Indoor grow rooms are a great way to maintain a garden without worrying about outside factors like weather and pests. To grow plants indoors, though, you’ll need grow lights.
The purpose of grow lights is to mimic the sun and give your plants all the light they need to grow strong and healthy. HPS grow lights are a great option, but unlike the sun, the energy that these grow lights need isn’t free. Indoor gardening can use a good amount of electricity that will be reflected in your bill each month.
But how much will it really cost when it comes to running an HPS grow light system in your indoor garden?
Table of Contents
- How Do HPS Grow Lights Work?
- Voltage and Wattage
- How Much Energy Do HPS Lights Use?
- How to Calculate Your Energy Bill
- Ideal Grow Room Setups with Monthly Energy Costs
- How to Reduce Energy Costs
- HPS Grow Light Costs: The Bottom Line
In this guide, we’ll help you figure the costs of running HPS lights in your grow room. We’ll provide you with all the equations you’ll need and even include real equipment as examples for what a certain type of grow room setup might cost you.
To understand how much it costs to run HPS grow lights, we’ll have to first look at exactly how these lights work.
- The “HPS” stands for “high pressure sodium,” which means these grow bulbs are filled with sodium along with other gases and chemicals that create light when they’re properly heated.
- The HPS light’s ballast uses electricity to send energy to the bulb through the arc tube in order to heat the metals, chemicals, and salts within the bulb.
Once heated, the contents of the bulb create light.
- Since heat creates this light, the stronger and more powerful the light is, the hotter the bulb is.
- As a result, in order to avoid overheating in your grow room, you may have to offset the heat from your HPS plant light with fans and/or cooling systems.
Understanding energy comes down to looking at three important factors: voltage, amperage, and wattage.
Voltage and wattage are related to each other, but they are not the same thing.
- Voltage is the force that causes electrons to flow. It’s the energy available at the source, like an electric plug.
- Wattage is the overall power of the electrons used by a circuit, or how much work the electricity does. Wattage is calculated by multiplying voltage by current (or amps).
Voltage is an important thing to note for electrical compatibility in your grow room.
- For example, some appliances run at 120v, while others run at 240v. However, these generally use the same amount of energy, as a 240v circuit divides the energy between two conductors.
- So, a 240v circuit might pull 5 amps from 2 conductors, while a 120v circuit would draw 10 amps from a single conductor. So even though one has a higher voltage, they both end up with the same wattage.
What’s really important to pay attention to when it comes to your energy usage is the wattage of your grow room equipment, as this is what your electricity company will measure and charge you at. Generally, they charge by the amount of kilowatts per hour, or KWH, you use.
To look at exactly how much energy it takes to run HPS lights in your grow room, we’ll have to look at more than just the grow lights themselves. We also need to take your cooling systems and fans into account.
Let’s take a look at some grow room equipment examples to get an idea of the amount of energy used by HPS grow light setups.
Grow Lights: Starting with the wattage and voltage of the grow lights, we’ll use the Yield Lab 600w HPS Air Cool Hood Reflector Digital Grow Light Kit as an example. This grow kit uses 600 watts of power at 120 volts when it’s running.
- Now, since HPS grow lights tend to be quite bright and produce a lot of heat, you’re probably going to need to cool things down a bit (even with the cool hood reflector). You’ll need to factor fans into the equation. These will be used predominantly for temperature control. At the very least, you’ll need them to get some air circulating in your grow room.
- Grow Room Ventilation: We’ll look at two different fans for this example. First, let’s factor in the Yield Lab 6 Inch 440 CFM Air Duct Fan Vent System, which operates at 110v and uses 135 watts of power when running. We’ll also take a look at a 6” Desk & Clip Fan that uses 15 watts of power at 120 volts.
When calculating how much energy you’re using in your grow room, you’ll measure it in terms of kilowatts per hour (KWH). One kilowatt is equal to 1000 watts, so KWH is measuring how many thousand watts your equipment will be using over one hour. That’s what your electric company will be charging you based on!
Using all the equipment listed above, it would equate to about 750 watts of power per hour while your equipment is running, which is equal to .75 KWH. Keep in mind that this is only while your equipment is running — it’s not a 24-hour calculation! Once you know how much energy you’ll be using, we’ll look at how to figure out the cost of running your grow room equipment.
Converting energy usage to money is the part where things get a little more complicated, although the equation itself is quite simple. We can’t give you an exact number, because you’ll need to consider the specific rates of your own electricity company. These rates will fluctuate based on a few factors.
You’ll want to take the following factors into account in order to determine a realistic rate at which you’ll be charged for your electricity usage.
- Electric Company Rates: For starters, electricity companies generally charge based on tiered rates. This means that once you reach the threshold of one rate, you’ll move up to the text tier, which will raise your bill.
- Seasonal Electric Rate Changes: Electricity rates generally change during high-usage seasons, like summer, when everyone’s blasting their air conditioning. So the season that you’re growing in will also play a role in how much it’s going to cost you.
Once you’ve figured out an accurate rate for your electric bill, it’s time to calculate how much the energy from your grow lights will cost you. To do this, simply multiply the total energy your grow room will be using (using KWH) by the rate your energy provider will be charging you at.
Here’s an example:
- If you’re using a Yield Lab Professional Series 1000W HPS Open Wing Double Ended, you’ll have to account for 1000w of power at a time.
- Add two 4” Yield Lab 4 Inch 190 CFM Air Duct Fans, which use 87w each.
- With the equipment mentioned above, that’s 1164w total, which is equal to 1.164 KWH while running.
- You’ll then multiply that 1.164 KWH by the KWH rate your electricity provider charges — let’s say it’s $0.12/KWH.
- When you multiply those two numbers together, that will show you how much each hour of running your equipment will cost you.
Note: That’s just the price for one hour. As such you’ll have to multiply that value by the number of hours a day you’re going to be running your equipment.
- Even though you won’t be running all of your equipment all of the time, it’s a good idea to tally everything up and use it in your calculations in order to account for any fluctuations in price.
- For example, an ebb and flow system will only be used for about 20 minutes at a time a few times a day. So, you should add all that time up and calculate it into your total energy usage. In this example, we’ll say that the vegging stage is 16 hours, and the flowering stage is 12 hours, so we’ll multiply the 1.164 KWH by both of those numbers to get 18.624 and 13.968.
- Now, we’ll multiply the rate you’ll be charged by each of these numbers to get your estimated costs. To figure out the price of the vegging stage, we’ll multiply the total energy per day by the rate of $0.12 (18.624 x .12) to get a total of ~$2.23 per day.
- For the flowering stage, the same equation (13.968 x .12) gives us ~$1.67 per day.
- The final step to calculate your estimated cost for the month is to multiply that number by 30 or 31 (or 28 for February). With the example we’re using, that would be about $66.90/month during vegging, or $50.10 while flowering.
Since each grow room setup is different, we’ll take a look at a few possibilities and how much each of them would cost you to run. Although they vary a bit in cost, these are all great options to consider for your own grow room!
Keep in mind that each of these calculations is based on an electricity rate of $0.12/KWH, so the costs will vary depending on your own electricity provider’s rates!
If you’re working with a simple 5x5 soil grown grow room, this is a great option.
Let’s take a look at the cost of running equipment for a 5x5 grow room:
- Grow Light: Yield Lab 600w HPS Air Cool Hood Reflector Digital Grow Kit (600w)
- Ventilation: Yield Lab 6 inch 440 CFM Air Duct Fan Vent System (135w) and Active Air Heavy Duty 16” Metal Wall Mount Fan (80w)
- Grow Room Energy Usage and Cost: Altogether, running this equipment will use 815 watts of power per hour, which is equal to .815 KWH. If you’re using this setup during the vegging stage, that’s about 16 hours a day, so we’ll multiply .815 by 16 to get a total of 13.04 KWH a day. Multiplied by our rate of $0.12/KWH, that would cost you about $1.56 a day which is around $46.80 a month.
- Plant Count: 2-3 Plants
Now, let’s say you’re using a 4x5ft Complete Perpetual HID Hydro Indoor Grow Tent System.
This system is complete with everything you’ll need for your grow.
- Grow Lights: Yield Lab 400W HPS+MH Cool Tube Reflector Grow Light Kit (400w) and 24 Watt Advance Spectrum All Blue LED Grow Light Panel (24w each)
- Ventilation: Yield Lab 6 Inch 440 CFM Air Duct Fan Vent System (135w)
- Hydroponic System: Greentree Hydroponics Multi Flow 6 Site Ebb and Flow Hydroponic System (70w)
- Additional Equipment: 4x Root Radiance Heat Mats (20w each)
- Grow Room Energy Usage and Cost: Altogether, this equipment gives you a total of 781w or .781 KWH. Running this equipment for 16 hours a day (the standard for the vegging stage) means you’ll be using 12.496 KWH a day. With our rate of $.12/KWH, that puts you at around $1.49 a day for a total of about $44.98 a month.
- Plant Count: 4-6 Plants and 4x Trays of Clones
If you’re able to spend a bit more when it comes to running a larger grow room, this is a great, high-power route to take.
An 8x8 grow room could be set up with the equipment listed below.
- Grow Light: 2x 600w Double Ended HPS grow lights (600w each)
- Ventilation: At least 2x Yield Lab 6 Inch 440 CFM Air Duct Fan Vent Systems (135w each) and 2x 16-inch oscillating fans (80w each)
- Grow Room Energy Usage and Cost: If we add the wattage of all that equipment, it would take a total of 1530 watts an hour to run your grow room — that’s 1.53 KWH per hour. Plugging that into our formula with a standard $0.12/KWH rate for 16 hours a day during the vegging stage, that gives you a total of 734.4 KWH a month for a cost of $88.12. Comparing this price to the others we’ve listed gives you an idea of how much those energy costs add up in a larger grow room.
- Plant Count: Up to 10 Plants
Note: Remember that areas around the world charge varying electricity rates at different times during the year. These are local examples, so make sure to plug in your own electrical rates before
If you’re worried about electricity costs in your grow room, remember that the number one way to keep costs low is to reduce your energy use as much as possible. One way to do this is to switch to LED grow lights.
- LED lights can help to reduce the heat in your grow room by a lot.
- This will in turn reduce the need for a lot of ventilation that would typically be required with an HID grow light setup.
If you install LED grow lights in your grow room, you won’t have to use as many powerful fans.
- Instead of running 135w inline fans, for example, you could use 80w ones instead.
- That would cut your usage down by over 35% and reduce your overall electricity costs!
Aside from buying new grow lights, here are a few practical ways to reduce grow room energy costs:
- Grow in a well ventilated area- It seem like a no-brainer, but the less heat your fans have to move, the less energy you'll use when growing. In well ventilated areas, opening a window or a door for fresh outdoor air will help bring down cooling costs.
- Grow in a well insulated area- In the colder months when outdoor conditions can dramatically affect your plants, a well insulated area will keep your plants' environment at optimal levels.
Consider changing the time you grow- Your electricity is billed in tiers, and those tiers change depending on the amount of energy used and the time of year. You can knock down electricity costs by planning your energy usage around when your home's growing, along with how much energy's used in your area, along with seasonal pricing.
- For example, if you're using lots of energy in your house all day, consider growing at night instead of during working hours.
- The key is using the energy you need without competing with the rest of your home and even your town.
Figuring out how much energy it will cost to maintain an indoor grow room can seem intimidating. Thankfully, it really isn’t as complicated as you might have previously thought!
All it takes to accurately figure out potential HPS grow light costs is a little math.
In this article, we provided a few examples of the costs of specific grow room setups to give you some estimates. That said, remember that you can always figure out the approximate cost of any setup you’re considering by plugging the equipment’s wattages and run times into the equations we’ve outlined in this article. It’s as simple as that!
Now you can figure out the best and most cost-efficient way to put together all of your equipment for the optimal grow room!