RV, off-grid and 12V systems

How Many Watts of Panel Does It Take to Refill a 12 V 100 Ah Battery Each Day in December Versus July?

Published September 23, 2026 · By the SolarPanelX editors · Prices and specs as of that date, from the pages under Sources

Summary

In New York, about 630 W in December and about 280 W in July. A 12.8 V, 100 Ah battery holds 1,280 Wh, and the panel wattage needed to put that back each day was worked backward from NLR PVWatts monthly figures. Sizing to the annual average gives about 360 W, so choosing winter or the average changes the answer by more than two times.

Working back from monthly output

For New York with south-facing panels at 20° and 14% losses, one 430 W panel came to about 27 kWh in December, 61 kWh in July, and 555 kWh over the year. Converting that to kWh per kilowatt per day and dividing 1,280 Wh by it:

Period	Per kW per day	Watts for 1,280 Wh
December	about 2.0 kWh	about 630 W
July	about 4.6 kWh	about 280 W
Annual average	about 3.5 kWh	about 360 W

This assumes refilling an empty battery and leaves out charging losses. Refilling from 80% used cuts each figure to 80% of the value shown.

At 630 W on 12 V, the controller limits also move. Victron's SmartSolar 100/30 is rated for 440 W at 12 V and the 100/50 for 700 W. The battery has its own limit: Victron recommends 50 A or less for the Lithium Battery Smart 12.8 V/100 Ah. Which panel, controller, and battery combinations work is set by each manufacturer's specifications; this site does not rule on compatibility.

Shopping for one? Browse RV and off-grid solar panels →

Sources

We have not tested these products. Specs, prices, stock and terms are as published on these pages on the date above and can change; check the manufacturer or retailer before you buy.

More RV, off-grid and 12V systems guides

RV, off-grid and 12V systemsWhat Makes Up an RV Electrical System, and Where Does Solar Fit In?An RV runs mainly on DC power stored in a leisure (house) battery. Solar is one way to refill that battery; shore power, the engine's alternator, and…Read the guide →RV, off-grid and 12V systemsHow Many Watts of Solar Does an RV Need for 720 Wh a Day?If the goal is only to replace each day's use, Victron Energy's worked example lands at 144 W. Victron itself calls that not ideal for an RV that…Read the guide →RV, off-grid and 12V systemsHow Many Watts of Solar Does a Shed Actually Need?It depends on what runs inside, not on the shed's floor area. A 20 W LED light for 3 hours, a 5 W camera around the clock, and 60 Wh of tool-battery…Read the guide →RV, off-grid and 12V systemsBefore Adding Solar to a Mobile or Manufactured Home, Where Do You Look First?At the data plate, a paper label fixed inside the home. HUD rules require it to state the roof load zone and wind load zone the home was designed for…Read the guide →RV, off-grid and 12V systemsIn What Order Do You Size the Battery and Panels for an Off-Grid Solar System?Start with daily watt-hours. The battery is sized by how many sunless days it has to cover, and the array by whether it can put that energy back each…Read the guide →RV, off-grid and 12V systemsDoes the Wattage in an Off-Grid Solar Kit's Name Tell You What You Are Buying?No, as two 12 V kits from Renogy show. The 200W Essential Kit's package list has two panels, a PWM charge controller, and cabling, with no battery or…Read the guide →RV, off-grid and 12V systemsWhat Does a Solar Charge Controller Do, and What Do the Numbers in "100/30" Mean?It sits between the panels and the battery and turns the array's output into charging the battery can take. Victron's MPPT controllers lock onto the…Read the guide →RV, off-grid and 12V systemsHow Much More Power Does an MPPT Controller Harvest Than PWM, and When Does the Gap Close?In Victron's worked example, a 100 W, 36-cell panel charging a 12 V battery at 25°C cell temperature yields 81 W through a PWM controller, 19% less…Read the guide →RV, off-grid and 12V systemsFor a 12V Solar Charge Controller, How Far Can Panel Voltage and Wattage Go?"12V" describes the battery side. The panel side has its own limits: on a Victron SmartSolar MPPT 100/30, open-circuit voltage from the array must…Read the guide →RV, off-grid and 12V systemsWhy Does a 12V Solar Setup Need Much Thicker Wire Than a 48V One?Current and cable length set the wire size, and system voltage sets the current. Moving 2,400 W takes 200 A at 12 V but only 50 A at 48 V, so the same…Read the guide →RV, off-grid and 12V systemsWhy Does One Solar Panel Kit Cost $290 and Another $3,200?Mostly because of the battery and the inverter. In Renogy's Solar Kits collection, a 200 W kit with two panels and a charge controller sells for…Read the guide →RV, off-grid and 12V systemsDoes an Inverter on a 12V Solar Kit Drain the Battery Even With Nothing Plugged In?Yes. Victron's Phoenix Inverter 12/375 draws 5.6 W at zero load, about 134 Wh over 24 hours. Renogy's 2,000 W inverter lists a no-load current under…Read the guide →RV, off-grid and 12V systemsWhat Changes When an RV's Victron MultiPlus-II Goes From Shore Power to Battery?On shore power or a generator, the U.S. MultiPlus-II 2x120V passes that AC straight through to the RV's loads and charges the battery at the same…Read the guide →RV, off-grid and 12V systemsCan One 300 W Panel Refill a 12 V, 100 Ah Battery in a Day?On an average day across the year, yes in Phoenix, no in New York or Seattle. Scaling NLR PVWatts per-kilowatt annual output down to 300 W gives about…Read the guide →RV, off-grid and 12V systemsWhat Do the Numbers Next to "100Ah" on a LiFePO4 Battery Spec Sheet Tell You?How capacity shrinks in the cold, the temperatures at which the battery can be charged, the maximum and recommended currents, and the conditions…Read the guide →RV, off-grid and 12V systemsHow Much Do Gel and LiFePO4 Batteries of the Same Size Differ in Weight and Cycle Life?Among Victron's own products, by more than three times in weight and five to seven times in cycle count. The 12 V GEL Deep Cycle 110 Ah weighs 33 kg…Read the guide →RV, off-grid and 12V systemsHow Many Amps Can an RV Lithium Battery Take From the Alternator, Shore Power, and Solar?Using Victron products, up to 50 A from the alternator through an Orion XS 12/12-50A, 30 A from shore power through a Blue Smart IP22 12/30, and up to…Read the guide →RV, off-grid and 12V systemsHow Many Solar Watts Keep a Starlink Mini Online Around the Clock?At the top of the Mini's listed average draw, 40 W, a full day comes to 960 Wh. Run through NLR's PVWatts model for New York, that takes roughly 270 W…Read the guide →RV, off-grid and 12V systemsWhich Ring Cameras Does Each Ring Solar Panel Plug Into?Ring's compatibility list assigns its barrel-plug Solar Panel (2.4W) to one group of cameras and its USB-C Solar Panel and Small Solar Panel to…Read the guide →RV, off-grid and 12V systemsWhy Is Rich Solar's 1600W Kit Built at 24V Instead of 12V?Because its charge controller takes only 800 W of solar at 12 V. The RS-MPPT60 in the 1600 Watt 24V Complete Solar Kit is rated for a maximum solar…Read the guide →RV, off-grid and 12V systemsHow Is BougeRV's Yuma CIGS Panel Different From the 100W Arch Pro?The Yuma 100W is a CIGS thin-film panel with 17% cell efficiency, against 25% for the Arch Pro 100W, so it needs about a fifth more area for the same…Read the guide →RV, off-grid and 12V systemsCan a Harbor Freight Thunderbolt 100W Panel Go Straight to a Battery?The owner's manual says no. The manual for SKU 71049 tells buyers to use an appropriate charge controller, sold separately, whenever the panel is…Read the guide →RV, off-grid and 12V systemsHow Many Miles a Day Can Solar Panels on a Car Add?Toyota says the 185 W solar roof on its latest Prius plug-in hybrid adds up to 8.7 km, about 5.4 miles, of electric range a day, based on annual…Read the guide →

All RV, off-grid and 12V systems guides · All guides and search