Happy New Year to all and congratulations to Diane Paterson who answered the quiz question from two weeks ago correctly. For those of you who did not read the

*Chronicle*on the 22^{nd}of December, here is a summary of the question, which was used as a way to explain the concept of payback period.Our daughter’s bike trailer represents an investment in energy efficiency in that it allows us to pedal her around town instead of driving. The IRD mileage reimbursement rate for 2012 was 77 cents per kilometre. (This takes into account all of the associated costs of driving: petrol, insurance, WOF, repairs, etc.) For us, this means a round-trip to centre city in are Subaru sets us back about $11.

The second-hand baby trailer cost $125, plus an additional $60 for minor repairs. How many round trips from Castlecliff to city centre – at a savings of $11 each – would it take to recoup the investment?

Diane wrote:

Hi Nelson,

Really enjoying your column and coveting a home energy audit, should I be so fortunate!! By my reckoning it will take you 17 round trips into town to recoup an investment of $185 on Verti’s baby trailer. $185/11 = 16 trips, $9 remainder.

I noticed you and the family in town with the trailer before Christmas, so I guess you have made a start.

Happy New Year and warm regards to all.

Di P

Payback period is usually expressed in units of time: weeks, months, years. But in this case the unit was the number of driving trips avoided. Probably the easiest way for anyone to see the potential savings made possible through energy efficiency is to use the example of a compact fluorescent light bulb.

A brief version of this ran months ago as a side bar with this column, but at the current auspicious time of the dawning of a new year, little Verti and I will use this opportunity to try to convince some readers to

*resolve*to change a light bulb in 2013. Here goes.A 25-watt compact fluorescent light bulb (CFL) emits the same amount of light as a 100-watt incandescent bulb. This is a savings of 75% every hour!

*Good Idea*

If you currently run one 100-watt incandescent for 10 hours each day, you’ll use 1,000 watt hours (1 kilowatt hour – kWh), or one “unit” of power as your electric bill probably says. Each unit costs around 28 cents.

Replacing that 100-watt incandescent with a 25-watt CFL would mean you use 250 watt hours, or 0.25 kWh, per day, costing only 7 cents. Therefore, your daily savings would be 21 cents by changing one light bulb.

CFLs cost $5 at most stores while incandescents cost $1. The difference of $4 is the up front cost one must pay for long-term savings. The question of the week is: How long will it take to pay back $4 at a daily savings of 21 cents?

400 cents divided by 21 cents per day = 19 days. This is child’s play, right Verti?

*Bad Idea*

Every proceeding 19 days you’ll save another $4, for an annual savings of $76.84. Change two light bulbs and it doubles. Change three and it triples. Change four…you get the picture.

Changing just five 100 watt incandescent light bulbs to 25 watt CFLs could save you $384.21. But there is a catch. You need to come up with $25 to buy them. Is it worth it? Anyone

*resolved*?Helpful tip: I buy my CFLs at one of the major supermarkets in town. Their ‘store brand’ of CFLs comes with a money back guarantee. I save the bar code from the box and staple the receipt to it just in case a bulb does not perform up to standard.

Peace, Estwing