How Much Solar Do I Need for My RV? Sized for the Month You Camp In

The month decides it, not the rig. On 1,500 Wh a day and a lithium bank, Quartzsite in December needs about 663 W of panel and the same rig in June needs 243 W. Size on the annual average everyone quotes and a December trip gets roughly half the power it needs — and in Seattle, no array that fits an RV roof will do it at all.

Download the monthly peak-sun-hours chart

Keep the 14-location chart for planning your next trip. It highlights the location and month selected above and includes all twelve months plus the annual average. Download a one-page landscape PDF in US Letter or A4, or print it in your browser. These are NASA averages for the named locations, not statewide figures or a forecast for your travel dates.

RV solar peak-sun-hours chart

Monthly average daily solar resource for flat panels at 14 U.S. locations. These are location samples, not state averages.

Reference chart: choose a location and month in the calculator to highlight them here.

All figures are peak sun hours per day. Ann = annual average. An asterisk (*) marks the selected location and period.

Location	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Ann
Quartzsite, AZ	3.48	4.50	5.94	7.29	8.16	8.49	7.63	7.11	6.24	5.04	3.79	3.11	5.90
Phoenix, AZ	3.43	4.43	5.89	7.28	8.17	8.50	7.49	6.91	6.16	5.01	3.78	3.08	5.85
Los Angeles, CA	3.16	4.04	5.38	6.65	7.49	8.10	7.93	7.45	6.26	4.79	3.57	2.86	5.65
Moab, UT	2.67	3.56	5.15	6.50	7.50	8.30	7.53	6.68	5.75	4.34	3.08	2.32	5.29
Orlando, FL	3.45	4.08	5.22	6.13	6.48	5.78	5.71	5.42	4.93	4.43	3.64	3.12	4.87
Denver, CO	2.59	3.54	4.73	5.77	6.47	7.22	7.00	6.31	5.37	3.98	2.87	2.29	4.85
Austin, TX	3.05	3.51	4.50	5.44	5.85	6.70	6.73	6.36	5.20	4.34	3.25	2.74	4.81
Asheville, NC	2.62	3.25	4.27	5.39	5.86	6.20	5.83	5.41	4.69	3.84	2.96	2.28	4.39
Bend, OR	1.51	2.45	3.57	5.03	6.15	7.11	7.72	6.56	4.91	3.12	1.76	1.26	4.27
Minneapolis, MN	1.81	2.97	3.68	4.66	5.42	6.04	6.40	5.36	4.15	2.72	1.77	1.31	3.86
Bar Harbor, ME	1.59	2.43	3.63	4.58	5.28	5.60	5.80	5.20	4.19	2.68	1.69	1.25	3.66
Kalispell, MT	1.08	2.03	3.11	4.42	5.52	5.97	7.08	5.79	4.05	2.37	1.17	0.82	3.62
Seattle, WA	1.03	1.92	2.85	4.15	5.25	5.73	6.33	5.40	3.91	2.28	1.22	0.85	3.42
Anchorage, AK	0.28	0.90	2.41	4.03	4.95	5.32	4.76	3.77	2.39	1.08	0.38	0.14	2.54

One peak sun hour represents 1 kWh/m² at 1,000 W/m². These figures describe solar energy, not daylight hours or hours at full panel output.

Use the lowest monthly value among the months you plan to camp. Long-term averages are not a forecast or a guaranteed minimum; cloudy spells need battery reserves or another charging source.

Campsite shade, tilt, panel temperature and system losses change output. Use the calculator for estimated array size; check your actual location if it is not listed.

Trip / location: __________________________ Months: ______________ Backup charging: __________________________

Source: NASA POWER, ALLSKY_SFC_SW_DWN, SYN1DEG; January 2001–December 2020 climatology. All 14 locations rechecked October 4, 2026; rounded to two decimals.

NASA POWER climatology documentation; location names link to their source data

rvtrove.com/electrical/how-much-solar-do-i-need-for-my-rv/

The annual average is nobody’s month

Monthly average peak sun hours per day for a flat surface. Change the location and month in the calculator to update this chart.

December: 3.11 h/day — 53% of the annual average (5.90 h/day).

Dashed line: annual average 5.90 h/day. An asterisk (*) marks your month.

Month	0369Bar, 0 to 9 hours	h/day
Jan		3.48
Feb		4.50
Mar		5.94
Apr		7.29
May		8.16
Jun		8.49
Jul		7.63
Aug		7.11
Sep		6.24
Oct		5.04
Nov		3.79
Dec*		3.11

Peak sun hours measure daily solar energy, not daylight duration or hours at full panel output. These long-term averages are not a forecast or a guaranteed minimum. Use the lowest monthly value among the months you plan to camp, then account for shade and system losses.

Source: NASA POWER location data, ALLSKY_SFC_SW_DWN, SYN1DEG. 20-year Meteorological and Solar Monthly & Annual Climatologies (January 2001 - December 2020); the same October 4, 2026 data snapshot used by the calculator and printable chart.

Every guide picks one peak-sun-hours figure — “four to five hours” is the usual phrasing — or an annual average, and divides daily watt-hours by it.

Here is what the months actually look like, from NASA’s monthly climatology:

Place	Annual	December	Sized on annual, December gets
Quartzsite, AZ	5.90	3.11	53% of what it needs
Denver, CO	4.85	2.29	47%
Bend, OR	4.27	1.26	30%
Seattle, WA	3.42	0.85	25%
Anchorage, AK	2.54	0.14	6%

Nobody camps in the annual average. If you go south for the winter, Quartzsite in December is your design month and the annual figure under-sizes you by nearly half. If you only ever go out in July, the annual figure over-sizes you and you have paid for panels you will never use.

The annual average is wrong in both directions. It is only ever right by accident.

Flat to the roof, not tilted to the sun

The second problem is subtler and it runs the same way.

Published sun-hour tables are almost always for a tilted, south-facing plane, because that is how a house array is mounted. An RV’s panels are bolted flat to the roof, and a flat panel collects global horizontal irradiance — a different, lower number.

The gap is widest exactly when it hurts most. In midsummer the sun is high and a flat panel loses little. In December the sun is low, a tilted panel gains a great deal from facing it, and a flat one does not.

One thing that needs no conversion: kWh/m²/day and peak sun hours are the same number. A peak sun hour means an hour at 1,000 W/m², which is the irradiance a panel’s rating is measured at, so 3.11 kWh/m²/day is 3.11 peak sun hours.

Roof area is the real limit

On an RV, panels do not run out because of money. They run out because of space.

A Victron 150 W panel is 1485 × 668 mm — 10.68 square feet each. Denver in December, on 1,500 Wh a day, needs seven of them: 74.7 square feet.

Usable roof is much less than the roof looks. Subtract the air conditioner, the vents, the skylight, the antenna and the fridge vent, and a 25-foot trailer might offer 60 square feet of clear run in awkward strips. The calculator asks for that number rather than assuming it, and it picks the panel that uses the least roof area rather than the one with the most watts — which is why a 190 W panel in the same footprint as a 150 W beats it, even though both “work”.

The derate, and the one number nobody publishes

The sum needs a factor for everything the laboratory rating does not include: soiling, shading, mismatch, wiring loss and panel temperature.

This page uses 0.75, and that is the only number on it that nobody publishes. It is the figure our battery charge time calculator already uses, reused so the two cannot disagree, and it is flagged in the result rather than buried.

What is published is one component of it. Victron gives a temperature coefficient of maximum power of −0.45% per °C, so a panel well above its 25°C rating gives up real output. But Victron publishes no NOCT for its panels, and where a maker does publish one, it is measured on an open, free-standing rack at 20°C air, 800 W/m² and a 1 m/s breeze — the conditions Victron’s own white paper lists — not lying flat on a roof. So there is no sourced way to turn an air temperature into a cell temperature on an RV, and this page names the coefficient rather than inventing the temperature to apply it to.

It is also why the calculator recommends rigid panels only. A flexible panel glued flush to the roof runs hotter than any derate here allows for — Victron puts the loss at 2 to 15% against a panel with air underneath — and no maker publishes the figure for its own panel. Flexible vs rigid RV solar panels covers what each maker does say.

Everything else in the calculation comes from a manufacturer or from NASA: charge efficiency, the controller’s 98%, the panel ratings, and the sun.

The two numbers this page does not work out

Solar sizing gets tangled with two neighbouring questions, and keeping them apart is most of what makes the answer usable.

Your daily watt-hours. Everything here scales directly off that one figure, and this page takes it as given rather than guessing at it. If you are working from “we run a 12V fridge, some lights and charge two laptops”, our amp draw calculator turns an appliance list into watt-hours. Get this wrong and every number on this page is wrong by the same proportion — it is the input worth spending ten minutes on.

The battery bank. Panels and batteries answer different questions. The array decides how much you can put back in a day; the bank decides how long you can go without putting anything back, and how much of a cloudy week you can ride out. A big array on a small bank spends the morning full and throws the afternoon away; what size lithium battery for an RV sizes the other half, and the cold that costs you sun in December costs you capacity at the same time.

The third neighbour is the charge controller, and it is the one that can be damaged by getting it wrong rather than merely disappointing — what size solar charge controller covers it.

When the honest answer is “solar cannot do this”

Ask for Seattle in December and the arithmetic returns 2,425 W of panel across 181 square feet. That is not a recommendation, it is a reductio — and the calculator says so instead of printing it as a target.

What it does instead is tell you what your roof can do. Five 150 W panels in Denver in December return about 1,250 Wh a day against 1,500 Wh of use: a gap of 250 Wh that no amount of flat panel closes in that month, because the roof is already full. That gap is the useful number, because it is what the alternator, a pedestal, or a generator has to cover.

There is one roof-side lever left, and it is angle. NASA POWER also publishes irradiance on tilted planes, and for Denver in December it puts a south-facing panel tilted to the latitude at 77% more than the same panel lying flat — is tilting RV solar panels worth it works that out for every month and place here. Applied to the same five panels, that is roughly 2,200 Wh a day — enough to close the gap. The catch is that it only holds while you are parked, with panels that tilt, facing south and unshaded; and in June the same tilt loses about 12% against flat, because the sun is already overhead. This calculator sizes the flat roof, because that is what you have when you arrive. A portable kit on a factory side port gets round the roof altogether — and what that port is wired to decides which kits fit. If you are buying panels and a controller together, the panels-and-kits roundup checks each kit’s panels against the controller it ships with.

Filling the roof and accepting the gap is usually the right call. So is going south — or, in winter, tilting.

Model	Rated	Size	Weight	Open circuit	Short circuit	Buy
BlueSolar 95W	95 W at STC, ±3% tolerance	770 x 668 x 30 mm	5.4 kg	20.4 V	5.7 A	Check price(opens in a new tab)
BlueSolar 130W	130 W at STC, ±3% tolerance	1020 x 668 x 30 mm	7.1 kg	24.8 V	6.53 A	Check price(opens in a new tab)
BlueSolar 150W	150 W at STC, ±3% tolerance	1485 x 668 x 30 mm	11.0 kg	22.3 V	8.69 A	Check price(opens in a new tab)
BlueSolar 190W	190 W at STC, ±3% tolerance	1485 x 668 x 30 mm	10.5 kg	25.5 V	9.17 A	Check price(opens in a new tab)
BlueSolar 285W	285 W at STC, ±3% tolerance	1550 x 880 x 35 mm	14.32 kg	38.9 V	9.08 A	Check price(opens in a new tab)

Where this goes wrong

• Sizing on the annual average. Nobody camps in it, and in December it under-sizes by two to four times across most of the country.
• Using a tilted sun-hour figure for a flat roof. Those tables are for house arrays. Most RV panels are bolted flat, and even ones that tilt are flat while you drive.
• Measuring the roof rather than the clear space on it. The air conditioner and the vents take the middle of it.
• Buying on watts instead of square feet. Two panels of the same footprint can differ by 40 W; on a full roof that is free power.
• Guessing the daily load. Every figure on this page scales directly off it — our amp draw calculator works it out from your appliances.
• Forgetting the controller. An array that fits the roof can still take the controller over its voltage limit on a cold morning: what size solar charge controller checks the voltage side.
• Blaming the array for a fault. If panels sized for the month deliver almost nothing in clear sun, the sizing is rarely the reason — a full battery, a cold lithium BMS or a blown fuse is far more likely, and four readings at the controller tell them apart.

Questions worth answering