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Size Your
MPPT Solar Charge Controller

Calculate the exact MPPT solar charge controller size required for your campervan build.
Match your solar panel array to your 12V or 24V leisure battery system accurately. 100% free tool.

1. Solar Panel Specifications

*Voltage and current variations caused by cold temperatures (-10°C) are calculated automatically by our tool.

2. Solar Array Configuration

3. Solar Wiring (Roof to MPPT)

✅

Healthy Configuration

Ready for your conversion.

🛒 Required Equipment

🎛️
MPPT Solar Charge Controller
MPPT -- / -- 1 Min. V input
2 Min. A charging current
🔌
Wiring ( mm²)
Optimal Estimated loss of 0%. No overheating expected.

📊 Production (Wh/day)

0 Wp
⚙️ Show technical details
  • Solar Array Power 0 Wp
  • Extreme Voltage (Voc -10°C) 0 V
  • Extreme Current (Isc -10°C) 0 A
  • Array Nominal Current (Impp) 0 A
  • Charging Current (No Margin) 0 A
  • Charging Current (+25% Margin) 0 A

Why Is It Essential to Properly Size Your Van's Solar System?

The electrical system of a campervan cannot be improvised. Before buying solar panels, cabling, or an MPPT charge controller, carrying out an accurate solar calculation is an essential step for the safety of your build and DVLA V5C compliance. Proper sizing addresses three major priorities:

  • Keep Your Van Safe: A solar cable that is too thin or an undersized charge controller can overheat under continuous load. Using correct cable cross-sections (in mm²) and respecting hardware limits is the golden rule for preventing electrical fires.
  • Protect Your Equipment: A solar panel's open-circuit voltage (Voc) increases significantly as ambient temperatures drop. If your MPPT charge controller receives an input voltage above its maximum rating on a freezing British winter morning, it will blow the internal electronics instantly.
  • Ensure Off-Grid Autonomy: Estimating the actual daily yield of your solar array across all four seasons (winter through summer) determines whether you can continuously power your 12V compressor fridge, lighting, and diesel heater without flattening your leisure battery bank (Lithium LiFePO4 or AGM).

How Does Our MPPT Solar Calculator Work?

To provide reliable and safe recommendations, the free VanLogic calculator relies on fundamental electrical laws and British auto-electrical standards. Here is a transparent overview of our calculation methods:

  • Solar Array Configuration (Series vs. Parallel): The tool calculates totals according to the laws of physics. When panels are connected in series, voltages (V) add together. In parallel, currents (A) add together.
  • Extreme Temperature Variations: Our simulator incorporates thermal coefficients to calculate the absolute maximum voltage at -10°C (which rises significantly in freezing conditions) and the absolute maximum current at +70°C (which peaks in direct summer sunlight). This guarantees you choose equipment that will never be damaged by seasonal UK weather extremes.
  • Cable Voltage Drop: To evaluate your roof cabling, we apply the electrical resistivity of copper. The tool approves your chosen cable cross-section (e.g. 4mm² or 6mm²) only if energy loss between the roof panels and the MPPT controller remains strictly below 3%.
  • MPPT Controller Sizing: The recommended controller size (e.g. MPPT 100/30) evaluates two key parameters: the maximum voltage input (which must exceed your cold-weather winter Voc) and maximum charging current. Charging current is calculated by dividing total solar wattage by absorption voltage (14.4V for a 12V battery), plus a 25% safety margin to protect the controller's internal electronics during edge-of-cloud solar spikes.
  • Estimated Daily Yield (Wh/day): Our production graphs combine your total array wattage with regional peak sun hours across the UK and Europe. We apply a realistic 75% efficiency factor to account for flat roof mounting, heat degradation, and MPPT conversion losses.
☀️ Master Solar Power in Your Van

Your charge controller is sized, but how should you wire your panels (series vs. parallel)? Discover best practices in our comprehensive guide to van electrical systems.

Read the Electrical & Power Guide →

FAQ: Sizing & Electrical Systems in Converted Vans

How do you calculate the electrical load for a converted van?

An electrical load calculation is the essential first step in your conversion. It involves listing all your appliances (compressor fridge, lights, water pump, USB sockets, heating) along with their power draw in Watts and daily usage time. Multiplying these values gives your total daily energy requirement in Watt-hours (Wh/day). This figure determines the exact leisure battery capacity and solar panel array required for off-grid living.

How many solar panels do I need for a campervan?

This depends directly on your daily electrical load audit. As a rule of thumb, we recommend installing a solar wattage (Wp) equal to or greater than your leisure battery's amp-hour capacity (Ah). For example, a 150Ah battery bank pairs well with a 150W to 200W solar array to comfortably replenish energy on a clear day.

How do you choose and size an MPPT solar charge controller?

Selecting an MPPT charge controller (e.g. 100/20 or 75/15) is based on two essential criteria:

  • Voltage Input (e.g. 100V): The controller must safely handle the total open-circuit voltage (Voc) of your panels, accounting for cold-weather spikes at -10°C (cold temperatures increase panel voltage).
  • Charging Current (e.g. 20A): The unit must deliver peak output charging current to your battery bank. Our simulator calculates this by dividing total solar wattage by system absorption voltage (14.4V for 12V systems), plus a 25% safety margin.

What is the difference between a Series and Parallel solar configuration?

Wiring your solar panels in different configurations alters the electrical properties of your array:

  • Series Configuration: Adds panel voltages (V) while keeping current (A) constant. This allows you to use thinner roof cabling (4mm²) and enables the MPPT controller to start charging earlier in the morning during overcast UK days.
  • Parallel Configuration: Adds panel currents (A) while keeping voltage (V) constant. This configuration handles partial shading better (e.g., shadows from roof racks or roof vents), as shading on one panel will not choke the output of the others.

Why is the solar cable cross-section so important?

With 12V or 24V direct current (DC), current (A) can be relatively high, creating electrical resistance and heat. If your cable cross-section (in mm²) is undersized for the length of the run, the cable will overheat and cause a dangerous voltage drop, wasting solar energy. Our tool ensures cable losses remain strictly below 3%.

What do Voc, Isc and Pmax mean on a solar panel?

These key specifications are stamped on the panel's rear rating label:

  • Pmax (Peak Power): The maximum theoretical output of the panel under standard test conditions, expressed in Watts (Wp).
  • Voc (Open-Circuit Voltage): The maximum voltage output when the panel is disconnected from a load. This is the critical figure used to prevent destroying your MPPT controller.
  • Isc (Short-Circuit Current): The maximum current output in Amps, used to size safety fuses and cable cross-sections.

How do winter and cold temperatures affect my solar system?

Solar panels produce a higher voltage in cold weather. Panel voltage increases noticeably when temperatures fall below 25C°. Applying a temperature coefficient is vital to calculate panel behaviour at -10C° in winter to avoid damaging your controller. However, shorter winter daylight hours will significantly reduce overall daily production (Wh).

Lithium, AGM or Gel battery: which should I choose?

While AGM and Gel batteries are cheaper upfront, Lithium (LiFePO4) is the industry standard for modern campervan builds. Lead-acid batteries (AGM/Gel) should never be discharged below 50% Depth of Discharge (DoD) without causing permanent damage. A Lithium battery can safely discharge to 90%–100%, weighs a third as much, and provides up to 10 times more charge cycles.

How do you determine the peak power of your electrical system?

Overall Peak Load (distinct from solar panel peak power) represents the worst-case scenario where every electrical appliance in your van is turned on at the same time (fridge, water pump, laptop chargers, diesel heater). This calculation is essential for correctly sizing your main mega fuse, battery cabling, and 230V inverter capacity.

Do I need solar panels if I drive every day?

Not necessarily. If your travel style involves driving for several hours daily, a DC-DC charger (B2B charger) can fully replenish your leisure battery via the vehicle's alternator. However, solar panels are essential if you plan to stay parked off-grid in one spot for multiple days. Having a solar panel also maintains your battery during winter storage or extended breaks between trips.

The Electrical Workshop