Cracked panel output V-A

spdas

Aloha, I have a few panels ~275W that are really shattered.   The Voltage seems to be at the rated Voltage of the panel, but the amperage is down to 1 amp or less.    Why is this?   If I got full voltage then it seems the all the "connections" inside the cells are connected, so why do I not have full amperage?    thanks Francis

BB.

The solar cells are really (more or less) just very thin pieces of "glass like" cells (Silicon in this case). There are (generally) top and bottom metal "fingers" or conductors on top and bottom of the cells. If you have shattered top glass, then very likely you have one or more shattered cells too.

When the cell(s) shatter, the top/bottom connectors can be disconnected from the rest of the cell. When this happens, there simply not enough area of electrically connected silicon left to generate/conduct the rated current (Imp rated current under full sun).

Example of broken solar cells (silicon breaks and conductors break away too):

When you measure voltage with a DMM--That is "open circuit" voltage and the meter may only be putting a 1,000,000 Ohm load on the panel:

• 40 VDC / 1,000,000 meter input resistance = 0.00004 amps

Obviously, almost any remaining electrical connection to the silicon cell will still output near volt Voc (voltage open circuit) output.

To reduce costs, (some, many, all?) cell manufactures have reduced the thickness of the cells so much, that they are now very fragile and if you tried to, very carefully, pick a raw cell up with your fingers, it would probably shatter. 

When the glass breaks, the cells have almost zero strength and will shatter too. And since all cells are in series (60 cells in series, each 1/2 volt Vmp = 30 Vmp for 60 cells). Just one cell that is less than 100% electrically "solid/connected" will reduce the overall panel current.

Add that broken glass lets oxygen and water/moisture into the cells/electrical connections--Even if the panel worked "normally", it would quickly fail (thermal cycling, rain, oxygen corrosion) over days/weeks/months.

-Bill

littleharbor2

BB. said:

Add that broken glass lets oxygen and water/moisture into the cells/electrical connections--Even if the panel worked "normally", it would quickly fail (thermal cycling, rain, oxygen corrosion) over days/weeks/months.

-Bill

Bill, I am curious and wanted to ask. In your opinion, If the encapsulant layer above and below the cells isn't breached wouldn't that protect the cells from oxygen/moisture intrusion?  The glass does give the laminate sandwich strength but isn't the backsheet more or less cosmetic?

BB.

LH2, you may well be correct. The sheets used between the glass cover, the cells, and the rear of the panel do seem to be very tough.

-Bill