Solar production calculator

HOW TO ESTIMATE THE PRODUCTION OF YOUR SOLAR PV SYSTEM

Accurately estimating the production of your solar PV system is an important step in anticipating both your monthly energy bills and your payback period. We recommend using PVWatts®, a solar production calculator developed by the National Renewable Energy Laboratory (NREL), to help estimate the monthly and annual energy production of your solar PV system.  

While PVWatts  is a powerful tool that uses 30 years of historical solar irradiation data and weather patterns, using the default settings could overstate your annual energy production estimates. We’ve put together some suggestions on how to best use this tool’s advanced settings to get the most accurate results. If you’re unsure of any of your system’s details, your registered contractor can help you fill in the blanks.  

SYSTEM INFORMATION

First, enter your location in the Resource Data tab of the PVWatts Calculator. Next, enter the following information into the PVWatts system info tab. Use the following table as a guide: 

DC system size (kW):Enter as applicable.
Module type:If you don’t have information about the module type in your system, choose “standard” as the default. 
Array type:Enter as applicable.
System losses (%): Click the “loss calculator” link to the right and use the following inputs: 
Soiling (%):
Shading (%): Enter as applicable 
Snow (%): 10% for ground-mounted or 20% for rooftop 
Mismatch (%):
Wiring (%):
Connections (%): 0.5 
Light-induced degradation (%): 1.5 
Nameplate rating (%):
Age (%): 2 (or as applicable) 
Availability (%):
Tilt (deg):If your tilt degree is unknown, use 41° for ground installations and 23° for rooftop installations. 
Azimuth (deg):If the azimuth orientation is unknown, use 180°. 

ADVANCED PARAMETERS

Click the “Advanced parameters” drop down below and enter the following information:

DC to AC size ratio:Enter as applicable.
Inverter efficiency (%):Enter as applicable.
Ground coverage ratio:0.4 (use default value).

Keep in mind that ground mounted installations in Manitoba will typically produce around 1200 kWh annually per installed kW of solar capacity and rooftop systems will typically produce around 1000 kWh annually per installed kW.  Use these numbers as a guide to confirm that your annual estimates from PVWatts are reasonable.

MONTHLY ESTIMATE CORRECTION FACTORS

PVWatts slightly overestimates or underestimates the monthly production estimates for Manitoban installations depending on the month. The following correction factors will provide a more accurate month-to-month estimate for your solar PV system’s production.  

PVWATTS CORRECTION FACTORS

January0.548
February1.443
March1.117
April0.864
May1.267
June1.138
July1.207
August1.082
September0.986
October0.925
November0.862
December0.776

In order to better estimate the monthly production of your solar PV system, simply multiply the monthly estimate from PVWatts by the corresponding correction factor for that month from the table above. For example, if the PVWatts calculator estimates that an installation will produce 1,000 kWh in June, a more accurate value for that month would be:  

1,000 kWh x 1.138 = 1,138 kWh  

This calculator allows you to estimate the production of your solar PV system. However, it’s important to keep in mind that other factors will likely impact the accuracy of these numbers. If you have any questions, be sure to reach out to your contractor for assistance. 

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Check out the rest of the articles in our solar series.


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