Solar Panel Size Calculator Guide for Campers, Vans and RVs

Most camper and RV builds need 300-600W of solar panels. A 400W setup paired with 200Ah of LiFePO4 batteries handles 90% of van life power needs comfortably.

The sizing formula: Take your daily energy consumption in watt-hours (typically 600-1,500Wh for van life), multiply by 1.5 to account for system losses, then divide by your location's peak sun hours (3-5 hours). The result is the solar wattage you need on your roof.

Step 1: Calculate Your Daily Power Consumption

Before sizing your solar panels, you need to understand how much power you actually use. Make a list of all your electrical devices and estimate daily usage. Be honest with yourself here -- most people underestimate their consumption, and that leads to frustration down the road.

Common Van Life Power Consumers

Lighting (LED)

Interior lights: 2-5 watts each, 4-6 hours daily = 8-30 watt-hours
Exterior lights: 10-20 watts, 2-3 hours = 20-60 watt-hours

Electronics

Laptop: 45-65 watts, 4-6 hours = 180-390 watt-hours
Phone charging: 10-15 watts, 2-3 hours = 20-45 watt-hours
Tablet: 10-15 watts, 2-4 hours = 20-60 watt-hours
USB outlets (active draw when devices connected): 5-10 watts, 8-10 hours = 40-100 watt-hours

Appliances

12V compressor fridge: 40-60 watts, 8-12 hours = 320-720 watt-hours
Water pump: 30-60 watts, 0.5-1 hour = 15-60 watt-hours
Ventilation fan (MaxxFan, Fiamma): 20-40 watts, 4-8 hours = 80-320 watt-hours
Diesel heater (Webasto, Espar, Chinese units): 10-30 watts, 8-12 hours = 80-360 watt-hours
Mobile router or hotspot: 5-15 watts, 12-24 hours = 60-360 watt-hours
Camera/security system: 5-10 watts, 24 hours = 120-240 watt-hours

High-Draw Items (if applicable)

External monitor: 20-40 watts, 4-6 hours = 80-240 watt-hours
Induction cooktop: 1,000-1,800 watts, 0.5-1 hour = 500-1,800 watt-hours (requires inverter, usually impractical on solar alone)
Hair dryer: 1,000-2,000 watts, 0.1-0.2 hours = 100-400 watt-hours
Electric kettle: 1,000-1,500 watts, 0.1 hours = 100-150 watt-hours

A few notes on high-draw items: induction cooktops, hair dryers, and electric kettles pull massive power through an inverter. If you plan to use these regularly, you will need a significantly larger solar and battery setup, or you should plan on supplementing with shore power or a generator. Most van lifers cook with gas instead.

Example Daily Consumption: 650-1,500 watt-hours for a typical setup without heavy inverter loads.

Step 2: Account for System Losses

Solar systems aren't 100% efficient. Account for these losses:

Charge controller efficiency: 85-95%
Battery efficiency: 85-90%
Wiring losses: 5-10%
Overall system efficiency: ~75-80%

Formula: Daily consumption / 0.8 = Required solar generation

If you need 1,000 watt-hours daily, you need roughly 1,250 watt-hours of solar generation.

Step 3: Calculate Required Solar Panel Wattage

Solar panels don't produce their rated power all day. In good conditions, expect about 4-6 peak sun hours daily, depending on location and season.

Formula: Required generation / Peak sun hours = Panel wattage needed

Sunny locations (southern Spain, Greece, Arizona): 5-7 peak hours
Average locations (central Europe, most of the US): 4-5 peak hours
Northern/cloudy areas (UK, Scandinavia, Pacific Northwest): 2-4 peak hours

Example: 1,250 watt-hours / 5 hours = 250 watts of solar panels

Seasonal Variation: The Factor Most People Ignore

Here is where a lot of first-time builders get tripped up. They size their system on a sunny summer day and then wonder why everything falls apart in November.

Solar production varies dramatically by season and latitude. The difference between summer and winter can be enormous, especially in northern Europe.

Rough Peak Sun Hour Estimates by Season

Southern Europe (Spain, southern France, Italy, Greece)

Summer: 6-7 peak sun hours
Winter: 3-4 peak sun hours

Central Europe (Germany, Netherlands, northern France)

Summer: 4-5 peak sun hours
Winter: 1-2 peak sun hours

Northern Europe and UK

Summer: 3-5 peak sun hours
Winter: 0.5-1.5 peak sun hours

Southern US (Arizona, Texas, Florida)

Summer: 6-7 peak sun hours
Winter: 4-5 peak sun hours

Northern US and Canada

Summer: 4-6 peak sun hours
Winter: 2-3 peak sun hours

What This Means in Practice

If you are a full-timer staying in northern Europe through winter, your 400W solar setup that happily produced 2,000Wh on a June day might only deliver 400-600Wh on a grey December day. That is a massive drop.

There are two practical approaches to this problem. First, you can oversize your solar for winter, which means carrying panels that are overkill for summer. Second -- and this is what most full-timers actually do -- you accept that solar alone will not cover your winter needs and supplement with DC-DC charging from your alternator or occasional shore power hookups.

If you mostly travel in summer or chase the sun southward in winter, you can size your system for average conditions and be fine.

Panel Placement and Angle

How and where you mount your panels matters almost as much as how many watts you have on the roof.

Flat-Mounted vs Tilted

Most van builds use flat-mounted panels bolted directly to the roof. This is the simplest approach: low profile, no wind resistance, and nothing to adjust. The downside is that flat panels lose 10-25% of potential output compared to panels tilted toward the sun, especially in winter when the sun sits low on the horizon.

Tiltable mounts fix this problem, but they add complexity. You need to stop, get on the roof (or use a ground-level mechanism), and adjust the angle. Some people build hinged brackets that let them tilt panels to 20-30 degrees, which is a good compromise for winter production.

East-West Split Mounting

An interesting approach that is gaining popularity: instead of pointing all panels south, mount some facing east and others facing west. You get less peak production at midday, but you get a wider production window through the morning and evening hours. This can actually yield more total daily energy in some scenarios, and it is especially useful if you are running a fridge that draws power all day.

Roof Obstructions

Real van roofs are not clean, flat surfaces. You have AC units, vent fans, antennas, roof racks, and skylights competing for space. Each of these can cast shadows, and even partial shading of a single panel can dramatically reduce output for the entire string if panels are wired in series.

Plan your layout carefully. Leave at least a few centimeters of clearance around each panel for airflow (panels lose efficiency as they heat up), and try to position panels where they won't be shaded by taller roof furniture at any sun angle.

Curved Roofs and Flexible Panels

Sprinter vans, Ducatos, and many other vans have curved roofs. Rigid panels require mounting rails or brackets to sit level, which eats into your interior height clearance. Flexible (semi-flexible) panels conform to the curve and add almost no height, which is appealing. However, they run hotter because there is no air gap beneath them, they tend to have shorter lifespans, and they generally cost more per watt. If you have the roof height to spare, rigid panels mounted on rails are the better long-term investment.

Series vs Parallel Wiring for Panels

How you wire your panels together affects performance, especially in partial shade conditions. We have a dedicated article on why VoltPlan diagrams default to series wiring, but here is the short version.

Series wiring (connecting positive to negative) increases voltage while keeping current the same. This is usually the better choice for van builds because higher voltage means lower current, which means thinner wires and less power lost in the wiring run from your roof to your charge controller. MPPT charge controllers handle series strings very efficiently.

Parallel wiring (connecting positive to positive, negative to negative) keeps voltage the same while increasing current. The main advantage is shade tolerance -- if one panel is shaded, the others keep producing. But the higher current requires thicker, more expensive wiring.

For most van builds with 2-4 panels of the same type, series is the way to go. If you have panels that get shaded at different times (like an east-west split setup), parallel or a mix of series-parallel can make sense. Check out the full series vs parallel guide for wiring diagrams.

Popular Solar Panel Configurations

Budget Setup (200-400 watts)

Best for: Weekend warriors, minimal power needs
Typical setup: 2 x 100W or 2 x 200W panels
Daily generation: 800-1,600 watt-hours (good sun)
Cost: 300-800 EUR

Mid-Range Setup (400-800 watts)

Best for: Full-time van life with moderate needs
Typical setup: 4 x 100W or 2 x 400W panels
Daily generation: 1,600-3,200 watt-hours (good sun)
Cost: 800-1,600 EUR

High-Power Setup (800+ watts)

Best for: Power-hungry setups, poor sun conditions
Typical setup: 6+ panels or high-efficiency panels
Daily generation: 3,200+ watt-hours (good sun)
Cost: 1,600+ EUR

Solar Panel Types: Monocrystalline vs Polycrystalline

Monocrystalline

Higher efficiency (18-22%)
Better performance in low light
More expensive
Black appearance

Polycrystalline

Lower efficiency (15-17%)
More affordable
Blue appearance
Good value for space-abundant setups

Recommendation: Choose monocrystalline for van life due to limited roof space.

Charge Controller Selection: MPPT vs PWM

The charge controller sits between your panels and your batteries, regulating the charging process. This is not a place to cut corners.

PWM (Pulse Width Modulation)

PWM controllers are simple and cheap (20-60 EUR). They essentially act as a switch, connecting the panels directly to the batteries and pulsing to regulate voltage. The problem is that they force panels to operate at battery voltage (around 12-14V), which wastes a significant chunk of the panel's potential output. A 100W panel connected through a PWM controller to a 12V battery might only deliver 70-75W in practice.

PWM controllers only make sense for very small setups (under 100W) where the cost savings outweigh the efficiency loss.

MPPT (Maximum Power Point Tracking)

MPPT controllers are the standard for any serious solar build. They convert the higher panel voltage down to battery voltage while maximizing current, capturing 20-30% more energy than PWM from the same panels. They cost more (100-400 EUR), but they pay for themselves quickly through better energy harvest.

Sizing Your MPPT Controller

When selecting an MPPT controller, you need to check three specifications:

Maximum input voltage (Voc): Add up the open-circuit voltage (Voc) of all panels in your series string. This must stay below the controller's maximum input voltage, even in cold weather (voltage increases as panels get cold). Add a 10-15% safety margin. For example, two panels with 22V Voc each gives 44V in series -- you want a controller rated for at least 50V input.

Maximum charge current: This is the output current to your batteries. A 30A controller on a 12V system can handle about 360W of solar (30A x 12V). A 50A controller handles about 600W.

Maximum panel wattage: Most controllers specify a maximum solar input wattage. Don't exceed it.

Popular Controllers Worth Considering

Victron SmartSolar series: Excellent build quality, Bluetooth monitoring, widely considered the gold standard. The 100/30 handles up to 400W on 12V systems.
Renogy Rover series: Good mid-range option, solid app support. The 40A model handles up to 520W at 12V.
EPEver Tracer series: Budget-friendly but capable. The Tracer 4210AN (40A) is popular for builds where cost matters. Less polished software than Victron.

Size your controller for your current panels plus room to grow. If you are starting with 200W but might add more later, get a 30A or 40A controller now rather than replacing a 20A unit in six months.

Battery Bank Sizing

Your battery bank should store 2-3 days of power consumption:

Daily consumption: 1,000 watt-hours
Required battery capacity: 2,000-3,000 watt-hours
12V battery amp-hours: 167-250 Ah

Consider lithium (LiFePO4) batteries for:

Longer lifespan (2,000+ cycles vs 500 for lead-acid)
Deeper discharge capability
Lighter weight
Faster charging

Real-World Build Examples

Theory is useful, but seeing actual configurations that work for real people is more helpful. Here are three common setups we see in the VoltPlan community.

The Weekend Camper

Use case: Weekend trips, occasional week-long holidays. Parks at home with shore power during the week.

Solar: 200W (2 x 100W rigid panels)
Battery: 100Ah LiFePO4
Charge controller: 20A MPPT
Daily consumption: ~400Wh (lights, phone charging, small fridge, fan)
Daily production (summer, central Europe): 800-1,000Wh

This setup comfortably covers a weekend without any stress. The battery holds enough for a full day of clouds, and the solar keeps up easily in decent weather. Total solar component cost: roughly 500-700 EUR.

The Full-Time Van Lifer

Use case: Living in the van year-round, traveling through Europe. Laptop for planning and entertainment, compressor fridge running 24/7, diesel heater in winter.

Solar: 400W (2 x 200W rigid panels)
Battery: 200Ah LiFePO4
Charge controller: 30A MPPT (Victron 100/30 or similar)
Daily consumption: ~800-1,000Wh (laptop, fridge, lights, fan, phone, router, diesel heater)
Daily production (summer, central Europe): 1,600-2,000Wh

This is the sweet spot for most full-timers. You have a comfortable surplus in summer and can get through most shoulder-season days on solar alone. In winter, you will need to supplement with driving (DC-DC charger) or occasional shore power. Total solar component cost: roughly 1,000-1,500 EUR.

The Remote Worker Van

Use case: Working full-time from the van. Laptop running 8+ hours, external monitor, reliable internet via mobile router, compressor fridge, all the creature comforts.

Solar: 600W+ (3 x 200W rigid panels)
Battery: 300Ah+ LiFePO4
Charge controller: 50A MPPT
Daily consumption: ~1,200-1,800Wh (laptop 8h, monitor, router 24/7, fridge, lights, fan, diesel heater, phone, tablet)
Daily production (summer, central Europe): 2,400-3,000Wh

This is a serious setup. The large battery bank provides a buffer for cloudy days, and the substantial solar array means you can usually stay self-sufficient in summer. But be realistic: if you are working from northern Europe in winter, solar alone will not cut it. A 30-40A DC-DC charger and regular driving, or occasional campsite hookups, become essential parts of the plan. Total solar component cost: roughly 2,000-3,000 EUR.

When Solar Alone Is Not Enough

Solar is fantastic, but it has limits. Knowing those limits saves you from oversizing your roof array and spending money that would be better used on complementary charging sources.

DC-DC Charging from the Alternator

A DC-DC charger takes power from your vehicle's alternator while you drive and feeds it into your leisure batteries at the correct voltage and current. A 30A DC-DC charger delivers roughly 360W continuously, which means even a 2-hour drive can put 700+ watt-hours into your batteries. For winter travel or rainy stretches, this is often the single most reliable charging source you have.

Shore Power

When you have access to a campsite or marina with power hookups, a mains charger can fully recharge your batteries overnight. Many full-timers plan one or two shore power nights per week during winter to keep their batteries healthy without running the engine.

Generator Backup

A small portable generator (1,000-2,000W) can be a lifesaver in extended bad weather or remote locations. They are noisy and require fuel, so most people treat them as emergency backup rather than a primary charging source.

The Smart Approach

The most resilient builds combine multiple charging sources: solar as the primary, DC-DC for driving days, and shore power or a generator as backup. Size your solar for your average needs in decent weather, and let the other sources fill the gaps. This approach is almost always cheaper and more practical than trying to solve every scenario with solar panels alone.

Installation Tips

Panel Mounting

Tiltable mounts increase winter production by 20-30%
Fixed mounts are simpler and more aerodynamic
Leave space between panels for airflow

Wiring

Use MC4 connectors for weatherproof connections
Size wires properly to minimize voltage drop
Install fuses/breakers for safety

Common Mistakes to Avoid

Underestimating power consumption: Track actual usage for a week before finalizing your design
Sizing for summer only: Plan for worst-case weather, or accept that you will need supplemental charging
Ignoring seasonal variation: Winter production in northern climates can drop to 20-30% of summer levels
Cheap charge controllers: A PWM controller on a 400W array wastes more money in lost energy than the price difference to MPPT
Poor battery maintenance: Properly maintain your batteries for maximum lifespan
Forgetting about shading: One shaded panel in a series string drags down the whole array
Not planning for growth: Buy a charge controller that can handle more panels than you start with

Using VoltPlan for Solar Design

Ready to design your complete solar system? VoltPlan makes it easy to:

Calculate your exact power needs with built-in consumption guides
Design solar panel layouts for your specific roof dimensions
Get automatic wire sizing and component recommendations
Export complete electrical diagrams for installation

Whether you're building your first van or upgrading an existing setup, proper solar planning ensures you'll have reliable off-grid power for all your adventures.

Start designing your solar system today with VoltPlan's free electrical system designer!

Frequently Asked Questions

How many watts of solar do I need for a camper?

Most campers need 300-600W of solar panels. A weekend camper with minimal electronics can get by with 200W, while a full-time van lifer working remotely needs 400-600W or more. Calculate your daily watt-hour consumption first, then size from there.

Is 200W of solar enough for a van?

200W is enough for light use: LED lights, phone charging, and a small 12V fridge on weekend trips in sunny climates. If you run a laptop, router, or diesel heater daily, you will need 400W or more to stay self-sufficient.

How many solar panels do I need for a 200Ah battery?

A 200Ah LiFePO4 battery stores about 2,400Wh. To fully recharge it in one day of sun, you need roughly 400-600W of solar panels, depending on your location's peak sun hours. In central Europe with 4 peak hours, 600W is ideal. In the US Southwest with 6 peak hours, 400W is sufficient.

What size charge controller do I need for my solar panels?

Divide your total solar wattage by your battery voltage (usually 12V) to get the minimum controller amperage. A 400W array on a 12V system needs at least a 30A MPPT controller. Always use MPPT over PWM -- PWM controllers waste 20-30% of your solar harvest.

Should I wire solar panels in series or parallel?

Series wiring is better for most installations. It produces higher voltage and lower current, which means smaller wires, less power loss, and lower cost. See our series vs parallel guide for detailed diagrams.

Free Off-Grid Sizing Tools

The numbers in this guide go straight into our free calculators:

Solar panel calculator — array wattage, panel count, and minimum MPPT controller current from your daily Wh and sun region.
Battery bank sizer to confirm the array can actually refill the bank in one good day.
Wire gauge calculator for the run from panels to MPPT and from MPPT to battery.

The full tour is in Free 12V electrical calculators for campers, boats & off-grid.