1. Energy savings calculation (ESC) for lighting
October 2010

2. Key parameters for energy use
The annual burning hours are estimated as it is not known how many hours per year a specific bulb is utilised. Research shows that there is much variation in burning hours mainly depending on the type of room.
Based on a lighting research the energy use is calculated based on the average capacity (Watt) and the average burning hours.
As this is also done for the reference situation, the energy savings are deemed (average) savings

3. Baseline
A reference situation is used and not the (real) before situation. The reference is a conventional or incandescent bulb.
The following assumptions are used:
an additional unit would otherwise have been installed with a conventional bulb with comparable capacity;
replacement of (broken) CFL units is negligible;
immediate replacement and use of CFL, so no ‘spare units’ (that will replace a conventional bulb at some point in the future).

4. Calculation data
In general we assume that a CFL lamp replaces a light bulb of 4.5 times its wattage, reducing the installed capacity therefore with 3.5 times its wattage.
Reference burning hours: the number of burning hours for an average lighting unit in the household for the year 2000: 482 hrs.
Uncertainty of the average burning hours.
the number of burning hours for an average conventional bulb (467 hours) can be seen as a lower boundary.
the number of burning hours of already installed CFLs (519 hours) can be seen as an upper boundary

5. Savings lifetime
The lifetime of a CFL is between 3,000-15,000 burning hours. In The Netherlands in most cases one calculates with an average of 6,000 burning hours; the value also indicate in the CEN CWA 27.
Based on an average burning hours value of 482 a year, the replacement is accounted as energy saving for 12 years

6. Formula
Annual electricity savings in year t = ns x [1/1000 x (Pold x bo – Pnew x bn)] in kWh/yr Pold = the average capacity in W of bulbs Pnew = the average capacity in W of CFLs sold in year t bo = bn = burning hours general average ns = number of CFL units sold in year t 1/1000 = conversion factor from W to kW

7. Input data For baseline: For the energy savings calculation
Burning hours: 482 hrs (annual)
Average capacity of the replaced lamp
For the energy savings calculation
Average capacity of CFL: 12.4 W
Life time: 6,000 burning hours or 12 years
CFL lamp replaces a light bulb of 4.5 times its wattage
Sales date CFLs:
Annual average of million in the years 2004, 2005, 2006 and 2007
The capacity of the CFLs in 2000 is different for the lighting zones in a house. We use the average value of 12.4 W from the year 2000

8. Energy savings
Annual electricity savings in year t= (5,678,000 /1000) x (3.5 x 12.4) x 482= 118,776,946 kWh/yr ≈ 118,8 TWh/yr (for the years 2004 thru 2007).
The savings at the end of the year 2007 will be the sum of the four years savings, as the savings lifetime is about 12 years.