DIY Solar Panel Kit 240W – 108 Mono Cells 3x6

The MR WATT 240W DIY solar panel kit contains 108 grade-A half-cut monocrystalline 3"x6" (78x156 mm) solar cells plus the accessories to connect them. With 108 cells you can build three long, narrow 12V panels to spread between skylights, antennas and the air conditioner, or a single high-voltage string to feed an MPPT controller. We designed this kit in-house.

Three panels or one string: how to wire them

• Three 36-cell panels in parallel: about 19 V and 4 A each, around 12 A in total. They work with a PWM or MPPT controller on a 12V battery, and each panel can have its own shape and position.
• 108 cells in series: about 57 V at maximum power with only 4 A. Such a low current lets you carry the energy a long way on thin cables, but you need an MPPT controller with a PV input of at least 100 V.

Mind the cold: the open-circuit voltage of the 108-cell string is about 67 V at 25 °C, and on a winter morning below freezing it can exceed 72-75 V. That figure, not the nominal one, is what must be compared with the controller's limit.

K108MS3-AH technical specifications

How big the panels will be

Each 36-cell panel in 2 columns of 18 is a strip of about 32x146 cm: three strips side by side cover about 96x146 cm, but you can also lay them apart wherever the roof is free. Sizes assume 3 mm between cells, frame excluded. You need a 60-80 W soldering iron with a flat tip, a smooth heat-insulating surface and an encapsulation method (EVA, clear silicone resin such as QSIL 216, or double glass), not included. Guides and videos are in the Learning Zone on mrwatt.eu and on our YouTube channel MRWattDIY.

What you can do with it every day

In Southern Europe 240 W produce on average about 0.9 kWh per day over the year and about 1 kWh on summer days. In a campervan that means summer self-sufficiency with a compressor fridge, lights, pump, laptop charging and a 12V TV in the evening; in a small off-grid cabin, lighting, device charging and a small water pump.

Frequently asked questions

What exactly is in the kit?

108 grade-A half-cut monocrystalline 78x156 mm solar cells, a few spare cells to make up for breakages during soldering or shipping, tab wire and bus wire, flux and a Schottky diode. The soldering iron, encapsulation materials, frames, junction boxes and charge controller are not included.

Which controller do I need for the 108-cell string?

An MPPT controller with a maximum PV input voltage of at least 100 V, because at low temperatures the string's open-circuit voltage exceeds 70 V. A 75 V controller is not enough. On a 12V battery choose a model with at least 20 A of output.

What if I fit three separate panels?

Wired in parallel they deliver about 12 A on a 12V battery: you need a PWM or MPPT controller rated at least 20 A. A blocking diode for each panel is recommended: one is included, the other two must be bought separately.

Is a charge controller always needed?

Yes. Connecting the panels straight to the battery overcharges it, causing electrolysis, electrolyte loss and in the worst cases a risk of explosion.

How long does it take to build?

With 108 cells this is a multi-day project. Finish one 36-cell panel first, check its voltage and current in the sun with a multimeter, and only then move on to the other two. The spare cells included cover the most common breakages.