Thursday, December 11, 2008

Tis the season...

...to pay big electric bills. Fa La La La La, La La, La, Ouch!

Feel like you need a personal nuclear reactor just to light your Festivus lights? You might not be far from the truth. You face three choices:
  1. Go without in the spirit of being a GreenerGeek
  2. Installing the traditional tiny lights and pay the electric company through the nose
  3. Buying LED lights, paying through the nose for high-tech, and ignore your power bill
In the spirit of reusing our existing traditional lights (avoiding the environmental impact of buying new lights and land-filling these), I did a few power measurements this season. It turns out it is pretty much directly proportional to bulb count.

As an example, our backyard display consists of 6 strands of Garlands wrapped around our deck (1,800 bulbs), and three strands wrapped around a small pine tree (300 bulbs). I measured 420 watts for those 2,100 bulbs, or about 0.2 watts each. Expressed another way, you can divide the bulb count by 5 to come up with the wattage.

Our front display consists of 6 strands of Garlands wrapped around two tall bushes (1,800 bulbs), 15 sets of Net Lights on our bushes (2,250 bulbs), and 2 simple strands outlining Bambi, or fake deer (200 bulbs). I measured the total power consumption of our front yard display (4,250 bulbs) at 855 watts.

Our total homage (6,350 bulbs) to the Chrismahanaquanzika season is a wallet-numbing 1,275 watts per hour, which costs just about $0.25. We run the lights from 4 PM until 10 PM, or 6 hours a day, 7 days a week for about 5 weeks. That means the total cost to run our holiday lights is about $105.



Now let's look at using LED lights.

The good news is that the LED bulb itself lasts much longer. The bad news is that it still uses the same sort of cheap socket connections which quickly fail. You are going to be pulling your hair out year after year keeping your expensive LED light strings working. But at least you won't land-fill them because they cost too much.

Speaking of cost, LED lights run about $50 for a set of 150 bulbs. The bad news is that is 16 times more than I spent on the same number of traditional lights. The good news is costs are coming down each year. Maybe we can afford them in another 5 years?

Well at least LED lights save money on power, right? That's the very good news. Yes they do! They use 1/14th the power. So divide the bulb count by 70 and you will have your power consumption.

So let's compare. My 6,350 traditional bulbs consume 1,275 watts, and cost me $105 to run for the season. If I changed over to LED bulbs, then my power bill would be $13, saving $92. But LED lamps would cost me $2,116 to purchase. Even if the strands lasted 10 years (wildly optimistic given build-quality), I would still be about $1,200 in the hole if I used LED technology.

The real bad news is that current LED technology is just a fun experiment. The economics are not even close to there yet.


Maybe the most green approach would be to use five 200 watt solar panel (an array size of about 8x10 feet) to capture enough sunlight during the day (8 hours) to generate the power used for the lights. That panels would cost about $4,500 and require a $1,500 grid-tied inverter (you sell the power to the electric company during the day, and draw power from the grid at night to run your lights). So for $6,000 out of pocket, you can offset your $105 power bill for your lights (and put another $900 or so in your pocket during the rest of the year).

Of course those solar panels will generate zero power if we have a white Christmas -- Bah humbug!

2 comments:

protomech said...

A 1kw system may be optimistic for powering the christmas lights.

1275 w * 6 hours/day = 7.7 kwhr/day

From here:
http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/

A flat south-facing latitude-tilt panel array in Rhode Island receives 4-5 hours/day averaged across the year, and 2-3 hours per day during December.

If you build for 2.5 hours/day and assume ~20% operational loss, then you would need a 4kw array. A 4kw array will run somewhere around $30k + installation and certification costs, though you should be able to recover 30% of that as a tax credit.

protomech said...

And averaged over the year, the 4kw system should produce around 5200 kwhr (438 kwhr/month), which should save you around $800/year in reduced electricity ($0.16/kwhr).