Been looking at my energy bills in the wake of some startlingly high ones and am struggling to do the maths around low-cost bulbs.
The basics. Our gas supply is much cheaper than electricity, weighing in 3.6p per kWh for the bulk of our usage compared to 9.7p per kWh for the bulk of our electricity. Of our not inconsiderable bill we run 65:35 in gas’ favour. Gas powers heating, hot water and the bulk of cooking so no surprise there. A quick calculation suggests gas generates six times more of our power than electricity.
We have abnormal electricity use. I run an a freakish amount of networking equipment for a non-geek. Two routers, two wifi networks, Mac servers, hard drives, laptops. We have halogen spotlights everywhere (12 in the kitchen alone). And despite that electricity represents less than a sixth of our total energy consumption.
Getting more efficient on the gas side is simple enough: lower the thermostat, cut back on hours of heating, wear more layers. The economics speak for themselves. I have already bought socks and jumpers, the wear and tear for keeping them on while in the house is minimal.
On the electrical side the trade off just isn’t as clear. Say (and this is a big assumption), I run 12 x 50W lights, 8 hours a day, (this would be the top end of my estimate; we generally turn lights off as we move round), I am looking at a 4.8kWh daily lighting budget. This translates into 46p a day or about £180 a year.
Say each bulb has a lifespan of 2,400 hours. It would mean each bulb needs replacing once a year. Assume each bulb costs £3. The total replacement cost is £36.
So over a year my lighting costs me £216. And over five years it costs £1030, but discount it back for time (say a 5% annual time discount, deflationary times after all), we have a net present cost of £977.
Now, energy efficient LED lights are now available from great stores like this, but boy are they expensive.
A typical LED light replacing a 50W GU10 halogen is the beast pictured.. It runs at six watts but has the brightness of a 50w halogen. Unfortunately, it’ll set you back around £20.
What are the economics of the LED bulbs?
Now assume the lighting needs I discussed about. 12 x 50W equivalent lights, 8 hours a day. These bulbs run to 6W, which equates to a 576kWh daily lighting budget running to 5.3p per day or about £20 a year.
Each bulb has a lifespan of 40,000 hours or about 15 years. At £20 a piece it’ll cost me £240 to pick up the bulbs. So my year one cost is £260. And over five years it will cost £340, or discounted for time £330.
So the economics look sensible–except for two things:
(a) The payback period of a year looks long for a . . . light bulb. Even though my model tells me so, I still need to persuade my heart that this is an investment with a positive pay back.
(b) Eight hours a day of continuous usage, 365 weeks a year is a really aggressive assumption even from the depths of the British winter. If I evened it out at say 4 hours per day, the payback period runs into nearly two years. And then I have to consider the forty seven 50W GU10s I have in the house–a seven hundred pound replacement cost just to get started.
Which makes me think: I am paying too little for my electricity. Or rather, energy efficiency is being under priced by the market, most likely because we aren’t pricing energy waste correctly.