Breakthrough Reported on Low-Cost Alternative to Silicon Solar Cells

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CIG are a type of thin film cell (like amorphous silicon types) and both should be quoted by the manufacturer after their period of initial Staebler-Wronski degradation (a few months).  After that they degrade at the same rate as standard silicon wafer cells (down another 20% in 20-25 years).

I have Sharp polycrystalline panels and these do put out their rated power of at least 170W in daily maxima bright sunshine in SE UK (so at about 52 degrees North).  I have them mounted on angled frames on a flat roof so they get lots of cooling air that helps.  Panels that are mounted on a pitched roof get hotter due to poor ventilation of the rear face and heat soak into the roof tiles so they output less.  In partially cloudy weather they can output up to 118% of their name plate power (I saw this today) due to concentration of rays diffracted by the cloud boundary that makes the light temporarily stronger than normal.  Typically, I see at least 100% to 105% of the name plate power on a clear blue-sky day (no haze).

This is real Amps measured into the 24V battery bank after going through a Morningstar MPPT charge controller.  The panels operate at 46.4V (two in series) and the MPPT controller DC-DC converts this to the battery voltage (24-29V).  So, much less power is wasted in the solar DC cables and the panels operate at their ideal maximum power point.  The real power of the panels is about 3% more than that as some energy is lost in the DC-DC converter (it gets warm when running at 14A output but is a fanless design so doesn't waste much).

I've discovered that it does pay to buy quality panels.  I started out buying cheap Chinese amorphous panels and they lied about the rated power, claiming they were 12Wp and 15Wp.  Both types after about 6 months use degraded to about 64% of their name plate power in the same location and lighting conditions as the Sharp panels. The amorphous ones are on a second controller because they operate at 35V in pairs.

Rather than buy more new panels, I now buy second hand good brand ones (Sharp, Kyocera, BP) from eBay and they are cheaper than the new unbranded cheap Chinese mono ones but they perform at very close to or above rated power, all have 20-25 year power warranties, are rated at +-5% or +10%-5% tolerance, and have superior build quality that looks like it will actually stand being outdoors for 25 years.

My best bargains have been a pair of Sharp 80Wp panels for £455 (£2.84/Wp or $4.55/Wp) and an unused BP 160Wp 24V panel at £375 (£2.34/Wp or $3.75/Wp). The BP one was bought by someone who then left it in a storeroom and forgot about it until he found it when moving house! 

The absolute cheapest panel I've bought was a used poor quality unbranded (cheap Chinese) 40W-ish monocrystalline panel. I've never seen it put out more than 34W but it looks identical to panels that are rated at 40-43W.  That only cost me £67 (£1.97/Wp or $3.15/Wp) but it only does light duty as a spare 12V battery charger because I need 24V PV strings and this one is an odd-one that I picked up. Its frame is a bit weak (thin aluminium) and it doesn't look like it would be waterproof for very long (the cells are spot glued on some kind of board with a glass plate overlaid - not permanent skin encapsulation (like the quality brands I bought). Its voltage is a bit on the low side too so it would be hard to find a partner that didn't suffer mis-match losses... It might have enough power to run a tracker for the 340Wp Sharp array though... :)

As for my poor amorphous panels... they are being phased out and sold off.  They take up too much space for too little power output.