Tuesday 15 January 2008

Some real life CFL data

My rabid objections to Minister Gormley's proposed mandatory imposition of energy efficient lighting on us poor slobs in Ireland can be found here and here and here. I have calmed down somewhat now and worked out the numbers. Overall I still think his carbon footprint numbers are still a bit high but his cost saving data for consumers actually looks reasonable. There is a clear benefit for me in switching to CFL or LED in terms of cost and carbon footprint, and I suspect that the same would be true for the vast majority of Irish householders despite my initial skepticism.

When we moved into the new apartment in September we had to fit out all of the light fittings so I have a handy starting date to use for some real world life time data on bulb lifetimes and I'm going to keep track now that we've got to a point where a significant number of them have blown and need to be replaced (5 out of 16).

All of the data is in the spreadsheet that I've shared here for the propeller heads if there are any apart from me. The headline numbers are below.

  • Daily Incandescent power load - 2.435 kWh
  • Daily CFL power load - 0.426 kWh
  • Net Daily Saving €0.20 / 0.48kg CO2

This takes into account the (minor) loss in heating resulting from the switch. So for us we can expect to save €72 per annum and prevent 176kg of CO2 emissions.

You can buy cheap CFL's but I wouldn't at the moment and I don't think anyone should, you'll still save money with the better ones. The first bulb to blow in this apartment was just such a cheap CFL that I put in our storeroom despite its 6000 hour life claims. Reasonably decent CFL's can be bought for around a €5 to €7 a pop that actually produce light that is (at least initially) reasonable to live with. We have 16 bulbs in our apartment so replacing them all with CFL's will cost us about €80-€120 initially and the ongoing replacement cost will be about half that every three years. In general good CFL's should give you many years of life but my experience makes me dubious about the common claims of 6-10 years. They certainly do degrade before failing and my experience is that those that are switched multiple times per day have a usable life of about 3000 hours vs the 1000 hours or so that has been my experience with typical incandescents in busy rooms. Incandescents are quite cheap but nice ones are not all that cheap and you will spend €1 on average at least across the typical bulbs in a house or apartment, and you will replace them 3 or more times as often. The actual cost of switching to my more expensive choice in CFL is closer to €2-€3 per bulb than the up front cost of €5-€7.

Overall then the choice of switching to CFL breaks even for me in terms of cost alone in about 6 months give or take a month or two and should yield a saving of €150-€180 over the course of the expected lifetime of the most heavily used lights. In general I think it's reasonable to assert that such a switch should save about €30-€40 per person per annum - given that there are two of us in this apartment and I think our consumption is probably typical.

The Carbon footprint effect is slightly more straightforward. We could reasonably expect to save around 90kg of CO2 per annum with this switch. If that is typical for the population as a whole then the annual saving could be in the order of 360 million kg. That's not quite the 700,000 tons of emissions that Minister Gormley talked about in the budget but it's twice as much as I had initially estimated and this number does take into account the loss in heating angle and to be fair to him the margin for error in this is at least 50%. One detail that I haven't factored in is the difference in the energy required to manufacture them but I can't see that it could be significant enough to make a serious difference, I will follow up on this when I can find any real data about it.

I still hate the light that CFL's produce so I'm going to do some research into LED's which are a much better technology all round - they produce much nicer light and I believe they are a lot less nasty to manufacture and dispose of.

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