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Why does PVWatts fail in OpenStudioApplication-1.2.1?

asked 2022-03-26 23:20:21 -0600

mattkoch's avatar

updated 2022-03-27 16:38:41 -0600

I am using OpenStudioApplication-1.2.1, which appears to be running EnergyPlus 9.5. I have written an EnergyPlus measure that adds a simple PVWatts system to the model. The following are the changes this measure produces in the in.idf file in the run folder.

PV Availability,                        !- Name
OnOff,                                  !- Schedule Type Limits Name
1.0;                                    !- Hourly Value

PV Transmittance (PV Surface 1),        !- Name
Fractional,                             !- Schedule Type Limits Name
0.1;                                    !- Hourly Value

PV Array (PV Surface 1),                !- Name
5,                                      !- PVWatts Version
5040.0,                                 !- DC System Capacity {W}
Premium,                                !- Module Type
FixedRoofMounted,                       !- Array Type
0.13043478260869568,                    !- System Losses
Surface,                                !- Array Geometry Type
,                                       !- Tilt Angle {deg}
,                                       !- Azimuth Angle {deg}
PV Surface 1,                           !- Surface Name
1.0;                                    !- Ground Coverage Ratio

PV Arrays,                              !- Name
PV Array (PV Surface 1),                !- Generator Name 1
Generator:PVWatts,                      !- Generator Object Type 1
5040.0,                                 !- Generator Rated Electric Power Output 1 {W}
PV Availability,                        !- Generator Availability Schedule Name 1
;                                       !- Generator Rated Thermal to Electrical Power Ratio 1

PV Inverter,                            !- Name
1.15,                                   !- DC to AC Size Ratio
0.96;                                   !- Inverter Efficiency

PV System,                              !- Name
PV Arrays,                              !- Generator List Name
Baseload,                               !- Generator Operation Scheme Type
,                                       !- Generator Demand Limit Scheme Purchased Electric Demand Limit {W}
,                                       !- Generator Track Schedule Name Scheme Schedule Name
,                                       !- Generator Track Meter Scheme Meter Name
DirectCurrentWithInverter,              !- Electrical Buss Type
PV Inverter;                            !- Inverter Name

And the following exist already in the in.idf file when the PVWatts system measure is not run.

OnOff,                                  !- Name
0,                                      !- Lower Limit Value {BasedOnField A3}
1,                                      !- Upper Limit Value {BasedOnField A3}
Discrete,                               !- Numeric Type
availability;                           !- Unit Type

PV Surface 1,                           !- Name
PV Transmittance (PV Surface 1),        !- Transmittance Schedule Name
,                                       !- Number of Vertices
8.9154, 5.69858725844097, 11.7348,      !- X,Y,Z Vertex 1 {m}
8.9154, 4.1148, 10.8204,                !- X,Y,Z Vertex 2 {m}
34.5186, 4.1148, 10.8204,               !- X,Y,Z Vertex 3 {m}
34.5186, 5.69858725844097, 11.7348;     !- X,Y,Z Vertex 4 {m}

PV Surface 1,                           !- Shading Surface Name
0.3,                                    !- Diffuse Solar Reflectance of Unglazed Part of Shading Surface
0.3,                                    !- Diffuse Visible Reflectance of Unglazed Part of Shading Surface
0;                                      !- Fraction of Shading Surface That Is Glazed

So, as far as I can tell, all this "connects" correctly. Yet, when I run the model, it fails with the following output:

Initializing workflow.
Processing OpenStudio Measures.
Translating the OpenStudio Model to EnergyPlus.
Processing EnergyPlus Measures.
Applying AddPVWattsSystemWithOptionalStorageAndCosts
Result: Success
Initial Condition: Model started with 0 PV Arrays.
Final Condition: Model finished with 1 PV Arrays.
Starting Simulation.
EnergyPlus Starting
EnergyPlus, Version 9.5.0-de239b2e5f, YMD=2022.03.26 22:45
Initializing Response Factors
Calculating CTFs for "4 IN CONCRETE FLOOR"
Calculating CTFs for "6 IN CONCRETE FLOOR"
Calculating CTFs for "DRY WALL"
Calculating CTFs for "IEAD ROOF (2018 IECC&#44 2A)"
Calculating CTFs for "NON-SWINGING DOOR (U-0.31)"
Calculating CTFs for "STEEL FRAME WALL (2018 IECC&#44 2A)"
Calculating CTFs ...
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1 Answer

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answered 2022-03-27 12:42:15 -0600

updated 2022-03-27 12:44:27 -0600

You are seeing EnergyPlus start to run, so this probably isn't an issue with the OpenStudio application. Seems like the error is coming from the PVWatts engine. "gcr" is the variable name for the Ground Coverage Ratio input, and while it should allow values up to 1 (as you've input), the "max=0.99" makes me think you should try a value below that. Or just put the default, since GCR only applies to arrays with one-axis tracking, and you're modeling a fixed array.

There's probably a bug here, but that might at least get you running.

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Yes, setting Ground Coverage Ratio to 0.5 indeed corrected the issue. Thank you very much, Eric!

mattkoch's avatar mattkoch  ( 2022-03-27 15:01:27 -0600 )edit
shorowit's avatar shorowit  ( 2022-03-28 11:05:57 -0600 )edit

Thanks @shorowit. I was going to try to replicate with an example file but other things came up.

ericringold's avatar ericringold  ( 2022-03-28 11:34:47 -0600 )edit

FYI, the latest version of EnergyPlus (22.1) does not generate this error anymore.

shorowit's avatar shorowit  ( 2022-09-12 16:32:30 -0600 )edit

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Asked: 2022-03-26 23:20:21 -0600

Seen: 127 times

Last updated: Mar 27 '22