Solar PV Energy Generation Estimate

  • We are modelling a building in Perth with a large PV System and our (external) PV generation estimates aren’t matching those of eToolLCDs. The system is 32kW capacity and eTool is only showing 44,160kWh generation from this per annum which is very low compared to generation prediction by SAM (System Advisor Model) for a 32kW system which is 51,000kWh.

    Great question. eToolLCD assumptions are generally referenced in either the bookmarks against the quantities in question, or in the template description.  The solar generation templates you’re using are quite old and the documentation on the assumptions was pretty poor so we’ve updated it and here’s what the template description states now:

    Default generation capacity taken from the annualised generation assumed in Schedule 5 of the Renewable Energy (Electricity) Regulations 2001.   These generation figures may be lower or higher than actuals or other estimates due to the following variables: 

    • Tilt and azimuth of panels
    • More accurate weather files for predictions in other systems
    • Differences between simulated and actual weather files
    • Overall system efficiency
      • Soiling
      • Shading
      • Mismatch
      • Wiring
      • Connections
      • Light-Induced Degradation
      • Nameplate Rating Variation
      • Age Degradation over life of system
      • Availability / Utilisation
      • Inverter efficiency

    Generally when these factors are all accounted for with reasonable assumptions the results actually correlate quite well with the annualised generation assumed in Schedule 5 of the Renewable Energy Regulations.  

    I just ran a quick calculation in PV Watts to double check our figures and using the default figures it returned 38,918kWh per year. I would really question the 51,000kWh per year figure for a 32kW system in Perth unless you are using the best panels (e.g. Sunpower with very low combined losses and superior generation guarantee warranties), the best inverters, oversized wiring and scheduling cleaning of the panels at regular intervals (e.g. fortnightly). Remember this is the generation averaged over the 25 year life of the system (not the first year’s generation).

    Hi Richard,

    We used both PV Watts and SAM (System Advisory Model) to generate results for 25yr average, and it still comes in around 51’000kWh/year on average over 25 years. I have noted the losses used as per SAM defaults, which I believe are in line with standards.

    Can you please confirm the Azimuth (deg) you have been using for your calculations? This particular project, we have reviewed roof and it is likely the panels will be able to face north, so our azimuth is 0.

    Soiling: 2%
    Shading: 3%
    Snow: 0% (Perth)
    Mismatch: 2%
    Wiring: 2%
    Connections: 0.5%
    Light-induced degradation: 1.5%
    Nameplate: 1%
    Age: 0.6%
    Availability: 3%
    Total System Losses: 14.59%

    Laura Smith
    CADDS Energy

    Hi Laura,

    You’re right, I hadn’t updated the azimuth. So you’re spot on, 51,000kWH seems solid. The Renewable Energy (Electricity) Regulations 2001 obviously build some conservatism into the numbers so the eToolLCD figures reflect this. Thanks for coming back to me and correcting the record for other users who stumble on this post.


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