DIY Solar Panel Kit 36W – 36 Poly Cells 3x3

The MR WATT 36W DIY solar panel kit contains 36 grade-A polycrystalline 3"x3" (78x78 mm) solar cells plus the accessories to connect them. With a soldering iron and an afternoon of work you can build a 12V nominal photovoltaic panel in the exact shape and size you need. We designed this kit ourselves for people who want to understand solar power hands-on, and for anyone who needs a custom-sized panel that simply isn't sold off the shelf.

Why the 3"x3" cell is the right size to start with

The 78x78 mm cell is a quarter of the classic 6" (156 mm) cell. That brings two practical advantages: it is easier to handle and solder than a full cell, and 36 pieces give you exactly the 36-cell string needed to charge a 12V battery through a charge controller. Small cells also allow shapes that large cells cannot: a long, narrow panel for a boat's gunwale, a square one for a garden light post, a compact module for a school project.

K36P-3x3-A technical specifications

Building the panel: the three choices that matter

• Layout: 4 rows of 9 cells give a narrow panel with a cell area of about 33x73 cm; 6 rows of 6 give a square of about 48x48 cm. Final dimensions depend on cell spacing (2-3 mm) and on the frame.
• Soldering: use a 60-80 W soldering iron with a flat screwdriver tip, apply flux on the busbars and lay the cells on glass or another smooth, heat-insulating surface. The ribbon is soldered to the front (negative) of one cell and taken to the back (positive) of the next.
• Encapsulation: bare cells are vulnerable to moisture and knocks. For a long-lasting panel use EVA sheets, clear silicone resin (for example QSIL 216) or a sandwich between two glass panes. Encapsulation materials are not included in the kit.

In the Learning Zone on mrwatt.eu and on our YouTube channel MRWattDIY you will find step-by-step guides and videos on soldering and assembling solar cells.

What you can do with it every day

In Southern Europe a 36 W panel produces on average about 0.13 kWh per day over the year, up to 0.2 kWh on summer days and less than half of that in winter. Paired with a charge controller and a 12V battery, in practice it can:

• recharge a 12V 7 Ah battery (about 84 Wh) in one or two sunny days;
• power a 5 W 12V LED strip for 3-4 hours every summer evening;
• keep the service battery of a boat or campervan topped up while it is laid up;
• run small low-power electronics: garden cameras, sensors, Arduino boards.

The kit is designed for off-grid systems: a grid-connected installation requires certified modules, not self-built panels.

Frequently asked questions

What exactly is in the kit?

36 grade-A polycrystalline 78x78 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 36 W, 12V nominal panel with about 18 V at maximum power, 21-22 V open-circuit and about 2 A of current. These are the typical values of panels used to charge 12V batteries through a PWM or MPPT controller.

Can I build a 6V or 24V panel instead?

Yes. 18 cells in series give a 6V nominal panel (about 9 V at maximum power): with the 36 cells in the kit you can build two 18 W panels, or wire them as two parallel strings for about 4 A. A 24V nominal panel needs 72 cells in series, so two kits.

Do I need a charge controller?

Yes, always, in any system with a battery. Connecting the panel straight to the battery overcharges it, causing electrolysis, electrolyte loss and in the worst cases a risk of explosion. A small PWM controller is enough for a 36 W panel; an MPPT gains a little more on cold, bright days.

I'm a beginner: can I build it myself?

Yes, the 3"x3" cell is one of the easiest formats to learn on. The cells are thin and fragile: work on a smooth surface, don't press down with the iron tip, and use 60-80 W to solder quickly without overheating the cell. The spare cells included are there precisely to cover your first breakages.