Older Used Panels/Equipment Worth Selling?

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Leomania
Leomania Registered Users Posts: 13 ✭✭
I'm considering replacing my 20-year old solar installation. It consists of 48 Siemens SM110 panels and two Xantrex SW4048 inverters plus battery charge controllers/disconnects. The inverters appear to have a reasonable value yet, and I feel certain I can give the panels away easily and I want to do that if I move ahead. Hate to see the panels just head to the landfill. But I'd like to make sure I'm not being overly optimistic about the desirability of the panels before making a call to rehome them. What's the reality of the situation?
Siemens SM100 x48 (3x16 panels) : Trace SW4048 Inverters x2 : Trace C40 DC Controller x3 : VMAXTanks SLR-125 AGM x4
Utility Interactive Mode : Time of Use Metered : 21 Years and Counting

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,522 admin
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    Look closely at the surface of the cells under glass (make sure glass is clean--Brown dirt on glass can look like "burn spots" on cells).

    Take your panels an lay them out on the ground on a sunny day around noon (pointing towards sun). The panel specs are:

    https://www.siemen.co.uk/sm110_sm100.html

    Measure the Voc (voltage open circuit)--All panels should be about the same. Any panel that is low (by over a volt or so), is probably questionable.

    Then measure the short circuit current of each panel (just a wire across the terminals, measure current with a DC Current Clamp meter, or a DMM set to 10 amp scale terminal to terminal). You will probably measure somewhere between 50% and 100% of Isc (short circuit current specification)... The idea is you have 48 match panels--And while actual Isc-measured will depend on sunlight, all should be again pretty close to each other (10% variation or so possible). Any panel(s) that is significantly under the group average is probably bad.

    In general, these two tests will find 80% of the bad panels... Measuring Imp and Vmp under load is ideal (one quick way is to connect a panel directly to a lead acid battery and measure the current). You will find close to 100% of any bad panels with this test--But be careful, connecting a panel "backwards" to a car sized lead acid battery will fry the cells in that panel immediately.

    Assuming that the panels past your testing, they should have another 10+ years of life left in them...

    For many reasons, the large format panels (200-300+ Watts) are very nice for large solar systems (fewer wiring connections, less mounting hardware, sealed jboxes, etc.)--A new retail panel is somewhere around $1-$2 per Watt (vs the $5-$10 per Watt you may have paid new)...

    If you take 1/2 that value, these panels probably have a "value" of less than $0.50 per Watt... Or say ~$25+/- or so (just some math modeling, not a reflection of the "market" for used panels).

    48 panels * 110 Watts * $0.25 per Watt = $1,320 guess at "retail value"...

    A "broker" may try to buy at pennies on the dollar... Or $100 or so... You can try Craig's List for sale (or for free) and find them a good home that way....

    Again, just an example of how to look at value... Quick check on Craig's List in my area--Lots of panels out there running from $0.10 to $0.50 per Watt to "make me an offer".

    You may wish to factor in "your labor" if you are going check each panel electrically as to what to do next (vs dump fees).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Leomania
    Leomania Registered Users Posts: 13 ✭✭
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    BB. said:
    Look closely at the surface of the cells under glass (make sure glass is clean--Brown dirt on glass can look like "burn spots" on cells).

    Take your panels an lay them out on the ground on a sunny day around noon (pointing towards sun). The panel specs are:

    https://www.siemen.co.uk/sm110_sm100.html

    Measure the Voc (voltage open circuit)--All panels should be about the same. Any panel that is low (by over a volt or so), is probably questionable.

    Then measure the short circuit current of each panel (just a wire across the terminals, measure current with a DC Current Clamp meter, or a DMM set to 10 amp scale terminal to terminal). You will probably measure somewhere between 50% and 100% of Isc (short circuit current specification)... The idea is you have 48 match panels--And while actual Isc-measured will depend on sunlight, all should be again pretty close to each other (10% variation or so possible). Any panel(s) that is significantly under the group average is probably bad.

    In general, these two tests will find 80% of the bad panels... Measuring Imp and Vmp under load is ideal (one quick way is to connect a panel directly to a lead acid battery and measure the current). You will find close to 100% of any bad panels with this test--But be careful, connecting a panel "backwards" to a car sized lead acid battery will fry the cells in that panel immediately.

    Assuming that the panels past your testing, they should have another 10+ years of life left in them...

    For many reasons, the large format panels (200-300+ Watts) are very nice for large solar systems (fewer wiring connections, less mounting hardware, sealed jboxes, etc.)--A new retail panel is somewhere around $1-$2 per Watt (vs the $5-$10 per Watt you may have paid new)...

    If you take 1/2 that value, these panels probably have a "value" of less than $0.50 per Watt... Or say ~$25+/- or so (just some math modeling, not a reflection of the "market" for used panels).

    48 panels * 110 Watts * $0.25 per Watt = $1,320 guess at "retail value"...

    A "broker" may try to buy at pennies on the dollar... Or $100 or so... You can try Craig's List for sale (or for free) and find them a good home that way....

    Again, just an example of how to look at value... Quick check on Craig's List in my area--Lots of panels out there running from $0.10 to $0.50 per Watt to "make me an offer".

    You may wish to factor in "your labor" if you are going check each panel electrically as to what to do next (vs dump fees).

    -Bill

    Bill, thanks for the great info. I think I'm going to offer up the whole set at a low price, just to make sure someone gets some use out of them. May be able to do a package deal with the inverters, charge controllers, etc. I'll see about whether the testing is worthwhile or not, I'm producing on each bank of 16 when the sun's in the right spot so there are plenty of good panels, for sure.
    Siemens SM100 x48 (3x16 panels) : Trace SW4048 Inverters x2 : Trace C40 DC Controller x3 : VMAXTanks SLR-125 AGM x4
    Utility Interactive Mode : Time of Use Metered : 21 Years and Counting