Can Energy Plus simulate directly semi-transparent photovoltaics?

asked 2016-02-18 09:00:12 -0600

luis melo
225 ●2 ●5

updated 2016-02-18 11:06:53 -0600

Aaron Boranian

14155 ●83 ●24 http://bigladdersoftware.com/

I cannot found specifications about semi transparent photovoltaics in inputoutput reference.

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I know you can assign PV to shading surfaces and to base surfaces. Base surfaces won't help you because they are opaque. Not sure what happens to PV production if you start making the shading surface translucent by assigning a transmittance schedule to it. It will let some light through but will it still produce as much PV? But this isn't building integrated PV in that the surface doesn't thermally interact with the building model other than blocking some sunlight. I don't know if PV can be associated with fenestration surfaces.

David Goldwasser ( 2016-02-18 11:07:06 -0600 )edit

@David Goldwasser if you look at the IDD for the Generator:Photovoltaic object, the surface list it can reference is "AllShadingAndHTSurfNames". If you search for this term in the IDD, you'll see that this includes building surfaces, shading surfaces, fenestration surfaces, SurfaceProperty:ExteriorNaturalVentedCavity, solar thermal collectors, PVT collectors, and rain water collectors.

Aaron Boranian ( 2016-02-18 13:36:53 -0600 )edit

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answered 2016-02-18 11:20:24 -0600

Aaron Boranian

14155 ●83 ●24 http://bigladdersoftware.com/

Modeling PV arrays in EnergyPlus is really a 3-step process:

Draw the geometry of the surface that contains the PV cells
Add a Generator:Photovoltaic object to the model. This object defines how the PV array generates electricity by referencing the PV surface and a performance efficiency object (next bullet point)
Add a PV performance object to the model (easiest is the Simple Approach). This object defines how efficient the PV array is at converting incident solar radiation into electricity

The Generator:Photovoltaic and PV performance objects do not have input fields related to transparency. However, it is possible to reference a Shading:Building:Detailed object for the PV array. This will be the easiest way to model semi-transparency, since the list of input fields for this object are short and one of them is Transparency Schedule, so you can model dynamic transparency throughout the simulation if you wanted.

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I'm just spit balling here but it seems to me that the transparency of the module would figure into the efficiency of the module and that you shouldn't have to go into the detail of defining a building shade?

Chris Jones ( 2016-02-18 12:04:23 -0600 )edit

Thank you, I'll try to do this and let you know about results!! But I guess that its possible!

luis melo ( 2016-02-18 13:28:03 -0600 )edit

I'll have @luis melo correct me if I'm wrong, but I think he wants to model a PV module that has a transparent back surface instead of an opaque back surface. Sunlight would hit the PV cells first, then some is transmitted to the back surface, then the last is transmitted through the back surface and out of the module.

Aaron Boranian ( 2016-02-18 13:31:58 -0600 )edit

Exactly, and study how much is possible to reduce the energy consumption for artificial lighting and HVAC using appropriate semi transparent photovoltaic windows.

luis melo ( 2016-02-19 04:13:29 -0600 )edit

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answered 2016-02-19 07:09:49 -0600

bryane
171 ●2

I studied the influence of semi-transparent PV on a large commercial building using E+. This is the way I did it, you may find another way. I ran two simulations 1) with the semi-transparent properties of the PV as windows (e.g. to calculate the change in loads). In this simulation no electricity is ‘generated’ you are just calculated the impact of the new fenestration. 2) using PV in place of these windows to calculate what would have been generated (the loads will not be correct as the fenestration will not be accurate because I believe in E+ PV can only go over walls, not windows). Use the results from (1) to determine the utilities and then subtract off what would be generated as calculated in (2). I did it at a fine resolution as I was particularly interested in the influence on peaks.

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What kind of "semi transparent properties" did you use for the fenestration? Did you use the simple model with measured values for SHGC, Light transmission, U value or a detailed model accounting for pane reflections etc?

If you were to add the semi-transparent PV laminate on top of an exsting roof glazing with an air gap (say 15cm), would it make sense to model it as an external shade with properties of the PV laminate? I have tried this but it gives me higher cooling +heating loads compared to a setup where the PV is integrated (semi transparent BIPV). It doesnt seem accurate!