Free tool · RV power sizing

What size battery bank and solar does your RV need?

Tick the 12V loads in your rig, set your battery type and how many days you want to camp without charging, and this tool sizes your house bank, solar array, charge controller, and inverter using accepted off-grid math. It is a planning estimate to get you in the right ballpark, not a wiring diagram and not a substitute for a qualified RV technician.

Read first: this is a free planning estimate, not an engineered design. It does not account for your specific wiring, fusing, battery placement, ventilation, or charging sources, all of which must follow NEC and RVIA practice and your equipment manuals. Real loads vary by make and model. A LiFePO4 bank needs a battery-management system and a DC-DC charger if you charge from the alternator. Confirm the final system with a qualified RV electrician before you buy or install. Use it as a starting point only.

Your system

Battery type System voltage Days of reserve Sun (peak hours)

Your daily loads

Tick what you run and adjust the hours per day. Amps are typical duty-averaged 12V figures; check your own gear's draw where you can. On a 24V system these still apply to 12V devices; convert any native-24V gear separately.

Use	Load	Amps	Hrs/day
	12V compressor fridge the compressor cycles; this is the duty-averaged draw, about 30 to 50 Ah/day for a 12V box	4
	Roof vent fan (MaxxFan / Fan-Tastic) about 4.5 A on high, 0.2 A on low; the best comfort-per-amp upgrade in a rig	2.5
	LED interior lights	2
	Fresh-water pump on-demand; draws 5 to 6 A only while running	5
	Phone and laptop charging a laptop pulls about 4 A while charging	3.5
	Propane / CO detector always-on safety parasitic load	0.1
	Propane furnace blower fan 12V blower and ignition; runs only in the cold; 4.5 to 8.5 A by model	6
	Diesel air heater about 8 to 10 A on glow startup for a minute or two, then 0.5 to 1.5 A running	1
	Starlink (12V) roughly 50 to 75 W; the big new draw for remote workers	4.5
	12V LED TV (24 to 32 in) about 30 to 45 W	3
	12V circulation / cabin fan	1.5
	12V stereo or Bluetooth speaker volume-dependent	2
	Inverter standby (no-load draw) the phantom load people forget; switch the inverter off when idle	0.5

Largest AC load at once, in watts (leave 0 if no inverter) This sizes the inverter only; it does not change the battery and solar numbers above. Solar runs your 12V house loads, not a rooftop air conditioner. To size the bank for an AC load you run regularly, add it to the loads above as a DC-equivalent: its watts divided by 12 is roughly its amps at 12V.

A planning estimate using accepted off-grid sizing math, not an engineered design. Have the final system sized and installed to NEC and RVIA practice by a qualified RV electrician.

How the RV solar sizing math works

The calculator above is just this five-step method, applied to the loads you pick. You can run it by hand with the same numbers.

Step 1: Add up your daily power use

List each 12V load, multiply its amps by the hours you run it per day, and total it to amp-hours per day. Size to your heaviest realistic day off-grid, which for most rigs is a cold or hot boondocking day with the fridge, the roof fan, and the furnace all working, not a hookup night. A 12V compressor fridge is almost always the biggest single house load because it runs around the clock, even though it only sips while the compressor is cycling.

Step 2: Size the house battery bank

Bank capacity = daily amp-hours x days of reserve x 1.1 for ageing and growth, divided by the usable share of the battery. Lead-acid (flooded, AGM, or gel) is sized to about 50% usable; LiFePO4 lithium to about 80%. Two days of reserve with no charging is a common boondocking baseline. LiFePO4 needs a battery-management system and must not be charged below freezing without internal heating; lead-acid loses capacity under heavy loads (the Peukert effect) and in the cold, so lean high if you run a big inverter or camp in winter. Lithium's '100% usable' spec is a capability, not a daily plan: the BMS cuts loads near 10 volts and cold and ageing shrink real capacity, which is why this tool plans to 80%.

Step 3: Size the solar array

Array watts = daily watt-hours x 1.1, divided by (peak sun-hours x 0.75). The 0.75 is the real-world off-grid derate for flat roof-mounted panels: heat, wiring, charge taper, and dust. It is a touch higher than the 0.7 used on a sailboat, which fights rig and bimini shading, but well below the 0.8-plus a tilted home array sees. Peak sun-hours run from about 1.5 in a Pacific Northwest winter to 7-plus in an Arizona summer and average around 5 across the US, so look up your own worst travel month with NREL's free PVWatts tool and size to that, not to the annual average. Tilting the panels in winter can claw back a lot of the shortfall.

Step 4: Size the charge controller

Controller amps = array watts divided by battery voltage, times 1.25. The 1.25 is the safety factor NEC 690.8 applies because panel current can run above its rated value when irradiance tops the 1,000 W per square metre lab figure. Choose an MPPT controller over PWM for the extra harvest in cold and partial light, and check the controller's maximum input voltage against the array's open-circuit voltage on a cold, sunny morning, when panel voltage peaks.

Step 5: Size an inverter, if you run AC loads

Continuous watts = your largest simultaneous AC load times 1.25, then confirm the surge rating covers motor startup (a residential fridge, a microwave, or a power tool can pull two to three times its running watts for a moment). Choose a pure sine wave inverter for sensitive electronics. Just as important, the battery bank has to deliver the current: keep about 100 Ah of 12V lithium, or roughly 200 Ah of 12V lead-acid (which sags more under load), per 1,000 W of inverter. One thing solar cannot do is run a rooftop air conditioner overnight: a rooftop AC draws 1,200 to 1,800 W continuously and would need a very large lithium bank and array, so plan it as a generator or shore-power job.

Typical RV 12V load reference

Representative draws for common RV and van equipment, the same figures the tool starts from. Your own gear's amps vary by make and model, so check the label or manual where you can. The 12V compressor fridge is almost always the biggest single house load; the furnace fan is the one that defines a cold-weather day.

Device	Amps (12V)	Typical hrs/day
12V compressor fridge	4	10
Roof vent fan (MaxxFan / Fan-Tastic)	2.5	6
LED interior lights	2	4
Fresh-water pump	5	0.5
Phone and laptop charging	3.5	3
Propane / CO detector	0.1	24
Propane furnace blower fan	6	2
Diesel air heater	1	4
Starlink (12V)	4.5	5
12V LED TV (24 to 32 in)	3	3
12V circulation / cabin fan	1.5	4
12V stereo or Bluetooth speaker	2	2
Inverter standby (no-load draw)	0.5	12

Once you have your numbers, here is the gear

Each piece of the house-power stack has its own tested-picks guide. Size first with the tool, then shop with these.

How we are paid: some links above go to Amazon, and if you buy through them we earn a commission at no extra cost to you. It does not change what we recommend. For the whole picture, see our RV and van gear guides.

Common questions

How do I calculate the battery bank size for my RV?

Total your daily power use in amp-hours (each 12V load's amps times the hours per day you use it), multiply by the days of reserve you want without charging (two is a common boondocking baseline), add about 10% for ageing, then divide by the usable share of the battery. Lead-acid is sized to about 50% usable and LiFePO4 lithium to about 80%, so the same daily use needs a much larger lead-acid bank. The calculator above does this math from the loads you select.

How much solar do I need for my RV or van?

Take your daily energy use in watt-hours and divide by your peak sun-hours times 0.75, the real-world derate for flat roof-mounted panels. As a rough feel, a rig using 100 amp-hours a day at 12V (about 1,200 watt-hours) needs roughly 300 watts of panel in strong sun, about 350 to 400 on an average day, and 500 to 600 in a weak-sun month. Look up your own worst travel month with NREL's free PVWatts tool and size to that, because a system sized for the summer average will fall short in December.

Lead-acid or lithium: how much capacity can I actually use?

Usable capacity is the catch. Flooded, AGM, and gel lead-acid batteries should be cycled to only about 50% depth of discharge to protect their life, so a 200 amp-hour lead-acid bank gives you about 100 usable amp-hours. LiFePO4 lithium is commonly planned to about 80%, so a 100 amp-hour lithium battery gives roughly 80 usable, weighs a third as much, and lasts several times as many cycles. Some lithium vendors advertise 100% usable, but the BMS cuts out near empty and cold and ageing shrink real capacity, which is why this tool plans to 80%.

Can I run my RV air conditioner on solar?

Not overnight, and not from a normal rig's system. A rooftop RV air conditioner draws roughly 1,200 to 1,800 watts continuously, so even an hour or two would need a very large lithium bank (think 600 amp-hours and up) plus a big inverter and a large array to recharge it. Solar's job in a rig is to keep the 12V house loads and devices running and to top the batteries; running the air conditioner is a generator, shore-power, or short-burst-on-a-huge-lithium-bank job. The calculator sizes the house system, not air conditioning.

What size charge controller do I need for my RV solar?

Divide your total array watts by the battery voltage to get the charging current, then multiply by 1.25 as the safety factor NEC 690.8 uses for bright-irradiance current spikes. A 400 watt array on a 12V bank works out to about 33 amps times 1.25, so roughly a 40 amp controller. Pick MPPT over PWM for the extra harvest, and confirm the controller's maximum input voltage covers your panels' open-circuit voltage on a cold, sunny day.

Does this calculator replace a qualified RV technician?

No. It is a planning estimate to get you in the right ballpark and help you shop. The real installation, wire gauge, fusing, battery placement, and ventilation must follow NEC and RVIA practice and your equipment's manuals, a LiFePO4 bank needs a battery-management system and alternator protection (a DC-DC charger) if you charge from the engine, and every bank needs properly sized overcurrent protection at the battery. Treat the numbers here as a starting point for that work, not the last word, and have the final system signed off by a qualified RV electrician.

Disclaimer

This calculator and page are provided for general informational and educational purposes only and give a planning estimate based on accepted off-grid sizing practice as of 2026. They are not engineering advice, not a system design, and not a substitute for a qualified RV electrician or installer. Real component draws, charging sources, wiring, fusing, ventilation, and battery placement vary by rig and must follow NEC and RVIA practice and the manufacturers' instructions. Every battery bank needs properly sized overcurrent protection (a fuse or breaker) at the battery, the solar input and every branch circuit need their own fusing sized to the wire (PV circuits at roughly 1.56x panel short-circuit current per NEC 690.8), and a LiFePO4 bank needs a battery-management system plus alternator protection (a DC-DC charger) if it is engine-charged and must not be charged below freezing without internal heating; this tool sizes capacity only and does none of that. We make no warranty, express or implied, as to accuracy, completeness, or fitness for any particular rig or installation. You alone are responsible for verifying and safely installing your electrical system, and Sorted Gear accepts no liability for any loss, injury, fire, or damage arising from reliance on this information. When in doubt, consult a qualified RV electrician. Last reviewed June 2026.