank or a backup charging source.

Quick answer: A cabin using 12 kWh/day in a 5 PSH location needs roughly a 3.2 kW solar array, 36 kWh battery bank for 3-day autonomy, and a 5 kW inverter with 60A charge controller.

Solar & Battery

Off-Grid Solar System Calculator

Size your complete off-grid system — solar array, battery bank, inverter, and charge controller — from daily energy usage and location.

Inputs

Daily energy usage (kWh)

kWh

Installation state

Peak sun hours: 5.5 hrs/day

Days of autonomy: 3 days

1 day7 days

Panel wattage

Battery voltage

System efficiency %: 80%

70% (lossy)90% (optimal)

Usable battery %: 80%

50% (conservative)100% (max)

Peak simultaneous AC load: 5.0 kW

0.5 kW20 kW

System summary

6 panels · 37.5 kWh battery

2.27 kW array · 3 day autonomy

System size

2.27 kW

Battery bank

781 Ah @ 48V

Inverter size

6.50 kW

Charge controller

65 A

Inverter sizing here is driven by your peak simultaneous AC load, while charge controller sizing includes a 25% current safety margin.

How we calculate off-grid system size

Solar array size is found by dividing daily energy needs (adjusted for system losses) by location peak sun hours. Battery capacity is calculated from daily usage multiplied by desired autonomy days, divided by the usable depth of discharge for the selected battery chemistry.

Array (kW) = (Daily kWh / System Efficiency) / Peak Sun Hours

Inverter rating is sized from peak simultaneous AC load with a 25% margin, and charge controller amperage is derived from array wattage divided by battery bank voltage with the same safety factor.

Frequently Asked Questions

How do I size an off-grid solar system?: Start by calculating your total daily energy consumption in kWh — list every appliance, its wattage, and daily run hours. Divide that by your location's peak sun hours to get the solar array size in kW. Add 20–25% for inverter losses and wiring inefficiency. For battery storage, multiply your daily usage by the number of backup days you want, then divide by your usable depth of discharge (80–90% for lithium, 50% for lead-acid). The calculator above automates all of these steps.
How many days of battery backup do I need for off-grid?: Most off-grid designers recommend 2–3 days of autonomy — the battery capacity to run the home with no solar input. In high-sun climates with reliable weather, 1.5 days may suffice. In cloudy regions or where the system must power critical loads year-round, 3–5 days is safer. The tradeoff is cost: each day of autonomy adds significant battery bank expense.
What size inverter do I need for an off-grid system?: Your inverter must handle the peak simultaneous load of all appliances that could run at once. Add up the running watts of your largest concurrent loads, then apply a 25% safety margin. Inverters are also rated for short surge capacity (2–3× running watts) to start motors in pumps, refrigerators, and air conditioners. A common off-grid home needs a 3,000–6,000W inverter.
What is the difference between 12V, 24V, and 48V battery systems?: 12V systems suit small setups (cabins, RVs) under ~1,000W. 24V handles medium loads up to ~3,000W with lower wire losses. 48V is the standard for whole-home off-grid systems — it reduces current by 4× compared to 12V for the same power, allowing thinner cables and higher efficiency. Most quality inverter-chargers above 3kW operate at 48V.
Can I go completely off-grid with solar panels?: Yes, but it requires careful system sizing and a backup plan for extended low-sun periods. A generator or wind turbine as a secondary charger dramatically improves reliability. Pure solar off-grid works best in high-sun climates with conservative energy usage. In northern latitudes or heavily wooded sites, winter solar production may drop 60–70%, requiring a larger battery bank or a backup charging source.

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Off-Grid System Calculator

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Reviewed April 2026

Methodology and source note

PowerSizing calculators use shared formulas, documented assumptions, and current planning inputs that are summarized on the methodology page. Use these tools for first-pass planning, comparison, and sanity checks, then confirm local code, pricing, utility tariff, and installer specifics before you buy equipment.