questios photovoltaic commercial

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Rei
questios photovoltaic commercial

I have a client and I´m perform a Photovoltaic (detailed), Commercial (distributed) real case and have some questions:

1) In module, Temperature Correction section. If I use the NOCT method and the panel goes to be on the roof, the option “Building integrated” takes into account that the panels will be on the roof?

2) In Shading and Snow,

a) 3D shade calculator. Please see the atached "3D shading scene calculations archive"
b) Self Shading for Fixed Subarrays…Section. What is the recommended Module aspect ratio value for modules “building integrated” on the roof?

3) In Electricity Rates, Rates for Demand Charges section. I´m not sure how to use this section. In what cases I have to use this section? Please see the attach “Variplast.sam” archive. Could you give me more information about this?

Rei

The consumption of the charges (Loads) is approximately 7,000 kWh/month. How do I enter this value in Photovoltaic Commercial SAM?

Paul Gilman

Hello,

1. The "mounting standoff" options determine whether and by how much SAM adjusts the rated NOCT temperature of the module in the cell temperature calculation. Both the "building integrated" and "greater than 3.5 in" options use the rated NOCT temperature without adjustment, and are therefore equivalent to each other. In your case, for a roof mounted system, you should choose one of the other options based on the distance between the back of the modules and the roof surface. The range of values for each option represents that distance in inches. For example "2.5-3.5 in" would be appropriate for a roof-mounted system where the distance between the module back and roof surface is between 2.5 inches and 3.5 inches.

https://sam.nrel.gov/node/74460

2a. When you close the 3D shade calculator, it calculates shade losses for your shading scene, and offers you to replace the SAM shading inputs with the data it calculated. Unfortunately, it is not possible to close the 3D shade calculator window without starting the calculations, which can take a little time depending on the complexity of the scene.

When the calculations are finished, it displays the two messages you show in the Word document. The first message, "Update timeseries shading and diffuse losses for the array (in subarray 1)?" is asking whether you want the 3D shade calculator to replace the shading inputs in SAM with the data it calculated. Click "Yes" if you want to replace the SAM inputs, or click "No" if you want to keep the SAM inputs and discard the data calculated by the 3D shade calculator.

If you click "Yes," another message may appear. In your case the message "WARNING: For subarray1, you specified 9 strings and have 1 strings in the 3D scene. Do you wish to continue with the 3D scene values?" That means that in SAM, in the Edit Shading Window, on the System Design page, the "Strings in parallel" input is 9, but in the scene you drew in the 3D shade calculator there is only 1 string. If you want to apply different shade losses to different strings in the array, then, in the 3D shade calculator you should use the "String" property of each active surface to indicate the string number of the surface. For example, in your scene, there are 3 active surfaces, and all of them have String = 1, which means that the combined losses for all three surfaces will be assigned to the single string in SAM.

I would recommend dividing your array into three subarrays. Use Subarray 1 for the active surface with Tilt=4 and Azimuth=-20, Subarray 2 for the smaller of the two active surfaces with Tilt=6 and Azimuth=225, and Subarray 3 for the remaining active surface. I don't know how your strings are laid out, but you could replace each large active surface with smaller ones, so that each of the 9 strings is represented by its own active surface. Be careful to assign the "Subarray" and "String" property of each surface. After you do that, the 3D shade calculator will calculate separate losses for each string, and assign them correctly to the shade loss tables in SAM.

2b. If you use an active surface for each string, and the modules in each string have the same orientation, the shade losses generated by the 3D shade calculator should account for self shading so you can disable the self-shading model in SAM.

3. Demand charges are electricity rates that a utility company charges customers for the maximum electricity usage in a month. For example, a demand rate of $10 means that each month, the electricity bill for a given month would include an amount equal to $10 multiplied by the peak kW delivered by the grid in that month. Some company have demand rates that vary by rate or block of kWh. The inputs in SAM are designed to handle basic demand rate and more complex tiered and time-of-use demand rates.

Best regards,
Paul.

Rei

Thank You Paul for your wide answer. I have another questión: The consumption of the charges (Loads) is approximately 7,000 kWh/month. How do I enter this value in Photovoltaic Commercial SAM?

Rei

Paul Sorry

1) From Answer 2a
a) How do I divide muy array into three subarray?
b) How do I assign the "Subarray" and "String" property of each surface?

2) From answer 2b

a) How can I put disable the self-shading model in SAM?

Thank you very mutch

Paul Gilman

1a. On the System Design page, under "DC Subarrays," check "Enable" for each subarray that you want to enable. For the subarrays, you would check "Enable" under "Subarray 2" and "Subarray 3."

1b. For each subarray that you enable, use the "Strings allocated to subarray" input to define the number of strings in each subarray. You can then change the array orientaion and tracking options for each subarray, and the shading and losses for each subarray on the Shading and Snow page and Losses page.

2a. To disable self shading for a subarray, on the Shading and Snow input page, for
"Self shading," choose "None."

Best regards,
Paul.

Rei

Thank you very mutch Paul, Your answers was very usefull. Can you check the attached file to see if it is well made?

Best
Rei

Paul Gilman

Dear Rei,

The latest version of your file looks good, and will result in a reasonable estimate of the effect of shading on the array output.

However, it does not make use of the 3D shade calculator's partial shading calculations, which work with crystalline Silicon modules, and can more accurately estimate the effect of partial shading of the array for modules with diodes. To make use of those calculations, you should replace each active surface in the 3D shading scene with a set of surfaces for each string in the subarray.

For example, for your file, on the System Design page in SAM, you can see that Subarray 1 has 5 strings, Subarray 2 has 4 strings, and Subarray 3 has 5 strings. To model that in the 3D shade calculator, you could replace the active surface for Subarray 1 with 5 smaller active surfaces. Assign the number 1 to the Subarray property for all five of those active surfaces, and assign the numbers 1-5 to the String property for each of those active surfaces. Similarly, create 4 active surfaces for Subarray 2, and 5 active surfaces for Subarray 3.

After you make those changes in the scene, the 3D shade calculator will calculate a set of shading losses for each string, and automatically assign them to each subarray on the Shading and Snow input page.

Best regards,
Paul.

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