Free calculator
Off-Grid Solar Calculator
Pick what the system is for, the appliances it runs and your state. Get the daily watt-hours, the LiFePO4 bank, the panel watts for your darkest month, the MPPT controller and inverter, the fuses and cable sizes, and a parts kit that works as one system.
Updated Oct 24, 2026
- Answer a few questions
- See the math behind every number
- Get models that actually fit
Every main part this tool can put in a kit
Panels, MPPT controllers, LiFePO4 batteries, inverters and all-in-one inverter/chargers. Ratings come from each listing or the maker's spec sheet.
Callsun 200W N-Type Bifacial Solar Panel
- Bifacial
- Voc 27.3 V
- 51.3 x 30.3 in
- 23.8 lb
Rigid 200 W bifacial glass panel with MC4 leads, the building block of every kit this tool builds.
- Split-cell design keeps one half producing when the other is shaded
- IP68 junction box, tempered glass, aluminum frame
- Callsun's store sells 2, 4, 8, 12 and 16 packs
- 51.3 x 30.3 in and 23.8 lb per panel
- Needs mounting hardware for a roof or ground rack
About $161.99 at Callsun, checked Oct 24, 2026
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Renogy Rover 40A MPPT Charge Controller (Bluetooth)
- 12/24 V
- 100 V PV input
- Bluetooth
40 A MPPT controller for 12 or 24 V lithium banks up to about 500 W of panels at 12 V, with the Bluetooth module in the box.
- Auto-detects 12 or 24 V
- Bluetooth module included for the Renogy DC Home app
- Fanless, silent
- 100 V PV input limit means at most two of our panels in series
- Lithium charging is set manually
$100 to $250, live price on Amazon
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Renogy Rover Lite 60A MPPT Charge Controller
- 12 to 48 V
- 150 V PV input
- Max 900 W at 12 V, 1,800 W at 24 V
60 A MPPT controller with a 150 V input, for 12 or 24 V banks that need more panels than a 40 A controller handles.
- 150 V PV input fits four of our panels in series
- 12, 24, 36 or 48 V battery
- Rated for full load from -31 F to 113 F
- Bluetooth module sold separately
$100 to $250, live price on Amazon
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LiTime 12V 100Ah LiFePO4 Battery
- 1.3 kWh
- 100 A BMS
- Max 4P4S
- 22.2 lb
1,280 Wh LiFePO4 battery with a 100 A BMS, the small building block for 12 V banks.
- Up to 4 in parallel or 4P4S
- 22.16 lb, 13 x 6.77 x 9.08 in
- 4,000+ cycles at 100% depth of discharge per LiTime
- 100 A BMS: a 2,000 W inverter at 12 V needs two in parallel
- Non-Bluetooth version
$250 to $500, live price on Amazon
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Show all 13 modelsShow fewer
LiTime 12V 230Ah Plus LiFePO4 Battery
- 2.9 kWh
- 200 A BMS
- Low-temp protection
2,944 Wh in one 12 V battery with a 200 A BMS, enough on its own for a 2,000 W inverter.
- 200 A BMS
- Low-temp charge cutoff below 32 F
- Most Wh per dollar of the 12 V LiTime line at our check
- The listing does not state a parallel limit, so this tool uses one
$250 to $500, live price on Amazon
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LiTime 24V 100Ah LiFePO4 Battery
- 2.6 kWh
- 100 A BMS
- Max 4P2S
- 45.9 lb
2,560 Wh native 24 V battery with a 100 A BMS, so a 24 V system needs no series wiring.
- Up to 4 in parallel (max 4P2S)
- Low-temp cutoff
- 45.85 lb
- 21 x 8.2 x 8.5 in, check the space
- Non-Bluetooth version
$500 to $1,000, live price on Amazon
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LiTime 12V 320Ah Mini LiFePO4 Battery (Bluetooth)
- 4.1 kWh
- 200 A BMS
- Bluetooth
- Max 4P4S
4,096 Wh with a 200 A BMS and Bluetooth, for 12 V RV and van banks that need the most storage per battery box.
- Up to 4P4S
- Bluetooth state of charge in the app
- 14.49 x 7.44 x 10.63 in
- Bluetooth wakes only after a first charge from a lithium charger
$500 to $1,000, live price on Amazon
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ECO-WORTHY Cubix100 48V 100Ah Server Rack Battery
- 5.1 kWh
- UL9540
- Server rack
- Wi-Fi and Bluetooth
5,120 Wh 48 V rack battery, UL9540 and UL1973 listed, with parallel and communication cables in the box.
- UL9540, UL9540A and UL1973 listed
- CAN/RS485 plus Bluetooth and Wi-Fi monitoring
- Parallel cables included, up to 32 units
- 100 A continuous per battery (retailer spec), so a 6,000 W inverter needs two
$500 to $1,000, live price on Amazon
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Renogy P2 1000W Pure Sine Wave Inverter (12V)
- 1,000 W continuous
- 2,000 W surge
- UL 458
- Hardwire terminal
1,000 W continuous, 2,000 W surge, 12 V pure sine inverter for sheds, vans and light cabin loads.
- UL 458 certified
- GFCI outlets plus a hardwire terminal
- 16.4 ft wired remote
- Included 3 ft cables are 4 AWG; this tool sizes heavier cable for the fuse
$100 to $250, live price on Amazon
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Renogy P2 2000W Pure Sine Wave Inverter (12V)
- 2,000 W continuous
- 4,000 W surge
- 1/0 AWG cables included
2,000 W continuous, 4,000 W surge, 12 V pure sine inverter, the most a 12 V bank should feed.
- 4,000 W surge for fridge and pump starts
- Two 1/0 AWG 3 ft cables included
- Hardwire terminal and remote
- Draws about 185 A from a 12 V bank at full load
$250 to $500, live price on Amazon
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Renogy 2000W Pure Sine Wave Inverter (24V)
- 2,000 W continuous
- 4,000 W peak
- 92% efficiency
- GFCI
2,000 W continuous, 4,000 W surge pure sine inverter for 24 V banks, half the battery current of a 12 V setup.
- 4,000 W peak
- 92% efficiency per Renogy
- Two GFCI outlets, terminal block and remote
- 24 V only
$250 to $500, live price on Amazon
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Growatt 3500W 48V All-in-One Solar Inverter
- 3,500 W continuous
- 48 V
- 4,500 W PV
- 7,000 W peak
+1 moreFewer
- UL 1741
3,500 W, 120 V inverter with a built-in MPPT charger for 48 V banks: one box replaces the controller and inverter.
- Up to 4,500 W of panels at 120 to 225 V
- 7,000 W peak
- UL 1741 certified
- String voltage must stay 120 to 225 V, so at least six of our panels in series
- 120 V only; 240 V needs two units or the 6,000 W split phase model
$500 to $1,000, live price on Amazon
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Growatt 6000W 48V Split Phase Off-Grid Inverter
- 6,000 W continuous
- 120/240V
- 120/240 V
- 2 MPPT
+2 moreFewer
- 550 V PV
- UL 1741
6,000 W 120/240 V split phase all-in-one with two MPPT inputs, for a tiny home or cabin with a well pump or 240 V loads.
- 120/240 V split phase
- Two MPPT inputs, up to 550 V PV
- 140 A battery charging, generator input
- The listing gives no surge rating
- Needs two 100 A rack batteries at full load
$1,000 to $2,000, live price on Amazon
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Some of these links pay us a commission and some do not; each card says which. Commissions do not affect which models the tool picks or how it ranks them. See our disclosure.
How this calculator works
- Daily energy. Watts x hours a day x duty cycle for each appliance (fridges and fans cycle), from our shared appliance table. AC loads go through the inverter, so we divide by 0.9 for inverter losses to get what the battery supplies.
- Sun hours. Monthly peak sun hours on a south-facing panel tilted at latitude from the NASA POWER climatology (CERES satellite data, 2001 to 2025), one city per state. Year-round use designs for the lowest month; spring-to-fall designs for the lowest month April to September. For a specific site, NREL's PVWatts gives a closer number you can enter instead.
- Battery bank. Daily battery Wh x days of autonomy / 0.9, so the LiFePO4 bank keeps a 10% reserve. Batteries are added in parallel up to the maker's limit, and enough of them that the BMS ratings carry the full inverter current.
- Panels. Daily battery Wh / (sun hours x 0.78). The 0.78 is PVWatts' default 14% system losses x 95% LiFePO4 charge efficiency x 96% for heat and MPPT conversion. Panels are then laid out in strings that fit the charger.
- Controller and strings. Array watts / battery volts x 1.25 (NEC 690.8) for the controller rating, within the maker's maximum PV watts. String Voc x 1.25 for a cold morning (NEC 690.7) must stay under the controller's input limit, and a 24 V bank needs at least two panels in series. We stop at two parallel strings per input so no string fuses are needed.
- Voltage and inverter. Continuous rating at least 1.25 x everything on at once; surge at least that load plus the largest motor start. "Pick for me" takes the lowest voltage where every part fits: 12 V for small systems and RVs, 24 V for loads over 1,000 W, and 48 V with an all-in-one inverter/charger past 2,000 W or for 240 V.
- Fuses and cable. Fuses at 1.25 x the current they protect, Class T at the battery. Cable ampacity at or above the fuse, from NEC Table 310.17 (copper, single conductor in free air, 90 C insulation). Keep battery runs short; long runs need a heavier gauge for voltage drop.
This is a planning tool, not a permit drawing. Anything tied into a building's wiring needs to meet NEC Article 690 and local code; have an electrician check it.
Worked examples
Weekend cabin in Colorado, used year-round
- Mini fridge, 4 LED lamps, ceiling fan, TV, laptop, phones
- Colorado, design for winter: 4.2 sun hours
- 2 days of autonomy, voltage picked for me
600 W of panels, a 5.1 kWh 24 V LiFePO4 bank, a 60 A MPPT controller and a 2,000 W inverter.
The loads use 1,682 Wh a day, 1,869 Wh from the battery after inverter losses. Two days at 90% usable is 4,153 Wh, so two LiTime 24 V 100 Ah batteries (5,120 Wh). 1,869 / (4.2 x 0.78) is 567 W, three 200 W panels in series. At 12 V those three panels would need a 63 A controller, more than the 60 A we list, so the tool moves to 24 V, where 600 W / 24 V x 1.25 is 32 A.
Van in Arizona, spring to fall
- Fridge, Starlink 8 h, laptop 6 h, lights, phones, coffee maker
- Arizona, design for summer: 6.6 sun hours
- 1 day of autonomy, 12 V
400 W of panels, one 2,944 Wh 12 V battery, a 60 A MPPT and a 2,000 W inverter on 1/0 cable and a 250 A Class T fuse.
1,851 Wh a day of loads is 2,057 Wh from the battery and 2,285 Wh of nameplate for one day, 179 Ah at 12 V. Two 200 W panels in series cover the 397 W the sun hours call for. The coffee maker pushes the all-on load to 1,136 W, so a 2,000 W inverter, which pulls about 185 A at 12 V: the LiTime 230 Ah has a 200 A BMS to carry it, the fuse is 185 x 1.25 rounded up to 250 A, and 1/0 cable is rated 260 A.
Tiny home in North Carolina, full time
- Full fridge, router, lights, laptop, TV, microwave, washer
- North Carolina, design for winter: 3.7 sun hours
- 2 days of autonomy, voltage picked for me
1,200 W of panels in one string, a 10.2 kWh 48 V rack bank and a 3,500 W all-in-one inverter/charger.
3,000 Wh a day is 3,333 Wh from the battery; two days at 90% is 7,407 Wh, so two 5,120 Wh ECO-WORTHY rack batteries. With everything on at once the load is 2,041 W, x 1.25 is a 2,600 W inverter, past the 2,000 W 24 V inverter, so the kit goes to 48 V. 1,149 W of panels rounds to six 200 W panels in series, which is also the minimum the Growatt needs to reach its 120 V MPPT start voltage.
Frequently asked questions
How many solar panels do I need for an off-grid cabin?
Divide the watt-hours you draw from the battery each day by your design sun hours and by about 0.78 for system losses. 1,000 Wh a day of AC loads is about 1,111 Wh from the battery, and at 4 sun hours that is 354 W of panels, two 200 W panels. Use your worst month's sun hours if you stay there in winter.
How big a battery bank do I need for off-grid solar?
Daily watt-hours from the battery x days of autonomy, divided by 0.9 so the LiFePO4 bank never runs to empty. For 1,111 Wh a day and 2 days that is 2,469 Wh, about 193 Ah at 12.8 V or 96 Ah at 25.6 V. Lead-acid needs about twice the nameplate because only half of it is usable.
What size charge controller do I need?
Panel watts divided by battery voltage, times 1.25. 400 W on a 12 V bank is 33 A, x 1.25 is 42 A, so a 60 A MPPT. The same 400 W on 24 V needs only 21 A. Also check the controller's maximum PV voltage: panel Voc x panels in series x 1.25 for cold mornings must stay under it.
Should my off-grid system be 12 V, 24 V or 48 V?
Pick the lowest voltage that keeps currents sane. 12 V suits RVs, vans and small sheds up to about 1,000 to 2,000 W of inverter; 24 V halves the current for cabins; 48 V is the norm for tiny homes, anything with a 3,000 W or bigger inverter, and 240 V loads like a well pump.
What size inverter do I need for off-grid?
Add the running watts of everything that can be on at once and multiply by 1.25, then check the surge rating covers that load plus the biggest motor start (a fridge compressor starts at several times its running watts). Pure sine wave only; modified sine inverters make motors run hot and some electronics fail.
How many days of autonomy should an off-grid system have?
Two to three days for a cabin or home you live in, one day for an RV or a shed you can do without. Each extra day adds a full day of battery, so a generator for long cloudy spells is often cheaper than a third or fourth day of storage.
What are peak sun hours?
The day's solar energy expressed as hours of full 1,000 W/m2 sun. A place with 4 peak sun hours delivers 4 kWh per square meter per day to a tilted panel, so a 200 W panel makes about 800 Wh before losses. It varies by month: across most of the US, December delivers half or less of what June does.
Can I use a power station instead of building a system?
Yes, for smaller loads. A power station is the battery, MPPT charger and inverter in one case, so you only add panels. It costs more per kWh than separate parts and tops out around 6 to 12 kWh, but there is no wiring, fusing or cable sizing to get wrong.
Marcus Reed
Founder and Editor, CrunchYourDollars
Marcus Reed builds the sizing tools on CrunchYourDollars. He is a software engineer with a long-running PC hardware and power supply habit, which is where the watts, watt-hours and surge math on this site comes from. Product specs are pulled from manufacturer data sheets, electricity rates from the U.S. Energy Information Administration, and water chemistry rules from the Water Quality Association. He is not a licensed electrician or plumber: the tools show the math and the matching models so you can make the call, and anything involving your electrical panel should be checked by a licensed pro.
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