Gabriela Peña Balderrama 6/10/2015

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Dear Taylor:


I am working with the Transport Exercise (the template with all the data by default) and I would like to get support for understanding the calculation of the Device retirements. Let me explain my question with numbers:

Working in the branch Demand/Cars. Scenario: Business as Usual, Vintage: All Vintages

- For 2010: The stock of cars is 6800 thousand devices
- The sum of the Device sales from 2010 to 2030 is: 16800 thousand
- The sum of the device retirements from 2010 to 2030 is: 16330.38 thousand
(I made the calculations outside Leap)

Using a simple balance the number of vehicles to 2030 should follow:

Vehicles (2030)=Vehicles (2010)-Total Retirements(2010-2030)+Total Sales (2010-2030)= 68000-16330.38+16800=7269.62 thousand

The calculation of Leap shows in 2030: 7106.35 thousand

Something is missing (163264 vehicles)... Please could you explain how Leap is calculating the Device Retirements each year?
My Leap version is 2014.0.1.14

Thanks in advance,
With regards

Gabriela

Taylor Binnington 6/16/2015
 

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Hi Gabriela,

One important detail about LEAP's stock turnover calculations (often overlooked) is that the Stock you specify in 2010 is an *end of year* stock. This means that it already accounts for any retirements which would have happened in 2010. I mention this because it might change how you do your own calculation outside of LEAP. Please let me know if it changes your result.

For a bit more context, you might find our short help page on stock turnover calculations useful. You can find that here:

http://www.energycommunity.org/WebHelpPro/Demand/Vintaging_Calculations.htm

Hope this helps. Otherwise, please send me a careful description (preferably an Excel doc) of you you've carried out your calculations, and I may be able to provide comments.

Taylor

Gabriela Peña Balderrama 6/23/2015
 

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Dear Taylor,

Thanks for the reply. Please find attached the excel sheet with the calculations explaining my question. If the stock specified in 2010 is a end-year stock, the retirements and sales should be accounted from 2011, but the results shows retirements and sales staring in 2010.
Thanks for your help.

---

Attachments:  Sheet1leapissue.xlsx [8]

Taylor Binnington 6/23/2015
 

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Hi Gabriela,

This is a great observation, and I admit it took me some time to track down.

The reason that your calculation disagrees with the value displayed in LEAP is because LEAP does not track the stock of vehicles of vintages greater than the maximum number of vintages. This number is set under Basic Params: Stocks.

In the Transport Exercise specifically, not all vehicles are retired before the maximum number of vintage years. This can be seen in the "Private Car Survival" lifecycle profile. However, after this maximum age, stocks of these vehicles are no longer tracked, and they longer appear in the Demand: Stock results.

Although this is not technically an error, I agree that it is confusing. We may consider adding diagnostics into LEAP to inform the user if the last entry of a Survival Profile is nonzero, which would flag this occurrence.

Please also make sure you are using the most up-to-date version of LEAP (2014.0.1.29 at the time of writing). This will address a problem with retirements in 2010, which should not be shown.

Hope this is clear,
Taylor

Gabriela Peña Balderrama 6/23/2015
 

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Dear Taylor,

Thanks for the reply. I already revised the improvements in the latest version of Leap and I found the Stock turnover related improvements in the 2014.1.16 version with the "First sales year" that solves the issue of retirementes in the base year. But for some reason I cannot update my Leap version to the latest one, please find attached the screenshot of the issue. Should I re-install Leap?

Regarding the same topic let me ask you other question. After revising the stock Analysis calculations in the link (http://www.energycommunity.org/WebHelpPro/Demand/Stock_Analysis_Calculations.htm) it is not clear how the Stocks are calculated. I was wondering if the expression could be written in a different way, please correct me if I am wrong (I sent an optional way to re-write the equation in the attached pdf file).

Thanks in advance

---

Attachments:  Leap.pdf [7]

Taylor Binnington 6/23/2015
 

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Hi,

I'm not sure why this is occurring. Are you certain you aren't already running the latest version of LEAP? Otherwise, you can always download the latest setup.exe file and simply run it, which will install the latest version ontop of your existing installation.

Regarding your alternative formulation of LEAP's stock calculations - it is not equivalent. Without going into details why, I'll try to explain LEAP's stock turnover calculations more clearly, focusing on the first two equations in this link:

http://www.energycommunity.org/WebHelpPro/Demand/Vintaging_Calculations.htm

The first equation contains the term

Sales_(t,v)

This should be interpreted as the total sales of a vehicle of vintage v. Since all vehicles sold in each year are only of a single vintage, the 'year' index on this term is not necessary - sales of a particular vintage only arise in a one particular year. However, if it's clearer, it could be added back in like this:

Sales_(t,v,year=y-v)

The next equation sums the stock across all vintages, including vintage zero: this is interpreted as new vehicles, which are given by the sales variable in the current year.

Hope this helps,
Taylor

Gabriela Peña Balderrama 6/23/2015
 

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Dear Taylor,

Thanks again for the reply and the clarification of the Equations. It is confusing to refer the calculation of the stocks based in the survival fraction of the SALES if is not clear that the sales is a parameter that already sums the stocks from the year before in each calculation and update the vintages. But now its clear.

Best regards
Gabriela

Taylor Binnington 6/23/2015
 

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Glad I could help.

Perhaps it's more natural to think that the survival profile refers to the previous year's stock, when in fact it is expressed as the fraction of the *original* stock of a particular vintage. And the 'original stock', meaning the total stock when the technology vintage is newly introduced, is simply given by the sales.

Taylor