Which Solar Panel to Choose: Monocrystalline, Bifacial and What Wattage for Your System

The panel types that really exist

Many guides still talk about three types: monocrystalline, polycrystalline and thin-film. The 2026 report from Fraunhofer ISE, a German public research institute, describes the market now:

• Monocrystalline silicon: about 98% of everything made in 2025 is silicon, and the dominant technology is monocrystalline. Commercial panels have gone from 17% to almost 25% efficiency (the share of light they turn into electricity) in ten years.
• Polycrystalline silicon: according to the same report, it has practically disappeared from the market. If you’re offered it, ask why: it’s hardly made any more.
• Thin-film: between 2 and 3% of the market.

So the useful question isn’t “mono or poly?”, but what wattage, what size and whether a bifacial panel suits you.

Is a bifacial panel worth it?

A bifacial panel captures light on both sides: sunlight on the front and light bouncing off the ground on the back. How much it gains depends on how light-coloured the ground is and how high the panel sits. A study by Purdue University and the U.S. NREL laboratory, published in the journal Applied Energy in 2018, worked it out for the whole world:

• Over ordinary ground, which reflects a quarter of the light, ground-mounted bifacial panels gain less than 10%.
• Over light-coloured ground that reflects half, with the panel raised one metre, the gain can reach 30%.

The study looks at ground-mounted panels. On a roof, with the panel close to the tiles, the back faces the roof and gets even less light, so it usually gains little. Where it makes most sense is on a raised ground structure over a light surface, like white gravel.

What wattage for your system size

According to Fraunhofer ISE, silicon wafers keep getting bigger, and with them the panels, which now reach about 750 W. More power per panel means a bigger, heavier panel. How to choose:

• Small system (a few lights, charging phones, a small fridge on a 12 V kit): few panels, with a wattage that suits your controller. If the panel runs at a higher voltage than the battery, you need an MPPT controller, which steps that voltage down to the battery’s (in the 2018 test we cite in what’s in a solar kit, the MPPT was precisely a step-down converter).
• A house roof: space is what decides. Measure the usable roof (without shade) and check the dimensions on the spec sheet: sometimes more small panels fit than large ones, or the other way round. Fewer panels means fewer connections and fewer mounts.
• Large or ground-mounted system: the most powerful panels are usually used, and this is where a bifacial panel over light ground can pay off.

In every case, the combined voltage and current of the panels must fit what your controller or inverter accepts: their spec sheets say so, and it’s one of the things the installer checks. And panels that go together should be identical: the World Bank’s Global Solar Atlas counts differences between panels as one of a system’s losses.

What to check on a panel’s spec sheet

• Power (Pmax), in watts. According to PVEducation, it’s measured at 25 °C under light of 1 kW per square metre; on a roof it runs hotter and gives a bit less.
• Dimensions and weight, to know how many fit and whether the roof or structure can take them.
• Voltages and currents, to check they match the controller or inverter.
• The manufacturer’s warranty, and what power it guarantees over the years: panels lose a little each year (the U.S. NLR laboratory assumes 0.7%).

How many panels you need is worked out by the solar panel calculator, which also tells you which batteries, controller and inverter you need. Installation, always by a qualified installer or electrician.