To Time, or Not to Time
If your business or the building in which your business occupies has a lighted parking lot, building attached lighting, or any other outdoor lighting, chances are they are on a dusk-til-dawn timer. When the sun goes down, the sensor connected to the lights is activated and then as the sun rises, they turn off.
And since we have been tracking the sun and the stars for such a long time, the calculations are accurate for basically anywhere that’s not the North Pole or Antarctica. So when we calculate the time that outdoor lights would be on, it’s pretty accurate. The only thing that we can’t easily control for is additional shading (or other environmental effects) or positioning of the sensor, which might turn lights on or off, earlier or later. But generally, still pretty accurate.
To calculate how many nighttime hours there are in a year, you’ll need to seek the sunrise/sunset times for your area. Every coordinate on Earth has a different sunrise/sunset time, so you should check out the US Naval Operations Duration of Daylight/Darkness Table website (http://aa.usno.navy.mil/data/docs/Dur_OneYear.php). If you want to get more specific, and I’ll explain later in this post, the Sunrise/Sunset Table (http://aa.usno.navy.mil/data/docs/RS_OneYear.php) is for you.
Essentially, take the times from each day for your city (Excel makes this really easy to do) and add them together. I’ll save you some time and tell you that during 2014 in Fresno, there were 4310.57 hours of darkness. Now, what to do with this? Add up the wattage of all your outdoor light sources, divide by 1000 and multiply it by 4310.57; that’ll give you the annual kilowatt-hours for the year. Multiply that by your average energy rate and you’ll get a good estimate. If you’re paying 21 cents a kilowatt-hour, with a 3 kilowatt lighting load, you’d expect to see about $2,700 in annual costs. If you’re using a lighting technology other than LED, you may want to compare wattages of LED lamps with comparable lumens to see if it would be advantageous to convert to LED lights.
Should you want a more accurate picture painted, or your business is on a Time-of-Use rate, then it’s best to find out the actual sunrise and sunset times. In the PG&E region has three time periods: On Peak, Partial Peak and Off Peak. Here’s the table of times below:
Summer Period A (May-October)
|
||
Peak:
|
12:00 noon to 6:00 pm
|
Monday through Friday (except
holidays)
|
Partial-Peak:
|
8:30 am to 12:00 noon
|
Monday through Friday (except
holidays)
|
6:00 pm to 9:30 pm
|
Monday through Friday (except
holidays)
|
|
Off-Peak:
|
9:30 pm to 8:30 am
|
Monday through Friday (except
holidays)
|
All Day
|
Saturday, Sunday, and Holidays
|
|
Winter Period B (November-April)
|
||
Partial-Peak:
|
8:30 am to 9:30 pm
|
Monday through Friday (except
holidays)
|
Off-Peak:
|
9:30 pm to 8:30 am
|
Monday through Friday (except
holidays)
|
All Day
|
Saturday, Sunday, and Holidays
|
|
Source: http://www.pge.com/tariffs/CommercialCurrent.xls. Accessed April 6, 2015.
We can get more specific numbers with the Sunrise/Sunset table because we know when the lights are likely to turn on. And because the energy charge changes throughout the day, we can get a more accurate picture using that data. If you happen to be on a Non-Time-of-Use rate, you might even find it would be advantageous to switch to a different rate, when exclusively looking at outdoor lighting of course.
For those in the Fresno area, I saved you the headache of calculating this yourself:
For the A1 rate: Kilowatts x 827.55 + 118.93
For the A6 rate: Kilowatts x 729.76 + 269.23
If your lighting demand is larger than 1.53 KW, it would be best on the A-6 rate.
Using this information, you can now easily see how much energy you can save by switching your outdoor lights to a different technology. Add in the cost of maintenance (replacing the lamp), and any rebates there might be, and you’ll be able to also factor in the life cycle cost of that upgrade.