The biggest barrier for many when it comes to growing cannabis at home is the hike to their electricity bill. If you’re worried about getting a big number on your next electricity invoice, you can calculate the cost of electricity in advance.
Your first step is to figure out how many watts you’re using when your grow room setup is running. This is the aspect of your grow that you have the most control over. You can choose what you run, and you can choose efficient appliances from the beginning.
Every appliance in your room uses a certain number of watts of power per hour. This number should be listed on the appliance packaging. Depending on your setup, you can be using a wildly different number of watts. A small grow tent with four plants may be using a single 300-watt LED light and a 100-watt exhaust fan. Resulting in 400 watts per hour.
Meanwhile, a larger operation with 40 plants might use four banks of 1000-watt HID lights, four 250-watt exhaust fans, and 800-watt AC unit. That’s 5800 watts per hour for ten times as many plants. The difference in lights is the big change here. HID grow lights are much hotter. They also use more watts of energy to generate the same amount of light as an LED light bank. So, they use more power and require the addition of the AC unit so the plants don’t overheat.
Number of Hours Running
Once you know your expected wattage per hour, just multiple that by the number of hours your grow room will be running. Cannabis plants need 18+ hours of light during the vegetative phase, and 12 hours during the flowering phase, so you have less control over this number.
So, for example, the small grow tent early that uses 400 watts per hour will use 4800 watts a day during the flowering phase, and 7200 watts during the vegetative phase (400 watts/hour*12 hours=4800). Meanwhile, the bigger HID setup will use 105,400 watts during the flowering stage (5800 watts/hour* 18 hours). That is a significant difference.
Cost of Electricity per Kilowatt Hour
The final step is to multiply the daily watts used by how much electricity costs. In the US, electricity is billed by the kilowatt-hour, or how many thousands of watts you used per hour for how many hours. This is usually a few cents per kilowatt-hour, and you have no control over this rate outside of moving.
If you assume that electricity costs 5 cents per kilowatt hour, we can do the math like this:
4800 watts/hour * .05 $/kilowatt-hour / 1000 watts/kilowatt = .24
That comes out to 24 cents a day – not even the cost of a gumball. Over 30 days, that’s $7.20 – that won’t hugely affect your electricity bill!
On the other hand, a bigger grow with inefficient grow lights can kill your budget.
During the vegetative stage, our larger grow operation’s math will look like this:
105,400 watts/hour * .05 $/kilowatt-hour / 1000 watts/kilowatt =$5.27
Per day, it’s not so bad, but over the course of the month, that’s an additional $158 that you’ll be paying.
Electricity is a part of cannabis grow’s budgeting plan. However, big numbers at the end of the month are a good reason to invest in efficient electrical appliances. LED grow lights use on average about half to two-thirds of the wattage of many HID grow lights. This means that using an LED light can cut your electricity bill by at least 30% a month, if not more.