Panels after ten year use on sale! Is it worth buying it?

Peejay
Peejay Registered Users Posts: 3
in Solar Beginners Corner #1
Hi all, this is my first posting in this!

I am from India, where the RE revolution is picking up momentum slowly. Still the prices are high. Local Government offer more than 50% subsidy for the domestic installations through special agencies ....but the off-grid systems are yet to find its regular buyers. The storage- batteries are quite expensive. Net metering and grid-tie are now common topics for discussion. The 50Hz supply may be a hurdle, I do not know any other reasons, why it is still at the discussion tables. ( In our state we still depend on the Hydro-gen of power...this year less rain and power cut for more than three to four hours in the hot sunny days.)


70watt PV panels used for more than ten years on sale after an auction from Government owned Power house. Made in 1998-99 by BHEL, a government owned industry.

The after market seller offer these panels for half the current per watt price. No warranty. Whereas the new panels are sold with 25 year warranty!

With the wisdom I gained from you by short reading the postings, I measured the average Voc = 18V and Isc = 3.5 to 3.8A at 1200 noon to 1 pm on a hot bright sunny day (43 degreeC!)

One panel is with Isc= 0.38A!!

More than 1000 panels are available for sale.....is it worth buying it?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #2
    Re: Panels after ten year use on sale! Is it worth buying it?

    Welcome to the Forum PeeJay!

    I would say it is not a good deal... 1/2 of their design life gone. One panel already failing. Sounds like their output is already degraded by ~20%. No warranty. 1/2 of retail for new--no bargain. Look closely at the panels too. Look for brown/black spots/bubbles or other "strange" things under the glass (another reason to reject a panel that is not near "free").

    Another issue is the Voc voltage... If you are going to charge batteries, the minimum Voc should be in the 21-22 volt range or so. That gives you a Vmp of ~17.5 to 18.6 volts (cool panels, if they were soaking in hot sun, Voc/Vmp measured would be less--perhaps in the 18 volt range). If the panel voltage is too low, then you cannot use them directly to recharge 12 volt battery bank (or multiples, for 24/48 volt battery bank). The panels should be around 36 cells in series for ~18 volt Vmp.

    Inexpensive charge controllers are PWM (pulse wave modulation) type (simple "on/off" switching) and need the "matched" panels to battery bank for best efficiency.

    If the Vmp spec. for these panels is significantly less than ~17.5 volts (standard test conditions STC), then you have to put two more more panels in series to get high enough voltage to recharge your battery bank (which needs ~15+ volts for 12 volt deep cycle batteries). And if you put them in series, you need a more expensive MPPT type charge controller (maximum power point tracking--uses a switch mode computer controlled internal power down converter) to efficiently match your Vmp-array to battery bank voltage.

    So--See if you can find the STC rated Vmp for the panels... But, unless you have no other reasonably priced panels available, I would walk away from these.

    It sounds like you are looking for more than a few panels to supply some emergency lighting. A few panels may be worth getting to play with. But anything more--...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
    Re: Panels after ten year use on sale! Is it worth buying it?

    welcome,
    i'm not sure of the differences in monies from here to there, but we are seeing new pvs here at below $1 per watt. i don't know how that would compare and we aren't familiar with what is available in your country. i would think many of the chinese and japanese pvs would also be available, but would there be any high import tariffs on them is another question. even if reasonable in price we do understand that many do not make the kind of money to invest into such a thing.

    in general you should want to know if you intend your system to be grid tied, off grid, or both as in a battery backed gt system. after that determine how much pv power you may want/need and the same for the batteries if applicable. after that you can look around at what is available and start putting something together on paper. you can ask us questions on it and we will answer if we can. be sure to include specifications of any equipment you are addressing and other pertinent information that we may need to comment on a system.
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  • Peejay
    Peejay Registered Users Posts: 3
    #4
    Re: Panels after ten year use on sale! Is it worth buying it?

    Thank you for the fast responses. The dealer is ready to replace the defective panels,till he have the stock, if we can find them before he sell all the junk!.
    New panels will cost approx INR60 per watt. (1USD=INR 55!).
    The present offer is INR 20 per watt for the used one, and it is selling like hot cakes.

    I am aiming for a 1000watt domestic off grid system. MPPT controller(EP Solar from china), 1400watt pure sign wave inverter unit(Whirlpool- indigenous) 2 x 180AH battery pack.
    All together it is a fortune, to spend and sit looking at it! USD 200 + 200 + 600, plus another 400 for the used panel. (1400 x 55 =INR77000)

    Will collect the spec and post the details.

    Hell of a lot of information with you! it will take time for me to chew it and get the juice out of it......but really tasty and I luv it. Great work.

    Got few details:cut and paste.
    L1270 : 70 WP module(NCEnegy)

    www.bheledn.com
    Data Sheet of 70 Wp & 75 Wp Module

    1. Pv Module Type No. L1270
    2. Configurantion Single Glass Laminated Type With 36 Nos. Of Solar Cells In Series Configuration.
    3. Overall Size 1203 (±3) × 528 (±2) × 38.5 (±1) mm
    4. Weight 7.5 Kg.(Typical.)
    5. Typical Electrical Characteristics: Open Circuit Voltage (Voc) 21.0 V
    Short Circuit Current (Isc) 4.6 V
    Voltage At Peak Power Point (Vm) 16.4 V
    Peak Power (Pmax) 70 Wp or 75 Wp
    Note: Electrical Specifications Mentioned
    Above Are At Standard Test Conditions Of 100 mw/cm2. Solar Isolation (AM 1.5) And At 250C Cells Temperature

    MPPT controller

    www.epsolarpv.com
    Model Tracer-4210RN

    Rated system voltage 12/24V auto work

    Rated battery current 40A

    Rated load current 20A

    Max.battery voltage 32V

    Max.PV open circuit voltage 100VDC

    Max.PV input power 12V 520W， 24V 1040W

    Self-consumption <10mA（24V）

    Charge Circuit Voltage Drop ≤0.26V

    Discharge Circuit Voltage Drop ≤0.15V

    Communication TTL232 / 8 pin RJ45

    Temp.compensation -30mV/℃/12V（25℃）

    Working temperature -35℃～+55℃

    Storage temperature range -35℃～+80℃
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #5
    Re: Panels after ten year use on sale! Is it worth buying it?

    Sounds like a good start (~1/3rd retail, no shipping/taxes/etc.).

    Looking at your system. I always like to have a "balanced" system (size battery bank to loads, size solar array/charging to battery bank, etc.). First, the battery bank.

    2 * 180 AH @ 12 volt batteries? That would be 12 volt @ 360 AH or 24 volt at 180 AH. Not a large bank so check that it will sustain your loads. Nominally, we would recommend 1-3 days of storage, and 50% maximum discharge. 2 days and 50% discharge is a good round number (25% discharge per day) (note, batter capacity varies with the load--faster discharge rates, and the batteries have less apparent AH capacity).
    • 2*180AH*12 volts * 0.25 discharge = 1,000 Watt*Hours per day/discharge cycle.

    A 1,400 watt AC inverter will run at full load:
    1,000 WH * 0.85 inverter eff * 1/1,400 watt load = 0.61 hours = 36 minutes

    Not very long at full load.

    A Flooded Cell battery will supply ~C/8 discharge which would mean an "average" load should be:
    • 2 * 180 AH * 12 volts * 1/8 rate of discharge * 0.85 inverter eff = 459 watt average load recommended

    And maximum surge/starting current would be C/2.5:
    • 2 * 180 AH * 12 volts * 1/2.5 rate of discharge * 0.85 inverter eff = 1,469 watt surge load recommended

    Does that battery bank supply your loads?

    Next, recharging. We start by recommending 5% to 13% rate of charge for the battery bank. a 2*180AH*12 volt battery bank would need:
    • 2 * 180 AH * 12 volts * 1/0.77 panel+controller derating * 0.05 rate of charge = 281 Watt array minimum
    • 2 * 180 AH * 12 volts * 1/0.77 panel+controller derating * 0.10 rate of charge = 561 Watt array nominal
    • 2 * 180 AH * 12 volts * 1/0.77 panel+controller derating * 0.13 rate of charge = 729 Watt array maximum "cost effective" array

    So, your 1,000 watt array is a bit on the large side--But it will work. I would suggest that you use a charge controller with a remote battery temperature sensor to ensure the controller monitors the battery temperature and adjusts the charging voltage to charging temperature (hot batteries need lower battery charging voltage).

    A 1,000 watt solar array would produce (roughly) this amount of usable solar power on an average sunny day (we use ~4 hours of full noon time equivalent sun as an average number):
    • 1,000 watt array * 0.52 overall system efficiency * 4 hours of sun per day = 2,080 Watt*Hours per day (AC power)

    During summer/sunny seasons, you may get more sun (5-6 hours per day), and during monsoon season, you may get 2 hours per day (depends on your local weather). Of course, your solar array need 100% shade free sun. Any shading will (usually) dramatically reduce the solar array output (no pipes, trees, power lines, etc. blocking your panels).

    How is it looking so far?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Peejay
    Peejay Registered Users Posts: 3
    #6
    Re: Panels after ten year use on sale! Is it worth buying it?
    How is it looking so far?

    -Bill

    Bill,

    From my young age I ran away from mathematics....in the college days we enjoyed classic western movies in the nearby movie house when the maths prof. used all types of symbols in our class room. Now you are frightening me with the same type of symbols. Let me do the homework with pencil and paper. Need time!

    Batteries are the worst part in this system. The 1.4 inverter need 24V input-hence 2 x 180AH.

    One innocent question: Let me get the old panel-20 nos already at my doorstep, only little money paid, balance I have time.
    The MPPT is on its way from China. The inverter is still in the dealers shelf, just pay the money it will be mine for ever.
    180 AH is the available standard size. If we have to enhance, then have to buy multiple units of lower size- further cost escalation.
    Can I go ahead with the 2 x 180? Let the backup be low for the time being.
    Will try to add more when I get out of the present crisis....is it wise?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #7
    Re: Panels after ten year use on sale! Is it worth buying it?
    Peejay wrote: »
    Bill,

    From my young age I ran away from mathematics....in the college days we enjoyed classic western movies in the nearby movie house when the maths prof. used all types of symbols in our class room. Now you are frightening me with the same type of symbols. Let me do the homework with pencil and paper. Need time!

    No difficult math here... I am using your numbers instead of variables so you can see exactly how it relates too you... Notice, that if you double the size (AH) of the battery bank, you should double the min/max array sizes.
    Batteries are the worst part in this system. The 1.4 inverter need 24V input-hence 2 x 180AH.

    For you--Not a problem. If these are two 12 volt @ 180 AH batteries... You can wire them in parallel for a 12 volt @ 360 AH battery bank. Or in series for a 24 volt @ 180 AH battery bank (still the same amount of energy/power available).

    And, a 24 volt bank will be your friend. You can use smaller diameter copper wire (lower costs, can send power longer distances, lower voltage drop, higher allowable voltage drop). Plus your 12/24 volt charge controller can manage a 2x larger array when feeding a 24 volt battery bank (charge controllers are typically rated at maximum output current--So if you double the bank voltage, it doubles the power flow === Power = V*I; double V, and P doubles--Or double V, and 1/2 I or 1/2 the current so smaller diameter wire).
    One innocent question: Let me get the old panel-20 nos already at my doorstep, only little money paid, balance I have time.
    The MPPT is on its way from China. The inverter is still in the dealers shelf, just pay the money it will be mine for ever.
    180 AH is the available standard size. If we have to enhance, then have to buy multiple units of lower size- further cost escalation.
    Can I go ahead with the 2 x 180? Let the backup be low for the time being.
    Will try to add more when I get out of the present crisis....is it wise?

    Yep, you will be fine--In fact, if you want to use 4 batteries (two in series, then those two strings in parallel) would be fine too (just talk to us more about the correct way to wire up the series/parallel battery bank).

    -Bill "math is your friend" B. :-)
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #8
    Re: Panels after ten year use on sale! Is it worth buying it?

    "You can wire them in parallel for a 12 volt @ 360 AH battery bank. Or in series for a 24 volt @ 24 volt battery bank"

    bill did not write that clearly and it may confuse you. last part should read, "Or in series for a 180 ah @ 24 volt battery bank"
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #9
    Re: Panels after ten year use on sale! Is it worth buying it?

    Thank you Niel... Fixed the mistake.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Nila
    Nila Solar Expert Posts: 173 ✭✭
    #10
    Re: Panels after ten year use on sale! Is it worth buying it?

    Hey,

    Welcome to the forum,

    Im from tamilnadu, I think you can find even cheaper panels (brand new ) than the 60/watt pricing you were stating.

    I would send a PM as to where to look for them ;)
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  • Nila
    Nila Solar Expert Posts: 173 ✭✭
    #11
    Re: Panels after ten year use on sale! Is it worth buying it?

    Forgot to mention that.
    Panel cost is only the PART of the system.

    You have to also include costs for mounting/civil stuff, wires/fuses/disconnects.. may be combiner if you have more than few panels .
    At times they cost like 50% of the panels cost lol
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