String monitoring verus Sub array monitoring

Hello all,

in an effort to contain projected O&M costs (4mW facility), we are considering dumping string level monitoring and instead monitor at the sub array level using the inverter itself. (500kW blocks).

Any opinions out there on which way to go, i.e. string verus subarray level monitoring ?


Thx

Dan

Comments

  • solar_davesolar_dave Solar Expert Posts: 2,389 ✭✭✭✭
    Re: String monitoring verus Sub array monitoring

    well it is all about cost vs benefit. With all other conditions being equal the inverter measurements should be adequate to determine if an issue is taking place in an array. This assumes no shading, same inputs to the inverters .....
  • BB.BB. Super Moderators, Administrators Posts: 32,612 admin
    Re: String monitoring verus Sub array monitoring

    Look at the ability of central monitoring to actually identify string failures... Say it can with 2% accuracy:
    • 0.02 * 4,000 kW * 5 hours of sun = 400 kWH per day "losses"
    • 400 kWH * $0.08 tariff rate = $32 per day
    Now, you have identified the system needs maintenance--How will your guy(s) go out and identify failed strings? Go out with a clamp on Amp DC Meter to identify string that are 50% under performing?

    Say 500 kW block, how many tests (open service boxes, clamp on each array string)? Figure $100 per hour service costs plus travel plus repairs (bad cable connection / bad panel(s). x8 blocks for 4MW system?

    Vs you can identify single string failures... How many single string failures will you allow before you send out a repair crew?

    And who is responsible for paying for identifying poor performance, for diagnosing down to the string level, for repair/replacement? Do you have a proactive plan to identify systemic problems (say 80% of the problems are due to corrosion of combiner boxes--condensation/poor design of wire clamping screws, etc.)....

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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