Off-Grid Solar System: Components, Sizing and Costs

An off-grid solar system lets a cabin, tiny house, RV base, farm building or full home run on renewable energy with no utility connection at all. Because there is no grid to fall back on, sizing matters far more than with grid-tied solar: undersize the battery and the lights go out after two cloudy days; oversize everything and the project costs twice what it should. This guide explains each component and then walks through sizing step by step, with a worked example that matches the defaults of our off-grid solar calculator.

An off-grid solar power system is a stand-alone electrical system that generates electricity with photovoltaic (PV) panels, stores it in batteries and converts it to household AC power with an inverter. A photovoltaic cell is a semiconductor device that converts sunlight directly into direct-current (DC) electricity; panels are groups of cells. If you are new to PV, read how solar panels work first, or the wider solar energy guide.

What is an off-grid solar system?

An off-grid solar system is a solar power setup that is not connected to the utility grid and relies on batteries to supply power at night and during cloudy weather. It is the opposite of a grid-tied system, which uses the grid as its “battery” through net metering.

There are three common configurations:

System type	Grid connection	Batteries	Works in a blackout?	Typical use
Grid-tied	Yes	No	No (shuts down for safety)	Most suburban homes
Hybrid (grid-tied with storage)	Yes	Yes	Yes, for backed-up loads	Homes wanting backup
Off-grid	No	Yes, essential	Yes, it is the only source	Cabins, remote homes, farms

Off-grid makes most sense when a grid line extension would be expensive, for seasonal properties, or for owners who value complete energy independence. Many off-grid homes also keep a propane or diesel generator, or a home wind turbine, for long winter stretches with little sun.

What are the components of an off-grid solar system?

Every off-grid solar system has four core components: solar panels, a charge controller, a battery bank and an inverter. Wiring, fuses, breakers, disconnects and a monitoring system tie them together.

1. Solar array. The panels, mounting racks and wiring. Rated in watts (W) or kilowatts (kW) under standard test conditions.
2. Charge controller. Regulates current from the panels into the batteries so they charge correctly and are not overcharged. MPPT (maximum power point tracking) controllers convert higher panel voltage into charging current and harvest more energy than older PWM (pulse-width modulation) controllers, especially in cold weather or when panel voltage is well above battery voltage.
3. Battery bank. Stores energy for nights and cloudy days. Rated in kilowatt-hours (kWh) or in amp-hours (Ah) at a nominal voltage (12, 24 or 48 V). One kWh equals 1,000 watt-hours; see what a kilowatt-hour is.
4. Inverter. Converts the battery’s DC into 120/240 V AC for household appliances. Off-grid inverters must be sized for both continuous load and surge (startup) load. Many modern units are inverter-chargers that also include an MPPT controller and a generator input.
5. Balance of system. DC and AC breakers, fuses, a battery monitor or shunt, grounding, surge protection and code-compliant disconnects. In the US, installations follow the National Electrical Code (NEC, NFPA 70), mainly Article 690 for PV and Article 706 for energy storage.

How do you size an off-grid solar system?

Size in this order: daily load, then battery bank, then solar array, then charge controller, then inverter. Each step feeds the next. The worked example uses the default inputs of our calculator: 5 kWh a day, 2 days of autonomy, LiFePO4 at 80% usable, a 48 V bank, 3.5 peak sun hours in the worst month, and 400 W panels.

Step 1: Calculate your daily energy use

List every appliance, its power in watts and the hours it runs per day. Multiply watts by hours to get watt-hours, then add them up. Our watts to kWh converter helps with the arithmetic.

Example: LED lighting, a refrigerator, a well pump, laptops, a TV, a washing machine and a few small kitchen appliances can add up to about 5 kWh per day. For comparison, DOE puts a typical US home at about 10,649 kWh a year, roughly 29 kWh a day, so off-grid homes almost always cut loads first by choosing efficient appliances and moving heating, cooking and hot water to propane, wood or solar thermal.

Step 2: Size the battery bank

Battery kWh = daily kWh × days of autonomy ÷ usable depth of discharge ÷ inverter efficiency.

• Days of autonomy is how many days the batteries must carry the load with no solar input. Two to three days is common; more for cloudy climates or critical loads.
• Depth of discharge (DoD) is the share of the battery’s capacity you use. Our calculator assumes 80% for LiFePO4 and 50% for lead-acid/AGM.
• Inverter efficiency accounts for conversion losses; the calculator assumes 90%.

Example: 5 × 2 ÷ 0.80 ÷ 0.90 = 13.9 kWh. At 48 V, that is 13,889 ÷ 48 = 290 Ah.

To check how long a given bank will last under a specific load, use the battery runtime calculator.

Step 3: Size the solar array

Array kW = daily kWh ÷ inverter efficiency ÷ peak sun hours ÷ array derate.

• Peak sun hours are the daily solar energy at your site expressed as hours of full 1,000 W/m² sunlight. Use the worst month (usually December or January in the US), not the annual average. NREL’s PVWatts tool and solar resource maps give monthly values by location; the solar panel angle calculator helps tilt the array for winter sun.
• Derate covers losses from heat, dust, wiring, controller and battery charging. The calculator uses 75% for off-grid charging.

Example: 5 ÷ 0.90 ÷ 3.5 ÷ 0.75 = 2.12 kW. With 400 W panels, each produces about 400 × 3.5 × 0.75 = 1.05 kWh a day, so you need 5.56 ÷ 1.05 = 5.3, rounded up to 6 panels (2.4 kW).

For grid-tied comparisons or a quick panel count, see the solar panel calculator.

Step 4: Size the charge controller

Controller amps = array watts ÷ battery voltage × 1.25.

Example: 2,116 W ÷ 48 V × 1.25 = 56 A (calculated on the required array size). If you install the full six-panel 2.4 kW array, the same formula gives about 63 A, so a 60 to 70 A MPPT controller, or two smaller ones, is the practical choice. Also check that each string’s open-circuit voltage (Voc), raised by cold weather, stays below the controller’s maximum PV input voltage. The solar charge controller calculator checks both amps and voltage.

Step 5: Size the inverter

Inverter continuous rating must exceed the largest combination of loads that run at the same time; its surge rating must cover motor starts (well pumps, refrigerators, power tools).

The calculator’s rule of thumb is at least daily kWh ÷ 4, so 1.25 kW for this example, but real homes usually choose 3 to 5 kW so a well pump, microwave and fridge can run together. List your simultaneous loads and add their watts.

Worked example summary

Step	Formula	Result (5 kWh/day example)
Daily load	Sum of appliance Wh	5 kWh
Battery bank	5 × 2 ÷ 0.8 ÷ 0.9	13.9 kWh (290 Ah at 48 V)
Solar array	5 ÷ 0.9 ÷ 3.5 ÷ 0.75	2.12 kW (6 × 400 W)
Charge controller	2,116 W ÷ 48 V × 1.25	56 A minimum
Inverter	Largest simultaneous load (min. 5 ÷ 4)	1.25 kW or more

How bank voltage changes the numbers

The same 13.9 kWh bank and 2.12 kW array look very different at lower voltages:

Bank voltage	Battery capacity needed	Controller current (2.12 kW array)
12 V	about 1,157 Ah	about 220 A
24 V	about 579 Ah	about 110 A
48 V	about 290 Ah	about 56 A

That is why a 12 V system of this size is impractical: 220 A of charging current needs very heavy cables and multiple controllers.

How many solar panels do you need to go off-grid?

Most off-grid cabins need 3 to 6 panels of 400 W, while a full-size home using 20 to 30 kWh a day needs roughly 22 to 32 panels, plus 55 to 85 kWh of LiFePO4 battery. The exact count depends on daily kWh and worst-month sun. The table applies the same formulas and assumptions as the worked example above: 3.5 peak sun hours, 75% array derate, 90% inverter efficiency, 2 days of autonomy and 80% usable LiFePO4.

Daily use	Typical setting	Solar array	400 W panels	LiFePO4 battery (2 days)
2 kWh	Weekend cabin, lights, phone, small fridge	0.85 kW	3	5.6 kWh
5 kWh	Efficient full-time cabin	2.12 kW	6	13.9 kWh
10 kWh	Small efficient home, propane for heat and cooking	4.23 kW	11	27.8 kWh
20 kWh	Larger home, some electric cooking	8.47 kW	22	55.6 kWh
30 kWh	Close to the US average home (DOE: about 29 kWh/day)	12.7 kW	32	83.3 kWh

Sunnier sites need fewer panels: at 5 peak sun hours the 5 kWh example drops to about 1.5 kW. Check your own location’s monthly values in PVWatts and plug them into the off-grid solar calculator.

Will a 400W solar panel run a fridge?

On its own, usually not around the clock: a 400 W panel delivers roughly 0.9 to 1.5 kWh of usable AC energy a day depending on the season, and it produces nothing at night, so a refrigerator also needs a battery and, for most models, a second panel in winter.

One 400 W panel at 3.5 winter peak sun hours and a 75% derate charges about 1.05 kWh a day, or about 0.95 kWh after a 90% efficient inverter. At 5.5 summer sun hours that rises to about 1.5 kWh. Compare that with the fridge’s daily use:

• Efficient modern fridge rated around 400 kWh a year on its EnergyGuide label (about 1.1 kWh a day): one panel covers it in summer, two panels in a 3.5-hour winter month, plus about 1.5 kWh of LiFePO4 per night of storage.
• Older or larger fridge averaging 150 W (the default in our electricity usage calculator), or 3.6 kWh a day: about 4 panels and a 10 kWh battery for 2 days of autonomy.

The label figure or a plug-in watt meter beats any rule of thumb. The inverter also has to handle the compressor’s startup surge, which can be several times its running watts.

Can you run air conditioning on off-grid solar?

Yes, but cooling is one of the biggest loads an off-grid system can carry: a 1,000 W window unit running 8 hours uses about 8 kWh a day, which takes about 6 panels of 400 W in a 5.5-sun-hour summer, while a 3.5 kW central AC needs roughly three times that.

The math is the same as for any load. A window AC: 1,000 W × 8 h = 8 kWh a day; 8 ÷ 0.9 ÷ 5.5 ÷ 0.75 = 2.15 kW of array, so 6 panels. A 3-ton central AC at 3,500 W for 8 hours uses 28 kWh a day and needs about 7.5 kW (19 panels) just for cooling. Wattages are the typical values from our appliance presets; your unit’s label rules.

Cooling has one advantage off-grid: demand peaks when the sun is strongest, so adding panels is cheaper than adding batteries. Only the hours after sunset need storage; 4 evening hours of a window unit need about 4 ÷ 0.8 ÷ 0.9 = 5.6 kWh of LiFePO4. An inverter-driven mini-split is usually more efficient than a window unit and ramps up gradually, which eases inverter surge sizing.

LiFePO4 vs lead-acid: which battery is best for off-grid solar?

LiFePO4 (lithium iron phosphate) is the better choice for most new off-grid systems because more of its capacity is usable, it lasts many more cycles and it needs no maintenance; lead-acid is cheaper upfront.

LiFePO4 is a lithium-ion chemistry that uses iron phosphate as the cathode, first reported by John Goodenough’s group in 1997 (Padhi et al., 1997). It is more thermally stable than the nickel-manganese-cobalt (NMC) chemistry used in many EVs, and it is now the standard for home storage. Lead-acid batteries come as flooded (needing water top-ups), AGM (absorbed glass mat) or gel types.

Factor	LiFePO4	Lead-acid / AGM
Usable depth of discharge (site assumption)	80%	50%
Battery needed for 5 kWh/day, 2 days	13.9 kWh	22.2 kWh
Cycle life	3,000–5,000 cycles for a common 12 V 100 Ah unit (Battle Born spec)	Lower; falls quickly with deep discharge
Maintenance	None; built-in battery management system	Flooded types need watering and equalizing
Cold-weather charging	Must not charge below freezing unless heated	Charges in cold, with reduced capacity
Upfront cost per kWh	Higher	Lower

With lead-acid, the same example needs 5 × 2 ÷ 0.5 ÷ 0.9 = 22.2 kWh of nameplate capacity (463 Ah at 48 V), 60% more than LiFePO4. Lead-acid also loses capacity if left partly charged for long periods, which happens often in winter off-grid use.

How much does an off-grid solar system cost?

Costs scale with daily kWh and days of autonomy, and batteries are usually the largest single cost; small cabin systems cost a few thousand dollars, while whole-home off-grid systems typically reach tens of thousands.

For a rooftop system that stays connected to the utility, see our breakdown of grid-tied solar panel cost.

Published benchmarks for off-grid systems are scarce because every system is custom. For battery storage, NREL’s 2024 Annual Technology Baseline models a residential 5 kW / 12.5 kWh battery using a pack cost of about $283 per kWh and an inverter cost of about $183 per kWh (2022 dollars), before installation, permitting and balance-of-system costs. Applying that pack cost to the 13.9 kWh example gives roughly $3,900 for battery cells and modules alone.

What drives the total price:

• Battery capacity and chemistry, set by daily load and days of autonomy.
• Array size, set by the worst month’s sun, not the annual average.
• Inverter size, set by surge and simultaneous loads.
• Backup generator, which lets you cut days of autonomy and array size.
• Installation, permits and trenching, especially if the array is ground-mounted away from the house.

Cutting your daily load is the cheapest upgrade: every kWh you remove from the daily total removes about 2.8 kWh of LiFePO4 battery (for 2 days of autonomy) and about 0.42 kW of array in the example above.

Are there tax credits for off-grid solar?

The federal Residential Clean Energy Credit (Section 25D) no longer applies to new systems: the IRS states it is not available for property placed in service after December 31, 2025. It previously covered both solar panels and battery storage at 30%, including off-grid systems at a dwelling.

Check state and utility programs for remaining incentives, and USDA’s Rural Energy for America Program (REAP) if the system serves an agricultural operation or rural small business.

What are the pros and cons of going off-grid?

Off-grid solar gives full energy independence and no electricity bills, but it costs more per kWh than grid-tied solar and requires active energy management.

Pros: no utility bills or connection fees, immunity to grid outages, power where lines don’t reach, and a quiet, clean, renewable energy supply.

Cons: batteries are expensive and need eventual replacement; surplus summer power is wasted unless you add loads; winter shortfalls usually need a generator; you are responsible for all maintenance. For the broader trade-offs of PV, see solar energy pros and cons and our main solar energy guide.

History of off-grid solar and battery storage

Off-grid solar is older than grid-tied solar: PV’s first jobs were powering satellites, lighthouses and remote equipment far from any power line, and every one of those systems relied on a battery. The story runs in parallel with battery chemistry, from Gaston Planté’s lead-acid cell in 1859 to the lithium iron phosphate cathode reported in 1997.

Batteries came first. In 1859 the French physicist Gaston Planté built the first rechargeable battery, lead plates in sulfuric acid giving about two volts per cell, and presented a nine-cell battery to the French Academy of Sciences in 1860 (ETHW; Kurzweil, 2010). Lead-acid remained the default for solar storage for over a century.

PV went off-grid from the start. Vanguard 1 carried a small solar array in 1958. On Earth, Japan installed a 242 W PV array on a lighthouse in 1963, and in the 1970s solar cells began powering navigation lights on offshore oil and gas rigs, lighthouses and railroad crossings, where grid power was not affordable. In 1972 a French cadmium sulfide PV system ran an educational TV at a village school in Niger, and in 1978 NASA’s Lewis Research Center installed a 3.5 kW system on the Papago reservation in Arizona that supplied water pumping and power for 15 homes until the grid arrived in 1983 (DOE solar timeline).

Lithium changed storage. John Goodenough’s group reported the lithium cobalt oxide cathode in 1980 (Mizushima et al., 1980), Akira Yoshino built a lithium-ion battery without metallic lithium in 1985, and the first commercial lithium-ion batteries went on sale in 1991; the three pioneers shared the 2019 Nobel Prize in Chemistry with Stanley Whittingham. In 1997 Akshaya Padhi, K. S. Nanjundaswamy and Goodenough described phospho-olivines, including LiFePO4, as cathode materials (Padhi et al., 1997). Its iron-based, thermally stable chemistry is why LiFePO4 now dominates new off-grid banks.

Year	Milestone	Source
1859	Gaston Planté invents the rechargeable lead-acid battery	ETHW
1958	Vanguard 1 flies a solar array in orbit	NASA
1963	242 W PV array on a Japanese lighthouse, then the world’s largest	DOE
1972	CdS PV system powers a village school TV in Niger	DOE
1978	3.5 kW village PV system on the Papago reservation, Arizona	DOE
1980	Lithium cobalt oxide cathode reported	Mater. Res. Bull.
1991	First commercial lithium-ion batteries	Nobel Prize
1997	LiFePO4 (phospho-olivine) cathode reported	J. Electrochem. Soc.
2019	Nobel Prize in Chemistry for lithium-ion batteries	Nobel Prize

Scientific references

• Kurzweil, P. (2010). “Gaston Planté and his invention of the lead–acid battery — The genesis of the first practical rechargeable battery.” Journal of Power Sources, 195(14), 4424–4434. doi:10.1016/j.jpowsour.2009.12.126
• Mizushima, K., Jones, P. C., Wiseman, P. J. & Goodenough, J. B. (1980). “LixCoO2 (0 < x ≤ 1): A new cathode material for batteries of high energy density.” Materials Research Bulletin, 15(6), 783–789. doi:10.1016/0025-5408(80)90012-4
• Padhi, A. K., Nanjundaswamy, K. S. & Goodenough, J. B. (1997). “Phospho-olivines as positive-electrode materials for rechargeable lithium batteries.” Journal of The Electrochemical Society, 144(4), 1188–1194. doi:10.1149/1.1837571
• National Fire Protection Association (2023). NFPA 70: National Electrical Code, Articles 690 (solar PV systems) and 706 (energy storage systems). NFPA

Bottom line

An off-grid solar system combines panels, a charge controller, a battery bank and an inverter, and it must be sized for your worst month, not an average day. For 5 kWh a day with 2 days of autonomy and 3.5 peak sun hours, plan on about 13.9 kWh of 48 V LiFePO4 (290 Ah), a 2.1 kW array of six 400 W panels, a controller of at least 56 A and an inverter sized to your largest simultaneous load. LiFePO4 needs about 38% less nameplate capacity than lead-acid and lasts thousands of cycles. With the federal 25D credit gone for systems placed in service after 2025, cutting loads first is the surest way to make independent, clean, renewable power affordable. Run your own numbers in the off-grid solar calculator.