Topic: exercise 1 part 1.6 Lighting using growth rate of -1% Subscribe | Previous | Next
John O' Shea 2/24/2013
1777 Views Hi,
I have a quick question. I entered the changes to the energy intensity of lighting in urban houses as "Growth(-1%)", but the values you would expect to get are different to those being produced by the program e.g. for 2040 the program is giving a value of 295.9kWh per household surely this should be 280kWh if its a reduction of 1% (i.e. 4kWh) per year. What causes this anomaly and would it be correct to leave the results as is?
Kind regards
Charlie Heaps 2/25/2013
1775 Views Hi John,
Bear in mind that you are applying the -1% growth in each year (i.e. its a COMPOUND growth rate). So in the first year when the intensity is 400 kwh the decline is indeed 4 kwh. But by 2039, the value has declined to 298.87. 1% of that is 2.99. So the value in 2040 = 298.87 - 2.99 = 295.88.
The same kind of effect applies in reverse when you a apply a positive growth rate. I.E. the absolute increases for a given positive percentage growth get bigger in each year.
I hope this helps,
Charlie