When you are going to run a grow room, you must know how to calculate the electricity consumption, then you wouldn’t be shocked by monthly energy bill.
But how to calculate the electricity a LED grow light use? There are three important factors you must figure out.
Wattage of LED grow light
Working time of LED grow light per day
What wattage LED grow light do your plants need?
Just like you must buy proper shoes size to your feet, you should choose correct LED grow light for your lovely plants.
A reasonable rule-of-thumb for you to calculate is that 25-40 watts LED grow light per square foot of growing space for large flowering plants.
For example, your grow tent is 4x4ft footprint for medical flowering, the suitable wattage should be 4feet x 4feet x 40 watts= 640 watts.
Of course you could choose higher wattage LED grow light and dim its light intensity for different stages. But too much light will hurt your plants. Because strong light and heat will destroy the chlorophyll in the leaf. The result comes to pale, bleached and faded areas on the leaf. And the leaf color finally becomes brown and dark.
Therefore, it is necessary to choose a suitable LED grow light for your plants.
How long should LED grow light work per day?
It depends on what crop you grow in your grow room. Marijuana needs 18 hours of light per day at vegging stage, and 12 hours of light per day at flowering stage. And if you grow lettuce and other leafy greens, they normally need 14 hours of light per day. You can decide the working time of the LED grow light according to your experience. And also the plants will give reaction on lights. Too less light will make plant weak, and too much light will burn the plant.
If your grow room is built with glass roof and transparent walls, the plant can grow under sunlight at the daytime. Then the LED grow light just need to work at morning and evening time. It could save a lot of energy consumption.
How much is electricity rate in your city?
If you are planting to grow several strains plants in grow tent, you just need to use residential electricity. But if you own a big greenhouse, you should run it with commercial electricity. Normally commercial electricity rate is a little cheaper than residential electricity.
For example, the average New Jersey commercial rate is 14.2 ¢/kWh, but the average New Jersey residential electricity rate is 17 ¢/kWh.
In Australia, the price of electricity is 22.1 c/kWh for households and 18.5 c/kWh for businesses.
Before you build your own grow room, it is necessary to investigate the local electric rate, low electric rate will save you a lot of money.
How to calculate the electricity a LED grow light use?
After we make above three factors clear, things become quite easy to calculate the electricity cost now. Here is a calculation formula for your reference:
Monthly Electricity Cost(USD) = Power consumption(kWh) x working time(Hours) x Electricity Rate (USD/kWh)
For example, you have 3 units 1000w LED grow light in the grow tent in your house, the total power wattage is 3 x 1000 watts = 3 000 watts. It means the power consumption is 3000 watts / 1000 = 3 kWh. (In this example, power output 1000w is a theoretical data, as we know the LED grow light doesn’t always work with full output. But it doesn’t matter for us to use this maximum data to calculate the electricity cost.)
The LED grow lights work around 12 hours per day. Then their monthly working time is 12 x 30 = 360 hours
And if your house is located in New Jersey, the residential electric rate is 14.2 ¢/kWh.
All details is clear. Let’s put all above data into the calculation formula.
The monthly electricity cost is equal to 3 kWh x 360 hours x 14.2 ¢/kWh = 153.36 USD.
It means you have to pay 153.36USD per month for your grow lights.
Another example, you have a greenhouse in Australia, there are total 20 units 800 wattage LED grow light in the greenhouse. Because the plants can receive the sunlight at the daytime. The grow lights work only 6 hours after sunset. Let’s calculate how much electricity bill your will get at the end of month.
Total wattage is 50 x 800 = 40 000 watts. It means the power consumption is 40 000 / 1000 = 40 kWh.
And the LED grow lights monthly working time is 6 x 30 = 180 hours.
Also we know the Australia electricity rate is 18.5 c/kWh for businesses.
Then the monthly electricity cost is
40 kWh x 180 hours x 18.5 c/kWh = 1 332 USD.
It means you will receive a electricity bill with 1,332USD at every month.
Do grow lights take a lot of electricity?
At last, we can answer the question. And every growers care about the result. If you understand above calculation, you will say the result is pending.
The answer could be yes. Actually, if you run a grow room, the electricity cost would be a big expense that you can’t ignore. Especially when you have to run it long time per day. Even if your greenhouse can have sunlight at daytime, the effect will decrease during the winter time. LED grow light will play an important role in this period.
But the answer could be no as well. LED grow light is widely used in grow rooms in now days, we could see it in vertical farming, container systems and many greenhouse projects. Comparing to traditional lamps, LED grow light can provide more efficient light than HID, HPS and other lamps. You can use same electricity but grow more plants with LED grow light. We believe you could get the maximum benefit by LED grow light working in your grow room.