How much electricity does it take to grow cannabis indoors from seed to harvest, and how much will you actually be paying for electricity each month?
When growing marijuana indoors, the cost of electricity is important, however, it can be confusing trying to predict how much it's going to end up costing you!
Luckily, it's relatively straightforward to figure your costs in electricity once you have the right information!
This guide will teach you how to determine how much electricity you'll be using each month for your garden. Once you know how much electricity you're using, you can easily figure out the cost. I'll also share a few estimates for the electricity cost of grow lights, fans, ACs, and more, so you'll have a ballpark figure even if you're not sure exactly how much you pay for electricity.
You need this information:
Here's the formula which can be used not only to figure out the cost of electricity for the marijuana grow, but also the cost per month:
Cost of Electricity x Number of Hours x (Watts / 1000) = Total Cost
Note: You need to divide the watts (W) by 1000 to plug it into the cost formula; this is to convert your number to kW so it plays nice with the kWh measurement you get from the electricity company. I'll explain below with a few examples.
Real-Life Example with 250W HPS Light
Cost Electricity x Number of Hours x (Watts / 1000) = Total Cost
$0.37 kWh x 1,746 hours x 0.250 kW = $161
However, one thing that's very important to remember when doing any estimations is that although your grow light may account for a lot of your electricity bill, fans and pumps and other things in your grow room also take electricity. It can really start to add up if you don't pay attention, giving you a much higher-than-expected electricity bill!
Remember to Calculate Energy Cost for Everything That Uses Electricity, Not Just Your Grow Light!
Continuing the above example, in that same grow I also used an exhaust fan, two circulating fans, and for my hydroponic tub I also used a water pump and an air pump. Although they seem like pretty small items, they can start to add up over the length of the grow.
Cost of Electricity for Other Items
You can view the full breakdown here. But you can see that these other items cost 3/4 as much electricity as the grow light at $161!
Here are more examples to give you an idea of possible cost projections if your electricity cost $0.25/kWh. This is higher than most people's electricity rate so hopefully your amounts will be much lower than these!
Compare Grow Lights @ $0.25/kWh
Amounts are for if the lights are kept on for 18 hours a day for 30 days (540 hours). In the flowering stage your lights will be on for only 12 hours/day so for those months you'll only need to calculate for 360 hours (12 hours x 30 days).
MH/HPS Grow Lights
LED Grow Light Examples
Note: Advanced Platinum is just one example of an LED brand that works well for growing cannabis.
Compare Various Fans @ $0.25/kWh
Amounts are for if the fans are kept on for 24 hours a day for 30 days (720 hours):
Hydroponic Pumps and Accessories @ $0.25/kWh
Amounts are for if the pumps are kept on for 24 hours a day for 30 days (720 hours):
Air Conditioner Examples @ $0.25/kWh
Amounts are for if the ACs are kept on continuously for 12 hours a day for 30 days (360 hours) - hopefully you don't have to keep your AC on this often or this long!
If it's your first grow, when it comes to figuring out an estimated per-grow cost I recommend planning on it taking 5 months to get to harvest time (even though the average grow is usually about 3-4 months). Although you will hopefully get to harvest sooner, it's better to estimate for too much money and have it cost less than the other way around!
Five months gives you plenty of time to mess up in the vegetative stage, use a long-flowering strain and still be ready for harvest. After you get some experience you'll have a much better idea of how long it usually takes to get to harvest using your personal style and preferred strains. One other thing to remember is you'll use less energy in the flowering stage because your lights will only be on 12 hours a day. You can figure that time out separately if you want, but I'm just going to pretend the lights are on 18/6 to make things simpler.
So now that you've begun to figure out your per-month prices, you can multiply them by 5 to get an estimate of how much a whole grow will cost you for each item!
Example Setup ($0.25/kWh)
Monthly Electricity Cost: $90
That's a total of $90/month in electricity, so if you multiply that by 5 months you get $450 cost of electricity for the whole grow.
Once you've had a grow or two under your belt it's a good idea to start looking at cost and reward to make sure you're growing what you need for the price you want.
Let's say you spend $450 on electricity in the grow, but produce 5 ounces of buds, that means you're paying $90/ounce for electricity (plus the cost of setup and supplies). If that's a good price for you then you can celebrate a good harvest, but if you're not getting the right prices in your grow, it's a good idea to evaluate and figure out what you need to change to get the results you're looking for!
How do I determine my yields?
For example, in the same previous grow I spent about $280 in electricity throughout the grow (if you add everything together). I harvested a little over 6 ounces which means I spent a little under $50/ounce in electricity. Considering it costs around $350 for a high-quality ounce in my area, that's some pretty significant savings!
Another thing to consider when trying to estimate costs is how long a specific cannabis plant needs in the flowering stage before it's ready to harvest. Some plants need up to 3 months in the flowering stage, so when determining cost it's a good idea to factor in that extra time. Sometimes it's worth it to pay more for better buds, but you should know that's what you're getting into!
Now that you've got a handle on figuring out your costs, let's take a brief moment to talk a little bit about electrical safety.
If you're getting set up with a new grow room, or just getting started growing in a space for the first time, there's a few things you need to do before you ever plug anything in! In addition to standard electrical safety precautions inside the grow room, you want to make sure your grow space can actually support the amount of power you need.
Once you know which plugs you're going to use for your grow, you need to calculate how much energy your grow lights and fans will need (as explained in today's article). Armed with that knowledge, you can make sure your outlets can support that much energy usage.
All electrical outlets in your house are on a circuit, and each electrical outlet in your grow room belongs to a circuit. Often the circuit breaker box has labels for which outlets in the house are on each circuit, but sometimes you need to figure it out yourself.
Once you know which circuits your plugs are on, the next step is to open your circuit breaker box and see what number is listed next to the circuit(s) you plan to use.
Let's say you're using 120V outlets like most standard American outlets. If the circuit breaker is labeled for 15 Amps that means that circuit can handle 1800W worth of appliances (15A x 120V = 1800W). If it's labeled with a 20 it means that the circuit can handle 2400 watts (20A x 120V = 2400W). For 30 Amps it's 3600W.
If your appliances on a circuit combined equals more than those total watt numbers, you're going to trip the circuit breaker at some point and everything on that circuit will shut off as a safety precaution.
Important: With all this in mind, it's crucial to note that the limit of how much load a circuit can take is 20% lower for "continuous loads". A "continuous load" is something that needs power for 3+ hours, so pretty much ALL of the power you will be using is a continuous load. This means you'll want to split your power usage between circuits (not just outlets) when needed, and stay below the following wattages:
I have examples of different wattages listed in the main article, but consider that a 1000W light + 10,000 BTU air conditioner is already enough to go well beyond the 1444W safety limit if you have a 15A circuit breaker and even surpasses the 1800W maximum load limit!
Because of this we once had to power an AC with an extension cord that went to another room so it wasn't using the same circuit as the lights and fans! Believe it not or, this is actually safer than putting extra load on an already overburdened circuit.
It's impossible to do all of these things at the same time, and sometimes you'll have to choose between strategies, but this should help give you ideas on ways to possibly cut electricity use during your grow!
Using a less powerful grow light while your plants are young will save electricity!
Manage Temperature / Air
For your exhaust system, try as best you can to keep ducting in as straight (and short) a line as possible - this makes it much more efficient at removing heat!
I hope that helps get you started with figuring out the cost of electricity and setting up your grow room so you spend as little as possible while producing the results you want!