Check the math before a calculator result becomes advice.

Installed solar target

Daily watt-hours are divided by expected peak-sun hours, increased for real-world RV losses, then rounded up to full 200W-class panels so the watt target matches the roof-panel count.

panel watts = ceil(round up((daily Wh / peak sun hours) x 1.2) / 200W) x 200W

Estimated daily harvest

Installed panel watts are derated for flat mounting, heat, dust, wiring loss, and non-perfect operating conditions.

daily harvest Wh = panel watts x peak sun hours x 0.78

Battery target

Daily watt-hours are converted into amp-hours at 12V and adjusted by battery chemistry and desired autonomy.

battery Ah = daily Wh / 12V / usable depth x autonomy days

RV panels are usually flat-mounted and exposed to heat, dust, wiring loss, shade, and imperfect sun angles.

A small margin keeps the recommendation from depending on lab-rated panel output.

Listed amp-hours are not the same as practical off-grid reserve.

Effective system cost

Solar hardware and installation are added together, then reduced by replacement value the owner would have spent anyway.

effective cost = hardware cost + install labor - avoided replacement value

Annual net savings

Generator fuel, generator maintenance, and avoided paid nights are added, then annual maintenance is subtracted.

annual net savings = generator fuel savings + generator maintenance savings + campground savings - annual maintenance

Simple payback

The effective cost is divided by annual net savings when the savings are positive.

payback years = effective cost / annual net savings

This is usually the easiest number to over-credit. Solar only saves campground fees when it changes a paid night into a lower-cost dry-camping night.

Fuel alone understates generator cost, but maintenance cost varies by generator type, oil interval, load, age, and owner behavior.

Resale may help the ownership-window value, but it is not counted as yearly cash savings or guaranteed payback.

Usable roof area

The roof rectangle is reduced by edge setbacks, obvious obstructions, and a layout buffer for real-world spacing.

usable sq ft = ((roof length - setbacks) x (roof width - setbacks) - obstruction sq ft) x (1 - buffer)

Panel count

Portrait and landscape panel counts are estimated from the adjusted roof rectangle, then capped by usable area.

panel count = min(rectangle fit count, floor(usable sq ft / panel sq ft))

Controller target

Installed watts are converted into a conservative MPPT output-current target at the selected battery voltage.

controller amps = round up((installed watts / battery voltage) x 1.25)

Simple square-foot math misses rails, roof curves, service paths, brackets, wire routing, and awkward obstruction shapes.

The fitted roof watts still need a real-world RV harvest derate for heat, flat mounting, dust, wiring, shade, and controller behavior.

The calculator screens panel choices before purchase, but the final roof layout still needs tape-measure verification.

Raw sun-hour window

Panel nameplate watts are multiplied by entered peak-sun hours before real-world losses are applied.

raw Wh = solar watts x peak sun hours

Seasonal ideal tilt

The ideal tilt estimate starts with latitude, then adjusts higher for winter and lower for summer.

ideal tilt = latitude + season offset

Adjusted harvest

Tilt, orientation, shade, dirt, and system losses are multiplied together so stacked penalties are visible.

harvest Wh = raw Wh x tilt factor x orientation factor x shade factor x soiling factor x system factor

Lower winter sun makes flat RV panels less productive, especially in desert and shoulder-season camping.

A flat panel does not meaningfully face south, east, or west the way a tilted portable panel does.

Partial shade can be non-linear, so the entered shade percentage should reflect output loss rather than just shaded panel area.

Cold Voc per panel

Panel open-circuit voltage rises below the 25C spec-sheet test temperature, so cold-weather Voc is adjusted by the entered coefficient.

cold Voc = panel Voc x (1 + (25C - coldest C) x coefficient)

Maximum safe series count

The controller PV voltage limit is reduced by a small cushion, then divided by cold Voc per panel.

max series panels = floor((controller max Voc x 0.95) / cold Voc)

Parallel current

Each parallel string adds panel short-circuit current, which is compared against the entered controller PV input-current limit.

array Isc = parallel strings x panel Isc

Cold-weather Voc estimates depend on accurate panel specs and temperature assumptions, so a small cushion avoids designing exactly on the limit.

A controller can be voltage-safe while still clipping or exceeding the entered output-current target.

The calculator is only as accurate as the exact panel data sheet, controller manual, and cold-weather assumption entered.

Daily appliance load

Each appliance is watts multiplied by hours per day, then the rows are added together.

daily Wh = sum(appliance watts x hours/day)

Loss-adjusted load

A 12% system-loss buffer is added so inverter and wiring losses do not disappear from the plan.

adjusted daily Wh = daily Wh + round up(daily Wh x 0.12)

Required amp-hours

Adjusted daily watt-hours are multiplied by autonomy days and converted into amp-hours at the chosen bank voltage.

required Ah = adjusted daily Wh x autonomy days / voltage / usable depth

Inverters, chargers, wiring, and conversion losses make real battery demand higher than raw appliance math.

Module count is a layout sanity check, not a product recommendation.

Large 12V parallel banks can become harder to protect, balance, and service cleanly.

Usable capacity

Nominal watt-hours are multiplied by practical usable-depth assumptions so sticker amp-hours are not treated as equal.

usable Wh = battery count x Ah each x bank voltage x usable depth

Lifetime usable kWh

Usable kWh is multiplied by entered cycle life, then battery and charger costs are divided across that lifetime energy estimate.

cost per usable kWh-cycle = total entered cost / (usable kWh x cycle life)

Runtime comparison

Usable watt-hours are divided by the entered daily load to estimate reserve before recharge.

days from bank = usable Wh / daily Wh

Lead-acid and lithium batteries can have the same amp-hour label but very different practical off-grid reserve.

Cycle value only matters if the bank is used enough to make replacement pressure visible.

Converters, solar controllers, DC-DC chargers, alternator protection, shunts, cabling, and labor can change the value case more than battery price alone.

Energy to replace

The state-of-charge gap is converted into watt-hours from bank amp-hours and voltage.

Wh to replace = battery Ah x bank voltage x ((target SOC - current SOC) / 100)

Effective charge watts

Charge-source output is derated so the result does not assume ideal charger, wiring, and environmental conditions.

effective watts = source watts x charge-source derate

Solar days to target

For solar, daily loads are subtracted from derated daily harvest before estimating refill days.

solar days = Wh to replace / max(0, daily solar harvest Wh - daily load Wh)

Flat RV panels rarely hold lab-rated output once heat, angle, dust, shade, controller behavior, and wiring losses are included.

Charger output, AC-to-DC conversion, wiring, and battery acceptance usually reduce usable refill power.

AGM batteries and some lithium/BMS/charger combinations slow near the target SOC, especially close to full.

Alternator input draw

The requested charger output is converted to 12V alternator-side current after charger efficiency is included.

alternator input amps = charger output amps x battery voltage / 12V / charger efficiency

Safe alternator allowance

The alternator rating is reduced by the reserve percentage so the house charger does not claim the whole alternator.

safe input amps = alternator rated amps x (1 - reserve percent)

Drive-day recovery

The recommended charger amps are converted into usable charging watts, then multiplied by the entered drive hours.

Wh recovered = recommended charger amps x battery voltage x charger efficiency x drive hours

Headlights, HVAC blower, engine electronics, fans, and heat already consume alternator output before the house bank starts charging.

A charger can be too large for the battery chemistry or bank size even if the alternator appears to support it.

The calculator flags a planning gauge, but final wire and fuse sizing still needs device manuals, routing, insulation, temperature, and terminal limits.

Running load

The battery charger draw is added to every listed AC load that may run at the same time.

running watts = charger watts + simultaneous AC load watts

Startup load

The calculator adds the largest single startup delta to the running load instead of assuming every motor starts at once.

startup watts = running watts + largest(startup watts - running watts)

Altitude derate

The entered derate percentage reduces generator running and surge output before margins are checked.

effective watts = generator watts x (1 - altitude derate percent)

Portable generators often lose output at elevation. The exact value should come from the generator manual when available.

Small changes in fuel quality, heat, dirty air filters, charger settings, and appliance startup behavior can consume thin margins.

The estimate assumes the largest compressor or motor starts while other loads are already running. Multiple simultaneous starts can be worse.

Service watts

The service amperage is multiplied by voltage and by the number of 120V legs available.

service watts = amps x pedestal voltage x service legs

Continuous target

Total service watts are reduced by the chosen continuous-load percentage before sustained loads are judged comfortable.

continuous target watts = service watts x continuous target percent

Load stack

The entered appliance watts and charger watts are added together before margin and load-shedding advice are calculated.

total load watts = appliance watts + battery charger watts

The calculator checks total wattage for 50A service, but a real RV panel can still have one leg overloaded while total watts look fine.

Air conditioners, water heaters, space heaters, and battery chargers can be sustained loads that deserve more margin than a quick microwave burst.

A dogbone adapter lets the cord connect, but the RV still has to fit the actual service feeding it.

Effective DC charging

The charger amperage and bank voltage are multiplied by a conservative generator-charging efficiency factor.

effective charge watts = charger amps x battery voltage x 0.82

Generator AC load

The charger AC draw is estimated from DC output, then other AC loads are added so headroom is visible.

total AC load watts = ((charger amps x battery voltage) / 0.82) + other AC loads

Runtime and fuel

The daily energy gap is divided by effective charge watts, then multiplied by the fuel-burn rate and trip length.

daily runtime hours = daily energy gap Wh / effective charge watts; trip fuel = runtime x burn rate x days

Converter and inverter-charger efficiency, wiring, charger profile, and battery acceptance keep generator charging from matching ideal paper output.

Startup surges, altitude, heat, eco-mode behavior, and extra AC loads make a generator uncomfortable near its rating.

Fuel use varies heavily by model and load, so the calculator should be adjusted after a real measured camp test.

Furnace daily BTU

Furnace rating is multiplied by the hours it may run and the estimated burner duty cycle.

furnace daily BTU = furnace BTU/hr x furnace hours/day x duty cycle

Daily propane pounds

Daily BTU demand is divided by a practical propane energy-content estimate.

daily propane lb = total daily BTU / 21,600 BTU per lb

Runtime after reserve

Tank capacity is reduced by the chosen reserve before dividing by daily propane use.

estimated days = propane lb x (1 - reserve %) / daily propane lb

RV cylinders are usually labeled in pounds, while onboard tanks and refill planning often use gallons.

Weather, insulation, wind, thermostat setting, slide-outs, and door openings move furnace use more than the furnace nameplate alone.

A refill plan should leave margin for colder nights, inaccurate gauges, appliance cycling, and route changes.

Nightly blower Wh

Blower watts are multiplied by the heating window and duty-cycle estimate.

nightly blower Wh = blower watts x heating hours/night x duty cycle

Battery nights

Nightly blower and other overnight loads are compared against the usable battery window.

battery nights = usable battery Wh / nightly total Wh

Furnace propane nights

Furnace BTU per night is converted to propane pounds, then compared against usable propane after reserve.

propane nights = usable propane lb / ((BTU/hr x hours x duty cycle) / 21,600)

Furnace fan draw varies by model, duct restriction, motor condition, voltage, and return-air flow.

Cold nights are often limited by usable reserve, not nameplate amp-hours.

The estimate does not include propane fridge, water heater, cooking, or generator fuel unless those are checked separately.

Usable battery Wh

Battery amp-hours are multiplied by voltage and the user-entered state-of-charge window.

usable battery Wh = battery Ah x battery voltage x ((start SOC - stop SOC) / 100)

AC battery draw per hour

Running watts are divided by inverter efficiency so DC-side draw is visible.

AC battery Wh per hour = AC running watts / inverter efficiency

Solar-assisted runtime

Solar harvest is added to usable battery reserve after subtracting other daily loads, then divided by AC draw.

runtime hours = (usable battery Wh + solar harvest Wh - other daily Wh) / AC battery Wh per hour

The battery supplies more energy than the AC load receives because conversion losses happen inside the inverter.

Flat roof mounting, panel heat, shade, wiring, and controller behavior keep solar harvest below nameplate watts.

A setup can have enough running watts and still fail when the compressor starts, especially without a measured soft-start profile.

Base fridge Wh

Rated watts are multiplied by hours per day and duty cycle to estimate the daily appliance energy before conditions are adjusted.

base fridge Wh = rated watts x hours per day x duty cycle

Battery-side fridge Wh

Ambient adjustment is added, and residential AC fridge profiles are divided by inverter efficiency.

fridge battery Wh = adjusted fridge Wh / inverter efficiency when AC fridge mode applies

Solar coverage

Panel watts are derated and multiplied by sun hours, then compared against fridge-only and whole-rig demand.

solar harvest Wh = solar watts x sun hours x (1 - solar derate)

Fridge nameplate watts do not run continuously for most compressor fridges; heat, ventilation, and use pattern drive the duty cycle.

Hot weather, poor cabinet ventilation, sun on the fridge wall, and frequent door openings increase daily watt-hours.

Solar can cover the refrigerator and still fail the day once internet, fans, controls, lighting, and charging loads are included.

Running load stack

Each AC load is multiplied by quantity, then added so simultaneous demand is visible.

total running watts = sum(load running watts x quantity)

Startup estimate

The calculator assumes all listed loads are already running and one motor or compressor starts at a time.

startup watts = total running watts + largest(startup watts - running watts)

DC current

The inverter output target is converted back to battery-side current using battery voltage and inverter efficiency.

DC amps = design watts / (battery voltage x inverter efficiency)

Long-running inverter loads should not depend on a unit operating at its paper limit.

If two compressors, pumps, or motors start together, real surge can be higher than the planning estimate.

An inverter can be correctly sized while the battery bank still runs short or cannot safely deliver the current.

Round-trip length

The one-way cable path is doubled because DC current travels out and back through the circuit.

round-trip feet = one-way feet x 2

Voltage drop

Load amps are multiplied by copper conductor resistance for the round-trip distance.

voltage drop = load amps x conductor resistance ohms

Design current

The entered load current is multiplied by the continuous-load planning factor.

design amps = load amps x continuous-load factor

Aluminum wiring has different resistance, sizing requirements, terminal compatibility, and installation rules.

Low-voltage DC circuits can lose useful charging or inverter performance before ampacity alone looks unsafe.

Actual allowed ampacity depends on insulation rating, ambient temperature, bundling, conduit, terminal limits, and code rules.

Cargo capacity

The calculator uses the entered cargo-capacity sticker number, or falls back to GVWR minus UVW if no sticker value is entered.

base cargo capacity = entered CCC or max(0, GVWR - UVW)

Fluid weight

Water is converted from gallons to pounds, then propane pounds are added directly.

fluid lb = (fresh + gray + black gallons) x 8.34 + propane lb

Tow-vehicle payload

For towable rigs, loaded trailer weight is multiplied by the hitch or pin percentage and then cab cargo is added.

tow payload used = loaded trailer weight x hitch % + cab cargo

Fresh, gray, and black water can erase several hundred pounds of payload before upgrades are counted.

Tow-vehicle payload is often the limiting sticker even when trailer GVWR still appears workable.

Real safety checks need loaded axle weights, tire ratings, wheel ratings, hitch ratings, and manufacturer limits.

Average tire load

Each measured axle weight is divided by the number of tires on that axle.

average load per tire = axle weight / tire count

Imbalance-adjusted tire load

The average per-tire load is increased by the side-to-side imbalance buffer to account for one side of the RV carrying more than half the axle.

adjusted load per tire = average load per tire x (1 + imbalance %)

Tire reserve

The adjusted load is compared with the entered load rating per tire.

reserve % = (tire rating - adjusted load per tire) / tire rating

Dry weights and brochure weights miss the water, tools, batteries, solar, food, passengers, and cargo that tires actually carry.

Axle weights hide side-to-side load differences from slides, kitchens, tanks, storage bays, and battery placement.

Inflation pressure depends on the exact tire model, size, load range, manufacturer table, placard guidance, speed, heat, and professional judgment.

Weighted total score

Road access and legal confidence are weighted most heavily, then solar, connectivity, logistics, and comfort scores are added.

score = access x 0.20 + legal x 0.22 + solar x 0.14 + connectivity x 0.16 + logistics x 0.14 + comfort x 0.14

Connectivity score

Casual use can lean on one decent connection, while critical work rewards redundancy between cell signal and satellite sky view.

critical score = max(cell x 0.75, sky x 0.90) x 0.85 + min(cell, sky) x 0.15

Service-distance score

Water, dump, and grocery distances are converted to declining scores and penalized further on longer stays.

logistics score = water distance score x 0.38 + dump distance score x 0.38 + grocery distance score x 0.24 - long-stay penalty

A site with perfect views and sun still fails if overnight use is not allowed or the road is not suitable for the rig.

Some campsite problems should not be averaged away by strong solar, views, or internet.

The calculator is intentionally conservative when the final road or exit path is uncertain.

Workday browsing and email

The daily browsing and email estimate is multiplied by the number of work days in the month.

work browsing GB = work days per month x browsing/email GB per work day

Weekly activities to monthly data

Weekly video calls, remote desktop, and streaming are converted with a 4.33-week month so recurring habits do not get undercounted.

monthly GB = weekly hours x GB per hour x 4.33

Buffered monthly estimate

The calculator adds cloud backup, app updates, and background-device use before applying the safety buffer.

estimated monthly GB = unbuffered GB x (1 + safety buffer %)

A four-week shortcut undercounts recurring video calls and streaming across a normal calendar month.

A stack can be adequate overall while still pushing expensive or throttled data onto the wrong plan.

Video quality, meeting platforms, OS updates, cloud sync, and device settings can change data use enough that fixed defaults would be misleading.

Total trip cost

Site fees, fallback nights, fuel costs, service fees, daily utilities, and a per-night share of gear costs are added together.

total cost = site fees + fallback fees + driving fuel + service fuel + service fees + generator fuel + utilities + amortized gear

Cost per night

The full trip cost is divided by nights so a free campsite can be compared against a paid campground stay.

cost per night = total trip cost / trip nights

Gear break-even

Upfront gear and memberships are compared against recurring per-night savings before amortized gear is added.

break-even nights = gear and membership cost / recurring savings per night

A high fuel number can be fixed by choosing a closer site, reducing water/dump trips, or improving power recovery. Those are different decisions.

A free campsite can look cheaper on cash flow while still taking many nights to repay solar, batteries, generators, satellite gear, or memberships.

The right comparison is the campground or paid site you would realistically book on that route, not a generic national average.

Fresh water needed

People, days, showers, cooking style, dishwashing method, climate, and pets are combined into a trip-water estimate.

gallons needed = people x days x habit rates + pet water + climate water

Days until empty

Actual fresh tank size is divided by estimated daily gallons for the full crew.

days until empty = fresh tank gallons / gallons per day

Waste estimate

Gray and black estimates are split from total water use so waste capacity is not ignored.

gray gallons = gallons needed x 0.58; black gallons = gallons needed x 0.16

This covers drinking, handwashing, toilet flush water, and light daily use.

Navy showers can stay low, but shower frequency still moves total trip water quickly.

Heat, dust, pets, and hydration needs make desert water plans less forgiving.

Power days

Usable battery reserve is compared against the daily power gap left after average solar harvest.

power days = usable battery Wh / max(1, daily Wh - solar harvest Wh)

Fresh-water days

Fresh tank capacity is divided by estimated daily fresh-water use for the full crew.

fresh days = fresh tank gallons / fresh gallons per day

Waste-tank days

Gray and black tank capacities are divided by their own estimated daily fill rates.

tank days = tank gallons / gallons per day for that tank

A battery bank that is refilled every day behaves differently from one that is steadily draining.

Adding battery does not extend the stay if gray tank capacity is already the bottleneck.

The tool avoids implying unlimited stays when legal limits, weather, food, waste, and route logistics still matter.

Daily tank movement

Fresh, gray, and black movement are calculated from traveler count, per-person use, gray-water share, and starting tank levels.

daily fresh = people x gallons/person/day; daily gray = daily fresh x gray share; daily black = people x black gallons/person/day

Service cadence

The shortest tank limit sets the paper interval for dumping, refilling, or moving to a service night.

service cadence days = minimum(fresh days, gray days, black days)

Support cost

Service-run fuel and entered dump/water fees are spread across the planning window, then shown as a weekly cost.

weekly service cost = ((service fuel cost + service fees) / planning days) x 7

Dump stations, potable-water spigots, fees, closures, and overnight rules change too often to promise from a static calculator.

A planned reset night can be cheaper and safer than forcing a long service run from a free site.

Full-time travel often starts a planning window with partially used tanks, not a perfect campground reset.

Workday risk

The planner weighs the cost of downtime before recommending redundancy.

higher work criticality + lower downtime tolerance = stronger backup plan

Route risk

Remote and mixed public-land routes increase the need for different access methods.

remote route risk increases backup and satellite priority

Power friction

Connectivity recommendations are tempered by whether the rig can support always-on devices.

lean power budget reduces always-on satellite/router recommendations

Cellular plans, tower congestion, and satellite pricing change too quickly for a static speed calculator to stay honest.

Two plans on the same network can fail in the same location.

An internet setup that drains the battery is not actually reliable.