Family Aquaponics System (Low Density)
We developed this aquaponic system for three reasons: we were looking for a system that gave more economical commercial production of vegetables; we had many requests for a system that was possible to operate on alternate energy; and because there was a need for a simple and easy to operate family or small community system for serious vegetable production (75-125 pounds per month).
This type of system uses only one-fifth of the electricity and fish food that our original High-Density commercial systems did, but has the SAME vegetable production! We call this type of system an LD (Low Density) system, because of the lower density of fish in the system. The only drawback we’ve been able to find in the LD systems compared to our commercial systems is that they’re not organically certified yet. We’ve applied to get them certified and expect certification soon.
Although we started out with University of the Virgin Islands-type systems (UVI-type systems) three years ago, we are switching over to our new LD systems as quickly as possible; here’s why:
Family/Off-Grid Aquaponics System under construction
1. Our standard commercial systems were built with the best technology we were aware of at the time: the system design we brought back from the excellent 2007 University of the Virgin Islands Aquaponics Short Course. Since then we’ve had three years to gather data on fish production in the 70-76 degree F water we grow in, and loearned that we’re losing money on the fish portion of these systems. The expenses for electricity (for pumping and aeration) fish food, and labor to feed and harvest the fish wind up being between $4-4.50 per pound, and when compared to the actual income for the fish (at prices of $3-5/pound) results in a net loss! Of course, there’s a bigger purpose for the fish than just making money on their own: they are supplying the organic fertilizer for the plants, which are 95% of the total income from our systems. What this all means is that (generally speaking) if you try to grow MORE fish than is necessary to fertilize your vegetables, you will make less money overall because the fish portion of the operation will contribute a higher LOSS to the balance sheet. If you are unable to get $5/pound for the fish, the loss the fish contribute gets even bigger.
The University of the Virgin Islands program was started by aquaculturists whose goal was always to raise as much fish as possible. In their 80-88 degree F water temperature range they can grow four times as much fish there as here in Hawaii. Unfortunately, they did not have the economic motivators to improve their systems that we have in the private sector. In a university, where they do not have to pay for a program from the income the program generates, finding out if a program can potentially generate a profit is a simple equation consisting of the sale price of fish on one side of the balance, and expenses (fish food, electricity, and labor) on the other. Based on the spreadsheet runs we’ve done, it looks like it will ONLY be profitable to try to raise more fish in a place where you have these four factors working for you: warm water temperature range, really cheap electricity, cheap labor, and cheap fish food. But in our temperature range, with our prices for fish food and electricity, trying to raise more fish than is necessary to provide fertilizer for the plants results in less net income.
2. Our Low Density Family System is much simpler than UVI-model commercial systems and costs less than half to build. It produces the same amount of vegetables per square foot of raft area, but only one-fifth the fish production of the more expensive and complicated UVI-type systems. This might look like a drawback, but is not really because the fish portion of the aquaponics operates at a small loss anyway. The benefit is that an LD-type system runs on one-fifth the electricity and fish food the UVI-type systems do, which also makes it economically feasible to power one of these systems from alternate energy sources such as wind and solar. A solar power system for a Family System costs about the same as the system itself. In other words, for about the same cost as the materials alone for a UVI-type system, you can get the materials AND an alternate power system for a comparably sized Family System.
Family Aquaponics System air pump with Victor
Here’s the explanation for the design decisions we made in developing this new type of aquaponics system. We’re often asked: Why do aquaponics systems use so much electricity? First, the UVI-model systems use a small amount (approximately 20% of the total power required by the system) to run a circulation pump that pumps water through the system 24/7. The bulk of the electricity used by these systems (80%) powers the aeration system which puts oxygen into the water for the fish to breathe. This consists of an efficient air pump or a low-pressure, high-volume regenerative blower that also runs 24/7. The amount of aeration, the size of the blower, and the amount of electricity it uses are directly proportional to the amount of fish in the system. Imagine squeezing 300 people into a 3-car garage. You can just barely get them in there, right? Now, imagine putting duct tape on all the doors and windows so no new air can come in. The people are going to need some mechanical ventilation pretty soon! So you duct an air blower into the garage and the people are fine (as long as the blower is operating, anyway).
This is exactly the situation you have when fish are crowded into a small tank. They use up the available oxygen in the water very quickly, and unless we put more oxygen in, the fish simply die. If you have more fish in the tank, you need to put more oxygen in, which requires more electrical consumption. If you have less fish, you don’t need as much oxygen or electricity.
Family Aquaponics System with taro, lettuce, and school farm tour
Because of this, we approached designing our Family System by asking ourselves “How small an amount of fish is necessary to keep the plants growing well?”. If we could reduce the amount of fish required, we would also reduce the amount of electrical consumption required to keep them breathing comfortably, AND the amount of fish food required (the two largest ongoing expenses in aquaponics after labor costs). Our original UVI-type systems operated with a loading of 1-1/2 pounds of fish per square foot of raft in the system; the first family Low-Density system we designed using this criterion operates with a loading of 0.3 pounds of fish per raft, and requires one-fifth of the electricity to operate per raft than our original UVI-type commercial systems did.
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We ran an experiment in which this system, with 80 lbs of fish in it, was switched off during the dark 12 hours of every 24. Although HIGHLY EXPERIMENTAL at first (we chewed our fingernails) three months later this is working just fine. It drops the total power consumption of the system to 0.7 kW per day, which is 60 watts for 12 hours out of every 24. This would require a much smaller alternate energy investment for alternate energy-powered systems.
Family Aquaponics System with lettuce and taro
This system is designed to be a viable off-grid system. It is important to note that if you’re using alternate energy systems to power this aquaponics system, the size of the alternate energy system is directly proportionate to the amount of electricity you need to use. The energy used for the 256 square foot system in our plans is 24 watts for the water pump, and 36 watts for the air pump that runs the aeration system, for a total of 60 watts, 12 hours per day. If you have good wind or sun at your location, you can run this family system from a 500 watt electric wind turbine, or a solar photovoltaic array of about of 300 watts, both with appropriate energy storage capacity. If you scale your system up to the 512 square foot family system, you need to scale everything up appropriately: you will have more fish, which will need more aeration, which will need more electricity and a larger alternate energy system. But the more fish will also power more aquaponics troughs and grow more vegetables; this is the corollary to “you never get something for nothing”: when you scale a system up in size, you always get something for something.
Friendly Aquaponics Farm
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