Assigning priority to meet demand

mikdale · Post by **mikdale** » Fri Jun 26, 2009 2:21 am

Hi all

I have run into a bit of difficulty (again!)

I'm trying to model the global energy system. I have a set pattern for demand (following a logistic growth up to some limit). This demand is then met by the various supply technologies, assigning priority based on values of energy return up to the capacity for that technology and then passing any left over demand onto the next technology in the list and so on until all demand has been met. I'm sure this is an easy economic problem that is figured out all the time by first years.

I'm having real trouble figuring out how I can model this in PLE Plus (and having the sense that I'll probably need to upgrade).

Any help that anyone can offer would be greatly appreciated.

Many thanks

Mik

bob@vensim.com · Post by **bob@vensim.com** » Fri Jun 26, 2009 9:25 am

from your description this is simply

supply1 = MIN(capacity1,demand)
supply2 = MIN(capacitry2,demand-supply1)
supply3=MIN(capacity3,demand-supply1-supply2)

and so on. See also appendix E of the Reference manual.

mikdale · Post by **mikdale** » Mon Jun 29, 2009 4:59 am

Hi Bob

Thanks for the reply. The equations you suggest deal with the value of each of the supplies but I'm not sure how to assign those values based on which energy source has the highest payback value. Does that make sense?

So, sometimes let's say oil has the highest energy return so is assigned priority to meet residual demand, at some other time coal may have a higher energy return and so be assigned top priority. I'm not sure how to switch between energy sources in this way. At the moment I'm using an IF THEN ELSE statement as I only have renewable and non-renewable sources, but I'm not sure how to generalise this to more than two sources.

I'd be grateful of a suggestion

Mik

Post by **Administrator** » Mon Jun 29, 2009 6:19 am

If I were building a model with more than two sources, I would use subscripts (but these are not available in PLE Plus). You could then use the allocation functions within Vensim (http://www.vensim.com/documentation/html/22330.htm).

Is upgrading an option?

Tony.

bob@vensim.com · Post by **bob@vensim.com** » Mon Jun 29, 2009 9:25 am

Check the molecules for market share formulations. These are all continuous (sharing not strict ordering) but you can control the extent of sharing by making attractiveness very sensitive to relative price. Capacity has to be added in as a second stage computation. Unfortunately, it is still hard to get something reasonably behaved - ergo the allocation functions discussed in Appendix E to the reference manual.