RV Solar Power: Panel Sizing, Batteries and What Solar Can Actually Run

RV solar power has a simple promise and a persistent misunderstanding. The promise: silent electricity harvested from your roof, every sunny day, with no hookup and no generator. The misunderstanding: panels alone do not power an RV — they refill a battery bank, and it is the battery that runs your evening. Size the two together, in the right order, and solar becomes the backbone of comfortable off-grid camping. Size either one wrong and you have bought expensive roof decoration. This guide works through the sizing maths, the component choices, and an honest list of what solar can and cannot run.

The Order of Operations: Loads, Battery, Then Panels

Step 1 — count your daily loads in amp-hours. The baseline our RV battery guide works out for a typical off-grid evening — furnace fan on a cold night, LED lights, water pump, refrigerator controls, device charging — comes to roughly 75–80 amp-hours per night, before daytime use. Laptop work, a 12V compressor fridge in summer heat, fans and entertainment can carry a full day to 120–200Ah for active full-timers. Your number, measured or honestly estimated, is the foundation of everything else.

Step 2 — size the battery bank to the loads. Batteries are storage, and the usable fraction depends on chemistry: lead-acid gives up about half its nameplate capacity in daily service, lithium (LiFePO4) 80–100%. One night's 80Ah therefore wants roughly 160Ah of lead-acid or a single 100Ah lithium battery, and two nights of autonomy doubles it. That is as far as this guide goes on batteries — chemistry comparisons, charging profiles, care rules and prices live in the battery guide, and solar sizing assumes its numbers.

Step 3 — size the panels to refill the bank. The working rule used by installers: in decent sun, a solar array delivers roughly 25–30 amp-hours per day per 100 watts of panel into a 12V system (about 4–6 effective peak sun hours, after real-world losses). So a rig using 100Ah a day needs roughly 350–400 watts of panel to break even on a sunny day, and 600–800 watts to recover from a cloudy stretch while still living normally. Geography moves the number hard: the desert Southwest in spring can beat the rule by half again; the Pacific Northwest in November may deliver a third of it.

The Components, and What They Cost

Panels: rigid glass panels are cheapest per watt and live permanently on the roof; flexible panels suit curved roofs and save weight at a shorter lifespan; portable folding panels park in the sun while the rig sits in shade — often the smartest first buy. Blended DIY kit pricing commonly runs roughly $0.75–$1.50 per watt for panels as of October 2026, with a complete 400W DIY system (panels, controller, cabling, mounts) typically landing around $700–$1,500 in parts.
Charge controller: the MPPT type is the correct default — it harvests meaningfully more than the cheap PWM type, especially in cold bright weather — and it must be sized to the array and matched to your battery chemistry's charging profile.
Inverter: sizes to the loads you want in AC, not to the panels. A 2,000–3,000W pure sine wave inverter covers a microwave or hair dryer one at a time; it also sips power at idle, so switch it off when unused.
Monitoring: a shunt-based battery monitor is not optional equipment for a solar rig — it is how you know the system's actual state, because lithium's flat voltage curve makes voltage readings nearly meaningless.

Professional installation of a mid-size system (600–800W, lithium bank, inverter) is a several-thousand-dollar job all-in — typically roughly $3,000–$8,000 as of October 2026 depending on the battery capacity chosen — and you can find solar installers and RV electrical specialists through the RV Frontier provider directory.

What Solar Can Actually Run

With a sensibly sized system — say 600W of panel, 200–300Ah of lithium, and a 2,000W+ inverter — solar comfortably runs: all LED lighting, the water pump, furnace and fridge fans, a 12V compressor refrigerator around the clock, laptops, phones, TV, fans, a CPAP machine overnight, and short bursts of microwave or coffee maker through the inverter. Solar struggles with: roof air conditioning (roughly 1,200–1,800 watts sustained — possible only with very large arrays and battery banks, and even then measured in hours, not days), electric space and water heating, and anything with a heating element you hoped to run for hours. The honest headline: solar replaces the generator for everything except air conditioning and deep-winter heating loads, and many boondockers keep a small generator purely as the cloudy-week backup. That pairing — solar first, generator rarely — is the standard architecture in serious boondocking setups, and it is also why solar-equipped rigs feature prominently among the listings buyers browse on RV Frontier: the work is done, and the receipts show in the asking price.

Roof-Mounted, Portable, or Both

Where the panels live changes what the system is like to own. Roof-mounted panels are fit-and-forget: always deployed, always charging on travel days, nothing to store or set up — but they harvest whatever the parking spot offers, and the best campsites are often shaded. Portable panels (suitcase kits and folding blankets, typically 100–200W) chase the sun while the rig sits in the shade, tilt perfectly at the low winter sun, and leave with you if you change rigs — at the cost of setup every stop, storage space, and a cable run someone can trip over or walk off with. Many experienced boondockers run both: a modest roof array that handles the baseline, plus a portable panel aimed at the morning sun for the top-up. If the budget forces a choice, weekenders usually get more from portable; full-timers living off-grid for weeks usually get more from the roof.

Winter, Latitude and Honest Derating

Panel ratings are laboratory numbers — full sun, panel cool, sun directly overhead. Real output is the rating multiplied by the sun you actually get. In the northern states and Canada in December and January, expect short days, a low sun angle and frequent cloud to cut daily harvest to a fraction of the summer figure; the same 600W array that sails through a June in Utah may deliver a quarter of that in a grey Michigan January. Cold panels themselves are slightly more efficient, which does not rescue a short day. Practical winter answers, in order: tilt the panels if your mounts allow it, add portable panels you can aim, trim loads ruthlessly (the furnace fan is already eating the budget), and accept the generator's role in deep winter rather than sizing an enormous array for the worst fortnight of the year. Size for the typical month; survive the worst week with the backup.

Roof Space, Shade and Other Reality Checks

Measure your roof before falling in love with a wattage: vents, air conditioners and skylights fragment the usable area, and a fifth wheel's long roof may take 1,200W+ where a camper van manages 300–400W. One shaded panel in a series string can drag the string's output down disproportionately, which is why larger installs use parallel wiring or multiple controllers. Tilt helps in winter and at northern latitudes; most travellers accept flat mounting and the 10–25% seasonal penalty for the simplicity. Finally, protect the investment the way our maintenance guidance recommends for roofs generally — panel mounts are roof penetrations, and their sealant joins the inspection routine.

The Bottom Line

Solar is arithmetic, not magic: count your amp-hours, store at least a night and a half of them in a battery bank you understand, fit enough panel to refill that bank in a normal sunny day, and keep expectations honest about air conditioning. Do it in that order and the system disappears into the background of the trip — which is exactly what good RV solar power is supposed to do.