A growroom that’s not a huge draw on the electricity bill every month is on every avid indoor gardener’s wish list. While many believe this is a pipe dream, it can be achieved by harnessing the power of the sun. Here’s how to calculate your energy requirements to determine whether solar power is a viable option for you.
Maintaining a solar-powered growroom is likely at the top of every grower’s wish list, both on the commercial and hobby levels. However, the cost-effectiveness of a solar-powered hobby garden poses a serious hurdle in the logistics of this sort of layout. Luckily, there is extensive research in this field, with rapid improvements in both solar technologies and the equipment being powered.
Just like standard electricity, there’s no limit to what can be powered through solar energy. The limitation for hobby gardeners lies in the investment required to build a growroom that is powered completely by renewable energy. Although this goal may currently be out of reach for many hobby gardeners, supplementing your power generation with renewable energy may reduce costs significantly. Here are some tips to help you determine if adding solar power makes sense for your set-up.
Calculate Your Consumption
First, let’s identify the electricity needed to power an entire growroom on a monthly basis. Say we have a simple 4- by 4-ft. tent, with a centralized flood and drain system holding four plants, 20 gal. of water, one 600-W HPS bulb, and an oscillating fan.
In one month, on a 24-hour lighting schedule for plants in the vegetative stage, we would use 14,400 watt hours per day, or just over 400 kWh per month, on lighting alone. After one month of vegetation, your plants may decrease their lighting demands by 50% for the subsequent two-month flowering phase. This is great news for the year-round grower, as for two-thirds of the year, using this set-up and strategy, you will only need about 7,000 watt hours per day, or 196 kWh per month.
If your plants are on a standard feed schedule for a typical flood and drain system, you may choose to flood your table four times per day, for one hour each time. You want to make sure you choose a submersible pump that can deliver water to plants’ root zones somewhat quickly so they get an adequate amount of time to feed and hydrate. For a 20-gal. reservoir, you may choose a pump that is capable of 130 gal. per hour. This would flood your entire table within 10 minutes, which is reasonable if your timer is set to stay flooded for the remainder of the hour. To calculate the watts required to power this pump, we multiply the amps times the volts, which in this case equates to approximately 25 W. At four sessions per day, this comes to 100 watt hours per day, or 3 kWh per month.
Airflow is important when using lights that generate a fair amount of heat, such as HPS bulbs. Assuming you’re running a 50-W oscillating fan for 24 hours per day alongside your lights, this would take approximately 1,200 watt hours per day, or 33 kWh per month.
For this basic, beginner’s set-up, we are looking at a maximum rating of less than 450 kWh per month to power the whole room. Keep in mind this set-up is just a simple example to help demonstrate some averages and ideas.
Determine the Power Rating
The west coast of the United States averages 2,400 hours of sunlight per year, or 6.5 hours per day. Depending on the location of your solar panel set-up and the amount of trees and shade obstructing the sun, let’s assume you get five hours of direct sunlight per day. To calculate the capacity of the solar panel set-up you need, divide your average daily kWh consumption by the hours of sunlight your panels are exposed to. Using this example and the numbers above, you would need a 3-kW system. If you are brave enough to invest in a DIY solar set-up of this caliber, these can range anywhere from $5,000 – $15,000 brand new. And if you have it professionally installed, it may cost well above $15,000. You may be able to find a used one for substantially less, but make sure you do your homework before buying new or used.
Statistics — The average American household uses between 900-1,000 kWh of energy per month, at a rate of approximately $0.12 per kWh, or up to $0.25 per kWh if you’re a California resident! You can see how energy consumption from both your household utilities and your growroom can quickly accumulate, especially if you plan to power an amped-up growroom. Check your local rates to find out if renewable energy may save you a few bucks in the long run.
Light Sources — Another way to save energy in the growroom is by using high-powered LED lights. These are investments in and of themselves, so make sure you keep a running tally of your total expenses when comparing the costs to the benefits of a solar-powered system. Additionally, if you are in a location that averages an unusually high number of sunlight hours per day, you can get away with a system with a lower power rating, hence a cheaper price.
Maintenance — There are replacement fees to keep in mind when deciding to go solar. Check the warranty on the panels and inverters you are considering and incorporate this data into your long-term payoff structure. Luckily, solar panels typically last around 25 years before needing to be replaced, so this shouldn’t necessarily be your main concern when shopping for a small system.
Incentives — Another bonus to installing solar panels includes potential tax credits and rebates. There is currently a 30% federal tax credit issued to those who install solar panel systems, but this is set to expire next year. Check with your local state’s government to find out the incentives and rebates associated with investing in a solar energy system. These sorts of perks may not be available for long, but they will certainly help offset some of the costs until standard pricing on solar equipment drops.
Technology Advancements — One final aspect to keep a close eye on is the development of new and improved solar technologies. For example, SoliCulture has developed solar panels that use a red dye to convert green wavelengths to red, improving two functions of solar energy. Because plants absorb red wavelengths best, the red light emitted by these panels may help optimize plant production. Also, any red light the plants do not absorb is directed back to the solar cell to help boost power. Research trials are currently being conducted at the University of California, Davis to gauge the effects this technology has on the optimization of solar-powered greenhouses.
To reap the rewards of an investment in solar power, growers must carefully plan out their garden designs, and find the threshold where the investment level will be profitable. It is difficult however, to predict the advances in technology in the coming years, as we’ve seen exponential growth in even the last 4-5 years. The last thing we want to do is put a bunch of time and money into something that quickly becomes outdated, or manifests as a step sideways, or worse. That’s a fast track from a grower’s dream-come-true to a grower’s worst nightmare! Don’t let this scare you off, though. Supplementing your power generation with solar panels might be a good way to learn about how the technology works, while saving money and helping the environment.