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Off-grid solar

Size it for December. Then it works all year.

An off-grid fridge, Wi-Fi, lights and phones need about 1,250 W of panels and a 9.7 kWh battery in Maryland. Your state's winter sun changes that a lot. Work out yours.
Size my systemEvery state

Solar data updated · How we calculate this

Your loads, your state

2. What you run each day
  • Refrigerator2.3 kWh
  • Chest or upright freezer—
  • LED light bulb (9 W)180 Wh
  • Phone charge (15 Wh each)30 Wh
  • Wi-Fi router (10 W)240 Wh
  • CPAP with heated humidifier (28 W)—
  • Laptop (60 W)—
  • TV (typical main TV)—
  • Microwave—
  • Well pump (1/3 HP, 1,000 W)—
  • Furnace blower fan (1/3 HP, 700 W)—
  • 12 V compressor cooler—

Hours are example settings. Change them to how you live. Watts × hours a day = watt-hours (Wh) a day.

3. Days the battery must last with little sun
4. Battery type

Your use

2.7 kWh a day

Solar panels

1,250 W

About 4 × 400 W panels. In December, 1 kW of panels in Baltimore makes about 2.20 kWh a day.

Battery bank

9.7 kWh

2.7 kWh × 3 days ÷ 85% usable.

Sized for December, the darkest month. The rest of the year you will have spare power. The US Department of Energy also advises a backup generator for long cloudy spells.

Off-grid solar in Maryland

Kits you can buy for this

Complete kits from each brand's own store: the power station, batteries and that brand's own panels. One button puts every item in the brand's cart; you review and check out on their site. Prices checked Oct 26, 2026 and they change.

Disclosure: We may earn a commission if you buy through these links. It never changes our recommendations. How we make money.

How the calculation works

Daily use (Wh) = watts × hours a day, added up for everything you run. That is the US Department of Energy's method. For fridges, freezers, TVs and microwaves we use the average yearly use from the EIA's 2020 household survey, divided by 365, because they cycle on and off.

Panel watts = daily use ÷ December kWh per kW per day.The December figure is the PVWatts model's output for 1 kW of south-facing panels at a 20 degree tilt near the city shown for each state, already net of 14% system losses and 96% inverter efficiency. We divide the December total by 31 days.

Battery = daily use × days with little sun ÷ usable share. We count 85% of a lithium battery's rated capacity as usable (the same figure we use across the site for power stations) and 50% for lead-acid AGM, the depth Renogy rates its AGM battery at.

Panels on a steeper tilt, which suits snowy places, catch more low winter sun than our 20 degree model. Shade from trees or hills cuts output, and short winter days hit hardest. If you can, check your exact site in the free PVWatts calculator.

For vans and RVs, see Camper Volts.

Off-grid solar size in every state

The essentials (2.7 kWh a day: a fridge, Wi-Fi, four LED bulbs for 5 hours and two phone charges), sized for December with 3 days of lithium storage. Weakest winter sun first.

Off-grid solar panel and battery size by state for an essentials load in December
StateModeled nearDecember kWh per kW a dayPanelsBattery
AlaskaAnchorage0.2312.0 kW9.7 kWh
WashingtonSeattle1.132,430 W9.7 kWh
OregonPortland1.262,170 W9.7 kWh
VermontBurlington1.451,890 W9.7 kWh
MichiganDetroit1.461,890 W9.7 kWh
WisconsinMilwaukee1.551,770 W9.7 kWh
IdahoBoise1.671,640 W9.7 kWh
MinnesotaMinneapolis1.691,630 W9.7 kWh
North DakotaFargo1.721,600 W9.7 kWh
IllinoisChicago1.831,500 W9.7 kWh
OhioColumbus1.841,500 W9.7 kWh
IndianaIndianapolis1.851,480 W9.7 kWh
ConnecticutBridgeport1.901,450 W9.7 kWh
West VirginiaCharleston1.941,420 W9.7 kWh
MainePortland1.951,410 W9.7 kWh
MontanaBillings1.961,400 W9.7 kWh
KentuckyLouisville2.001,370 W9.7 kWh
Rhode IslandProvidence2.001,370 W9.7 kWh
New JerseyNewark2.041,350 W9.7 kWh
New YorkNew York City2.051,340 W9.7 kWh
New HampshireManchester2.061,330 W9.7 kWh
MassachusettsBoston2.081,320 W9.7 kWh
South DakotaSioux Falls2.131,290 W9.7 kWh
PennsylvaniaPhiladelphia2.181,260 W9.7 kWh
DelawareWilmington2.181,260 W9.7 kWh
MarylandBaltimore2.201,250 W9.7 kWh
IowaDes Moines2.211,250 W9.7 kWh
TennesseeNashville2.321,190 W9.7 kWh
NebraskaOmaha2.331,180 W9.7 kWh
District of ColumbiaWashington2.371,160 W9.7 kWh
VirginiaVirginia Beach2.491,100 W9.7 kWh
UtahSalt Lake City2.501,100 W9.7 kWh
MissouriKansas City2.511,100 W9.7 kWh
AlabamaBirmingham2.551,080 W9.7 kWh
GeorgiaAtlanta2.561,070 W9.7 kWh
ArkansasLittle Rock2.611,050 W9.7 kWh
North CarolinaCharlotte2.641,040 W9.7 kWh
MississippiJackson2.721,010 W9.7 kWh
South CarolinaCharleston2.751,000 W9.7 kWh
WyomingCheyenne2.77990 W9.7 kWh
TexasHouston2.90950 W9.7 kWh
KansasWichita2.93940 W9.7 kWh
LouisianaNew Orleans2.96930 W9.7 kWh
FloridaJacksonville3.00920 W9.7 kWh
OklahomaOklahoma City3.04910 W9.7 kWh
ColoradoDenver3.08890 W9.7 kWh
CaliforniaLos Angeles3.42800 W9.7 kWh
NevadaLas Vegas3.42800 W9.7 kWh
ArizonaPhoenix3.57770 W9.7 kWh
New MexicoAlbuquerque3.70740 W9.7 kWh
HawaiiHonolulu4.05680 W9.7 kWh

What to do with the numbers

Under about 1,000 W of panels and a few kWh of battery, an all-in-one portable power station with solar input can do the job. See what size cabin solar kit you need. Bigger than that, you are looking at a component system with a separate inverter and battery bank, plus a backup generator, as the US Department of Energy advises.

Comparing that with the cost of bringing in a power line? See how to go off grid.

Frequently asked questions

How do I size an off-grid solar system?

Add up the watt-hours you use in a day (watts × hours for each appliance, the US Department of Energy method). Divide by what 1 kW of panels makes in a December day where you live to get panel watts. Then multiply the daily use by the days you want to ride through with little sun and divide by the share of the battery you can use (85% for lithium) to get battery size. Our calculator does all three with PVWatts output for your state.

Why size for December instead of the yearly average?

An off-grid system has no grid to fall back on, so it must keep up in the darkest month. December is the lowest-output month in our PVWatts model in all 50 states and DC (in West Virginia January ties it). In Maryland, 1 kW of panels makes about 2.20 kWh a day in December, only 47% of what it makes in June. Size for the yearly average and the batteries run flat every winter.

How many solar panels do I need to run a fridge off grid?

A typical US fridge uses about 2.3 kWh a day (EIA: 839 kWh a year). In Maryland in December that takes about 1,040 W of panels, or 3 panels of 400 W. In Alaska, with the weakest December sun, it takes about 10.0 kW.

How many days of battery storage do I need off grid?

There is no single rule. The US Department of Energy advises sizing batteries for cloudy stretches and keeping a backup generator. We start at 3 days. Pick more if your winters bring long runs of cloud, fewer if you have a generator you are happy to run.

Can I use lead-acid batteries off grid?

Yes, but you need a bigger bank. Renogy rates its AGM deep-cycle battery at 50% depth of discharge, against the 85% of rated capacity we count as usable for lithium. So the same days of storage take about 1.7 times the rated capacity in AGM.

Estimates only. Real output depends on your exact site, panel angle, shade, snow and equipment. Size a real system with an installer or an off-grid supplier before you buy. See our disclaimer.

Sources

  1. PVWatts v8 solar model (National Laboratory of the Rockies, formerly NREL, run via its PySAM package) on NASA POWER hourly weather — monthly output per kW by state, average of 2015-2024 hourly weather; 1 kW DC fixed roof mount, 20 degree tilt, facing south (180 degrees), standard module, 14% system losses, 96% inverter efficiency, DC/AC ratio 1.2 (PVWatts defaults except tilt). Checked against the PVWatts web API for eight states: within 8%, 3% on average.
  2. PVWatts v8 API documentation (National Laboratory of the Rockies) — monthly AC output; 14% system losses
  3. US DOE Energy Saver, Estimating appliance and home electronic energy use (archived copy) — watts × hours a day ÷ 1,000 = kWh a day
  4. US DOE Energy Saver, Balance-of-system equipment for renewable energy systems (archived copy) — balance-of-system equipment (batteries, controllers, inverters, wiring) could be half of a stand-alone system's cost; size batteries for cloudy weather, with a backup generator
  5. EIA Residential Energy Consumption Survey 2020, table CE4.6.EL.ST — refrigerators: 839 kWh a year per household
  6. EIA Residential Energy Consumption Survey 2020, table CE5.3b (detailed electricity end use) — separate freezers 570 kWh, most-used TV 210 kWh, microwaves 107 kWh a year per household
  7. Eugene Water & Electric Board, Generator sizing considerations — running and starting watts: well pump 1/3 HP 1,000 W (+2,000 W to start), furnace fan blower 1/3 HP 700 W (+1,400), refrigerator/freezer 700 W (+2,200), microwave 1,000 W, laptop 60 W, phone charger 20 W
  8. US DOE Energy Saver, Energy efficient lighting fact sheet (2021) — a 1,100-lumen LED screw-in bulb uses as little as 9 W
  9. EnergySage, How many watts does a Wi-Fi router use? — 5 to 20 W; we use 10 W
  10. TidBITS, iPhone battery-life tables — iPhone 16 battery 13.84 Wh; we use 15 Wh a charge to allow for charging losses
  11. ResMed battery guide (AirSense 10) — 28 W with heated humidifier, about 11 W without
  12. Dometic CFX3 35 specifications — 0.98 Ah an hour at 12 V on a 90°F day
  13. Renogy Deep Cycle AGM Battery 12V 100Ah product page — rated at 50% depth of discharge

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Photo: Watt A Lot on Unsplash (Unsplash License).