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Solar PV: Types of Solar PV Panels

By Ian Mander, 24-30 April 2019

 

A solar photovoltaic panel is made of multiple cells connected in series. There are there main types of solar photovoltaic panel: amorphous, monocrystalline, and polycrystalline. They each have their own benefits and suitabilities, but of course all need to be kept clean to work their best.

 

Amorphous cells

These look like wide grey stripes going across the full width of the panel, separated by thin gaps.

One of the main claimed advantages of amorphous silicon solar PV panels is that they perform better in low light conditions such as hazy or cloudy days. This is true in very dim light, hence why amorphous solar panels are used in solar powered calculators, which are typically used indoors where the light is much dimmer than outdoors. However, in bright light they are significantly less efficient (up to 10.2% in the lab) than monocrystalline and polycrystalline panels.

On the flip side, they are also less expensive than the other panel types because they are much simpler to make – another significant advantage.

However, in the first six months of operation, amorphous silicon panel performance can drop 10-30%. They deteriorate faster than the other types, and have shorter warranties accordingly.

If solar panel space is limited or long term operation is important, amorphous solar panels are not the way to go.

Amorphous silicon panels are the most commonly available variety of film solar panels in New Zealand. Other varieties are cadmium telluride (CdTe), copper indium gallium selenide (CIGS), and dye-sensitized solar cell (DSC).

 

Monocrystalline solar cells

These are an even dark (black) colour with no individual crystals visible, and are generally square with the corners missing (because thin wafers have been cut from large round crystals, then trimmed to make better use of the area in a panel).

Monocrystalline panels are the most efficient type (up to 26.7% in the lab) and several websites say they generally have better heat tolerance than the other types. (Which is good because I have seen the back of my monocrystalline panel hit 59 °C.)

This study (PDF) shows you should expect a mean 0.8% (median 0.5%) drop in performance per year.

Flexible solar panels are most likely to be monocrystalline. The cheap ones can degrade by 15% in 18 months (and also lose up to 16% when they get hot, as shown in this test). Flexible solar panels degrade more quickly than rigid solar panels and may not have acceptable performance after just 2 years. Flexible panels are thus not recommended.

 

Polycrystalline cells

These look like lots of large bluish crystals at different orientations jumbled together. Individual cells are rectangular in shape.

Polycrystalline panels are easier to make than monocrystalline cells and thus a little less expensive than monocrystalline panels, and a little less efficient (up to 22.3% in the lab). Because of the price, polycrystalline cells are the most commonly available in the world.

 

Solar panel performance

Solar panel testing (ongoing).

Panel Type Dimensions & Area Cells Open Circuit Voltage Short Circuit Current MPP Efficacy
Small Polycrystalline
(16-17%)
2" × 5/8" × 36 = 45 in² = 0.029 m² 36 20.2 V 0.22 A 15.81 V × 0.155 A = 2.45 W
(or more)
84.4 W/m²
Medium Amorphous
(10-11% new,
much lower now)
312 mm × 214 mm = 0.067 m² 30 23.1 V 0.20 A    
Large Amorphous
(10-11% new,
much lower now)
295 mm × 448 mm = 0.13 m² 30 23.7 V 0.24 A

16.64 V × 0.168 A = 2.80 W

MPPT voltage = 16.7 V

21.2 W/m²
Oversize Monocrystalline
(16% implied claim)
1360 mm × 895 mm = 1.217 m²
(it's actually a bit less)
36 22.4 V
(claimed*)
11.94 A
(claimed)

19 V × 7.1 A = 135 W
(best observed)

MPPT voltage = 18.2 V
(claimed)

112 W/m²

* It's very hard to test this because the direct output from the panel is not accessible, only the output from the controller (which turns off the output if no battery is connected).

Note the difference in efficacy between the crystalline panels and the old amorphous panel. This is worth considering even if the purchase price of an amorphous panel is much less or if using the panels in "dim" light – the light has to be very much dimmer for an old amorphous panel to pull ahead.

 

The best approach

Any solar panel which is going to produce a significant amount of energy will be big and heavy (eg, 15.3 kg for a 200 W panel). It's a lot of area for not a huge amount of power. Wouldn't a generator work out better, especially in cloudy weather? Wouldn't a generator be less expensive?

A 1200 W petrol generator would produce more electricity, more reliably, and only costs about the same as a 100 Ah SLA battery and box. But it's also noisier and more polluting (not withstanding construction process and an unknown amount of embedded energy in the solar PV system, which I am unable to quantify), and requires ongoing fuel, oil and maintenance.

The initial setup of solar panel(s) and energy storage is more expensive, and going to solar is a commitment to be at the mercy of the weather, a commitment to spend rather more than the bare minimum money on a power solution, and a commitment to use renewable energy instead of readily available fossil fuels. But in the long term, especially, it offers several significant advantages.

 



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