Lighting-only energy savings is essentially the money you save from the simple wattage reduction when switching to more efficient lighting products. A “lighting-only” number is a good place to start because it is the most conservative savings calculation in a lighting retrofit and it represents the bulk of the savings you will capture on most retrofit projects. Further, it is to be trusted. It’s plain science and math.
Step 1: Gather your facts
You will need to pull together the following items before we dive into the calculations
- Old lighting product wattage: In our example, this is 400 watts.
- New lighting product wattage: In our example, this is 150 watts.
- Running time: How much time out of the day is the product lit?
- BC Hydro Electricity rate at this time is $0.1073 per kWh.
Step 2: Calculate energy savings per lighting fixture
Old Product Wattage – New Product Wattage
= Energy Savings per Lighting Fixture
400 Watts (Old Metal Halide) – 150 Watts (New LED)
= 250 Watts Saved per Lighting Fixture
Step 3: Calculate annual running time
The amount of time that a product is lit has a significant impact of savings and payback.
In our example, we assumed the lighting is on 12 hours per day and 365 days per year.
Daily Run Time x Annual Days of Operation
= Total Annual Run Time
12 Hours per Day x 365 Days per Year
= 4,380 Hours
Step 4: Calculate total annual energy savings
BC Hydro charges $0.1037 for electricity by the “Kilo Watt Hour”
- 1000 Watts = 1 kW
- kW’s of Lighting = Number of Lighting Fixtures x Total Wattage of each fixture
- kWh’s = Total kW’s x hours of use (Per Day/Week/Month/Year)
Energy Savings per Lighting Fixture x Total Annual Run Time ÷ 1,000
= Total Energy Savings
250 Watts Saved per Lighting Fixture x 4,380 Hours per Year ÷ 1,000
=1095 kWh Saved
Step 5: Calculate annual dollar savings
Okay, so we know we’re saving a boatload of electricity, but we need to see how it translates to real dollars.
Total Energy (kWh) Savings x Electricity Rate
= Total Dollar Savings (from Lighting Only)
Our Example (Watts Commonly Found In Warehouses & Parking Lots):
1095 kWh Saved x $0.1037 per kWh
= $113.55 Saved Per Lighting Fixture Per Year
- $1135.52 Saved Per 10 Lighting Fixtures Per Year
- $5,677.58 Saved Per 50 Lighting Fixtures Per Year
- $11355.15 Saved Per 100 Lighting Fixtures Per Year
Now that you’re a pro on figuring out how much you can save per lighting fixture, you can scale to any size product and get a “gut-check” on the savings estimates that find their way to your desk.