Rooftop solar panels on a suburban house under a clear blue sky

Off-grid solar in Montana

Montana off grid: size for December.

Near Billings, 1 kW of panels makes about 1.96 kWh a day in December, 37% of what it makes in July. The essentials need about 1,400 W of panels and a 9.7 kWh battery.

Size my system Cabin and home sizes

Solar data updated October 15, 2026 · All states

Size an off-grid system in Montana

1. Where is the place?

Showing numbers for Montana.

2. What you run each day

RefrigeratorHow many: Refrigerator×2.3 kWh
Chest or upright freezerHow many: Chest or upright freezer×—
LED light bulb (9 W)How many: LED light bulb (9 W)×hours a day180 Wh
Phone charge (15 Wh each)How many: Phone charge (15 Wh each)a day30 Wh
Wi-Fi router (10 W)How many: Wi-Fi router (10 W)×hours a day240 Wh
CPAP with heated humidifier (28 W)How many: CPAP with heated humidifier (28 W)×hours a day—
Laptop (60 W)How many: Laptop (60 W)×hours a day—
TV (typical main TV)How many: TV (typical main TV)×—
MicrowaveHow many: Microwave×—
Well pump (1/3 HP, 1,000 W)How many: Well pump (1/3 HP, 1,000 W)×hours a day—
Furnace blower fan (1/3 HP, 700 W)How many: Furnace blower fan (1/3 HP, 700 W)×hours a day—
12 V compressor coolerHow many: 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

1,400 W

About 4 × 400 W panels. In December, 1 kW of panels in Billings makes about 1.96 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.

Kits you can buy for this in Montana

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.

Recommended · Covers it for the least
Bluetti Apex 300 + B300K + 700 W solar
120/240 V home-style system you can grow to 19 kWh
What's in the cart
- 1 ×Apex 300 (2,764.8 Wh) + B300K battery (2,764.8 Wh) + two 350 W solar panels, Bluetti bundle (opens in a new tab)$3,698
- 2 ×BLUETTI B300K expansion battery for Apex 300 (2,764.8 Wh) (opens in a new tab)$2,158
Add a battery2
BLUETTI B300K expansion battery for Apex 300 (2,764.8 Wh), $1,079 each. Up to 5 (Bluetti: the Apex 300 takes up to six B300K batteries).
- Battery: 3.4 days of your use
- Panels: 50% of December need
- Runs it all at once: yes
- 120/240 V
In December the panels make about 50% of a day's use; the battery covers the gap until it runs low.
Total, 3 items$5,856
11 kWh battery · 700 W of panels
Add this kit to your cart at Bluetti (opens in a new tab)
Opens Bluetti's own cart with all 3 items. You check out on their site. Prices checked Oct 26, 2026.
Another brand that covers it
Jackery Explorer 5000 Plus + 1,000 W solar
120/240 V and 7,200 W output, for well pumps and home circuits
What's in the cart
- 1 ×Explorer 5000 Plus (5,040 Wh) + two SolarSaga 500 X panels, Jackery bundle (opens in a new tab)$4,639
- 1 ×Jackery Battery Pack 5000 Plus (5,040 Wh) (opens in a new tab)$2,599
Add a battery1
Jackery Battery Pack 5000 Plus (5,040 Wh), $2,599 each. Up to 1 (Jackery sells the 5000 Plus as a 10 kWh set with one Battery Pack 5000 Plus; we offer no more than that).
- Battery: 3.1 days of your use
- Panels: 71% of December need
- Runs it all at once: yes
- 120/240 V
In December the panels make about 71% of a day's use; the battery covers the gap until it runs low.
Total, 2 items$7,238
10 kWh battery · 1,000 W of panels
Add this kit to your cart at Jackery (opens in a new tab)
Opens Jackery's own cart with all 2 items. You check out on their site. Prices checked Oct 26, 2026.
Jackery's product description says up to 4,000 W input in its solar section.
Another brand that covers it
EcoFlow DELTA Pro 3 + 2 Extra Batteries + 800 W solar
The DELTA Pro 3 at its full 12.3 kWh
What's in the cart
- 1 ×DELTA Pro 3 (4,096 Wh) + two Smart Extra Batteries (4,096 Wh each), EcoFlow bundle (opens in a new tab)$6,169
- 1 ×Two EcoFlow 400 W portable solar panels (2-pack) (opens in a new tab)$1,099
- Battery: 3.8 days of your use
- Panels: 57% of December need
- Runs it all at once: yes
- 120/240 V
In December the panels make about 57% of a day's use; the battery covers the gap until it runs low.
Total, 2 items$7,268
12 kWh battery · 800 W of panels
Add this kit to your cart at EcoFlow (opens in a new tab)
Opens EcoFlow's own cart with all 2 items. You check out on their site. Prices checked Oct 26, 2026.

Solar output through the year near Billings

kWh per month from 1 kW of panels near Billings, Montana

kWh per month from 1 kW of panels near Billings, Montana
Jan	75 kWh
Feb	92 kWh
Mar	123 kWh
Apr	128 kWh
May	139 kWh
Jun	158 kWh
Jul	165 kWh
Aug	147 kWh
Sep	126 kWh
Oct	103 kWh
Nov	71 kWh
Dec	61 kWh

December gives 61 kWh per kW for the month; July gives 165. A system sized for July would fall short every winter.

Cabin and home sizes in Montana

Off-grid solar and battery size in Montana for three example cabins and homes
Use	A day	Panels	Battery (3 days)
Weekend cabinLights, phones and a 12 V compressor cooler instead of a fridge	492 Wh	250 W	1.7 kWh
Part-time cabinA full-size fridge, Wi-Fi, lights, a laptop and a TV	3.7 kWh	1,860 W	13 kWh
Full-time homeFridge, freezer, well pump, furnace blower, microwave and the rest	11 kWh	5,520 W	38 kWh

See which kits fit each size, or what going off grid costs.

These sizes assume panels at a 20 degree tilt. A steeper tilt, which also sheds snow, catches more low winter sun, and many off-grid homes in the far north run a generator for the darkest weeks rather than buying panels for December alone.

For vans and RVs, see Camper Volts.

Similar winter sun

Frequently asked questions

How much solar do I need to live off grid in Montana?

Size for December. Near Billings, 1 kW of panels makes about 1.96 kWh a day in December in the PVWatts model. A fridge, Wi-Fi, four LED bulbs and two phone charges (2.7 kWh a day) need about 1,400 W of panels and a 9.7 kWh lithium battery for 3 days with little sun. A full-time home with a freezer, well pump and furnace blower needs about 5,520 W and 38 kWh.

Is Montana good for off-grid solar in winter?

Montana ranks 36th of 51 states and DC for December solar output in our model, 11% less than the middle state. December output is 37% of July, the best month here, so a system sized for winter has plenty of spare power in summer.

How big a battery bank do I need off grid in Montana?

Battery size depends on use, not on sun: daily watt-hours × days of storage ÷ the usable share (85% for lithium). For 2.7 kWh a day and 3 days, that is 9.7 kWh. The US Department of Energy advises sizing for cloudy stretches and keeping a backup generator.

Why does winter matter so much for off-grid solar in Montana?

Short days and low sun. To cover the same 2.7 kWh a day, panels near Billings would need only about 520 W in July but 1,400 W in December. Off grid, there is no utility to cover the gap, so the winter number is the one to buy.

Estimates only. Output is modeled near Billings; mountains, coast, shade and snow change it. Size a real system with an installer or an off-grid supplier before you buy. See our disclaimer.

Sources

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.
PVWatts v8 API documentation (National Laboratory of the Rockies) — monthly AC output; 14% system losses
US DOE Energy Saver, Estimating appliance and home electronic energy use (archived copy) — watts × hours a day ÷ 1,000 = kWh a day
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
EIA Residential Energy Consumption Survey 2020, table CE4.6.EL.ST — refrigerators: 839 kWh a year per household
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
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
US DOE Energy Saver, Energy efficient lighting fact sheet (2021) — a 1,100-lumen LED screw-in bulb uses as little as 9 W
EnergySage, How many watts does a Wi-Fi router use? — 5 to 20 W; we use 10 W
TidBITS, iPhone battery-life tables — iPhone 16 battery 13.84 Wh; we use 15 Wh a charge to allow for charging losses
ResMed battery guide (AirSense 10) — 28 W with heated humidifier, about 11 W without
Dometic CFX3 35 specifications — 0.98 Ah an hour at 12 V on a 90°F day
Renogy Deep Cycle AGM Battery 12V 100Ah product page — rated at 50% depth of discharge

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