DIY Solar Panel Kit 100W – 36 Mono Cells 5x5

The MR WATT 100W DIY solar panel kit contains 36 grade-A monocrystalline 5"x5" (125x125 mm) solar cells plus the accessories to connect them. With 36 cells in series you get the most common format in off-grid systems: the 100 W, 12V nominal panel fitted to campervans and boats to charge the service battery. The difference is that you build it yourself, in the shape your space requires. We designed this kit in-house.

Why the 125 mm cell is the best compromise for a 100W panel

Each 125x125 mm cell delivers about 2.8 W at roughly 5 A. That current is easily handled by a small 10 A PWM controller and carried by standard ribbon and cable sizes. The cell is large enough to reach 100 W with only 36 series connections, yet small enough to handle and solder comfortably even on a first build.

K36M-125x125-A technical specifications

How big your panel will be

• 4 rows of 9 cells: a cell area of about 51x115 cm, the classic rectangular format of 100 W panels.
• 6 rows of 6 cells: a square of about 77x77 cm, handy on short roofs or between two skylights.

Sizes assume 3 mm between cells; add the frame on top. For soldering you need a 60-80 W iron with a flat tip and a smooth, heat-insulating work surface; for encapsulation, EVA sheets, clear silicone resin (for example QSIL 216) or a sandwich between two glass panes, not included in the kit. The Learning Zone on mrwatt.eu and our YouTube channel MRWattDIY have step-by-step guides and videos.

What you can do with it every day

In Southern Europe a 100 W panel produces on average about 0.37 kWh per day over the year, over 0.4 kWh on summer days. With a charge controller and a 12V battery, a weekend in a campervan is covered for LED lights, water pump and phone and laptop charging, and in summer a good part of the consumption of a 12V compressor fridge.

Frequently asked questions

What exactly is in the kit?

36 grade-A monocrystalline 125x125 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, frame, junction box and charge controller are not included.

What panel do I get by connecting the 36 cells in series?

A 100 W, 12V nominal panel with about 19 V at maximum power, 22-23 V open-circuit and about 5 A of current. These are the typical values of panels used to charge 12V batteries through a PWM or MPPT controller.

Should I choose 125 mm or 156 mm cells?

For the same number of cells, the 156 mm cell gives about 60% more power but almost doubles the current (over 8 A) and the panel area. The 125 mm cell is the right choice if your space only fits a 100 W panel or if you want a panel that is easier to solder and wire.

Which charge controller do I need?

A controller is always required: connecting the panel straight to the battery overcharges it, causing electrolysis and in the worst cases a risk of explosion. At about 5 A a 10 A PWM controller is enough; a 10-15 A MPPT gains a few extra watts on cold, bright days.

Can I build a 24V panel?

A 24V nominal panel needs 72 cells in series: you can buy two kits or go straight for our 200 W kit with 72 cells of the same size.